org.apache.cocoon.components.modules.input
Class ChainMetaModule

java.lang.Object
  org.apache.avalon.framework.logger.AbstractLogEnabled
      org.apache.cocoon.components.modules.input.AbstractInputModule
          org.apache.cocoon.components.modules.input.AbstractMetaModule
              org.apache.cocoon.components.modules.input.ChainMetaModule

All Implemented Interfaces:

Disposable, Component, Composable, Configurable, LogEnabled, ThreadSafe, InputModule

public class ChainMetaModule
extends AbstractMetaModule
implements ThreadSafe

This modules allows to "chain" several other modules. If a module returns "null" as attribute value, the next module in the chain is queried until either a value can be obtained or the end of the chain is reached.

A typical example would be to "chain" request parameters, session attributes, and constants in this order. This way, an application could have a default skin that could be overridden by a user in her/his profile stored in the session. In addition, the user could request a different skin through passing a request parameter.

Usage:

Any number of <input-module/> blocks may appear in the component configuration. The @name attribute is used as the name of the requested input module. The complete <input-module/> block is passed at run-time to the module and thus can contain any configuration data for that particular module.

Configuration:

It can be controlled whether it returns a flat or a deep view, i.e. whether only values from the first module are returned if non-null or they are merged with values from other modules <all-values>true</all-values>. The same is possible for the attribute names (<all-names/>). In addition, empty strings could be treated the same as null values (<empty-as-null/>).

Version:

CVS $Id: ChainMetaModule.html 1304258 2012-03-23 10:09:27Z ilgrosso $

Author:

Christian Haul

Field Summary

Fields inherited from class org.apache.cocoon.components.modules.input.AbstractMetaModule

defaultInput, initialized, input, INPUT_MODULE_SELECTOR, inputConf, inputSelector, manager

Fields inherited from class org.apache.cocoon.components.modules.input.AbstractInputModule

settings

Fields inherited from interface org.apache.cocoon.components.modules.input.InputModule

ROLE

Constructor Summary

ChainMetaModule()

Method Summary

void	configure(Configuration config) Configures the database access helper.
void	dispose() Dispose exactly one cached InputModule.
Object	getAttribute(String attr, Configuration modeConf, Map objectModel) Standard access to an attribute's value.
Iterator	getAttributeNames(Configuration modeConf, Map objectModel) Returns an Iterator of String objects containing the names of the attributes available.
Object[]	getAttributeValues(String attr, Configuration modeConf, Map objectModel) Returns an array of String objects containing all of the values the given attribute has, or null if the attribute does not exist.
void	lazy_initialize() Initialize the meta module with exactly one other input module.

Methods inherited from class org.apache.cocoon.components.modules.input.AbstractMetaModule

compose, getNames, getNames, getValue, getValue, getValue, getValue, getValues, getValues, getValues, getValues, obtainModule, releaseModule

Methods inherited from class org.apache.avalon.framework.logger.AbstractLogEnabled

enableLogging, getLogger, setupLogger, setupLogger, setupLogger

Methods inherited from class java.lang.Object

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

Constructor Detail

ChainMetaModule

public ChainMetaModule()

Method Detail

configure

public void configure(Configuration config)
               throws ConfigurationException

Description copied from class: AbstractInputModule

Configures the database access helper. Takes all elements nested in component declaration and stores them as key-value pairs in settings. Nested configuration option are not catered for. This way global configuration options can be used. For nested configurations override this function.

Specified by:

configure in interface Configurable

Overrides:

configure in class AbstractInputModule

Throws:

ConfigurationException

lazy_initialize

public void lazy_initialize()

Description copied from class: AbstractMetaModule

Initialize the meta module with exactly one other input module. Since "meta" modules require references to components of the same role, initialization cannot be done in initialize() when also implementing ThreadSafe since at that point the component selector is not yet initialized it would trigger the creation of a new one resulting in an endless loop of initializations. Therefore, every module needs to call this method when it first requires access to another module if the module itself has not been initialized. Override this method and dispose() to keep references to more than one module.

Overrides:

lazy_initialize in class AbstractMetaModule

dispose

public void dispose()

Description copied from class: AbstractMetaModule

Dispose exactly one cached InputModule. To work on more than one, override this method and initialize().

Specified by:

dispose in interface Disposable

Overrides:

dispose in class AbstractMetaModule

getAttributeValues

public Object[] getAttributeValues(String attr,
                                   Configuration modeConf,
                                   Map objectModel)
                            throws ConfigurationException

Description copied from interface: InputModule

Returns an array of String objects containing all of the values the given attribute has, or null if the attribute does not exist. As an alternative, InputModule.getAttributeNames(Configuration, Map) together with InputModule.getAttribute(String, Configuration, Map) can be used to get the values one by one.

Specified by:

getAttributeValues in interface InputModule

Overrides:

getAttributeValues in class AbstractInputModule

Parameters:

attr - a String that specifies what the caller thinks would identify an attributes. This is mainly a fallback if no modeConf is present.

modeConf - column's mode configuration from resource description. This argument is optional.

Throws:

ConfigurationException

getAttributeNames

public Iterator getAttributeNames(Configuration modeConf,
                                  Map objectModel)
                           throws ConfigurationException

Description copied from interface: InputModule

Returns an Iterator of String objects containing the names of the attributes available. If no attributes are available, the method returns an empty Iterator.

Specified by:

getAttributeNames in interface InputModule

Overrides:

getAttributeNames in class AbstractInputModule

Parameters:

modeConf - column's mode configuration from resource description. This argument is optional.

Throws:

ConfigurationException

getAttribute

public Object getAttribute(String attr,
                           Configuration modeConf,
                           Map objectModel)
                    throws ConfigurationException

Description copied from interface: InputModule

Standard access to an attribute's value. If more than one value exists, the first is returned. If the value does not exist, null is returned. To get all values, use InputModule.getAttributeValues(String, Configuration, Map) or InputModule.getAttributeNames(Configuration, Map) and InputModule.getAttribute(String, Configuration, Map) to get them one by one.

Specified by:

getAttribute in interface InputModule

Overrides:

getAttribute in class AbstractInputModule

Parameters:

attr - a String that specifies what the caller thinks would identify an attribute. This is mainly a fallback if no modeConf is present.

modeConf - column's mode configuration from resource description. This argument is optional.

Throws:

ConfigurationException