Package org.apache.commons.configuration2.builder.combined

Class MultiFileConfigurationBuilder<T extends FileBasedConfiguration>

java.lang.Object
org.apache.commons.configuration2.builder.BasicConfigurationBuilder<T>
org.apache.commons.configuration2.builder.combined.MultiFileConfigurationBuilder<T>
Type Parameters:
T - the concrete type of Configuration objects created by this builder
All Implemented Interfaces:
ConfigurationBuilder<T>, EventSource
Direct Known Subclasses:
ReloadingMultiFileConfigurationBuilder
public class MultiFileConfigurationBuilder<T extends FileBasedConfiguration> extends BasicConfigurationBuilder<T>

A specialized ConfigurationBuilder implementation providing access to multiple file-based configurations based on a file name pattern.

This builder class is initialized with a pattern string and a ConfigurationInterpolator object. Each time a configuration is requested, the pattern is evaluated against the ConfigurationInterpolator (so all variables are replaced by their current values). The resulting string is interpreted as a file name for a configuration file to be loaded. For example, providing a pattern of file:///opt/config/${product}/${client}/config.xml will result in product and client being resolved on every call. By storing configuration files in a corresponding directory structure, specialized configuration files associated with a specific product and client can be loaded. Thus an application can be made multi-tenant in a transparent way.

This builder class keeps a map with configuration builders for configurations already loaded. The getConfiguration() method first evaluates the pattern string and checks whether a builder for the resulting file name is available. If yes, it is queried for its configuration. Otherwise, a new file-based configuration builder is created now and initialized.

Configuration of an instance happens in the usual way for configuration builders. A MultiFileBuilderParametersImpl parameters object is expected which must contain a file name pattern string and a ConfigurationInterpolator. Other properties of this parameters object are used to initialize the builders for managed configurations.

Since:
2.0

  • Constructor Details

    • MultiFileConfigurationBuilder

      public MultiFileConfigurationBuilder(Class<? extends T> resCls)
      Creates a new instance of MultiFileConfigurationBuilder without setting initialization parameters.
      Parameters:
      resCls - the result configuration class
      Throws:
      IllegalArgumentException - if the result class is null

    • MultiFileConfigurationBuilder

      public MultiFileConfigurationBuilder(Class<? extends T> resCls, Map<String,Object> params)
      Creates a new instance of MultiFileConfigurationBuilder and sets initialization parameters.
      Parameters:
      resCls - the result configuration class
      params - a map with initialization parameters
      Throws:
      IllegalArgumentException - if the result class is null

    • MultiFileConfigurationBuilder

      public MultiFileConfigurationBuilder(Class<? extends T> resCls, Map<String,Object> params, boolean allowFailOnInit)
      Creates a new instance of MultiFileConfigurationBuilder and sets initialization parameters and a flag whether initialization failures should be ignored.
      Parameters:
      resCls - the result configuration class
      params - a map with initialization parameters
      allowFailOnInit - a flag whether initialization errors should be ignored
      Throws:
      IllegalArgumentException - if the result class is null

  • Method Details

    • addEventListener

      public <E extends Event> void addEventListener(EventType<E> eventType, EventListener<? super E> l)
      Adds an event listener for the specified event type. This listener is notified about events of this type and all its sub types. This implementation also takes care that the event listener is added to the managed configuration object. This implementation ensures that the listener is also added to managed configuration builders if necessary. Listeners for the builder-related event types are excluded because otherwise they would be triggered by the internally used configuration builders.
      Specified by:
      addEventListener in interface EventSource
      Overrides:
      addEventListener in class BasicConfigurationBuilder<T extends FileBasedConfiguration>
      Type Parameters:
      E - the type of events processed by this listener
      Parameters:
      eventType - the event type (must not be null)
      l - the listener to be registered (must not be null)

    • configure

      public MultiFileConfigurationBuilder<T> configure(BuilderParameters... params)
      Appends the content of the specified BuilderParameters objects to the current initialization parameters. Calling this method multiple times will create a union of the parameters provided. This method is overridden to adapt the return type.
      Overrides:
      configure in class BasicConfigurationBuilder<T extends FileBasedConfiguration>
      Parameters:
      params - an arbitrary number of objects with builder parameters
      Returns:
      a reference to this builder for method chaining

    • constructFileName

      protected String constructFileName(MultiFileBuilderParametersImpl multiParams)
      Determines the file name of a configuration based on the file name pattern. This method is called on every access to this builder's configuration. It obtains the ConfigurationInterpolator from this builder's parameters and uses it to interpolate the file name pattern.
      Parameters:
      multiParams - the parameters object for this builder
      Returns:
      the name of the configuration file to be loaded

    • createInitializedManagedBuilder

      protected FileBasedConfigurationBuilder<T> createInitializedManagedBuilder(String fileName, Map<String,Object> params) throws ConfigurationException
      Creates a fully initialized builder for a managed configuration. This method is called by getConfiguration() whenever a configuration file is requested which has not yet been loaded. This implementation delegates to createManagedBuilder() for actually creating the builder object. Then it sets the location to the configuration file.
      Parameters:
      fileName - the name of the file to be loaded
      params - a map with initialization parameters for the new builder
      Returns:
      the newly created and initialized builder instance
      Throws:
      ConfigurationException - if an error occurs

    • createInterpolator

      protected ConfigurationInterpolator createInterpolator()
      Creates the ConfigurationInterpolator to be used by this instance. This method is called when a file name is to be constructed, but no current ConfigurationInterpolator instance is available. It obtains an instance from this builder's parameters. If no properties of the ConfigurationInterpolator are specified in the parameters, a default instance without lookups is returned (which is probably not very helpful).
      Returns:
      the ConfigurationInterpolator to be used

    • createManagedBuilder

      protected FileBasedConfigurationBuilder<T> createManagedBuilder(String fileName, Map<String,Object> params) throws ConfigurationException
      Creates a builder for a managed configuration. This method is called whenever a configuration for a file name is requested which has not yet been loaded. The passed in map with parameters is populated from this builder's configuration (i.e. the basic parameters plus the optional parameters for managed builders). This base implementation creates a standard builder for file-based configurations. Derived classes may override it to create special purpose builders.
      Parameters:
      fileName - the name of the file to be loaded
      params - a map with initialization parameters for the new builder
      Returns:
      the newly created builder instance
      Throws:
      ConfigurationException - if an error occurs

    • getConfiguration

      public T getConfiguration() throws ConfigurationException
      Gets the configuration provided by this builder. An implementation has to perform all necessary steps for creating and initializing a ImmutableConfiguration object. This implementation creates the result configuration on first access. Later invocations return the same object until this builder is reset. The double-check idiom for lazy initialization is used (Bloch, Effective Java, item 71). This implementation evaluates the file name pattern using the configured ConfigurationInterpolator. If this file has already been loaded, the corresponding builder is accessed. Otherwise, a new builder is created for loading this configuration file.
      Specified by:
      getConfiguration in interface ConfigurationBuilder<T extends FileBasedConfiguration>
      Overrides:
      getConfiguration in class BasicConfigurationBuilder<T extends FileBasedConfiguration>
      Returns:
      the configuration
      Throws:
      ConfigurationException - if an error occurs

    • getInterpolator

      protected ConfigurationInterpolator getInterpolator()
      Gets the ConfigurationInterpolator used by this instance. This is the object used for evaluating the file name pattern. It is created on demand.
      Returns:
      the ConfigurationInterpolator

    • getManagedBuilder

      public FileBasedConfigurationBuilder<T> getManagedBuilder() throws ConfigurationException
      Gets the managed FileBasedConfigurationBuilder for the current file name pattern. It is determined based on the evaluation of the file name pattern using the configured ConfigurationInterpolator. If this is the first access to this configuration file, the builder is created.
      Returns:
      the configuration builder for the configuration corresponding to the current evaluation of the file name pattern
      Throws:
      ConfigurationException - if the builder cannot be determined (e.g. due to missing initialization parameters)

    • getManagedBuilders

      protected ConcurrentMap<String,FileBasedConfigurationBuilder<T>> getManagedBuilders()
      Gets the map with the managed builders created so far by this MultiFileConfigurationBuilder. This map is exposed to derived classes so they can access managed builders directly. However, derived classes are not expected to manipulate this map.
      Returns:
      the map with the managed builders

    • removeEventListener

      public <E extends Event> boolean removeEventListener(EventType<E> eventType, EventListener<? super E> l)
      Removes the event listener registration for the given event type and listener. An event listener instance may be registered multiple times for different event types. Therefore, when removing a listener the event type of the registration in question has to be specified. The return value indicates whether a registration was removed. A value of false means that no such combination of event type and listener was found. This implementation also takes care that the event listener is removed from the managed configuration object. This implementation ensures that the listener is also removed from managed configuration builders if necessary.
      Specified by:
      removeEventListener in interface EventSource
      Overrides:
      removeEventListener in class BasicConfigurationBuilder<T extends FileBasedConfiguration>
      Type Parameters:
      E - the type of events processed by this listener
      Parameters:
      eventType - the event type
      l - the event listener to be removed
      Returns:
      a flag whether a listener registration was removed

    • resetParameters

      public void resetParameters()
      Removes all initialization parameters of this builder. This method can be called if this builder is to be reused for creating result objects with a different configuration. This implementation clears the cache with all managed builders.
      Overrides:
      resetParameters in class BasicConfigurationBuilder<T extends FileBasedConfiguration>