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

Class BaseConfigurationBuilderProvider

java.lang.Object
org.apache.commons.configuration2.builder.combined.BaseConfigurationBuilderProvider
All Implemented Interfaces:
ConfigurationBuilderProvider
Direct Known Subclasses:
CombinedConfigurationBuilderProvider, FileExtensionConfigurationBuilderProvider, MultiFileConfigurationBuilderProvider
public class BaseConfigurationBuilderProvider extends Object implements ConfigurationBuilderProvider

A fully-functional, reflection-based implementation of the ConfigurationBuilderProvider interface which can deal with the default tags defining configuration sources.

An instance of this class is initialized with the names of the ConfigurationBuilder class used by this provider and the concrete Configuration class. The ConfigurationBuilder class must be derived from BasicConfigurationBuilder. When asked for the builder object, an instance of the builder class is created and initialized from the bean declaration associated with the current configuration source.

ConfigurationBuilder objects are configured using parameter objects. When declaring configuration sources in XML it should not be necessary to define the single parameter objects. Rather, simple and complex properties are set in the typical way of a bean declaration (i.e. as attributes of the current XML element or as child elements). This class creates all supported parameter objects (whose names also must be provided at construction time) and takes care that their properties are initialized according to the current bean declaration.

The use of reflection to create builder instances allows a generic implementation supporting many concrete builder classes. Another reason for this approach is that builder classes are only loaded if actually needed. Some specialized Configuration implementations require specific external dependencies which should not be mandatory for the use of CombinedConfigurationBuilder. Because such classes are lazily loaded, an application only has to include the dependencies it actually uses.

Since:
2.0

  • Constructor Details

    • BaseConfigurationBuilderProvider

      public BaseConfigurationBuilderProvider(String bldrCls, String reloadBldrCls, String configCls, Collection<String> paramCls)
      Creates a new instance of BaseConfigurationBuilderProvider and initializes all its properties.
      Parameters:
      bldrCls - the name of the builder class (must not be null)
      reloadBldrCls - the name of a builder class to be used if reloading support is required (null if reloading is not supported)
      configCls - the name of the configuration class (must not be null)
      paramCls - a collection with the names of parameters classes
      Throws:
      IllegalArgumentException - if a required parameter is missing

  • Method Details

    • configureBuilder

      protected void configureBuilder(BasicConfigurationBuilder<? extends Configuration> builder, ConfigurationDeclaration decl, Collection<BuilderParameters> params) throws Exception
      Configures a newly created builder instance with its initialization parameters. This method is called after a new instance was created using reflection. This implementation passes the parameter objects to the builder's configure() method.
      Parameters:
      builder - the builder to be initialized
      decl - the current ConfigurationDeclaration
      params - the collection with initialization parameter objects
      Throws:
      Exception - if an error occurs

    • createBuilder

      protected BasicConfigurationBuilder<? extends Configuration> createBuilder(ConfigurationDeclaration decl, Collection<BuilderParameters> params) throws Exception
      Creates a new, uninitialized instance of the builder class managed by this provider. This implementation determines the builder class to be used by delegating to determineBuilderClass(). It then calls the constructor expecting the configuration class, the map with properties, and theallowFailOnInit flag.
      Parameters:
      decl - the current ConfigurationDeclaration
      params - initialization parameters for the new builder object
      Returns:
      the newly created builder instance
      Throws:
      Exception - if an error occurs

    • createParameterObjects

      protected Collection<BuilderParameters> createParameterObjects() throws Exception
      Creates a collection of parameter objects to be used for configuring the builder. This method creates instances of the parameter classes passed to the constructor.
      Returns:
      a collection with parameter objects for the builder
      Throws:
      Exception - if an error occurs while creating parameter objects via reflection

    • determineBuilderClass

      protected String determineBuilderClass(ConfigurationDeclaration decl) throws ConfigurationException
      Determines the name of the class to be used for a new builder instance. This implementation selects between the normal and the reloading builder class, based on the passed in ConfigurationDeclaration. If a reloading builder is desired, but this provider has no reloading support, an exception is thrown.
      Parameters:
      decl - the current ConfigurationDeclaration
      Returns:
      the name of the builder class
      Throws:
      ConfigurationException - if the builder class cannot be determined

    • determineConfigurationClass

      protected String determineConfigurationClass(ConfigurationDeclaration decl, Collection<BuilderParameters> params) throws ConfigurationException
      Determines the name of the configuration class produced by the builder. This method is called when obtaining the arguments for invoking the constructor of the builder class. This implementation just returns the pre-configured configuration class name. Derived classes may determine this class name dynamically based on the passed in parameters.
      Parameters:
      decl - the current ConfigurationDeclaration
      params - the collection with parameter objects
      Returns:
      the name of the builder's result configuration class
      Throws:
      ConfigurationException - if an error occurs

    • getBuilderClass

      public String getBuilderClass()
      Gets the name of the class of the builder created by this provider.
      Returns:
      the builder class

    • getConfigurationBuilder

      public ConfigurationBuilder<? extends Configuration> getConfigurationBuilder(ConfigurationDeclaration decl) throws ConfigurationException
      Gets the builder for the configuration source managed by this provider. This method is called during processing of the combined configuration definition file. This implementation delegates to some protected methods to create a new builder instance using reflection and to configure it with parameter values defined by the passed in BeanDeclaration.
      Specified by:
      getConfigurationBuilder in interface ConfigurationBuilderProvider
      Parameters:
      decl - the bean declaration with initialization parameters for the configuration builder
      Returns:
      the ConfigurationBuilder object created by this provider
      Throws:
      ConfigurationException - if an error occurs

    • getConfigurationClass

      public String getConfigurationClass()
      Gets the name of the configuration class created by the builder produced by this provider.
      Returns:
      the configuration class

    • getParameterClasses

      public Collection<String> getParameterClasses()
      Gets an unmodifiable collection with the names of parameter classes supported by this provider.
      Returns:
      the parameter classes

    • getReloadingBuilderClass

      public String getReloadingBuilderClass()
      Gets the name of the class of the builder created by this provider if the reload flag is set. If this method returns null, reloading builders are not supported by this provider.
      Returns:
      the reloading builder class

    • inheritParentBuilderProperties

      protected void inheritParentBuilderProperties(ConfigurationDeclaration decl, Collection<BuilderParameters> params)
      Passes all parameter objects to the parent CombinedConfigurationBuilder so that properties already defined for the parent builder can be added. This method is called before the parameter objects are initialized from the definition configuration. This way properties from the parent builder are inherited, but can be overridden for child configurations.
      Parameters:
      decl - the current ConfigurationDeclaration
      params - the collection with (uninitialized) parameter objects

    • initializeParameterObjects

      protected void initializeParameterObjects(ConfigurationDeclaration decl, Collection<BuilderParameters> params) throws Exception
      Initializes the parameter objects with data stored in the current bean declaration. This method is called before the newly created builder instance is configured with the parameter objects. It maps attributes of the bean declaration to properties of parameter objects. In addition, it invokes the parent CombinedConfigurationBuilder so that the parameters object can inherit properties already defined for this builder.
      Parameters:
      decl - the current ConfigurationDeclaration
      params - the collection with (uninitialized) parameter objects
      Throws:
      Exception - if an error occurs

    • isAllowFailOnInit

      protected boolean isAllowFailOnInit(ConfigurationDeclaration decl)
      Determines the allowFailOnInit flag for the newly created builder based on the given ConfigurationDeclaration. Some combinations of flags in the declaration say that a configuration source is optional, but an empty instance should be created if its creation fail.
      Parameters:
      decl - the current ConfigurationDeclaration
      Returns:
      the value of the allowFailOnInit flag