org.codehaus.commons.compiler

Interface IExpressionEvaluator

All Superinterfaces:

ICookable, IMultiCookable

public interface IExpressionEvaluator
extends ICookable, IMultiCookable

An engine that evaluates expressions in JVM bytecode.

The syntax of the expression to compile is that of a Java expression, as defined in JLS7, section 15. Notice that a Java expression does not have a concluding semicolon.

Example:

   a + 7 * b
 

(Notice that this expression refers to two parameters "a" and "b", as explained below.)

The expression may optionally be preceeded with a sequence of import directives like

   import java.text.*;
   new DecimalFormat("####,###.##").format(10200020.345345)
 

(Notice that the import directive is concluded with a semicolon, while the expression is not.) This feature is not available if you compile many expressions at a time (see below).

To set up an IExpressionEvaluator object, proceed as follows:

1. Create an IExpressionEvaluator-derived class
2. Configure the IExpressionEvaluator by calling any of the following methods:
• setExpressionType(Class)
• setParameters(String[], Class[])
• setThrownExceptions(Class[])
• setParentClassLoader(ClassLoader)
• setDefaultImports(String[])
3. Call any of the ICookable.cook(String, java.io.Reader) methods to scan, parse, compile and load the expression into the JVM.

After the IExpressionEvaluator object is set up, the expression can be evaluated as often with different parameter values (see evaluate(Object[])). This evaluation is very fast, compared to the compilation.

Less common methods exist that allow for the specification of the name of the generated class, the class it extends, the interfaces it implements, the name of the method that executes the expression, the exceptions that this method (i.e. the expression) is allowed to throw, and the ClassLoader that is used to define the generated class and to load classes referenced by the expression.

If you want to compile many expressions at the same time, you have the option to cook an array of expressions in one IExpressionEvaluator by using the following methods:

• setMethodNames(String[])
• setParameters(String[][], Class[][])
• setExpressionTypes(Class[])
• setStaticMethod(boolean[])
• setThrownExceptions(Class[][])
• IMultiCookable.cook(String[], Reader[])
• evaluate(int, Object[])

Notice that these methods have array parameters in contrast to their one-expression brethren.

Notice that for functionally identical IExpressionEvaluators, Object.equals(java.lang.Object) will return true. E.g. "a+b" and "c + d" are functionally identical if "a" and "c" have the same type, and so do "b" and "d".

'JLS7' refers to the Java Language Specification, Java SE 7 Edition.

Field Summary

Fields

Modifier and Type	Field and Description
static Class<?>	ANY_TYPE Deprecated. Since autoboxing was introduced in JANINO, this feature is no longer necessary because you can use expression type Object.class
static String	DEFAULT_CLASS_NAME The fully qualified name of the generated class, iff not reconfigured by setClassName(String).
static Class<?>	DEFAULT_EXPRESSION_TYPE The type of all expressions that were not reconfigured with setExpressionTypes(Class[]).

Method Summary

Modifier and Type	Method and Description
<T> T	createFastEvaluator(Reader reader, Class<? extends T> interfaceToImplement, String... parameterNames)
<T> T	createFastEvaluator(String expression, Class<? extends T> interfaceToImplement, String... parameterNames) If the parameter and return types of the expression are known at compile time, then a "fast" expression evaluator can be instantiated through createFastEvaluator(String, Class, String[]).
Object	evaluate(int idx, Object... arguments) Null arguments is equivalent with new Object[0].
Object	evaluate(Object... arguments) Evaluates the expression with concrete parameter values.
Class<?>	getClazz()
Class<?>	getDefaultExpressionType()
String[]	getDefaultImports()
Method	getMethod()
Method	getMethod(int idx)
Method[]	getResult()
void	setClassName(String className)
void	setCompileErrorHandler(ErrorHandler compileErrorHandler) Installs an ErrorHandler which is invoked during compilation on each error.
void	setDebuggingInformation(boolean debugSource, boolean debugLines, boolean debugVars) Determines what kind of debugging information is included in the generates classes.
void	setDefaultExpressionType(Class<?> defaultExpressionType) Reconfigures the "default expression type"; if no expression type is configured for an expression, then, when cooking this IExpressionEvaluator, the "default expression type" is used for the expression
void	setDefaultImports(String... defaultImports)
void	setExpressionType(Class<?> expressionType) Defines the type of the expression.
void	setExpressionTypes(Class<?>[] expressionTypes) Configures the types of the expressions.
void	setExtendedClass(Class<?> extendedType)
void	setImplementedInterfaces(Class<?>[] implementedTypes) Configures the interfaces that the generated class implements.
void	setMethodName(String methodName)
void	setMethodNames(String[] methodNames)
void	setOverrideMethod(boolean overrideMethod)
void	setOverrideMethod(boolean[] overrideMethod)
void	setParameters(String[][] parameterNames, Class<?>[][] parameterTypes)
void	setParameters(String[] parameterNames, Class<?>[] parameterTypes)
void	setParentClassLoader(ClassLoader parentClassLoader) The "parent class loader" is used to load referenced classes.
void	setReturnType(Class<?> returnType) Deprecated. Use setExpressionType(Class) instead
void	setStaticMethod(boolean staticMethod)
void	setStaticMethod(boolean[] staticMethod)
void	setThrownExceptions(Class<?>[] thrownExceptions)
void	setThrownExceptions(Class<?>[][] thrownExceptions)
void	setWarningHandler(WarningHandler warningHandler) By default, warnings are discarded, but an application my install a custom WarningHandler.

Methods inherited from interface org.codehaus.commons.compiler.ICookable

cook, cook, cook, cook, cook, cook, cook, cook, cookFile, cookFile, cookFile, cookFile, getBytecodes, setSourceVersion, setTargetVersion

Methods inherited from interface org.codehaus.commons.compiler.IMultiCookable

cook, cook, cook, cook, cook, cook, cook, cook, cookFiles, cookFiles, cookFiles, cookFiles

Field Detail

DEFAULT_CLASS_NAME

static final String DEFAULT_CLASS_NAME

The fully qualified name of the generated class, iff not reconfigured by setClassName(String).

See Also:

Constant Field Values

DEFAULT_EXPRESSION_TYPE

static final Class<?> DEFAULT_EXPRESSION_TYPE

The type of all expressions that were not reconfigured with setExpressionTypes(Class[]).

ANY_TYPE

@Deprecated
static final Class<?> ANY_TYPE

Deprecated. Since autoboxing was introduced in JANINO, this feature is no longer necessary because you can use expression type Object.class

Special value for setExpressionType(Class) that indicates that the expression may have any type.

Method Detail

setParentClassLoader

void setParentClassLoader(@Nullable
                          ClassLoader parentClassLoader)

The "parent class loader" is used to load referenced classes. Useful values are:

System.getSystemClassLoader()	The running JVM's class path
Thread.currentThread().getContextClassLoader() or null	The class loader effective for the invoking thread
ClassLoaders.BOOTCLASSPATH_CLASS_LOADER	The running JVM's boot class path

The parent class loader defaults to the current thread's context class loader.

setDebuggingInformation

void setDebuggingInformation(boolean debugSource,
                             boolean debugLines,
                             boolean debugVars)

Determines what kind of debugging information is included in the generates classes. The default is typically "-g:none".

setCompileErrorHandler

void setCompileErrorHandler(@Nullable
                            ErrorHandler compileErrorHandler)

Installs an ErrorHandler which is invoked during compilation on each error. (By default, the compilation throws a CompileException on the first error and terminates.)

If the given ErrorHandler throws a CompileException, then the compilation terminates and the exception is propagated.

If the given ErrorHandler does not throw a CompileException but completes normally, then the compilation may or may not continue, depending on the error. Iff the compilation completes normally but errors were reported, then it will throw a CompileException indicating the number of errors.

In other words: The ErrorHandler may throw a CompileException or not, but the compilation will definitely throw a CompileException if one or more compile errors have occurred.

Parameters:

compileErrorHandler - null to restore the default behavior (throwing a CompileException)

setWarningHandler

void setWarningHandler(@Nullable
                       WarningHandler warningHandler)

By default, warnings are discarded, but an application my install a custom WarningHandler.

Parameters:

warningHandler - null to indicate that no warnings be issued

evaluate

@Nullable
Object evaluate(@Nullable
                           Object... arguments)
                    throws InvocationTargetException

Evaluates the expression with concrete parameter values.

Each argument value must have the same type as specified through the "parameterTypes" parameter of setParameters(String[], Class[]).

Arguments of primitive type must passed with their wrapper class objects.

The object returned has the class as specified through setExpressionType(Class).

This method is thread-safe.

Null arguments is equivalent with new Object[0].

Parameters:

arguments - The actual parameter values

Throws:

InvocationTargetException

setDefaultExpressionType

void setDefaultExpressionType(Class<?> defaultExpressionType)

Reconfigures the "default expression type"; if no expression type is configured for an expression, then, when cooking this IExpressionEvaluator, the "default expression type" is used for the expression

getDefaultExpressionType

Class<?> getDefaultExpressionType()

Returns:

The currently configured "default expression type"

See Also:

setDefaultExpressionType(Class)

setImplementedInterfaces

void setImplementedInterfaces(Class<?>[] implementedTypes)

Configures the interfaces that the generated class implements.

setReturnType

@Deprecated
void setReturnType(@Deprecated
                                Class<?> returnType)

Deprecated. Use setExpressionType(Class) instead

setExpressionType

void setExpressionType(Class<?> expressionType)

Defines the type of the expression.

Defaults to Object.class, which, thanks to autoboxing, allows for any expression type (including primitive types).

If expressionType is void.class, then the expression must be an invocation of a void method.

setExpressionTypes

void setExpressionTypes(Class<?>[] expressionTypes)

Configures the types of the expressions.

Unless this method is called, all expressions have type Object.class.

If any expression has type void.class, then it must be an invocation of a void method.

setOverrideMethod

void setOverrideMethod(boolean overrideMethod)

See Also:

IScriptEvaluator.setOverrideMethod(boolean)

setOverrideMethod

void setOverrideMethod(boolean[] overrideMethod)

See Also:

IScriptEvaluator.setOverrideMethod(boolean[])

setParameters

void setParameters(String[] parameterNames,
                   Class<?>[] parameterTypes)

See Also:

IScriptEvaluator.setParameters(String[], Class[])

setParameters

void setParameters(String[][] parameterNames,
                   Class<?>[][] parameterTypes)

See Also:

IScriptEvaluator.setParameters(String[][], Class[][])

setClassName

void setClassName(String className)

See Also:

IClassBodyEvaluator.setClassName(String)

setExtendedClass

void setExtendedClass(Class<?> extendedType)

See Also:

IClassBodyEvaluator.setExtendedClass(Class)

setDefaultImports

void setDefaultImports(String... defaultImports)

See Also:

IClassBodyEvaluator.setDefaultImports(String...)

getDefaultImports

String[] getDefaultImports()

See Also:

IClassBodyEvaluator.getDefaultImports()

setStaticMethod

void setStaticMethod(boolean staticMethod)

See Also:

IScriptEvaluator.setStaticMethod(boolean)

setStaticMethod

void setStaticMethod(boolean[] staticMethod)

See Also:

IScriptEvaluator.setStaticMethod(boolean[])

setMethodName

void setMethodName(String methodName)

See Also:

IScriptEvaluator.setMethodName(String)

setMethodNames

void setMethodNames(String[] methodNames)

See Also:

IScriptEvaluator.setMethodNames(String[])

setThrownExceptions

void setThrownExceptions(Class<?>[] thrownExceptions)

See Also:

IScriptEvaluator.setThrownExceptions(Class[])

setThrownExceptions

void setThrownExceptions(Class<?>[][] thrownExceptions)

See Also:

IScriptEvaluator.setThrownExceptions(Class[][])

evaluate

@Nullable
Object evaluate(int idx,
                           @Nullable
                           Object... arguments)
                    throws InvocationTargetException

Null arguments is equivalent with new Object[0].

Throws:

InvocationTargetException

createFastEvaluator

<T> T createFastEvaluator(String expression,
                          Class<? extends T> interfaceToImplement,
                          String... parameterNames)
                   throws CompileException

If the parameter and return types of the expression are known at compile time, then a "fast" expression evaluator can be instantiated through createFastEvaluator(String, Class, String[]). Expression evaluation is faster than through evaluate(Object[]), because it is not done through reflection but through direct method invocation.

Example:

 public interface Foo {
     int bar(int a, int b);
 }
 ...
 ExpressionEvaluator ee = CompilerFactoryFactory.getDefaultCompilerFactory().newExpressionEvaluator();

 // Optionally configure the EE here...
 ee.setClassName("Bar");
 ee.setDefaultImports(new String[] { "java.util.*" });
 ee.setExtendedClass(SomeOtherClass.class);
 ee.setParentClassLoader(someClassLoader);

 // Optionally configure the EE here...
 Foo f = (Foo) ee.createFastEvaluator(
     "a + b",                    // expression to evaluate
     Foo.class,                  // interface that describes the expression's signature
     new String[] { "a", "b" }   // the parameters' names
 );
 System.out.println("1 + 2 = " + f.bar(1, 2)); // Evaluate the expression
 

All other configuration (implemented type, static method, return type, method name, parameter names and types, thrown exceptions) are predetermined by the interfaceToImplement.

Notice: The interfaceToImplement must be accessible by the compiled class, i.e. either be declared public, or with protected or default access in the package of the compiled class (see setClassName(String).

Throws:

CompileException

createFastEvaluator

<T> T createFastEvaluator(Reader reader,
                          Class<? extends T> interfaceToImplement,
                          String... parameterNames)
                   throws CompileException,
                          IOException

Throws:

CompileException

IOException

See Also:

createFastEvaluator(String, Class, String[])

getMethod

Method getMethod()

See Also:

IScriptEvaluator.getMethod()

getMethod

Method getMethod(int idx)

See Also:

IScriptEvaluator.getMethod(int)

getClazz

Class<?> getClazz()

See Also:

IClassBodyEvaluator.getClazz()

getResult

Method[] getResult()

See Also:

IScriptEvaluator.getResult()