## org.apache.commons.configuration
Interface Configuration

All Known Subinterfaces:
  FileConfiguration

All Known Implementing Classes:
  AbstractConfiguration, AbstractFileConfiguration, AbstractHierarchicalFileConfiguration, AbstractHierarchicalFileConfiguration.FileConfigurationDelegate, AppletConfiguration, BaseConfiguration, BaseWebConfiguration, CombinedConfiguration, CompositeConfiguration, DatabaseConfiguration, DataConfiguration, DefaultConfigurationBuilder, HierarchicalConfiguration, HierarchicalXMLConfiguration, JNDIConfiguration, MapConfiguration, PropertiesConfiguration, PropertyListConfiguration, ServletConfiguration, ServletContextConfiguration, ServletFilterConfiguration, ServletRequestConfiguration, SubnodeConfiguration, SubsetConfiguration, SystemConfiguration, XMLConfiguration, XMLPropertiesConfiguration, XMLPropertyListConfiguration

    public interface Configuration

The main Configuration interface.

This interface allows accessing and manipulating a configuration object. The major part of the methods defined in this interface deals with accessing properties of various data types. There is a generic `getProperty()` method, which returns the value of the queried property in its raw data type. Other getter methods try to convert this raw data type into a specific data type. If this fails, a `ConversionException` will be thrown.

For most of the property getter methods an overloaded version exists that allows to specify a default value, which will be returned if the queried property cannot be found in the configuration. The behavior of the methods that do not take a default value in case of a missing property is not defined by this interface and depends on a concrete implementation. E.g. the ``AbstractConfiguration`` class, which is the base class of most configuration implementations provided by this package, per default returns null if a property is not found, but provides the ``setThrowExceptionOnMissing()`` method, with which it can be configured to throw a `NoSuchElementException` exception in that case. (Note that getter methods for primitive types in `AbstractConfiguration` always throw an exception for missing properties because there is no way of overloading the return value.)

With the `addProperty()` and `setProperty()` methods new properties can be added to a configuration or the values of properties can be changed. With `clearProperty()` a property can be removed. Other methods allow to iterate over the contained properties or to create a subset configuration.

Version:
  $Id: Configuration.java 449017 2006-09-22 17:27:00Z oheger $
Author:
  Commons Configuration team

Method Summary
`void` `addProperty(String key, Object value)` Add a property to the configuration.
`void` `clear()` Remove all properties from the configuration.
`void` `clearProperty(String key)` Remove a property from the configuration.
`boolean` `containsKey(String key)` Check if the configuration contains the specified key.
`BigDecimal` `getBigDecimal(String key)` Get a `BigDecimal` associated with the given configuration key.
`BigDecimal` `getBigDecimal(String key, BigDecimal defaultValue)` Get a `BigDecimal` associated with the given configuration key.
`BigInteger` `getBigInteger(String key)` Get a `BigInteger` associated with the given configuration key.
`BigInteger` `getBigInteger(String key, BigInteger defaultValue)` Get a `BigInteger` associated with the given configuration key.
`boolean` `getBoolean(String key)` Get a boolean associated with the given configuration key.
`boolean` `getBoolean(String key, boolean defaultValue)` Get a boolean associated with the given configuration key.
`Boolean` `getBoolean(String key, Boolean defaultValue)` Get a `Boolean` associated with the given configuration key.
`byte` `getByte(String key)` Get a byte associated with the given configuration key.
`byte` `getByte(String key, byte defaultValue)` Get a byte associated with the given configuration key.
`Byte` `getByte(String key, Byte defaultValue)` Get a `Byte` associated with the given configuration key.
`double` `getDouble(String key)` Get a double associated with the given configuration key.
`double` `getDouble(String key, double defaultValue)` Get a double associated with the given configuration key.
`Double` `getDouble(String key, Double defaultValue)` Get a `Double` associated with the given configuration key.
`float` `getFloat(String key)` Get a float associated with the given configuration key.
`float` `getFloat(String key, float defaultValue)` Get a float associated with the given configuration key.
`Float` `getFloat(String key, Float defaultValue)` Get a `Float` associated with the given configuration key.
`int` `getInt(String key)` Get a int associated with the given configuration key.
`int` `getInt(String key, int defaultValue)` Get a int associated with the given configuration key.
`Integer` `getInteger(String key, Integer defaultValue)` Get an `Integer` associated with the given configuration key.
`Iterator` `getKeys()` Get the list of the keys contained in the configuration.
`Iterator` `getKeys(String prefix)` Get the list of the keys contained in the configuration that match the specified prefix.
`List` `getList(String key)` Get a List of strings associated with the given configuration key.
`List` `getList(String key, List defaultValue)` Get a List of strings associated with the given configuration key.
`long` `getLong(String key)` Get a long associated with the given configuration key.
`long` `getLong(String key, long defaultValue)` Get a long associated with the given configuration key.
`Long` `getLong(String key, Long defaultValue)` Get a `Long` associated with the given configuration key.
`Properties` `getProperties(String key)` Get a list of properties associated with the given configuration key.
`Object` `getProperty(String key)` Gets a property from the configuration.
`short` `getShort(String key)` Get a short associated with the given configuration key.
`short` `getShort(String key, short defaultValue)` Get a short associated with the given configuration key.
`Short` `getShort(String key, Short defaultValue)` Get a `Short` associated with the given configuration key.
`String` `getString(String key)` Get a string associated with the given configuration key.
`String` `getString(String key, String defaultValue)` Get a string associated with the given configuration key.
`String[]` `getStringArray(String key)` Get an array of strings associated with the given configuration key.
`boolean` `isEmpty()` Check if the configuration is empty.
`void` `setProperty(String key, Object value)` Set a property, this will replace any previously set values.
`Configuration` `subset(String prefix)` Return a decorator Configuration containing every key from the current Configuration that starts with the specified prefix.

Method Detail

### subset

    Configuration subset(String prefix)

  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.

  Parameters:
    `prefix` - The prefix used to select the properties.
  Returns:
    a subset configuration
  See Also:
    `SubsetConfiguration`

### isEmpty

    boolean isEmpty()

  Check if the configuration is empty.

  Returns:
    `true` if the configuration contains no property, `false` otherwise.

### containsKey

    boolean containsKey(String key)

  Check if the configuration contains the specified key.

  Parameters:
    `key` - the key whose presence in this configuration is to be tested
  Returns:
    `true` if the configuration contains a value for this key, `false` otherwise

### addProperty

    void addProperty(String key,
                     Object value)

  Add a property to the configuration. If it already exists then the value stated here will be added to the configuration entry. For example, if the property:

      resource.loader = file

  is already present in the configuration and you call

      addProperty("resource.loader", "classpath")

  Then you will end up with a List like the following:

      ["file", "classpath"]

  Parameters:
    `key` - The key to add the property to.
    `value` - The value to add.

### setProperty

    void setProperty(String key,
                     Object value)

  Set a property, this will replace any previously set values. Set values is implicitly a call to clearProperty(key), addProperty(key, value).

  Parameters:
    `key` - The key of the property to change
    `value` - The new value

### clearProperty

    void clearProperty(String key)

  Remove a property from the configuration.

  Parameters:
    `key` - the key to remove along with corresponding value.

### clear

    void clear()

  Remove all properties from the configuration.

### getProperty

    Object getProperty(String key)

  Gets a property from the configuration. This is the most basic get method for retrieving values of properties. In a typical implementation of the `Configuration` interface the other get methods (that return specific data types) will internally make use of this method. On this level variable substitution is not yet performed. The returned object is an internal representation of the property value for the passed in key. It is owned by the `Configuration` object. So a caller should not modify this object. It cannot be guaranteed that this object will stay constant over time (i.e. further update operations on the configuration may change its internal state).

  Parameters:
    `key` - property to retrieve
  Returns:
    the value to which this configuration maps the specified key, or null if the configuration contains no mapping for this key.

### getKeys

    Iterator getKeys(String prefix)

  Get the list of the keys contained in the configuration that match the specified prefix.

  Parameters:
    `prefix` - The prefix to test against.
  Returns:
    An Iterator of keys that match the prefix.
  See Also:
    `getKeys()`

### getKeys

    Iterator getKeys()

  Get the list of the keys contained in the configuration. The returned iterator can be used to obtain all defined keys. Note that the exact behavior of the iterator's `remove()` method is specific to a concrete implementation. It may remove the corresponding property from the configuration, but this is not guaranteed. In any case it is no replacement for calling ``clearProperty(String)`` for this property. So it is highly recommended to avoid using the iterator's `remove()` method.

  Returns:
    An Iterator.

### getProperties

    Properties getProperties(String key)

  Get a list of properties associated with the given configuration key. This method expects the given key to have an arbitrary number of String values, each of which is of the form `key=value`. These strings are splitted at the equals sign, and the key parts will become keys of the returned `Properties` object, the value parts become values.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated properties if key is found.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a String/List.
    `IllegalArgumentException` - if one of the tokens is malformed (does not contain an equals sign).

### getBoolean

    boolean getBoolean(String key)

  Get a boolean associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated boolean.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Boolean.

### getBoolean

    boolean getBoolean(String key,
                       boolean defaultValue)

  Get a boolean associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated boolean.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Boolean.

### getBoolean

    Boolean getBoolean(String key,
                       Boolean defaultValue)

  Get a `Boolean` associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated boolean if key is found and has valid format, default value otherwise.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Boolean.

### getByte

    byte getByte(String key)

  Get a byte associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated byte.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Byte.

### getByte

    byte getByte(String key,
                 byte defaultValue)

  Get a byte associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated byte.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Byte.

### getByte

    Byte getByte(String key,
                 Byte defaultValue)

  Get a `Byte` associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated byte if key is found and has valid format, default value otherwise.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Byte.

### getDouble

    double getDouble(String key)

  Get a double associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated double.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Double.

### getDouble

    double getDouble(String key,
                     double defaultValue)

  Get a double associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated double.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Double.

### getDouble

    Double getDouble(String key,
                     Double defaultValue)

  Get a `Double` associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated double if key is found and has valid format, default value otherwise.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Double.

### getFloat

    float getFloat(String key)

  Get a float associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated float.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Float.

### getFloat

    float getFloat(String key,
                   float defaultValue)

  Get a float associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated float.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Float.

### getFloat

    Float getFloat(String key,
                   Float defaultValue)

  Get a `Float` associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated float if key is found and has valid format, default value otherwise.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Float.

### getInt

    int getInt(String key)

  Get a int associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated int.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Integer.

### getInt

    int getInt(String key,
               int defaultValue)

  Get a int associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated int.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Integer.

### getInteger

    Integer getInteger(String key,
                       Integer defaultValue)

  Get an `Integer` associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated int if key is found and has valid format, default value otherwise.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Integer.

### getLong

    long getLong(String key)

  Get a long associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated long.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Long.

### getLong

    long getLong(String key,
                 long defaultValue)

  Get a long associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated long.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Long.

### getLong

    Long getLong(String key,
                 Long defaultValue)

  Get a `Long` associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated long if key is found and has valid format, default value otherwise.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Long.

### getShort

    short getShort(String key)

  Get a short associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated short.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Short.

### getShort

    short getShort(String key,
                   short defaultValue)

  Get a short associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated short.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Short.

### getShort

    Short getShort(String key,
                   Short defaultValue)

  Get a `Short` associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated short if key is found and has valid format, default value otherwise.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a Short.

### getBigDecimal

    BigDecimal getBigDecimal(String key)

  Get a `BigDecimal` associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated BigDecimal if key is found and has valid format

### getBigDecimal

    BigDecimal getBigDecimal(String key,
                             BigDecimal defaultValue)

  Get a `BigDecimal` associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated BigDecimal if key is found and has valid format, default value otherwise.

### getBigInteger

    BigInteger getBigInteger(String key)

  Get a `BigInteger` associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated BigInteger if key is found and has valid format

### getBigInteger

    BigInteger getBigInteger(String key,
                             BigInteger defaultValue)

  Get a `BigInteger` associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated BigInteger if key is found and has valid format, default value otherwise.

### getString

    String getString(String key)

  Get a string associated with the given configuration key.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated string.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a String.

### getString

    String getString(String key,
                     String defaultValue)

  Get a string associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated string if key is found and has valid format, default value otherwise.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a String.

### getStringArray

    String[] getStringArray(String key)

  Get an array of strings associated with the given configuration key. If the key doesn't map to an existing object an empty array is returned

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated string array if key is found.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a String/List of Strings.

### getList

    List getList(String key)

  Get a List of strings associated with the given configuration key. If the key doesn't map to an existing object an empty List is returned.

  Parameters:
    `key` - The configuration key.
  Returns:
    The associated List.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a List.

### getList

    List getList(String key,
                 List defaultValue)

  Get a List of strings associated with the given configuration key. If the key doesn't map to an existing object, the default value is returned.

  Parameters:
    `key` - The configuration key.
    `defaultValue` - The default value.
  Returns:
    The associated List of strings.
  Throws:
    `ConversionException` - is thrown if the key maps to an object that is not a List.

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