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:
Serializable, Cloneable, Configuration, ConfigurationBuilder, ConfigurationErrorListener, ConfigurationListener, FileConfiguration, FileSystemBased, Reloadable, EntityRegistry, EntityResolver
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.

A custom EntityResolver can be used for all XMLConfigurations by adding 

<entity-resolver config-class="EntityResolver fully qualified class name">
The CatalogResolver can be used for all XMLConfiguration by adding 
<entity-resolver catalogFiles="comma separated list of catalog files">

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 1366930 2012-07-29 20:05:36Z oheger $
Author:
Commons Configuration team
See Also:

  • Field Details

    • 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:

  • Constructor Details

    • 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 Details

    • 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

    • createAdditionalsConfiguration

      protected CombinedConfiguration createAdditionalsConfiguration(CombinedConfiguration resultConfig)
      Creates the CombinedConfiguration for the configuration sources in the <additional> section. This method is called when the builder constructs the final configuration. It creates a new CombinedConfiguration and initializes some properties from the result configuration.
      Parameters:
      resultConfig - the result configuration (this is the configuration that will be returned by the builder)
      Returns:
      the CombinedConfiguration for the additional configuration sources
      Since:
      1.7

    • initCombinedConfiguration

      protected void initCombinedConfiguration(CombinedConfiguration config, List<? extends HierarchicalConfiguration> 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 declarations 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

    • initFileSystem

      protected void initFileSystem() throws ConfigurationException
      Throws:
      ConfigurationException

    • 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.

    • configureEntityResolver

      protected void configureEntityResolver() throws ConfigurationException
      Throws:
      ConfigurationException

    • 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