org.apache.commons.configuration

Class DefaultConfigurationBuilder

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 szenarios).

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>
   <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. 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 pre-defined 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 silently ignored.

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 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.

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 alltogether 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 507219 2007-02-13 21:02:09Z oheger $

Author: Commons Configuration team

Nested Class Summary
static classDefaultConfigurationBuilder.ConfigurationBeanFactory
A specialized BeanFactory implementation that handles configuration declarations.
static classDefaultConfigurationBuilder.ConfigurationBuilderProvider
A specialized configuration provider class that allows to include other configuration definition files.
static classDefaultConfigurationBuilder.ConfigurationDeclaration

A specialized BeanDeclaration implementation that represents the declaration of a configuration source.

static classDefaultConfigurationBuilder.ConfigurationProvider

A base class for creating and initializing configuration sources.

static classDefaultConfigurationBuilder.FileConfigurationProvider
A specialized provider implementation that deals with file based configurations.
static classDefaultConfigurationBuilder.FileExtensionConfigurationProvider
A specialized configuration provider for file based configurations that can handle configuration sources whose concrete type depends on the extension of the file to be loaded.
Field Summary
static StringADDITIONAL_NAME
Constant for the name of the additional configuration.
static StringATTR_AT
Constant for the at attribute without the reserved prefix.
static StringATTR_ATNAME
Constant for the name of the at attribute.
static StringATTR_AT_RES
Constant for the reserved at attribute.
static StringATTR_FILENAME
Constant for the file name attribute.
static StringATTR_FORCECREATE
Constant for the forceCreate attribute.
static StringATTR_NAME
Constant for the reserved name attribute.
static StringATTR_OPTIONAL
Constant for the optional attribute without the reserved prefix.
static StringATTR_OPTIONALNAME
Constant for the name of the optional attribute.
static StringATTR_OPTIONAL_RES
Constant for the reserved optional attribute.
static DefaultConfigurationBuilder.ConfigurationProviderBUILDER_PROVIDER
Constant for the provider for configuration definition files.
StringconfigurationBasePath
Stores the base path to the configuration sources to load.
CombinedConfigurationconstructedConfiguration
Stores the configuration that is currently constructed.
static StringCONFIG_BEAN_FACTORY_NAME
Constant for the name of the configuration bean factory.
static String[]CONFIG_SECTIONS
An array with the names of top level configuration sections.
static DefaultConfigurationBuilder.ConfigurationProvider[]DEFAULT_PROVIDERS
An array with the providers for the default tags.
static String[]DEFAULT_TAGS
An array with the names of the default tags.
static StringEXT_XML
Constant for the XML file extension.
static DefaultConfigurationBuilder.ConfigurationProviderJNDI_PROVIDER
Constant for the provider for JNDI sources.
static StringKEY_ADDITIONAL_LIST
Constant for the key that points to the list nodes definition of the additional combiner.
static StringKEY_COMBINER
Constant for the key of the combiner in the result declaration.
static StringKEY_OVERRIDE
Constant for an expression that selects override configurations in the override section.
static StringKEY_OVERRIDE_LIST
Constant for the key that points to the list nodes definition of the override combiner.
static StringKEY_RESULT
Constant for the key of the result declaration.
static StringKEY_UNION
Constant for an expression that selects the union configurations.
Mapproviders
Stores a map with the registered configuration providers.
static DefaultConfigurationBuilder.ConfigurationProviderPLIST_PROVIDER
Constant for the provider for plist files.
static DefaultConfigurationBuilder.ConfigurationProviderPROPERTIES_PROVIDER
Constant for the provider for properties files.
static longserialVersionUID
The serial version UID.
static StringSEC_HEADER
Constant for the name of the header section.
static DefaultConfigurationBuilder.ConfigurationProviderSYSTEM_PROVIDER
Constant for the provider for system properties.
static DefaultConfigurationBuilder.ConfigurationProviderXML_PROVIDER
Constant for the provider for XML files.
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
voidaddConfigurationProvider(String tagName, DefaultConfigurationBuilder.ConfigurationProvider provider)
Adds a configuration provider for the specified tag.
AbstractConfigurationcreateConfigurationAt(DefaultConfigurationBuilder.ConfigurationDeclaration decl)
Creates a configuration object from the specified configuration declaration.
protected CombinedConfigurationcreateResultConfiguration()
Creates the resulting combined configuration.
ListfetchChildConfigs(ConfigurationNode node)
Returns a list with SubnodeConfiguration objects for the child nodes of the specified configuration node.
ListfetchChildConfigs(String key)
Returns a list with SubnodeConfiguration objects for the child nodes of the node specified by the given key.
ListfetchTopLevelOverrideConfigs()
Finds the override configurations that are defined as top level elements in the configuration definition file.
ConfigurationgetConfiguration()
Returns the configuration provided by this builder.
CombinedConfigurationgetConfiguration(boolean load)
Returns the configuration provided by this builder.
StringgetConfigurationBasePath()
Returns the base path for the configuration sources to load.
protected voidinitCombinedConfiguration(CombinedConfiguration config, List containedConfigs, String keyListNodes)
Initializes a combined configuration for the configurations of a specific section.
protected Objectinterpolate(Object value)
Performs interpolation.
DefaultConfigurationBuilder.ConfigurationProviderproviderForTag(String tagName)
Returns the configuration provider for the given tag.
protected voidregisterDefaultProviders()
Registers the default configuration providers supported by this class.
DefaultConfigurationBuilder.ConfigurationProviderremoveConfigurationProvider(String tagName)
Removes the configuration provider for the specified tag name.
voidsetConfigurationBasePath(String configurationBasePath)
Sets the base path for the configuration sources to load.

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.

ATTR_AT

static final String ATTR_AT
Constant for the at attribute without the reserved prefix.

ATTR_ATNAME

static final String ATTR_ATNAME
Constant for the name of the at attribute.

ATTR_AT_RES

static final String ATTR_AT_RES
Constant for the reserved at attribute.

ATTR_FILENAME

static final String ATTR_FILENAME
Constant for the file name attribute.

ATTR_FORCECREATE

static final String ATTR_FORCECREATE
Constant for the forceCreate attribute.

ATTR_NAME

static final String ATTR_NAME
Constant for the reserved name attribute.

ATTR_OPTIONAL

static final String ATTR_OPTIONAL
Constant for the optional attribute without the reserved prefix.

ATTR_OPTIONALNAME

static final String ATTR_OPTIONALNAME
Constant for the name of the optional attribute.

ATTR_OPTIONAL_RES

static final String ATTR_OPTIONAL_RES
Constant for the reserved optional attribute.

BUILDER_PROVIDER

private static final DefaultConfigurationBuilder.ConfigurationProvider BUILDER_PROVIDER
Constant for the provider for configuration definition files.

configurationBasePath

private String configurationBasePath
Stores the base path to the configuration sources to load.

constructedConfiguration

private CombinedConfiguration constructedConfiguration
Stores the configuration that is currently constructed.

CONFIG_BEAN_FACTORY_NAME

static final String CONFIG_BEAN_FACTORY_NAME
Constant for the name of the configuration bean factory.

CONFIG_SECTIONS

static final String[] CONFIG_SECTIONS
An array with the names of top level configuration sections.

DEFAULT_PROVIDERS

private static final DefaultConfigurationBuilder.ConfigurationProvider[] DEFAULT_PROVIDERS
An array with the providers for the default tags.

DEFAULT_TAGS

private static final String[] DEFAULT_TAGS
An array with the names of the default tags.

EXT_XML

static final String EXT_XML
Constant for the XML file extension.

JNDI_PROVIDER

private static final DefaultConfigurationBuilder.ConfigurationProvider JNDI_PROVIDER
Constant for the provider for JNDI sources.

KEY_ADDITIONAL_LIST

static final String KEY_ADDITIONAL_LIST
Constant for the key that points to the list nodes definition of the additional combiner.

KEY_COMBINER

static final String KEY_COMBINER
Constant for the key of the combiner in the result declaration.

KEY_OVERRIDE

static final String KEY_OVERRIDE
Constant for an expression that selects override configurations in the override section.

KEY_OVERRIDE_LIST

static final String KEY_OVERRIDE_LIST
Constant for the key that points to the list nodes definition of the override combiner.

KEY_RESULT

static final String KEY_RESULT
Constant for the key of the result declaration. This key can point to a bean declaration, which defines properties of the resulting combined configuration.

KEY_UNION

static final String KEY_UNION
Constant for an expression that selects the union configurations.

providers

private Map providers
Stores a map with the registered configuration providers.

PLIST_PROVIDER

private static final DefaultConfigurationBuilder.ConfigurationProvider PLIST_PROVIDER
Constant for the provider for plist files.

PROPERTIES_PROVIDER

private static final DefaultConfigurationBuilder.ConfigurationProvider PROPERTIES_PROVIDER
Constant for the provider for properties files.

serialVersionUID

private static final long serialVersionUID
The serial version UID.

SEC_HEADER

static final String SEC_HEADER
Constant for the name of the header section.

SYSTEM_PROVIDER

private static final DefaultConfigurationBuilder.ConfigurationProvider SYSTEM_PROVIDER
Constant for the provider for system properties.

XML_PROVIDER

private static final DefaultConfigurationBuilder.ConfigurationProvider XML_PROVIDER
Constant for the provider for XML files.

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)
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)
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

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

createConfigurationAt

private AbstractConfiguration createConfigurationAt(DefaultConfigurationBuilder.ConfigurationDeclaration decl)
Creates a configuration object from the specified configuration declaration.

Parameters: decl the configuration declaration

Returns: the new configuration object

Throws: ConfigurationException if an error occurs

createResultConfiguration

protected CombinedConfiguration createResultConfiguration()
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

fetchChildConfigs

private List fetchChildConfigs(ConfigurationNode node)
Returns a list with SubnodeConfiguration objects for the child nodes of the specified configuration node.

Parameters: node the start node

Returns: a list with subnode configurations for the node's children

fetchChildConfigs

private List fetchChildConfigs(String key)
Returns a list with SubnodeConfiguration objects for the child nodes of the node specified by the given key.

Parameters: key the key (must define exactly one node)

Returns: a list with subnode configurations for the node's children

fetchTopLevelOverrideConfigs

private List fetchTopLevelOverrideConfigs()
Finds the override configurations that are defined as top level elements in the configuration definition file. This method will fetch the child elements of the root node and remove the nodes that represent other configuration sections. The remaining nodes are treated as definitions for override configurations.

Returns: a list with subnode configurations for the top level override configurations

getConfiguration

public Configuration getConfiguration()
Returns the configuration provided by this builder. Loads and parses the configuration definition file and creates instances for the declared configurations.

Returns: the configuration

Throws: ConfigurationException if an error occurs

getConfiguration

public CombinedConfiguration getConfiguration(boolean load)
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

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

initCombinedConfiguration

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

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.

Parameters: value the value to be interpolated

Returns: the interpolated value

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

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.

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

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 pathes in this file are resolved relative to this file. Setting a base path makes sense if such relative pathes 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