The mediation engine of WSO2 ESB is driven off a set of XML configuration files. This allows the mediation configuration to be easily hand edited, backed up from the file system, or even included into version control for easier management and administration (e.g. moving a configuration from development, through QA, staging and into production). The configuration files that drives the mediation engine are stored in the ESB_HOME/repository/conf/synapse-config directory. These configuration files are written using the Synapse configuration language which is a simple and easy to learn domain specific language based on XML.
It is always recommended to use the graphical wizards and tools provided in the WSO2 ESB management console to setup the mediation configuration, thus avoiding having to write XML configurations manually. The ESB management console offers a rich set of tools that allows you to build mediation configurations easily without writing a single line of XML. However it is helpful to have a basic understanding on the Synapse configuration language as well as on how the mediation configuration is physically stored on the disk. A decent knowledge on the Synapse configuration language will enable you to develop efficient and concise mediation configurations. Understanding how the files are stored will allow you to use third party tools and scripts for configuration management activities.
This guide walks you through the Synapse configuration language and how various configuration files are stored under the synapse-config directory of the ESB. It starts off with a breif introduction to the high level concepts associated with mediation and then explores into how such concepts can be implemented using the Synapse configuration language in WSO2 ESB.
As the diagram below depicts, the mediation engine consists of Proxy services, Endpoints, Sequences and Startup jobs managed by the ESB. It also contains the interface to the Registry/Repository being used by the mediation engine. Items like sequences, endpoints and proxy services could be made to reference different configuration elements that are served through the Registry. When using the Registry to hold pieces of the configuration, certain elements such as endpoint definitions, sequences and local entries could be updated dynamically while the ESB is executing, and the Registry could trigger a re-load as configured.
Typically the ESB is deployed between the actual client and a backend service implementation to mediate the message flow in between. Thus WSO2 ESB can accept a message on behalf of the actual service, perform authentication, validation, transformation, logging, routing based on the content etc. and then decide the destination target endpoint for the message and direct it to an actual service implementation. The ESB can also detect timeouts, transport failures during communication or introduce load balancing, throttling or caching where necessary. For fault scenarios such as authentication failure, or schema validation failure, the WSO2 ESB can be configured to return a custom message or a SOAP fault to the requesting client without forwarding the request to the actual service.
WSO2 ESB can operate in four modes of operation:
In Service mediation, the ESB exposes a service endpoint on the ESB, that accepts messages from clients. Typically these services acts as proxies for existing (external) services, and the role of the ESB would be to "mediate" these messages before they are proxied to the actual service. In this mode, WSO2 ESB could expose a service already available in one transport, over a different transport; or expose a service that uses one schema or WSDL as a service that uses a different schema or WSDL etc. A Proxy service could define the transports over which the service is exposed, and point to the mediation sequences that should be used to process request and response messages through the proxy service. A proxy service maybe a SOAP or REST/POX service over http/s or SOAP, POX, Plain Text or Binary / Legacy service for other transports such as JMS and VFS file systems - e.g. CSV content being the payload
In Message mediation, WSO2 ESB can act as a transparent proxy for clients - if they are directed to point to WSO2 ESB as a http proxy. This way, WSO2 ESB could be configured to filter all messages on a network for logging, access control etc, and could "mediate" messages without the explicit knowledge of the original client. If the ESB receives a message that is not accepted by any proxy service, this message is handled through message mediation as well. Message mediation always processes messages according to the mediation sequence defined as "main".
With the task scheduling capabilities of WSO2 ESB, one or more tasks can be configured to execute in a periodic manner in the ESB runtime. Tasks are custom developed Java code which are deployed into the ESB by the user. Tasks could be written to inject messages into the service bus periodically, poll databases and message queues, cleanup the environment and ping backend services to check availability.
With event sources and the event publisher mediator, WSO2 ESB can act as an event broker. It can receive and manage subscription requests from client applications and then dispatch events to the subscribers based on a pre configured criteria. Also if required events can be mediated through sequences before delivering them to the subscribers. The subscription manager implementation is pluggable and WSO2 ESB ships with a registry based subscription manager and an in memory subscription manager.
The following section explaing the high level concepts associated with the WSO2 ESB mediation engine and how they map to various configuration elements in the ESB configuration. It is very important to understand these high level concepts regardless of how you are planning to develop mediation configuration. Even if you are using the graphical tools to develop configuration it is still necessary to understand these concepts.
WSO2 ESB defines a 'mediator' as a component that performs some mediation action on a message during the process flow. Thus a mediator gets full access to a message at the point where it is defined to gain control, and could inspect the message, modify it or take an external action depending on some attributes or values of the current message. A mediation sequence, commonly called a 'sequence' is a list of such mediators. A sequence may be named for re-use, or defined in-line or anonymously within a configuration. Sequences may be defined within the synapse.xml configuration or within the Registry. Writing a custom mediator in Java is easy and the supplementary documentation provides more details on this. The 'Class' and 'POJO (command)" mediators allows one to plugin a Java class easily into the mediation engine with minimal effort. In addition, the Script mediator allows one to provide an Apache BSF script (e.g. Javascript, Ruby, Groovy etc) for mediation.
A mediation configuration holds two special sequences named "main" and "fault". These may be defined within the synapse.xml, or externally via the Registry. If either is not found, a suitable default is generated at runtime by the ESB. The default "main" sequence will simply send a message without mediation, while the default "fault" sequence would log the message including the payload and any error/exception encountered and stop further processing. The 'fault' sequence executes whenever WSO2 ESB itself encounters an error while processing a message - or when a fault handler has not been defined to handle exceptions. A sequence can assign another named sequence as its "fault" handler sequence, and control branches to the fault handler if an error is encountered during the execution of the initial sequence.
An Endpoint definition within the mediation configuration defines an external service endpoint and any attributes or semantics that should be followed when communicating with that endpoint. An endpoint definition can be named for re-use, or defined in-line or anonymously within a configuration. Typically an endpoint would be based on a service Address or a WSDL. Additionally WSO2 ESB supports Failover and Load-balance endpoints - which are defined over a group of endpoints. Endpoints may be defined within the synapse-config configuration or within the Registry.
A proxy service is a virtual services hosted in the ESB runtime. For a service client it appears to be a real Web Service which accepts service requests. The proxy service mediates any accepted requests and forwards them to a specified endpoint, most of the time to an actual Web Service. The responses coming back from the target endpoint are mediated back to the client which sent the original service request. Proxy services often make references to sequences, endpoints and local entries. A proxy service can enforce various QoS requirements on a request and can be exposed over a user specified transport. Therefore they are often used to expose existing Web Services over a different transport or a QoS configuration. For an example a proxy service can be used to expose an HTTP service over JMS or it can be used to expose an unsecured service in a secured manner using WS-Security standards.
Unlike sequences and endpoints which can be stored and loaded from the registry, proxy services cannot be loaded from the registry. However a proxy service can make references to sequences and endpoints stored in the registry.
A Task is a custom Java class that implements the org.apache.synapse.startup.Task interface that defines a single "public void execute()" method. Such a task can be scheduled and managed via the ESB. The scheduling information for a task can be specified in the cron format or a simple format by the user. A task may also be specified as a one-time task where required, and can be used to trigger a callout or inject a message into the ESB.
A mediation configuration can refer to an external Registry / Repository for resources used such as WSDL's, Schemas, Scripts, XSLT or XQuery transformations etc. One or more remote registries may be hidden or merged behind a local Registry interface defined to a Synapse configuration. Resources from an external registry are looked up using "keys" - which are known to the external registry. WSO2 ESB ships with a simple URL based registry implementation that uses the file system for storage of resources, and URL's or fragments as "keys".
A Registry may define a duration for which a resource served may be cached by the ESB runtime. If such a duration is specified, WSO2 ESB is capable of refreshing the resource after cache expiry to support dynamic re-loading of resource at runtime. Optionally, a configuration could define certain "keys" to map to locally defined entities. These entities may refer to a source URL or file, or defined as in-line XML or text within the configuration itself. If a Registry contains a resource whose "key" matches the key of a locally defined entry, the local entry shadows the resource available in the Registry. Thus it is possible to override Registry resources locally from within a configuration. To integrate WSO2 ESB with a custom / new Registry or repository, one needs to implement the org.apache.synapse.registry.Registry interface to suit the actual Registry being used.
An event source is used to define the event source and the subscription manager configuration used in the eventing implementation of WSO2 ESB. An event source provides a service URL that can be used to the send subscriptions and events (events that are not required to go through a mediation flow).
Prioriy executors can be used to execute sequences with a given priority. Priority executors are used in high load scenarios where user wants to execute differrent sequences with different priorities. This allows user to control the resources allocated to executing sequences and prevent high priority messages from getting delayed and dropped. A priority has a valid meaning comparing to other priorities specified. For example if we have two priorities with value 10 and 1, message with priority 10 will get 10 times more resources than messages with priority 1.
The synapse-config directory which houses the mediation configuration (Synapse configuration) of WSO2 ESB contains several files and subdirectories. Usually the following set of child directories are available in the synapse-config directory.
Each of the above subdirectories can house multiple XML configuration files that define specific configuration elements of the Synapse configuration. For an example the 'endpoints' subdirectory can house zero or more XML files that contain endpoint configurations.
Inaddition to the above mentioned subdirectories, there can be files named synapse.xml and registry.xml at the top level of the synapse-config directory. The registry.xml contains the registry definition for the ESB. The synapse.xml can contain any type of configuration elements wrapped in a top level <definitions> element. This file is mainly there for backward compatibility reasons. Older versions of WSO2 ESB had only a single flat XML file named synapse.xml to load the entire Synapse configuration from. The synapse.xml file in the synapse-config directory resembles this flat configuration file so that a user could easily port an old configuration to a new ESB distribution. Basically a user can get the content of the old synapse.xml file and put it in the synapse-config/synapse.xml file.
A Synapse configuration looks like the following at the top level synapse.xml file:
<definitions> <registry provider="string">...</registry>? <localEntry key="string">...</localEntry>? <sequence name="string">...</sequence>? <endpoint name="string">...</endpoint>? <proxy name="string" ...>...</proxy>? <task name="string" ...>...</task>? <eventSource name="string" ...>...</eventSource>? <priorityExecutor name="string" ...>...</priorityExecutor>? mediator* </definitions>
The <definitions> elements in the synapse.xml holds the ESB configuration. While the <registry>, <sequence>, <endpoint>, <proxy>, <task> and <localEntry> elements refer to those discussed above, the built-in mediator elements names are already registered with the Synapse engine. Custom mediators written by a user may be included into the library directory, and would be dynamically picked up in a Sun JDK environment. A list of mediators found directly as children under the <definitions> element would be treated as the "main" sequence, if a named sequence with the name "main" cannot be found.
The <registry> element is used to define the remote registry used by the configuration. The registry provider specifies an implementation class for the registry implementation used, and optionally a number of configuration parameters as may be required for the configuration of the connection to the registry.
<registry provider="string"/> <parameter name="string">text | xml</parameter>* </registry>
Registry entries loaded from a remote registry may be cached as dictated by the registry, and reloaded after the cache periods expires if a newer version is found. Hence it is possible to define configuration elements such as (dynamic) sequences and endpoints, as well as resources such as XSLT's, Scripts or XSDs off the registry, and update the configuration as these are allowed to dynamically change over time.
WSO2 ESB ships with a built-in file system based registry implementation called the "FileSystemRegistry" and this can be configured as follows:
e.g. <registry provider="org.wso2.carbon.mediation.registry.ESBRegistry"> <parameter name="root">file:./repository/samples/resources/</parameter> <parameter name="cachableDuration">15000</parameter> </registry>
The "root" parameter specifies the root directory of the Registry for loaded resources. The FileSystemBasedRegistry keys are path fragments, that when combined with the root prefix would form the full URL for the referenced resource. The "cachableDuration" parameter specifies the number of milliseconds for which resources loaded from the Registry should be cached. More advanced registry implementations allows different cachable durations to be specified for different resources, or mark some resources as never expires. By default WSO2 ESB uses the WSO2 Governance Registry for storing resources. It is configured as follows:
e.g. <registry provider="org.wso2.carbon.mediation.registry.WSO2Registry"> <parameter name="cachableDuration">15000</parameter> </registry>
By default you will find the above bit of configuration in the top level registry.xml file in the synapse-config directory.
The <localEntry> element is used to declare registry entries that are local to the ESB instance, as shown below
<localEntry key="string" [src="url"]>text | xml</localEntry>
These entries are top level entries which are globally visible within the entire system. Values of these entries can be retrieved via the extension XPath function "synapse:get-property(prop-name)" and the keys of these entries could be specified wherever a registry key is expected within the configuration.
An entry can be static text specified as inline text or static XML specified as an inline XML fragment or specified as a URL (using the src attribute). A local entry shadows any entry with the same name from a remote Registry.
e.g. <localEntry key="version">0.1</localEntry> <localEntry key="validate_schema"> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" ... </xs:schema> </localEntry> <localEntry key="xslt-key-req" src="file:repository/samples/resources/transform/transform.xslt"/>
Local entries can be defined in the top level synapse.xml file or in the synapse-config/local-entries directory.
A <sequence> element is used to define a sequence of mediators that can be invoked later by name. The sequences named "main" and "fault" has special significance in a Synapse configuration. The "main" sequence handles any message that is accepted for 'Message Mediation', and the "fault" sequence is invoked if Synapse encounters a fault, and a custom fault handler is not specified for the sequence via its "onError" attribute. If the "main" or "fault" sequences are not defined locally or not found in the Registry, the Synapse ESB defines suitable defaults at initialization.
A Dynamic Sequence may be defined by specifying a key reference to a registry entry. As the remote registry entry changes, the sequence will dynamically be updated according to the specified cache duration and expiration. If tracing is enabled on a sequence, all messages being processed through the sequence would write tracing information through each mediation step to the trace.log file configured via the log4j.properties configuration. Setting the trace log level to TRACE would additionally dump the message and detailed trace information at each mediation step. A tracing enabled sequence propagates this setting to invoked sub-sequences.
<sequence name="string" [onError="string"] [key="string"] [trace="enable"]> mediator* </sequence>
e.g. <sequence name="main" onError="errorHandler"> .. <!-- a 'main' sequence that invokes the sequence named 'errorHandler' on a fault --> .. </sequence>
<sequence key="sequence/dynamic_seq_1.xml"/> where "sequence/dynamic_seq_1.xml" refers to the following sequence definition from the registry: <sequence name="dynamic_sequence" xmlns="http://ws.apache.org/ns/synapse"> .. </sequence>
Sequences can be defined in the top level synapse.xml file or in the synapse-config/sequences directory. The default main sequence and the fault sequence that ships with WSO2 ESB can be found in the sequences directory in two files named main.xml and fault.xml respectively.
Endpoints can be defined in the top level synapse.xml file or in the synapse-config/endpoints directory.
An <endpoint> element defines a destination for an outgoing message. An endpoint may be specified as an address endpoint, WSDL based endpoint, a load balancing endpoint or a fail-over endpoint as follows:
<endpoint [name="string"] [key="string"] [key-expression="string"]> address-endpoint | default-endpoint | wsdl-endpoint | load-balanced-endpoint | fail-over-endpoint </endpoint>
All above endpoint types can have a name attribute, and such named endpoints can be reffered by other endpoints, through the key attribute. For example if there is an endpoint named as "foo", the following endpoint can be used in any place, where "foo" has to be used.
<endpoint key="foo"/>
The "trace" attribute turns on detailed trace information for messages being sent to the endpoint. These are available in the trace.log configured via the log4j.properties file. Setting the trace log level to TRACE will dump detailed trace information including message payloads.
Address endpoint is an endpoint defined by specifying the EPR and other attributes of the endpoint directly in the configuration. The 'uri' attribute of the address element contains the EPR of the target endpoint. Message format for the endpoint and the method to optimize attachments can be specified in the format and optimize attributes respectively. Reliable messaging and security policies for the endpoint can be specified in the policy attribute of the enableRM and enableSec elements respectively. WS-Addressing can be engaged for the messaging going to the endpoint by the enableAddressing element. suspendDurationOnFailure attribute specifies the time duration in seconds to suspend this endpoint, if it is detected as failed. If this attribute is not specified, endpoint will never be recovered after a failure.
Address endpoints can timeout if responses fail to arrive at Synapse by a predefined timeout-duration specified in seconds. The timeout action specifies whether to discard responses that arrives late, or to trigger a fault. Synapse has a periodic timeout handler that triggers itself at each 15 second interval. Thus endpoint timeouts will have a +/- error on actual trigger time. Though this can be minimized by setting a System property "synapse.timeout_handler_interval" to a millisecond duration below the desired endpoint timeout, care must be taken as a lesser value may have a higher overhead on the system.
An endpoint that fails may be suspended for a specified duration after such a failure, during which new messages will not be processed through the endpoint. The 'suspendDurationOnFailure' could specify an optional value in seconds for which this endpoint should be suspended.
QoS aspects such as WS-RM and WS-Security and WS-Addressing may be enabled on messages sent to an endpoint using the enableRM, enableSec and enableAddressing elements. Optionally, the WS-RM and WS-Security policies could be specified using the 'policy' attributes.
<address uri="endpoint address" [format="soap11|soap12|pox|get"] [optimize="mtom|swa"] [encoding="charset encoding"] [statistics="enable|disable"] [trace="enable|disable"]> <enableRM [policy="key"]/>? <enableSec [policy="key"]/>? <enableAddressing [version="final|submission"] [separateListener="true|false"]/>? <timeout> <duration>timeout duration in milliseconds</duration> <action>discard|fault</action> </timeout>? <suspendDurationOnFailure> suspend duration in seconds </suspendDurationOnFailure>? <markForSuspension> [<errorCodes>xxx,yyy</errorCodes>] <retriesBeforeSuspension>m</retriesBeforeSuspension> <retryDelay>d</retryDelay> </markForSuspension> <suspendOnFailure> [<errorCodes>xxx,yyy</errorCodes>] <initialDuration>n</initialDuration> <progressionFactor>r</progressionFactor> <maximumDuration>l</maximumDuration> </suspendOnFailure> </address>
Following are some sample address URI definitions.
Transport | Sample address |
---|---|
HTTP | http://localhost:9000/soap/SimpleStockQuoteService |
JMS | jms:/SimpleStockQuoteService? transport.jms.ConnectionFactoryJNDIName=QueueConnectionFactory& java.naming.factory.initial=org.apache.activemq.jndi.ActiveMQInitialContextFactory& java.naming.provider.url=tcp://localhost:61616& transport.jms.DestinationType=topic |
mailto:guest@host | |
VFS | vfs:file:///home/user/directory |
vfs:file:///home/user/file | |
vfs:ftp://guest:guest@localhost/directory?vfs.passive=true | |
FIX | fix://localhost:9876?BeginString=4.4&SenderCompID=SYNAPSE&TargetCompID=EXEC |
Default endpoint is an endpoint defined for adding QoS and other configurations to the endpoint which is resolved from the 'To' address of the message context. All the configurations such as message format for the endpoint, the method to optimize attachments, reliable messaging, security policies for the endpoint can be specified as in the Address Endpoint. This endpoint differs from the address endpoint only in the uri attribute which will not be present in this endpoint. Following section describes the configuration of a default endpoint
<default [format="soap11|soap12|pox|get"] [optimize="mtom|swa"] [encoding="charset encoding"] [statistics="enable|disable"] [trace="enable|disable"]> <enableRM [policy="key"]/>? <enableSec [policy="key"]/>? <enableAddressing [version="final|submission"] [separateListener="true|false"]/>? <timeout> <duration>timeout duration in milliseconds</duration> <action>discard|fault</action> </timeout>? <suspendDurationOnFailure> suspend duration in seconds </suspendDurationOnFailure>? </default>
WSDL endpoint is an endpoint definition based on a specified WSDL document. The WSDL document can be specified either as a URI or as an inlined definition within the configuration. The service and port name containing the target EPR has to be specified with the 'service' and 'port' (or 'endpoint') attributes respectively. enableRM, enableSec, enableAddressing, suspendDurationOnFailure and timeout elements are same as for an Address endpoint.
<wsdl [uri="wsdl-uri"] service="qname" port/endpoint="qname"> <wsdl:definition>...</wsdl:definition>? <wsdl20:description>...</wsdl20:description>? <enableRM [policy="key"]/>? <enableSec [policy="key"]/>? <enableAddressing/>? <suspendDurationOnFailure>suspend-duration</suspendDurationOnFailure>? <markForSuspension> [<errorCodes>xxx,yyy</errorCodes>] <retriesBeforeSuspension>m</retriesBeforeSuspension> <retryDelay>d</retryDelay> </markForSuspension> <suspendOnFailure> [<errorCodes>xxx,yyy</errorCodes>] <initialDuration>n</initialDuration> <progressionFactor>r</progressionFactor> <maximumDuration>l</maximumDuration> </suspendOnFailure> <timeout> <duration>timeout-duration</duration> <action>discard|fault</action> </timeout>? </wsdl>
A Load balanced endpoint distributes the messages (load) arriving at it among a set of listed endpoints by evaluating the load balancing policy and any other relevant parameters. Policy attribute of the load balance element specifies the load balance policy (algorithm) to be used for selecting the target endpoint. Currently only the roundRobin policy is supported. failover attribute determines if the next endpoint should be selected once the currently selected endpoint has failed, and defaults to true. The set of endpoints among which the load is distributed can be listed under the 'loadBalance' element. Those endpoints can belong to any endpoint type mentioned in this document. For example, failover endpoints can be listed inside the load balance endpoint to load balance between failover groups etc.
The optional 'session' element makes the endpoint a session affinity based load balancing endpoint. If it is specified, sessions are bound to endpoints in the first message and all successive messages for those sessions are directed to their associated endpoints. Currently there are two types of sessions supported in SAL endpoints. Namely HTTP transport based session which identifies the sessions based on http cookies and the client session which identifies the session by looking at a SOAP header sent by the client with the QName '{http://ws.apache.org/ns/synapse}ClientID'. The 'failover' attribute mentioned above is not applicable for session affinity based endpoints and it is always considered as set to false. If it is required to have failover behavior in session affinity based load balance endpoints, list failover endpoints as the target endpoints.
<session type="http|simpleClientSession"/>? <loadBalance [policy="roundRobin"] [failover="true|false"]> <endpoint .../>+ </loadBalance>
Failover endpoints send messages to the listed endpoints with the following failover behavior. At the start, the first listed endpoint is selected as the primary and all other endpoints are treated as backups. Incoming messages are always sent only to the primary endpoint. If the primary endpoint fails, next active endpoint is selected as the primary and failed endpoint is marked as inactive. Thus it sends messages successfully as long as there is at least one active endpoint among the listed endpoints.
<failover> <endpoint .../>+ </failover>
Indirect Endpoint refers an actual endpoint by a key. This endpoint fetches the actual endpoint at runtime. Then it delegates the message sending to the actual endpoint. When Endpoints are stored in the registry and referred, this endpoint can be used. The key is a static value for this endpoint.
<endpoint key="" name="" />
Resolving Endpoint refers an actual endpoint using a dynamickey. The key is a XPath expression. The XPath is evaluated against the current message and key is calculated at run time. Then resolving endpoint fetches the actual endpoint using the calculated key. Then it delegates the message sending to the actual endpoint. When Endpoints are stored in the registry and referred, this endpoint can be used.
<endpoint name="" key-expression="" />
A <proxy> element is used to define a Synapse Proxy service.
<proxy name="string" [transports="(http |https |jms |.. )+|all"] [pinnedServers="(serverName )+"]> <description>...</description>? <target [inSequence="name"] [outSequence="name"] [faultSequence="name"] [endpoint="name"]> <inSequence>...</inSequence>? <outSequence>...</outSequence>? <faultSequence>...</faultSequence>? <endpoint>...</endpoint>? </target>? <publishWSDL key="string" uri="string"> ( <wsdl:definition>...</wsdl:definition> | <wsdl20:description>...</wsdl20:description> )? <resource location="..." key="..."/>* </publishWSDL>? <parameter name="string"> // optional service parameters such as (e.g. transport.jms.ConnectionFactory) string | xml </parameter> </proxy>
A proxy service is created and exposed on the specified transports through the underlying Axis2 engine, exposing service EPR's as per the standard Axis2 conventions - based on the service name. (Note: that currently Axis2 does not allow custom URI's to be set for services on some transports such as http/s) The Proxy service could be exposed over all enabled Axis2 transports such as http, https, JMS, Mail and File etc. or on a subset of these as specified with the optional 'transports' attribute.
You can give a list of Synapse server names where this proxy service should be deployed using 'pinnedServers' attribute. It takes the server names separated by comma or space character. If there is no pinned server list then proxy service will be started in all server instances. If a pinned server names list is given it will only start in the given named Synapse server instances. The Synapse server name is picked up either from the system property 'SynapseServerName' or through the axis2.xml parameter 'SynapseConfig.ServerName', failing which the hostname of the machine would be used or default to 'localhost'. You can give a name to a Synapse server instance by specifiying -DSynapseServerName=<ServerName> property when you execute the startup script, i.e. wso2server.bat or wso2server.sh. You can also edit the wrapper.conf to do this where Synapse is started as a service.
Each service could define the target for received messages as a named sequence or a direct endpoint. Target inSequence or endpoint is required for the proxy configuration, and a target outSequence defines how responses should be handled. Any supplied WS-Policies would apply as service level policies, and any service parameters could be passed into the proxy services' AxisService instance using the parameter elements (e.g. the JMS destination etc). If the proxy service should enable WS-Reliable Messaging or Security, the appropriate modules could be engaged, and specified service level policies will apply.
A Dynamic Proxy may be defined by specifying the properties of the proxy as dynamic entries by refering them with the key. (For example one could specify the inSequence or endpoint with a remote key, without defining it in the local configuration) As the remote registry entry changes, the properties of the proxy will dynamically be updated accordingly. (Note: proxy service definition itself can not be specified to be dynamic; i.e <proxy key="string"/> is wrong)
A WSDL for the proxy service can be published using the <publishWSDL> element. The WSDL document can be loaded from the registry by specifying the 'key' attribute or from any other location by specifying the 'uri' attribute. Alternatively the WSDL can be provided inline as a child element of <publishWSDL>. Artifacts (schemas or other WSDL documents) imported by the WSDL can be resolved from the registry by specifying appropriate <resource> elements:
<publishWSDL key="my.wsdl"> <resource location="http://www.standards.org/standard.wsdl" key="standard.wsdl"/> </publishWSDL>
In this example the WSDL is retrieved from the registry using the key 'my.wsdl'. It imports another WSDL from location 'http://www.standards.org/standard.wsdl'. Instead of loading it from this location, Synapse will retrieve the imported WSDL from the registry entry 'standard.wsdl'.
You can give the following as service parameters:
Parameter | Value | Default | Description |
---|---|---|---|
useOriginalwsdl | true|false | false | Use the given WSDL instead of generating the WSDL. |
modifyUserWSDLPortAddress | true|false | true | (Effective only with useOriginalwsdl=true) If true (default) modify the port addresses to current host. |
Transport specific parameters that may be set as service parameters:
Transport | Require | Parameter | Description |
---|---|---|---|
JMS | Optional | transport.jms.ConnectionFactory | The JMS connection factory definition (from axis2.xml) to be used to listen for messages for this service |
Optional | transport.jms.Destination | The JMS destination name (Defaults to the service name) | |
Optional | transport.jms.DestinationType | The JMS destination type. Accept values 'queue' or 'topic' | |
Optional | transport.jms.ReplyDestination | The destination where a reply will be posted | |
Optional | transport.jms.Wrapper | The wrapper element for the JMS message | |
VFS | Required | transport.vfs.FileURI | The primary File (or Directory) URI in the vfs* transport format, for this service |
Required | transport.vfs.ContentType | The expected content type for files retrieved for this service. The
VFS transport uses this information to select the appropriate message
builder. Examples:
|
|
Optional | transport.vfs.FileNamePattern | A file name regex pattern to match files against a directory specified by the FileURI | |
Optional | transport.PollInterval | The poll interval (in seconds) | |
Optional | transport.vfs.ActionAfterProcess | DELETE or MOVE | |
Optional | transport.vfs.MoveAfterProcess | The directory to move files after processing (i.e. all files process successfully) | |
Optional | transport.vfs.ActionAfterErrors | DELETE or MOVE | |
Optional | transport.vfs.MoveAfterErrors | The directory to move files after errors (i.e. some of the files succeed but some fail) | |
Optional | transport.vfs.ActionAfterFailure | DELETE or MOVE | |
Optional | transport.vfs.MoveAfterFailure | The directory to move after failure (i.e. all files fail) | |
Optional | transport.vfs.ReplyFileURI | Reply file URI | |
Optional | transport.vfs.ReplyFileName | Reply file name (defaults to response.xml) | |
Optional | transport.vfs.MoveTimestampFormat | Timestamp prefix format for processed file name. java.text.SimpleDateFormat compatible string. e.g. yyMMddHHmmss'-' |
VFS Transport URI examples (See http://commons.apache.org/vfs/filesystems.html for more samples)
file:///directory/filename.ext file:////somehost/someshare/afile.txt jar:../lib/classes.jar!/META-INF/manifest.mf jar:zip:outer.zip!/nested.jar!/somedir ftp://myusername:mypassword@somehost/pub/downloads/somefile.tgz[?vfs.passive=true]
A <task> element is used to define a Synapse Startup Task.
<task class="mypackage.MyTask" name="string" [pinnedServers="(serverName)+"]> <property name="stringProp" value="String"/> <property name="xmlProp"> <somexml>config</somexml> </property> <trigger ([[count="10"]? interval="1000"] | [cron="0 * 1 * * ?"] | [once=(true | false)])/> </task>
A task is created and scheduled to run at specified time intervals or as specified by the cron expression. The Task class specifies the actual task implementation class (which must implement org.apache.synapse.startup.Task interface) to be executed at the specified interval/s, and name specifies an identifier for the scheduled task.
Fields in the task class can be set using properties provided as string literals or as XML fragments. (For example; if the task implementation class has a field named "version" with a corresponding setter method, the configuration value which will be assigned to this field before running the task can be specified using a property with the name 'version')
There are three different trigger mechanisms to schedule tasks. A simple trigger is specified specifying a 'count' and an 'interval', implying that the task will run a 'count' number of times at specified intervals. A trigger may also be specified as a cron trigger using a cron expression. A one-time trigger is specified using the 'once' attribute as true in the definition and could be specified as true in which case this task will be executed only once just after the initialization of Synapse
You can give a list of Synapse server names where this task should be started using pinnedServers attribute. Refer to the explanation of this attribute under proxy services for more information.
A <eventSource> element is used to define an event source.
<eventSource name="string"> <subscriptionManager class="my.package.MyClass"> <parameter name="string"/> </subscriptionManager> </eventSource>
An event source is required to implement eventing in WSO2 ESB. Event sources are used to inject subscription messages into the ESB and provide a service URL for the users to send subscription requests. User can send messages to manage the subscriptions (unsubscribe, renew, get-status) in the event source as well.
Subscription manager configured inside the event source will be responsible for keeping track of the subscriptions, and provide operations to manage the subscriptions. Subscription storage will be decided based on the implementation of the subscription manager , e.g. Registry, memory, database. Additional information required to setup the subscription manager can be set as parameters.
Below is the Priority Executor Configuration
<priority-executor name="priority-executor"> <queues isFixed="true|false" nextQueue="class implementing NextQueueAlgorithm"> <queue [size="size of the queue"] priority="priority of the messages put in to this queue"/>* </queues> <threads core="core number of threads" max="max number of threads' keep-alive="keep alive time"/> </priority-executor>
An executor is a Thread Pool Executor with separate queues for different priorities.
The queues can have a fixed depths or they can have un-bounded capacities. This is controlled by the isFixed attribute.
An executor should have at least two or more queues. If only one queue is used there is no point in using a priority executor. It only adds some overhead.
A Queue can have a size and a priority. If the queues has unlimited length, no more than core threads will be used.
A Priority Executor has a core number of threads. When ESB is started with the priority executor, this number of threads will be created. Max is the maximum number of threads this executor will have. If the number of threads in the executor exceeds the core threads, they will be in active for the keep-alive time only. After the keep-alive time those threads will be be removed from the system.
A mediator token refers to any of the following tokens:
send | drop | log | property | sequence | validate | fault | callout | xslt | header | filter | switch | in | out | router | dblookup | dbreport | RMSequence | throttle | xquery | cache | clone | iterate | aggregate | class | pojoCommand | script | spring | event | entitlement | OAuth | transaction | smooks
In addition to the above, Synapse will be able to load custom mediators via the J2SE Service Provider model. Mediator extensions must implement the MediatorFactory interface. The Class and POJO Command mediators allow custom Java code to be easily invoked during mediation, while the Script mediator allows Apache BSF scripts such as Javascript, Ruby, Groovy etc to be used for mediation.
The send token represents a <send> element, used to send messages out of Synapse to some endpoint. The send mediator also copies any message context properties from the current message context to the reply message received on the execution of the send operation so that the response could be correlated back to the request. Messages may be correlated by WS-A MessageID, or even simple custom text labels (see the property mediator and samples)
In the simplest case shown below, the destination to send a message is implicit in the message via the 'To' address. Thus a request message will be sent to its 'To' address, and a response message would be sent back to the client. Removing the 'To' address of a message targets it back to the client, and thus a request message received may be returned to the client after changing its direction. (Note: to mark a message as a response set the property RESPONSE to true)
Note: A send operation may be blocking or non-blocking depending on the actual transport implementation used. As the default NIO based http/s implementation does not block on a send, care must be taken if the same message must be sent and then further processed (e.g. transformed). In such a scenario, it maybe required to first clone the message into two copies and then perform processing to avoid conflicts.
<send/>
If the message is to be sent to one or more endpoints, then the following is used:
<send> (endpointref | endpoint)+ </send>
where the endpointref token refers to the following:
<endpoint key="name"/>
and the endpoint token refers to an anonymous endpoint definition.
The drop token refers to a <drop> element which is used to stop further processing of a message:
<drop/>
Once the <drop> mediator executes, further processing of the current message stops. A the drop mediator does not necessarily close transports.
The log token refers to a <log> element which may be used to log messages being mediated:
<log [level="string"] [separator="string"]> <property name="string" (value="literal" | expression="xpath")/>* </log>
The optional level attribute selects a pre-defined subset of properties to be logged.
e.g.
A separator if defined will be used to separate the attributes being logged. The default separator is the ',' comma.
<property name="string" [action=set|remove] (value="literal" | expression="xpath") [scope=transport|axis2|axis2-client] [type="type name"]/>
The property token refers to a <property> element which is a mediator that has no direct impact on the message but rather on the message context flowing through Synapse. The properties set on a message can be later retrieved through the synapse:get-property(prop-name) XPath extension function. If a scope is specified for a property, the property could be set as a transport header property or an (underlying) Axis2 message context property, or as a Axis2 client option. If a scope is not specified, it will default to the Synapse message context scope. Using the property element with action specified as "remove" you can remove any existing message context properties.
With the type attribute, we can set properties with specific data types into the message context. When this attribute is not used the specified property value will be set as a string. Currently the following data type names are recognized by the property mediator's type attribute:
When the type attribute is assigned one of the above mentioned values, the specified property value will be converted to the specified type before setting it into the message context. The type OM can be used to convert the property value into an AXIOM OMElement. Please note that all type names mentioned above are case sensitive.
There are some well-defined properties that you can get/set on the Synapse message context scope:
There are some Axis2 and module properties that are useful which are set at scope="axis2"
There are some Axis2 client side properties/options that are useful which are set at scope="axis2-client"
The get-property() function allows any XPath expression used in a configuration to lookup information from the current message context. It is possible to retrieve properties previously set with the property mediator, and/or information from the Synapse or Axis2 message contexts or transport header. The function accepts the scope as an optional parameter as shown below:
synapse:get-property( [(axis2 | axis2-client | transport),] <property_name> [,<dateformat>] )
Some useful properties from the Synapse message context follows:
In addition to the above, one may use the get-property() function to retrieve Axis2 message context properties or transport headers. e.g. synapse:get-property('transport', 'USER_AGENT')
There are a set of predefined XPath variables when writing XPaths in the Synapse Configuration. Those are as follows;
Further there are some variable prefixes defined in Synapse XPaths which can be usefull in writing the configurations;
<sequence key="name"/>
A sequence ref token refers to a <sequence> element which is used to invoke a named sequence of mediators.
<validate [source="xpath"]> <property name="validation-feature-id" value="true|false"/>* <schema key="string"/>+ <on-fail> mediator+ </on-fail> </validate>
The <validate> mediator validates the result of the evaluation of the source xpath expression, against the schema specified. If the source attribute is not specified, the validation is performed against the first child of the SOAP body of the current message. If the validation fails, the on-fail sequence of mediators is executed. Properties could be used to turn on/off some of the underlying features of the validator (See http://xerces.apache.org/xerces2-j/features.html)
<makefault [version="soap11|soap12|pox"]> <code (value="literal" | expression="xpath")/> <reason (value="literal" | expression="xpath")> <node>? <role>? <detail>? </makefault>
The fault mediator transforms the current message into a fault message, but does NOT send it. The <send> mediator needs to be invoked to send a fault message created this way. The fault message "To" header is set to the "Fault-To" of the original message if such a header exists on the original message. If a 'version' attribute is specified, the created fault message will be created as a selected SOAP 1.1, SOAP 1.2 or POX fault.
<callout serviceURL="string" [action="string"]> <configuration [axis2xml="string"] [repository="string"]/>? <source xpath="expression" | key="string"> <target xpath="expression" | key="string"/> </callout>
The <callout> mediator performs a blocking external service invocation during mediation. The serviceURL and the optional action specifies the parameters for this external call. The source element specifies the payload for the request message using an XPath expression; or a registry key that will be used. The target element specifies a node, at which the resulting payload will be attached into the current message, or the name of a key/property using which the response would be attached to the current message context as a property.
As the callout mediator performs a blocking call, it cannot use the default non-blocking http/s transports based on Java NIO, and thus defaults to using the samples/axis2Client/client_repo/conf/axis2.xml as the Axis2 configuration, and samples/axis2Client/client_repo as the client repository unless these are specified separately
<xslt key="string" [source="xpath"]> <property name="string" (value="literal" | expression="xpath")/>* <feature name="string" value="true| false" />* <resource location="..." key="..."/>* </xslt>
The <xslt> mediator applies the specified XSLT transformation to the selected element of the current message payload. If the source element is not specified, it defaults to the first child of the soap body. Optionally parameters (XSLT) could be passed into the transformations through the 'property' elements. The 'feature' element defines any features which should be explicitly set to the TransformerFactory. The feature 'http://ws.apache.org/ns/synapse/transform/feature/dom' turns on DOM based transformations instead of serializing elements into Byte streams and/or temporary files. Though this would be better in performance than using byte streams, sometimes it may not work for all transformations.
Finally, the 'resource' element can be used to resolve XSLT imports and includes from the repository. It works in exactly the same way as the corresponding element in a <proxy> definition.
<xquery key="string" [target="xpath"]> <variable name="string" type="string" [key="string"] [expression="xpath"] [value="string"]/>? </xquery>
The XQuery mediator can be used to perform an XQuery transformation. The 'key' attribute specifies the XQuery transformation, and the optional 'target' attribute specifies the node of the message that should be transformed. This defaults to the first child of the SOAP body of the payload. The 'variable' elements define a variable that could be bound to the dynamic context of the XQuery engine in order to access those variables through the XQuery script .
It is possible to specify just a literal 'value', or an XPath expression over the payload, or even specify a registry key or a registry key combined with an XPath expression that selects the variable. The name of the variable corresponds to the name of variable declaration in the XQuery script. The 'type' of the variable must be a valid type defined by the JSR-000225 (XQJ API).
The supported types are:
<header name="qname" (value="literal" | expression="xpath") [action="set"]/> <header name="qname" action="remove"/>
The <header> mediator sets or removes a specified header from the current soap infoset. Currently the set header only supports simple valued headers. In the future we may extend this to have XML structured headers by embedding the XML content within the element itself. The optional action attribute specifies whether the mediator should set or remove the header. If omitted, it defaults to a set-header.
<smooks key="string"/>
The <smooks> mediator can be used to perform complex content transformation efficiently using the Smooks framework for XML processing. The key attribute should point to a local entry or a registry resource which contains a Smooks configuration file. For more information on Smooks transformation please visit the Smooks website.
<filter (source="xpath" regex="string") | xpath="xpath"> mediator+ </filter>
The <filter> mediator either test the given xpath expression as a boolean expression, or match the evaluation result of a source xpath expression as a String against the given regular expression. If the test succeeds, the filter mediator will execute the enclosed mediators in sequence.
One could also use this mediator to handle the failure case as well, in which case the configuration would be as follows
<filter (source="xpath" regex="string") | xpath="xpath"> <then [sequence="string"]> mediator+ </then> <else [sequence="string"]> mediator+ </else> </filter>
In this case the filter condition remains as earlier and the succeeded messages will be mediated using the the set of mediators enclosed in the 'then' element in sequence, while failed messages will be mediated using the set of mediators enclosed in the else element in sequence
<switch source="xpath"> <case regex="string"> mediator+ </case>+ <default> mediator+ </default>? </switch>
The <switch> mediator will evaluate the given source xpath expression into its string value, and match it against the given regular expressions. If the specified cases does not match and a default case exists, it will be executed.
<in> mediator+ </in>
<out> mediator+ </out>
The In and Out mediators will execute the child mediators over the current message if the message matches the direction of the mediator. Hence all incoming messages would pass through the "<in>" mediators and vice versa.
<router [continueAfter=(true | false)]> <route expression="xpath" [match="regEx"] [breakRouter=(true | false)]> <target [sequence="string"] [endpoint="string"]> <sequence ....../>? <endpoint ....../>? </target> </route>+ </router>
Router mediator is represented by the 'router' root tag and it can contain any number of routes which are represented with the 'route' tags. Router mediator can be configured to continue or to stop the mediation after the routing by setting the 'continueAfter' attribute value to be 'true' and 'false' respectively. Each and every route must contain an 'expression' attribute which is to specify the XPath over which the routing condition is evaluated. Apart from that there can be an optional 'match' attribute as well. If both expression and the match attirbutes are specified in a particualr route, the evaluated string value of the XPath over the current message will be campared with the reular expression provided as the value of the match attribute to see whether this route is matching for the current message. Where as if only the expression is specified, presence of the element specified by this XPath is considered as the routing condition.
One can configure a route to break routing or continue evaluating further routes to see any further matchings by setting the 'breakRouter' attribute to 'true' or 'false' respectively. For all the routes there has to be a 'target' element which contains the information about the routing path as a sequence or an endpoint both can be inlined as well as refered. If both an endpoint and a sequence is specified message will be first mediated through the sequence and sent to the endpoint after mediation. Particular target cannot contain an inline sequence and a refered sequence at the same time. The same applies to endpoit of the target as well.
<dblookup> <connection> <pool> ( <driver/> <url/> <user/> <password/> | <dsName/> <icClass/> <url/> <user/> <password/> ) <property name="name" value="value"/>* </pool> </connection> <statement> <sql>select something from table where something_else = ?</sql> <parameter [value="" | expression=""] type="CHAR|VARCHAR|LONGVARCHAR|NUMERIC|DECIMAL|BIT|TINYINT|SMALLINT|INTEGER|BIGINT|REAL|FLOAT|DOUBLE|DATE|TIME|TIMESTAMP"/>* <result name="string" column="int|string"/>* </statement>+ </dblookup>
The dblookup mediator is capable of executing an arbitrary SQL select statement, and then set some resulting values as local message properties on the message context. The DB connection used maybe looked up from an external DataSource or specified in-line, in which case an Apache DBCP connection pool is established and used. Apache DBCP connection pools support the following properties:
More than one statement may be specified, and the SQL statement may specify parameters which could be specified as values or XPath expressions. The types of parameters could be any valid SQL types. Only the first row of a result set will be considered and any others are ignored. The single <result> element contains the 'name' and the column' attributes. The 'name' attribute defines the name under which the result is stored in the Synapse message context, and the column attribute specifies a column number or name .
<dbreport> <connection> <pool> ( <driver/> <url/> <user/> <password/> | <dsName/> <icClass/> <url/> <user/> <password/> ) <property name="name" value="value"/>* </pool> </connection> <statement> <sql>insert into something values(?, ?, ?, ?)</sql> <parameter [value="" | expression=""] type="CHAR|VARCHAR|LONGVARCHAR|NUMERIC|DECIMAL|BIT|TINYINT|SMALLINT|INTEGER|BIGINT|REAL|FLOAT|DOUBLE|DATE|TIME|TIMESTAMP"/>* </statement>+ </dblreport>
The dbreport mediator is very similar to the dblookup mediator, but writes information to a Database, using the specified insert SQL statement.
<RMSequence (correlation="xpath" [last-message="xpath"]) | single="true" [version="1.0|1.1"]/>
The <RMSequence> mediator can be used to create a sequence of messages to communicate via WS-Reliable Messaging with an WS-RM enabled endpoint (<enableRM>). The simple use case of this mediator is to specify a single="true" property, because this means that only one message is involved in the same sequence. However if multiple messages should be sent in the same sequence, the correlation property should be used with a XPath expression that selects an unique element value from the incoming message. With the result of the XPath expression, Synapse can group messages together that belong to the same sequence. To close the sequence neatly, for the last message of the sequence also an XPath expression should be specified. With the version attribute the WS-RM specification version to be used can be specified, 1.0 or 1.1.
<throttle [onReject="string"] [onAccept="string"] id="string"> (<policy key="string"/> | <policy>..</policy>) <onReject>..</onReject>? <onAccept>..</onAccept>? </throttle>
The Throttle mediator can be used for rate limiting as well as concurrency based limiting. A WS-Policy dictates the throttling configuration and may be specified inline or loaded from the registry. Please refer to the samples document for sample throttling policies. The Throttle mediator could be added in the request path for rate limiting and concurrent access limitation. When using for concurrent access limitation, the same throttle mediator 'id' must be triggered on the response flow so that completed responses are deducted from the available limit. (i.e. two instances of the throttle mediator with the same 'id' attribute in the request and response flows). The 'onReject' and 'onAccept' sequence references or inline sequences define how accepted and rejected messages are to be handled.
<cache [id="string"] [hashGenerator="class"] [timeout="seconds"] [scope=(per-host | per-mediator)] collector=(true | false) [maxMessageSize="in-bytes"]> <onCacheHit [sequence="key"]> (mediator)+ </onCacheHit>? <implementation type=(memory | disk) maxSize="int"/> </cache>
The <cache> mediator will evaluate the hash value of an incoming message as described in the optional hash generator implementation (which should be a class implementing the org.wso2.caching.digest.DigestGenerator interface). The default hash generator is 'org.wso2.caching.digest.DOMHashGenerator'. If the generated hash value has been found in the cache then the cache mediator will execute the onCacheHit sequence which can be specified inline or referenced. The cache mediator must be specified with an 'id' and two instances with this same 'id' that correlates the response message into the cache for the request message hash. The optional 'timeout' specifies the valid duration for cached elements, and the scope defines if mediator instances share a common cache per every host instance, or per every cache mediator pair (i.e. 'id') instance. The 'collector' attribute 'true' specifies that the mediator instance is a response collection instance, and 'false' specifies that its a cache serving instance. The maximum size of a message to be cached could be specified with the optional 'maxMessageSize' attributes in bytes and defaults to unlimited. Finally the 'implementation' element may define if the cache is disk or memory based, and the 'maxSize' attribute defines the maximum number of elements to be cached.
<clone [id="id"] [continueParent=(true | false)] [sequential=(true | false)]> <target [to="uri"] [soapAction="qname"] [sequence="sequence_ref"] [endpoint="endpoint_ref"]> <sequence> (mediator)+ </sequence>? <endpoint> endpoint </endpoint>? </target>+ </clone>
The clone mediator closely resembles the Message Splitter EIP and will split the message into number of identical messages which will be processed in parallel. They can also be set to process sequentially by setting the value of the optional 'sequential' attribute to 'true'. The original message cloned can be continued or dropped depending on the boolean value of the optional 'continueParent' attribute. Optionally a custom 'To' address and/or a 'Action' may be specified for cloned messages The optional 'id' attribute can be used to identify the clone mediator which created a particular splitted message when nested clone mediators are used. This is particularly useful when aggregating responses of messages that are created using nested clone mediators.
<iterate [id="id"] [continueParent=(true | false)] [preservePayload=(true | false)] [sequential=(true | false)] (attachPath="xpath")? expression="xpath"> <target [to="uri"] [soapAction="qname"] [sequence="sequence_ref"] [endpoint="endpoint_ref"]> <sequence> (mediator)+ </sequence>? <endpoint> endpoint </endpoint>? </target>+ </iterate>
The iterate mediator implements another EIP and will split the message into number of different messages derived from the parent message by finding matching elements for the XPath expression specified. New messages will be created for each and every matching element and processed in parallel(default behavior) using either the specified sequence or endpoint. Created messages can also be set to process sequentially by setting the optional 'sequential' attribute to 'true'. Parent message can be continued or dropped in the same way as in the clone mediator. The 'preservePayload' attribute specifies if the original message should be used as a template when creating the splitted messages, and defaults to 'false', in which case the splitted messages would contain the split elements as the SOAP body. The optional 'id' attribute can be used to identify the iterator which created a particular splitted message when nested iterate mediators are used. This is particularly useful when aggregating responses of messages that are created using nested iterate mediators.
<aggregate [id="id"]> <correlateOn expression="xpath"/>? <completeCondition [timeout="time-in-seconds"]> <messageCount min="int-min" max="int-max"/>? </completeCondition>? <onComplete expression="xpath" [sequence="sequence-ref"]> (mediator +)? </onComplete> </aggregate>
The aggregate mediator implements the Message Aggregator EIP and will aggregate the messages or responses for splitted messages using either the clone or iterate mediators. At the same time it can aggregate messages on the presence of matching elements specified by the correlateOn XPATH expression. Aggregate will collect the messages coming into it until the messages collected on the aggregation satisfies the complete condition. The completion condition can specify a minimum or maximum number of messages to be collected, or a timeout value in seconds, after which the aggregation terminates. On completion of the aggregation it will merge all of the collected messages and invoke the onComplete sequence on it. The merged message would be created using the XPath expression specified by the attribute 'expression' on the 'onComplete' element. The optional 'id' attribute can be used to aggregate only responses for splitted messages that are created by a specific clone/iterate mediator. Aggregate ID should be same as the ID of the corresponding clone/iterate mediator that creates splitted messages. This is particularly useful when aggregating responses of messages that are created using nested clone/iterate mediators.
<syn:eventPublisher eventSourceName="event-source-name"/>
Event mediator publishes events to the given event source. Thus, the presence of defined event sources are necessary prior to the usage of this mediator.
<syn:entitlementService remoteServiceUrl="[IDENTITY_SERVER:PORT]/services" remoteServiceUserName="admin" remoteServicePassword="admin"/>
The Entitlement Mediator by passes the requests and evaluates the actions performed by the user against the XACML policy defined at the Policy Decision Point [WSO2 Identity Server]
<syn:oauthService remoteServiceUrl="[IDENTITY_SERVER:PORT]/services"/>
The OAuth Mediator by passes the requests and evaluates RESRfull invocations based on 2-legged OAuth.
<syn:transaction action="transaction-action" />
Transaction mediator can provide transaction facility for a set of mediators defined as its child mediators. A transaction mediator with the action "new" indicates the entry point for the transaction. A transaction is marked completed by a transaction mediator with the action "commit". The suspend and resume actions are used to pause a transaction at some point and start it again later. Additionally, the transaction mediator supports three other actions, i.e. use-existing-or-new, fault-if-no-tx, rollback.
<class name="class-name"> <property name="string" value="literal"> (either literal or XML child) </property> </class>
The class mediator creates an instance of a custom specified class and sets it as a mediator. The class must implement the org.apache.synapse.api.Mediator interface. If any properties are specified, the corresponding setter methods are invoked on the class, once, during initialization.
<pojoCommand name="class-name"> ( <property name="string" value="string"/> | <property name="string" context-name="literal" [action=(ReadContext | UpdateContext | ReadAndUpdateContext)]> (either literal or XML child) </property> | <property name="string" expression="xpath" [action=(ReadMessage | UpdateMessage | ReadAndUpdateMessage)]/> )* </pojoCommand>
The pojoCommand mediator creates an instance of the specified command class - which may implement the org.apache.synapse.Command interface or should have a public void method "public void execute()". If any properties are specified, the corresponding setter methods are invoked on the class before each message is executed. It should be noted that a new instance of the POJO Command class is created to process each message processed. After execution of the POJO Command mediator, depending on the 'action' attribute of the property, the new value returned by a call to the corresponding getter method is stored back to the message or to the context. The 'action' attribute may specify whether this behaviour is expected or not via the Read, Update and ReadAndUpdate properties.
Synapse supports Mediators implemented in a variety of scripting languages such as JavaScript, Python or Ruby. There are two ways of defining script mediators, either with the script program statements stored in a separate file which is referenced via the local or remote registry entry, or with the script program statements embedded in-line within the Synapse configuration. A script mediator using a script off the registry (local or remote) is defined as follows:
<script key="string" language="string" [function="script-function-name"]/>
The property key is the registry key to load the script. The language attribute specifies the scripting language of the script code (e.g. "js" for Javascript, "rb" for ruby, "groovy" for Groovy, "py" for Python..). The function is an optional attribute defining the name of the script function to invoke, if not specified it defaults to a function named 'mediate'. The function is passed a single parameter - which is the Synapse MessageContext. The function may return a boolean, if it does not, then true is assumed, and the script mediator returns this value. An inline script mediator has the script source embedded in the configuration as follows:
<script language="string">...script source code...<script/>
The execution context environment of the script has access to the Synapse MessageContext predefined in a script variable named 'mc' . An example of an inline mediator using JavaScript/E4X which returns false if the SOAP message body contains an element named 'symbol' which has a value of 'IBM' would be:
<script language="js">mc.getPayloadXML()..symbol != "IBM";<script/>
Synapse uses the Apache Bean Scripting Framework for the scripting language support, any script language supported by BSF may be used to implement a Synapse Mediator.
Implementing a Mediator with a script language can have advantages over using the built in Synapse Mediator types or implementing a custom Java class Mediator. Script Mediators have all the flexibility of a class Mediator with access to the Synapse MessageContext and SynapseEnvironment APIs, and the ease of use and dynamic nature of scripting languages allows rapid development and prototyping of custom mediators. An additional benefit of some scripting languages is that they have very simple and elegant XML manipulation capabilities, for example JavaScript E4X or Ruby REXML, so this makes them well suited for use in the Synapse mediation environment. For both types of script mediator definition the MessageContext passed into the script has additional methods over the standard Synapse MessageContext to enable working with the XML in a way natural to the scripting language. For example when using JavaScript getPayloadXML and setPayloadXML, E4X XML objects, and when using Ruby, REXML documents.
The Synapse configuration language could be easily extended, with configuration extensions as well as mediation extensions. The Spring mediator is such an example.
A Spring configuration could be created as a localEntry or remote registry entry providing a URL or a key reference to a Registry. The configuration is then created on first use or as necessary (as per registry lookup semantics) by the mediators which reference this configuration.
<localEntry key="string"/> <localEntry key="string" src="url"/>
The name attribute specifies a unique name for the configuration, and the src, key or inlined XML references to the Spring configuration
<spring:spring bean="exampleBean1" key="string"/>
The <spring> element creates an instance of a mediator, which is managed by Spring. This Spring bean must implement the Mediator interface for it to act as a Mediator. The key will reference the Spring ApplicationContext/Configuration used for the bean
The <spring> element creates an instance of a mediator, which is managed by Spring. This Spring bean must implement the Mediator interface for it to act as a Mediator. The key will reference the Spring ApplicationContext/Configuration used for the bean
Rule mediator is to integrate the WSO2 Rules component to the WSO2 ESB in order to define dynamic integration decisions in terms of rules.
<rule> <ruleset> <source [ key="xs:string" ]> [ in-Lined ] </source> <creation> <property name="xs:string" value="xs:string"/>* </creation> </ruleset> <session type="[stateless|stateful]"/>* <facts> <fact name="xs:string" type="xs:string" expression="xs:string" value="xs:string"/>+ </facts> <results> <result name="xs:string" type="xs:string" expression="xs:string" value="xs:string"/>* </results> [ <childMediators> <mediator/>* </childMediators> ] </rule>
The source is the only mandatory element of the ruleset. However, the properties required for the creation of the ruleset can also be specified within ruleset. The key attribute is a registry key, which is to lookup the rule script from the registry if the rule script is in the registry. The rule set can be given as a child node of source elemenent. If the rule set is non-XML, you may need to wrap it with a CDATA section inside a XML tag ex: <X><![CDATA[ native code]]></X>
Note : The key or in-lined rule script must be defined. Otherwise, the rule mediator configuration is invalid.
Rule Session specify the stateful or stateless behavior of the rule engine. If this has value ‘stateful’, then the rule engine will execute rules in a stateful manner, for any other value , it assumes as stateless. There are optional properties, which are used when creating the rule session. Rule session is optional and the default one is stateful.
Facts specify the facts being used in rule set. It also defines how to formulate facts from the message, etc. Results define how to handle results from the rule set execution. Usually, results adapters enrich the message with results. For example, If you are using POJO adapter (i.e. a java class as the type – the class name of a result), then we transform POJO into an XML and attached to the SOAP message.
As mentioned earlier the ESB management console provides tools that can be used to construct mediation configurations. When these tools are used to create endpoints, sequences, proxy services and other configuration elements they are also saved under the appropriate child directory under the synapse-config directory. For an example if you add an endpoint named 'foo' from the UI it will be saved to a file named 'foo.xml' in the synapse-config/endpoints directory. Further modifications to the endpoint 'foo' will be saved to the same configuration file.
However there is a slight exception with the Synapse configuration editor in the ESB management console (available under the 'Configure' menu). New elements add through this editor will be saved to the top level synapse.xml file in the synapse-config directory. Anyway, if an existing item is modified through the Synapse configuration editor it will be still saved back to the original file where it was loaded from.