org.xfp
Class Filter

java.lang.Object
  org.xfp.AttributeContainer
      org.xfp.Filter

Direct Known Subclasses:

AntTask, BeanCollectionSorter, BeanInstance, BeanXMLDecoder, BeanXMLEncoder, ByteArrayToInputStream, CheckAlreadyFiltered, CodecBinaryDecoder, CodecBinaryEncoder, CodecStringDecoder, CodecStringEncoder, DateGenerator, DeleteFile, DOMParser, FileReader, FileWriter, FOProcessor, FTPAbstractFilter, HTTPGet, InputStreamToByteArray, InputStreamToString, Iterator, JNDIAbstractFilter, JXPathAbstractFilter, ListGenerator, MapGenerator, MapIterator, PassThru, PatternMatcher, ReaderToString, StringToInputStream, XPathAbstractFilter, XSLTransformer

public abstract class Filter

extends AttributeContainer

Base class for all filters. Subclasses must provide a public method named 'execute' accepting 0 or 1 arguments of any type (but primitives) and returning any type (but primitives) or void. Example:

public List execute(String input)

Filters are parameterized by using JavaBeans setter methods.

Any Exception occurred during filter execution should not be trapped, the container takes care of handling exceptions.

Subclasses do not need to call super() constructor, since it is empty.

Filter instances are reused by the container, so make sure to correctly reset the Filter status in the reset method. Filters are never used concurrently by multiple threads, a Filter implementation does not have to be thread-safe.

TODO manage primitives in execute method. TODO discuss superclasses in signatures

Version:

$Id: Filter.java,v 1.1 2004/03/19 15:56:42 flaviotordini Exp $

Author:

Flavio Tordini

Nested Class Summary

static class	Filter.OnErrorEnum OnError typesafe enumeration.
static class	Filter.OnLoopErrorEnum OnLoopError typesafe enumeration.

Field Summary

Fields inherited from class org.xfp.AttributeContainer

name, parentContainer

Constructor Summary

Filter()

Method Summary

protected Filter.OnErrorEnum	getOnError() Gets the onError attribute of the Filter object.
void	initialize() Initializes the filter.
protected void	log(java.lang.String message) Subclasses can use this method to log for debugging purposes.
protected static Filter	newInstance(org.w3c.dom.Node filternode, org.w3c.dom.xpath.XPathEvaluator evaluator, java.lang.Class inputtype, AttributeContainer parent, org.apache.log4j.spi.LoggerRepository loggerRepository) Instantiates and initializes a Filter.
void	perform(org.xfp.FilterContext context, java.lang.Object parentoutput) Performing a filter consists of: provide filter attributes set filter properties invoke the 'execute' method call the 'release' method perform children filters release filter attributes Filter developers never call this method!
abstract void	reset() Resets filter status after execution.
java.lang.String	toString()

Methods inherited from class org.xfp.AttributeContainer

configureAttributes, disposeAttributes, getAttributes, getFullName, getName, initializeAttributes

Methods inherited from class java.lang.Object

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

Constructor Detail

Filter

public Filter()

Method Detail

initialize

public void initialize()
                throws java.lang.Exception

Initializes the filter. Called by the container to let the filter initialize properly. The default implementation is a no-op. Override this method to initialize your Filter.

Throws:

java.lang.Exception - Description of the Exception

See Also:

Initializable.initialize()

reset

public abstract void reset()

Resets filter status after execution. This method is called after execute(), even in case of exceptions. Since a Filter instance may be reused (and actually is), you must use this method to reset all your class members to their default value.

toString

public final java.lang.String toString()

See Also:

Object.toString()

perform

public final void perform(org.xfp.FilterContext context,
                          java.lang.Object parentoutput)
                   throws java.lang.Exception

Performing a filter consists of:

1. provide filter attributes
2. set filter properties
3. invoke the 'execute' method
4. call the 'release' method
5. perform children filters
6. release filter attributes

Filter developers never call this method!

Parameters:

parentoutput - output of the parent filter

context - Description of the Parameter

Throws:

java.lang.Exception - Description of the Exception

getOnError

protected final Filter.OnErrorEnum getOnError()

Gets the onError attribute of the Filter object. This value determines what to do in case of exception during filter execution.

Returns:

The onError value (one of the OnErrorEnum constants)

log

protected final void log(java.lang.String message)

Subclasses can use this method to log for debugging purposes.

Parameters:

message - Description of the Parameter

newInstance

protected static final Filter newInstance(org.w3c.dom.Node filternode,
                                          org.w3c.dom.xpath.XPathEvaluator evaluator,
                                          java.lang.Class inputtype,
                                          AttributeContainer parent,
                                          org.apache.log4j.spi.LoggerRepository loggerRepository)
                                   throws java.lang.Exception

Instantiates and initializes a Filter. Always use this method to get new instances, rather than directly instantiating a Filter impl. Filter developers never call this method!

Parameters:

filternode - Node representing a filter in XML configuration

evaluator - XPath Evaluator

inputtype - the input data type this filter will process (i.e. the parent filter output data type)

Returns:

Filter an initialized Filter instance

Throws:

java.lang.Exception - Description of the Exception