Package org.apache.nutch.metadata

Class MetaWrapper

java.lang.Object

org.apache.hadoop.io.GenericWritable

org.apache.nutch.util.GenericWritableConfigurable

org.apache.nutch.crawl.NutchWritable

org.apache.nutch.metadata.MetaWrapper

All Implemented Interfaces:

Configurable, Writable

public class MetaWrapper
extends NutchWritable

This is a simple decorator that adds metadata to any Writable-s that can be serialized by NutchWritable. This is useful when data needs to be temporarily enriched during processing, but this temporary metadata doesn't need to be permanently stored after the job is done.

Author:

Andrzej Bialecki

Constructor Summary

Constructors

Constructor	Description
MetaWrapper()
MetaWrapper(Writable instance, Configuration conf)
MetaWrapper(Metadata metadata, Writable instance, Configuration conf)

Method Summary

Modifier and Type	Method	Description
void	addMeta(String name, String value)	Add metadata.
String	getMeta(String name)	Get metadata value for a given key.
Metadata	getMetadata()	Get all metadata.
String[]	getMetaValues(String name)	Get multiple metadata values for a given key.
void	readFields(DataInput in)
void	setMeta(String name, String value)	Set metadata.
void	write(DataOutput out)

Methods inherited from class org.apache.nutch.crawl.NutchWritable

getTypes

Methods inherited from class org.apache.nutch.util.GenericWritableConfigurable

getConf, setConf

Methods inherited from class org.apache.hadoop.io.GenericWritable

get, set, toString

Methods inherited from class java.lang.Object

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

Constructor Details

MetaWrapper

public MetaWrapper()

MetaWrapper

public MetaWrapper(Writable instance,
 Configuration conf)

MetaWrapper

public MetaWrapper(Metadata metadata,
 Writable instance,
 Configuration conf)

Method Details

getMetadata

public Metadata getMetadata()

Get all metadata.

Returns:

a populated Metadata object

addMeta

public void addMeta(String name,
 String value)

Add metadata.

Parameters:

name - metadata name to add

value - metadata value to add

See Also:

• Metadata.add(String, String)

setMeta

public void setMeta(String name,
 String value)

Set metadata.

Parameters:

name - metadata key to set

value - metadata value to set

See Also:

• Metadata.set(String, String)

getMeta

public String getMeta(String name)

Get metadata value for a given key.

Parameters:

name - key to retrieve a value for

Returns:

metadata value

See Also:

• Metadata.getValues(String)

getMetaValues

public String[] getMetaValues(String name)

Get multiple metadata values for a given key.

Parameters:

name - key to retrieve values for

Returns:

a string array containing metadata values

See Also:

• Metadata.getValues(String)

readFields

public void readFields(DataInput in)
                throws IOException

Specified by:

readFields in interface Writable

Overrides:

readFields in class GenericWritableConfigurable

Throws:

IOException

write

public void write(DataOutput out)
           throws IOException

Specified by:

write in interface Writable

Overrides:

write in class GenericWritable

Throws:

IOException