org.netpreserve.jwarc

Class WarcReader

java.lang.Object

org.netpreserve.jwarc.WarcReader

All Implemented Interfaces:

Closeable, AutoCloseable, Iterable<WarcRecord>

public class WarcReader
extends Object
implements Iterable<WarcRecord>, Closeable

Constructor Summary

Constructors

Constructor and Description
WarcReader(InputStream stream)
WarcReader(Path path)
WarcReader(ReadableByteChannel channel)
WarcReader(ReadableByteChannel channel, ByteBuffer buffer) Create WarcReader with user-provided buffer.

Method Summary

Modifier and Type	Method and Description
void	calculateBlockDigest() Enable calculation of block digests for all WARC records which include the header "WARC-Block-Digest" and using the same digest algorithm as mentioned in the header.
void	close() Closes the underlying channel.
WarcCompression	compression() The type of WARC compression that was detected.
Iterator<WarcRecord>	iterator() Returns an iterator over the records in the WARC file.
Optional<WarcRecord>	next() Reads the next WARC record.
void	onWarning(java.util.function.Consumer<String> warningHandler) Registers a handler that will be called when the reader encounters an error it was able to recover from.
long	position() Returns the byte position of the most recently read record.
void	position(long newPosition) Seeks to the record at the given position in the underlying channel.
java.util.stream.Stream<WarcRecord>	records() Returns a Stream over the records in the WARC file.
void	registerType(String type, WarcRecord.Constructor<WarcRecord> constructor) Registers a new extension record type.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Constructor Detail

WarcReader

public WarcReader(ReadableByteChannel channel,
                  ByteBuffer buffer)
           throws IOException,
                  IllegalArgumentException

Create WarcReader with user-provided buffer. Data contained in the buffer is used as initial input before reading from the input channel. The buffer must be ready for reading (Buffer.flip() called).

Parameters:

channel - read WARC data from

buffer - buffer to read initial data from, later used to buffer data from channel

Throws:

IOException

IllegalArgumentException - if buffer is not readable or is not backed by an array

WarcReader

public WarcReader(ReadableByteChannel channel)
           throws IOException

Throws:

IOException

WarcReader

public WarcReader(InputStream stream)
           throws IOException

Throws:

IOException

WarcReader

public WarcReader(Path path)
           throws IOException

Throws:

IOException

Method Detail

next

public Optional<WarcRecord> next()
                          throws IOException

Reads the next WARC record.

This method will construct an appropriate subclass of WarcRecord based on the value of the WARC-Type header. New types may be registered using registerType(String, WarcRecord.Constructor).

The body channel of any previously read record will be closed.

Returns:

a instance of WarcRecord or an empty Optional at the end of the channel.

Throws:

IOException - if an I/O error occurs.

ParsingException - if the WARC record is invalid.

registerType

public void registerType(String type,
                         WarcRecord.Constructor<WarcRecord> constructor)

Registers a new extension record type.

Builtin types like "resource" and "response" may be overridden with a subclass that adds extension methods. The special type name "default" is used when a unregistered record type is encountered.

Parameters:

type - a value of the WARC-Type header

constructor - a constructor for a corresponding subclass of WarcRecord

calculateBlockDigest

public void calculateBlockDigest()

Enable calculation of block digests for all WARC records which include the header "WARC-Block-Digest" and using the same digest algorithm as mentioned in the header. The actually calculated record digests (WarcRecord.calculatedBlockDigest()) can be then compared to the pre-calculated digests (WarcRecord.blockDigest()). See also DigestingMessageBody.

position

public long position()

Returns the byte position of the most recently read record.

For compressed WARCs this method will only return a meaningful value if the compression was applied in such a way that the start of a new record corresponds to the start of a compression block.

position

public void position(long newPosition)
              throws IOException

Seeks to the record at the given position in the underlying channel.

Parameters:

newPosition - byte offset of the beginning of the record to seek to

Throws:

IOException - if an I/O error occurs

IllegalArgumentException - if the position is negative

UnsupportedOperationException - if the underlying channel does not support seeking

compression

public WarcCompression compression()

The type of WARC compression that was detected.

iterator

public Iterator<WarcRecord> iterator()

Returns an iterator over the records in the WARC file.

Specified by:

iterator in interface Iterable<WarcRecord>

records

public java.util.stream.Stream<WarcRecord> records()

Returns a Stream over the records in the WARC file.

onWarning

public void onWarning(java.util.function.Consumer<String> warningHandler)

Registers a handler that will be called when the reader encounters an error it was able to recover from.

close

public void close()
           throws IOException

Closes the underlying channel.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Throws:

IOException