org.apache.commons.configuration2

## Class SubsetConfiguration

- java.lang.Object
- - org.apache.commons.configuration2.event.BaseEventSource
  - - org.apache.commons.configuration2.AbstractConfiguration
    - - org.apache.commons.configuration2.SubsetConfiguration

- All Implemented Interfaces:
    Configuration, EventSource, ImmutableConfiguration, SynchronizerSupport

      public class SubsetConfiguration
      extends AbstractConfiguration

  A subset of another configuration. The new Configuration object contains every key from the parent Configuration that starts with prefix. The prefix is removed from the keys in the subset.

  It is usually not necessary to use this class directly. Instead the `Configuration.subset(String)` method should be used, which will return a correctly initialized instance.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected String` | `delimiter` The prefix delimiter
    `protected Configuration` | `parent` The parent configuration.
    `protected String` | `prefix` The prefix used to select the properties.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `SubsetConfiguration(Configuration parent, String prefix)` Create a subset of the specified configuration
    `SubsetConfiguration(Configuration parent, String prefix, String delimiter)` Create a subset of the specified configuration

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `addPropertyDirect(String key, Object value)` Adds a key/value pair to the Configuration.
    `protected void` | `clearPropertyDirect(String key)` Removes the specified property from this configuration.
    `protected boolean` | `containsKeyInternal(String key)` Actually checks whether the specified key is contained in this configuration.
    `protected String` | `getChildKey(String key)` Return the key in the subset configuration associated to the specified key in the parent configuration.
    `protected Iterator<String>` | `getKeysInternal()` Actually creates an iterator for iterating over the keys in this configuration.
    `protected Iterator<String>` | `getKeysInternal(String prefix)` Returns an `Iterator` with all property keys starting with the specified prefix.
    `ListDelimiterHandler` | `getListDelimiterHandler()` Returns the `ListDelimiterHandler` used by this instance.
    `Configuration` | `getParent()` Return the parent configuration for this subset.
    `protected String` | `getParentKey(String key)` Return the key in the parent configuration associated to the specified key in this subset.
    `String` | `getPrefix()` Return the prefix used to select the properties in the parent configuration.
    `protected Object` | `getPropertyInternal(String key)` Actually obtains the value of the specified property.
    `protected boolean` | `isEmptyInternal()` Actually checks whether this configuration contains data.
    `boolean` | `isThrowExceptionOnMissing()` Returns true if missing values throw Exceptions.
    `void` | `setListDelimiterHandler(ListDelimiterHandler listDelimiterHandler)` Sets the `ListDelimiterHandler` to be used by this instance.
    `void` | `setPrefix(String prefix)` Set the prefix used to select the properties in the parent configuration.
    `void` | `setThrowExceptionOnMissing(boolean throwExceptionOnMissing)` Allows to set the `throwExceptionOnMissing` flag.
    `Configuration` | `subset(String prefix)` Return a decorator Configuration containing every key from the current Configuration that starts with the specified prefix.

    - ### Methods inherited from class org.apache.commons.configuration2.AbstractConfiguration

      `addErrorLogListener, addProperty, addPropertyInternal, append, beginRead, beginWrite, clear, clearInternal, clearProperty, cloneInterpolator, containsKey, copy, endRead, endWrite, get, get, getArray, getArray, getBigDecimal, getBigDecimal, getBigInteger, getBigInteger, getBoolean, getBoolean, getBoolean, getByte, getByte, getByte, getCollection, getCollection, getConfigurationDecoder, getConversionHandler, getDouble, getDouble, getDouble, getEncodedString, getEncodedString, getFloat, getFloat, getFloat, getInt, getInt, getInteger, getInterpolator, getKeys, getKeys, getList, getList, getList, getList, getLogger, getLong, getLong, getLong, getProperties, getProperties, getProperty, getShort, getShort, getShort, getString, getString, getStringArray, getSynchronizer, immutableSubset, initLogger, installInterpolator, interpolate, interpolate, interpolatedConfiguration, isEmpty, isScalarValue, lock, setConfigurationDecoder, setConversionHandler, setDefaultLookups, setInterpolator, setLogger, setParentInterpolator, setPrefixLookups, setProperty, setPropertyInternal, setSynchronizer, size, sizeInternal, unlock`

    - ### Methods inherited from class org.apache.commons.configuration2.event.BaseEventSource

      `addEventListener, clearErrorListeners, clearEventListeners, clone, copyEventListeners, createErrorEvent, createEvent, fireError, fireEvent, getEventListenerRegistrations, getEventListeners, isDetailEvents, removeEventListener, setDetailEvents`

    - ### Methods inherited from class java.lang.Object

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

- - ### Field Detail

    - #### parent

          protected Configuration parent

      The parent configuration.

    - #### prefix

          protected String prefix

      The prefix used to select the properties.

    - #### delimiter

          protected String delimiter

      The prefix delimiter

  - ### Constructor Detail

    - #### SubsetConfiguration

          public SubsetConfiguration(Configuration parent,
                                     String prefix)

      Create a subset of the specified configuration
      Parameters:
        `parent` - The parent configuration (must not be null)
        `prefix` - The prefix used to select the properties
      Throws:
        `IllegalArgumentException` - if the parent configuration is null

    - #### SubsetConfiguration

          public SubsetConfiguration(Configuration parent,
                                     String prefix,
                                     String delimiter)

      Create a subset of the specified configuration
      Parameters:
        `parent` - The parent configuration (must not be null)
        `prefix` - The prefix used to select the properties
        `delimiter` - The prefix delimiter
      Throws:
        `IllegalArgumentException` - if the parent configuration is null

  - ### Method Detail

    - #### getParentKey

          protected String getParentKey(String key)

      Return the key in the parent configuration associated to the specified key in this subset.
      Parameters:
        `key` - The key in the subset.
      Returns:
        the key as to be used by the parent

    - #### getChildKey

          protected String getChildKey(String key)

      Return the key in the subset configuration associated to the specified key in the parent configuration.
      Parameters:
        `key` - The key in the parent configuration.
      Returns:
        the key in the context of this subset configuration

    - #### getParent

          public Configuration getParent()

      Return the parent configuration for this subset.
      Returns:
        the parent configuration

    - #### getPrefix

          public String getPrefix()

      Return the prefix used to select the properties in the parent configuration.
      Returns:
        the prefix used by this subset

    - #### setPrefix

          public void setPrefix(String prefix)

      Set the prefix used to select the properties in the parent configuration.
      Parameters:
        `prefix` - the prefix

    - #### subset

          public Configuration subset(String prefix)

      Description copied from interface: `Configuration`
      Return a decorator Configuration containing every key from the current Configuration that starts with the specified prefix. The prefix is removed from the keys in the subset. For example, if the configuration contains the following properties:

              prefix.number = 1
              prefix.string = Apache
              prefixed.foo = bar
              prefix = Jakarta

      the Configuration returned by `subset("prefix")` will contain the properties:

              number = 1
              string = Apache
              = Jakarta

      (The key for the value "Jakarta" is an empty string)

      Since the subset is a decorator and not a modified copy of the initial Configuration, any change made to the subset is available to the Configuration, and reciprocally.

      Specified by:
        `subset` in interface `Configuration`
      Overrides:
        `subset` in class `AbstractConfiguration`
      Parameters:
        `prefix` - The prefix used to select the properties.
      Returns:
        a subset configuration
      See Also:
        `SubsetConfiguration`

    - #### isEmptyInternal

          protected boolean isEmptyInternal()

      Description copied from class: `AbstractConfiguration`
      Actually checks whether this configuration contains data. This method is called by `isEmpty()`. It has to be defined by concrete subclasses.
      Specified by:
        `isEmptyInternal` in class `AbstractConfiguration`
      Returns:
        true if this configuration contains no data, false otherwise

    - #### containsKeyInternal

          protected boolean containsKeyInternal(String key)

      Description copied from class: `AbstractConfiguration`
      Actually checks whether the specified key is contained in this configuration. This method is called by `containsKey()`. It has to be defined by concrete subclasses.
      Specified by:
        `containsKeyInternal` in class `AbstractConfiguration`
      Parameters:
        `key` - the key in question
      Returns:
        true if this key is contained in this configuration, false otherwise

    - #### addPropertyDirect

          public void addPropertyDirect(String key,
                                        Object value)

      Description copied from class: `AbstractConfiguration`
      Adds a key/value pair to the Configuration. Override this method to provide write access to underlying Configuration store.
      Specified by:
        `addPropertyDirect` in class `AbstractConfiguration`
      Parameters:
        `key` - key to use for mapping
        `value` - object to store

    - #### clearPropertyDirect

          protected void clearPropertyDirect(String key)

      Description copied from class: `AbstractConfiguration`
      Removes the specified property from this configuration. This method is called by `clearProperty()` after it has done some preparations. It must be overridden in sub classes.
      Specified by:
        `clearPropertyDirect` in class `AbstractConfiguration`
      Parameters:
        `key` - the key to be removed

    - #### getPropertyInternal

          protected Object getPropertyInternal(String key)

      Description copied from class: `AbstractConfiguration`
      Actually obtains the value of the specified property. This method is called by `getProperty()`. Concrete subclasses must define it to fetch the value of the desired property.
      Specified by:
        `getPropertyInternal` in class `AbstractConfiguration`
      Parameters:
        `key` - the key of the property in question
      Returns:
        the (raw) value of this property

    - #### getKeysInternal

          protected Iterator<String> getKeysInternal(String prefix)

      Description copied from class: `AbstractConfiguration`
      Returns an `Iterator` with all property keys starting with the specified prefix. This method is called by `AbstractConfiguration.getKeys(String)`. It is fully implemented by delegating to `getKeysInternal()` and returning a special iterator which filters for the passed in prefix. Subclasses can override it if they can provide a more efficient way to iterate over specific keys only.
      Overrides:
        `getKeysInternal` in class `AbstractConfiguration`
      Parameters:
        `prefix` - the prefix for the keys to be taken into account
      Returns:
        an `Iterator` returning the filtered keys

    - #### getKeysInternal

          protected Iterator<String> getKeysInternal()

      Description copied from class: `AbstractConfiguration`
      Actually creates an iterator for iterating over the keys in this configuration. This method is called by `getKeys()`, it has to be defined by concrete subclasses.
      Specified by:
        `getKeysInternal` in class `AbstractConfiguration`
      Returns:
        an `Iterator` with all property keys in this configuration

    - #### setThrowExceptionOnMissing

          public void setThrowExceptionOnMissing(boolean throwExceptionOnMissing)

      Allows to set the `throwExceptionOnMissing` flag. This flag controls the behavior of property getter methods that return objects if the requested property is missing. If the flag is set to false (which is the default value), these methods will return null. If set to true, they will throw a `NoSuchElementException` exception. Note that getter methods for primitive data types are not affected by this flag. Change the behavior of the parent configuration if it supports this feature.
      Overrides:
        `setThrowExceptionOnMissing` in class `AbstractConfiguration`
      Parameters:
        `throwExceptionOnMissing` - The new value for the property

    - #### isThrowExceptionOnMissing

          public boolean isThrowExceptionOnMissing()

      Returns true if missing values throw Exceptions. The subset inherits this feature from its parent if it supports this feature.
      Overrides:
        `isThrowExceptionOnMissing` in class `AbstractConfiguration`
      Returns:
        true if missing values throw Exceptions

    - #### getListDelimiterHandler

          public ListDelimiterHandler getListDelimiterHandler()

      Returns the `ListDelimiterHandler` used by this instance. If the parent configuration extends `AbstractConfiguration`, the list delimiter handler is obtained from there.
      Overrides:
        `getListDelimiterHandler` in class `AbstractConfiguration`
      Returns:
        the `ListDelimiterHandler`

    - #### setListDelimiterHandler

          public void setListDelimiterHandler(ListDelimiterHandler listDelimiterHandler)

      Sets the `ListDelimiterHandler` to be used by this instance. This object is invoked every time when dealing with string properties that may contain a list delimiter and thus have to be split to multiple values. Per default, a `ListDelimiterHandler` implementation is set which does not support list splitting. This can be changed for instance by setting a `DefaultListDelimiterHandler` object.

      Warning: Be careful when changing the list delimiter handler when the configuration has already been loaded/populated. List handling is typically applied already when properties are added to the configuration. If later another handler is set which processes lists differently, results may be unexpected; some operations may even cause exceptions.

      If the parent configuration extends `AbstractConfiguration`, the list delimiter handler is passed to the parent.
      Overrides:
        `setListDelimiterHandler` in class `AbstractConfiguration`
      Parameters:
        `listDelimiterHandler` - the `ListDelimiterHandler` to be used (must not be null)

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