org.apache.commons.configuration
Class DefaultConfigurationBuilder

java.lang.Object
  org.apache.commons.configuration.event.EventSource
      org.apache.commons.configuration.AbstractConfiguration
          org.apache.commons.configuration.HierarchicalConfiguration
              org.apache.commons.configuration.AbstractHierarchicalFileConfiguration
                  org.apache.commons.configuration.XMLConfiguration
                      org.apache.commons.configuration.DefaultConfigurationBuilder

All Implemented Interfaces:

Cloneable, Configuration, ConfigurationBuilder, ConfigurationListener, EntityResolver, FileConfiguration, Serializable

public class DefaultConfigurationBuilder

extends XMLConfiguration

implements ConfigurationBuilder

A factory class that creates a composite configuration from an XML based configuration definition file.

This class provides an easy and flexible means for loading multiple configuration sources and combining the results into a single configuration object. The sources to be loaded are defined in an XML document that can contain certain tags representing the different supported configuration classes. If such a tag is found, the corresponding Configuration class is instantiated and initialized using the classes of the beanutils package (namely XMLBeanDeclaration will be used to extract the configuration's initialization parameters, which allows for complex initialization scenarios).

It is also possible to add custom tags to the configuration definition file. For this purpose register your own ConfigurationProvider implementation for your tag using the addConfigurationProvider() method. This provider will then be called when the corresponding custom tag is detected. For the default configuration classes providers are already registered.

The configuration definition file has the following basic structure:

 <configuration systemProperties="properties file name">
   <header>
     <!-- Optional meta information about the composite configuration -->
   </header>
   <override>
     <!-- Declarations for override configurations -->
   </override>
   <additional>
     <!-- Declarations for union configurations -->
   </additional>
 </configuration>
 

The name of the root element (here configuration) is arbitrary. The optional systemProperties attribute identifies the path to a property file containing properties that should be added to the system properties. If specified on the root element, the system properties are set before the rest of the configuration is processed.

There are two sections (both of them are optional) for declaring override and additional configurations. Configurations in the former section are evaluated in the order of their declaration, and properties of configurations declared earlier hide those of configurations declared later. Configurations in the latter section are combined to a union configuration, i.e. all of their properties are added to a large hierarchical configuration. Configuration declarations that occur as direct children of the root element are treated as override declarations.

Each configuration declaration consists of a tag whose name is associated with a ConfigurationProvider. This can be one of the predefined tags like properties, or xml, or a custom tag, for which a configuration provider was registered. Attributes and sub elements with specific initialization parameters can be added. There are some reserved attributes with a special meaning that can be used in every configuration declaration:

Attribute	Meaning
config-name	Allows to specify a name for this configuration. This name can be used to obtain a reference to the configuration from the resulting combined configuration (see below).
config-at	With this attribute an optional prefix can be specified for the properties of the corresponding configuration.
config-optional	Declares a configuration as optional. This means that errors that occur when creating the configuration are ignored. (However ConfigurationErrorListeners registered at the builder instance will get notified about this error: they receive an event of type EVENT_ERR_LOAD_OPTIONAL. The key property of this event contains the name of the optional configuration source that caused this problem.)

The optional header section can contain some meta data about the created configuration itself. For instance, it is possible to set further properties of the NodeCombiner objects used for constructing the resulting configuration.

The default configuration object returned by this builder is an instance of the CombinedConfiguration class. The return value of the getConfiguration() method can be casted to this type, and the getConfiguration(boolean) method directly declares CombinedConfiguration as return type. This allows for convenient access to the configuration objects maintained by the combined configuration (e.g. for updates of single configuration objects). It has also the advantage that the properties stored in all declared configuration objects are collected and transformed into a single hierarchical structure, which can be accessed using different expression engines. The actual CombinedConfiguration implementation can be overridden by specifying the class in the config-class attribute of the result element.

Additional ConfigurationProviders can be added by configuring them in the header section.

 <providers>
   <provider config-tag="tag name" config-class="provider fully qualified class name"/>
 </providers>
 

Additional variable resolvers can be added by configuring them in the header section.

 <lookups>
   <lookup config-prefix="prefix" config-class="StrLookup fully qualified class name"/>
 </lookups>
 

All declared override configurations are directly added to the resulting combined configuration. If they are given names (using the config-name attribute), they can directly be accessed using the getConfiguration(String) method of CombinedConfiguration. The additional configurations are altogether added to another combined configuration, which uses a union combiner. Then this union configuration is added to the resulting combined configuration under the name defined by the ADDITIONAL_NAME constant.

Implementation note: This class is not thread-safe. Especially the getConfiguration() methods should be called by a single thread only.

Since:

1.3

Version:

$Id: DefaultConfigurationBuilder.java 727834 2008-12-18 22:16:32Z rgoers $

Author:

Commons Configuration team

See Also:

Serialized Form

Nested Class Summary

static class	DefaultConfigurationBuilder.ConfigurationDeclaration A specialized BeanDeclaration implementation that represents the declaration of a configuration source.
static class	DefaultConfigurationBuilder.ConfigurationProvider A base class for creating and initializing configuration sources.
static class	DefaultConfigurationBuilder.FileConfigurationProvider A specialized provider implementation that deals with file based configurations.
static class	DefaultConfigurationBuilder.XMLConfigurationProvider A specialized configuration provider for XML configurations.

Nested classes inherited from class org.apache.commons.configuration.AbstractHierarchicalFileConfiguration

AbstractHierarchicalFileConfiguration.FileConfigurationDelegate

Nested classes inherited from class org.apache.commons.configuration.HierarchicalConfiguration

HierarchicalConfiguration.BuilderVisitor, HierarchicalConfiguration.Node, HierarchicalConfiguration.NodeVisitor

Field Summary

static String	ADDITIONAL_NAME Constant for the name of the additional configuration.
static int	EVENT_ERR_LOAD_OPTIONAL Constant for the type of error events caused by optional configurations that cannot be loaded.

Fields inherited from class org.apache.commons.configuration.HierarchicalConfiguration

EVENT_ADD_NODES, EVENT_CLEAR_TREE, EVENT_SUBNODE_CHANGED

Fields inherited from class org.apache.commons.configuration.AbstractConfiguration

END_TOKEN, EVENT_ADD_PROPERTY, EVENT_CLEAR, EVENT_CLEAR_PROPERTY, EVENT_READ_PROPERTY, EVENT_SET_PROPERTY, START_TOKEN

Constructor Summary

DefaultConfigurationBuilder()
Creates a new instance of DefaultConfigurationBuilder.

DefaultConfigurationBuilder(File file)
Creates a new instance of DefaultConfigurationBuilder and sets the specified configuration definition file.

DefaultConfigurationBuilder(String fileName)
Creates a new instance of DefaultConfigurationBuilder and sets the specified configuration definition file.

DefaultConfigurationBuilder(URL url)
Creates a new instance of DefaultConfigurationBuilder and sets the specified configuration definition file.

Method Summary

void	addConfigurationProvider(String tagName, DefaultConfigurationBuilder.ConfigurationProvider provider) Adds a configuration provider for the specified tag.
protected CombinedConfiguration	createResultConfiguration() Creates the resulting combined configuration.
protected void	fireError(int type, String propName, Object propValue, Throwable ex) Creates an error event object and delivers it to all registered error listeners.
Configuration	getConfiguration() Returns the configuration provided by this builder.
CombinedConfiguration	getConfiguration(boolean load) Returns the configuration provided by this builder.
String	getConfigurationBasePath() Returns the base path for the configuration sources to load.
protected void	initCombinedConfiguration(CombinedConfiguration config, List containedConfigs, String keyListNodes) Initializes a combined configuration for the configurations of a specific section.
protected void	initSystemProperties() If a property file is configured add the properties to the System properties.
protected Object	interpolate(Object value) Performs interpolation.
DefaultConfigurationBuilder.ConfigurationProvider	providerForTag(String tagName) Returns the configuration provider for the given tag.
protected void	registerConfiguredLookups() Registers StrLookups defined in the configuration.
protected void	registerConfiguredProviders() Registers providers defined in the configuration.
protected void	registerDefaultProviders() Registers the default configuration providers supported by this class.
DefaultConfigurationBuilder.ConfigurationProvider	removeConfigurationProvider(String tagName) Removes the configuration provider for the specified tag name.
void	setConfigurationBasePath(String configurationBasePath) Sets the base path for the configuration sources to load.

Methods inherited from class org.apache.commons.configuration.XMLConfiguration

addNodes, clear, clone, createDelegate, createDocument, createDocumentBuilder, createNode, createTransformer, getDocument, getDocumentBuilder, getPublicID, getRootElementName, getSystemID, initProperties, isAttributeSplittingDisabled, isValidating, load, load, registerEntityId, resolveEntity, save, setAttributeSplittingDisabled, setDocumentBuilder, setPublicID, setRootElementName, setSystemID, setValidating

Methods inherited from class org.apache.commons.configuration.AbstractHierarchicalFileConfiguration

addPropertyDirect, clearProperty, clearTree, configurationChanged, containsKey, fetchNodeList, getBasePath, getDelegate, getEncoding, getFile, getFileName, getKeys, getKeys, getProperty, getReloadingStrategy, getURL, isAutoSave, isEmpty, load, load, load, load, load, reload, save, save, save, save, save, save, setAutoSave, setBasePath, setDelegate, setEncoding, setFile, setFileName, setProperty, setReloadingStrategy, setURL, subnodeConfigurationChanged

Methods inherited from class org.apache.commons.configuration.HierarchicalConfiguration

clearNode, clearNode, clearReferences, configurationAt, configurationAt, configurationsAt, createAddPath, createSubnodeConfiguration, createSubnodeConfiguration, fetchAddNode, findLastPathNode, findPropertyNodes, getDefaultExpressionEngine, getExpressionEngine, getMaxIndex, getRoot, getRootNode, interpolatedConfiguration, nodeDefined, nodeDefined, removeNode, removeNode, setDefaultExpressionEngine, setExpressionEngine, setRoot, setRootNode, subset

Methods inherited from class org.apache.commons.configuration.AbstractConfiguration

addErrorLogListener, addProperty, append, clearPropertyDirect, copy, createInterpolator, getBigDecimal, getBigDecimal, getBigInteger, getBigInteger, getBoolean, getBoolean, getBoolean, getByte, getByte, getByte, getDefaultListDelimiter, getDelimiter, getDouble, getDouble, getDouble, getFloat, getFloat, getFloat, getInt, getInt, getInteger, getInterpolator, getList, getList, getListDelimiter, getLogger, getLong, getLong, getLong, getProperties, getProperties, getShort, getShort, getShort, getString, getString, getStringArray, getSubstitutor, interpolate, interpolateHelper, isDelimiterParsingDisabled, isThrowExceptionOnMissing, resolveContainerStore, setDefaultListDelimiter, setDelimiter, setDelimiterParsingDisabled, setListDelimiter, setLogger, setThrowExceptionOnMissing

Methods inherited from class org.apache.commons.configuration.event.EventSource

addConfigurationListener, addErrorListener, clearConfigurationListeners, clearErrorListeners, createErrorEvent, createEvent, fireEvent, getConfigurationListeners, getErrorListeners, isDetailEvents, removeConfigurationListener, removeErrorListener, setDetailEvents

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.commons.configuration.Configuration

addProperty, getBigDecimal, getBigDecimal, getBigInteger, getBigInteger, getBoolean, getBoolean, getBoolean, getByte, getByte, getByte, getDouble, getDouble, getDouble, getFloat, getFloat, getFloat, getInt, getInt, getInteger, getList, getList, getLong, getLong, getLong, getProperties, getShort, getShort, getShort, getString, getString, getStringArray, subset

Field Detail

ADDITIONAL_NAME

public static final String ADDITIONAL_NAME

Constant for the name of the additional configuration. If the configuration definition file contains an additional section, a special union configuration is created and added under this name to the resulting combined configuration.

EVENT_ERR_LOAD_OPTIONAL

public static final int EVENT_ERR_LOAD_OPTIONAL

Constant for the type of error events caused by optional configurations that cannot be loaded.

See Also:

Constant Field Values

Constructor Detail

DefaultConfigurationBuilder

public DefaultConfigurationBuilder()

Creates a new instance of DefaultConfigurationBuilder. A configuration definition file is not yet loaded. Use the diverse setter methods provided by file based configurations to specify the configuration definition file.

DefaultConfigurationBuilder

public DefaultConfigurationBuilder(File file)

Creates a new instance of DefaultConfigurationBuilder and sets the specified configuration definition file.

Parameters:

file - the configuration definition file

DefaultConfigurationBuilder

public DefaultConfigurationBuilder(String fileName)
                            throws ConfigurationException

Creates a new instance of DefaultConfigurationBuilder and sets the specified configuration definition file.

Parameters:

fileName - the name of the configuration definition file

Throws:

ConfigurationException - if an error occurs when the file is loaded

DefaultConfigurationBuilder

public DefaultConfigurationBuilder(URL url)
                            throws ConfigurationException

Creates a new instance of DefaultConfigurationBuilder and sets the specified configuration definition file.

Parameters:

url - the URL to the configuration definition file

Throws:

ConfigurationException - if an error occurs when the file is loaded

Method Detail

getConfigurationBasePath

public String getConfigurationBasePath()

Returns the base path for the configuration sources to load. This path is used to resolve relative paths in the configuration definition file.

Returns:

the base path for configuration sources

setConfigurationBasePath

public void setConfigurationBasePath(String configurationBasePath)

Sets the base path for the configuration sources to load. Normally a base path need not to be set because it is determined by the location of the configuration definition file to load. All relative paths in this file are resolved relative to this file. Setting a base path makes sense if such relative paths should be otherwise resolved, e.g. if the configuration file is loaded from the class path and all sub configurations it refers to are stored in a special config directory.

Parameters:

configurationBasePath - the new base path to set

addConfigurationProvider

public void addConfigurationProvider(String tagName,
                                     DefaultConfigurationBuilder.ConfigurationProvider provider)

Adds a configuration provider for the specified tag. Whenever this tag is encountered in the configuration definition file this provider will be called to create the configuration object.

Parameters:

tagName - the name of the tag in the configuration definition file

provider - the provider for this tag

removeConfigurationProvider

public DefaultConfigurationBuilder.ConfigurationProvider removeConfigurationProvider(String tagName)

Removes the configuration provider for the specified tag name.

Parameters:

tagName - the tag name

Returns:

the removed configuration provider or null if none was registered for that tag

providerForTag

public DefaultConfigurationBuilder.ConfigurationProvider providerForTag(String tagName)

Returns the configuration provider for the given tag.

Parameters:

tagName - the name of the tag

Returns:

the provider that was registered for this tag or null if there is none

getConfiguration

public Configuration getConfiguration()
                               throws ConfigurationException

Returns the configuration provided by this builder. Loads and parses the configuration definition file and creates instances for the declared configurations.

Specified by:

getConfiguration in interface ConfigurationBuilder

Returns:

the configuration

Throws:

ConfigurationException - if an error occurs

getConfiguration

public CombinedConfiguration getConfiguration(boolean load)
                                       throws ConfigurationException

Returns the configuration provided by this builder. If the boolean parameter is true, the configuration definition file will be loaded. It will then be parsed, and instances for the declared configurations will be created.

Parameters:

load - a flag whether the configuration definition file should be loaded; a value of false would make sense if the file has already been created or its content was manipulated using some of the property accessor methods

Returns:

the configuration

Throws:

ConfigurationException - if an error occurs

createResultConfiguration

protected CombinedConfiguration createResultConfiguration()
                                                   throws ConfigurationException

Creates the resulting combined configuration. This method is called by getConfiguration(). It checks whether the header section of the configuration definition file contains a result element. If this is the case, it will be used to initialize the properties of the newly created configuration object.

Returns:

the resulting configuration object

Throws:

ConfigurationException - if an error occurs

initCombinedConfiguration

protected void initCombinedConfiguration(CombinedConfiguration config,
                                         List containedConfigs,
                                         String keyListNodes)
                                  throws ConfigurationException

Initializes a combined configuration for the configurations of a specific section. This method is called for the override and for the additional section (if it exists).

Parameters:

config - the configuration to be initialized

containedConfigs - the list with the declaratinos of the contained configurations

keyListNodes - a list with the declaration of list nodes

Throws:

ConfigurationException - if an error occurs

registerDefaultProviders

protected void registerDefaultProviders()

Registers the default configuration providers supported by this class. This method will be called during initialization. It registers configuration providers for the tags that are supported by default.

registerConfiguredProviders

protected void registerConfiguredProviders()
                                    throws ConfigurationException

Registers providers defined in the configuration.

Throws:

ConfigurationException - if an error occurs

registerConfiguredLookups

protected void registerConfiguredLookups()
                                  throws ConfigurationException

Registers StrLookups defined in the configuration.

Throws:

ConfigurationException - if an error occurs

initSystemProperties

protected void initSystemProperties()
                             throws ConfigurationException

If a property file is configured add the properties to the System properties.

Throws:

ConfigurationException - if an error occurs.

interpolate

protected Object interpolate(Object value)

Performs interpolation. This method will not only take this configuration instance into account (which is the one that loaded the configuration definition file), but also the so far constructed combined configuration. So variables can be used that point to properties that are defined in configuration sources loaded by this builder.

Overrides:

interpolate in class AbstractConfiguration

Parameters:

value - the value to be interpolated

Returns:

the interpolated value

fireError

protected void fireError(int type,
                         String propName,
                         Object propValue,
                         Throwable ex)

Description copied from class: EventSource

Creates an error event object and delivers it to all registered error listeners.

Overrides:

fireError in class EventSource

Parameters:

type - the event's type

propName - the name of the affected property (can be null)

propValue - the value of the affected property (can be null)

ex - the Throwable object that caused this error event