org.apache.hadoop.metrics

Class ContextFactory

java.lang.Object

org.apache.hadoop.metrics.ContextFactory

@InterfaceAudience.LimitedPrivate(value={"HDFS","MapReduce"})
@InterfaceStability.Evolving
public class ContextFactory
extends Object

Factory class for creating MetricsContext objects. To obtain an instance of this class, use the static getFactory() method.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ContextFactory() Creates a new instance of ContextFactory

Method Summary

Methods

Modifier and Type	Method and Description
Collection<MetricsContext>	getAllContexts() Returns all MetricsContexts built by this factory.
Object	getAttribute(String attributeName) Returns the value of the named attribute, or null if there is no attribute of that name.
String[]	getAttributeNames() Returns the names of all the factory's attributes.
MetricsContext	getContext(String contextName)
MetricsContext	getContext(String refName, String contextName) Returns the named MetricsContext instance, constructing it if necessary using the factory's current configuration attributes.
static ContextFactory	getFactory() Returns the singleton ContextFactory instance, constructing it if necessary.
static MetricsContext	getNullContext(String contextName) Returns a "null" context - one which does nothing.
void	removeAttribute(String attributeName) Removes the named attribute if it exists.
void	setAttribute(String attributeName, Object value) Sets the named factory attribute to the specified value, creating it if it did not already exist.

Methods inherited from class java.lang.Object

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

Constructor Detail

ContextFactory

protected ContextFactory()

Creates a new instance of ContextFactory

Method Detail

getAttribute

public Object getAttribute(String attributeName)

Returns the value of the named attribute, or null if there is no attribute of that name.

Parameters:

attributeName - the attribute name

Returns:

the attribute value

getAttributeNames

public String[] getAttributeNames()

Returns the names of all the factory's attributes.

Returns:

the attribute names

setAttribute

public void setAttribute(String attributeName,
                Object value)

Sets the named factory attribute to the specified value, creating it if it did not already exist. If the value is null, this is the same as calling removeAttribute.

Parameters:

attributeName - the attribute name

value - the new attribute value

removeAttribute

public void removeAttribute(String attributeName)

Removes the named attribute if it exists.

Parameters:

attributeName - the attribute name

getContext

public MetricsContext getContext(String refName,
                        String contextName)
                          throws IOException,
                                 ClassNotFoundException,
                                 InstantiationException,
                                 IllegalAccessException

Returns the named MetricsContext instance, constructing it if necessary using the factory's current configuration attributes.

When constructing the instance, if the factory property contextName.class exists, its value is taken to be the name of the class to instantiate. Otherwise, the default is to create an instance of org.apache.hadoop.metrics.spi.NullContext, which is a dummy "no-op" context which will cause all metric data to be discarded.

Parameters:

contextName - the name of the context

Returns:

the named MetricsContext

Throws:

IOException

ClassNotFoundException

InstantiationException

IllegalAccessException

getContext

public MetricsContext getContext(String contextName)
                          throws IOException,
                                 ClassNotFoundException,
                                 InstantiationException,
                                 IllegalAccessException

Throws:

IOException

ClassNotFoundException

InstantiationException

IllegalAccessException

getAllContexts

public Collection<MetricsContext> getAllContexts()

Returns all MetricsContexts built by this factory.

getNullContext

public static MetricsContext getNullContext(String contextName)

Returns a "null" context - one which does nothing.

getFactory

public static ContextFactory getFactory()
                                 throws IOException

Returns the singleton ContextFactory instance, constructing it if necessary.

When the instance is constructed, this method checks if the file hadoop-metrics.properties exists on the class path. If it exists, it must be in the format defined by java.util.Properties, and all the properties in the file are set as attributes on the newly created ContextFactory instance.

Returns:

the singleton ContextFactory instance

Throws:

IOException