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java.lang.Objectorg.apache.hadoop.io.GenericWritable
public abstract class GenericWritable
A wrapper for Writable instances.
When two sequence files, which have same Key type but different Value types, are mapped out to reduce, multiple Value types is not allowed. In this case, this class can help you wrap instances with different types.
Compared with ObjectWritable, this class is much more effective,
because ObjectWritable will append the class declaration as a String
into the output file in every Key-Value pair.
Generic Writable implements Configurable interface, so that it will be
configured by the framework. The configuration is passed to the wrapped objects
implementing Configurable interface before deserialization.
getTypes(), defines
the classes which will be wrapped in GenericObject in application.
Attention: this classes defined in getTypes() method, must
implement Writable interface.
public class GenericObject extends GenericWritable {
private static Class[] CLASSES = {
ClassType1.class,
ClassType2.class,
ClassType3.class,
};
protected Class[] getTypes() {
return CLASSES;
}
}
| Constructor Summary | |
|---|---|
GenericWritable()
|
|
| Method Summary | |
|---|---|
Writable |
get()
Return the wrapped instance. |
Configuration |
getConf()
Return the configuration used by this object. |
protected abstract Class<? extends Writable>[] |
getTypes()
Return all classes that may be wrapped. |
void |
readFields(DataInput in)
Deserialize the fields of this object from in. |
void |
set(Writable obj)
Set the instance that is wrapped. |
void |
setConf(Configuration conf)
Set the configuration to be used by this object. |
String |
toString()
|
void |
write(DataOutput out)
Serialize the fields of this object to out. |
| Methods inherited from class java.lang.Object |
|---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
| Constructor Detail |
|---|
public GenericWritable()
| Method Detail |
|---|
public void set(Writable obj)
obj - public Writable get()
public String toString()
toString in class Object
public void readFields(DataInput in)
throws IOException
Writablein.
For efficiency, implementations should attempt to re-use storage in the existing object where possible.
readFields in interface Writablein - DataInput to deseriablize this object from.
IOException
public void write(DataOutput out)
throws IOException
Writableout.
write in interface Writableout - DataOuput to serialize this object into.
IOExceptionprotected abstract Class<? extends Writable>[] getTypes()
public Configuration getConf()
Configurable
getConf in interface Configurablepublic void setConf(Configuration conf)
Configurable
setConf in interface Configurable
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