Package org.apache.commons.configuration2

# Class XMLConfiguration

java.lang.Object
org.apache.commons.configuration2.event.BaseEventSource
org.apache.commons.configuration2.AbstractConfiguration
org.apache.commons.configuration2.AbstractHierarchicalConfiguration<ImmutableNode>
org.apache.commons.configuration2.BaseHierarchicalConfiguration
org.apache.commons.configuration2.XMLConfiguration

All Implemented Interfaces:
  `Cloneable`, `Configuration`, `EventSource`, `FileBasedConfiguration`, `HierarchicalConfiguration<ImmutableNode>`, `ImmutableConfiguration`, `ImmutableHierarchicalConfiguration`, `FileBased`, `FileLocatorAware`, `InputStreamSupport`, `SynchronizerSupport`, `InMemoryNodeModelSupport`, `NodeKeyResolver<ImmutableNode>`, `NodeModelSupport<ImmutableNode>`

public class XMLConfiguration extends BaseHierarchicalConfiguration implements FileBasedConfiguration, FileLocatorAware, InputStreamSupport

A specialized hierarchical configuration class that is able to parse XML documents.

The parsed document will be stored keeping its structure. The class also tries to preserve as much information from the loaded XML document as possible, including comments and processing instructions. These will be contained in documents created by the `save()` methods, too.

Like other file based configuration classes this class maintains the name and path to the loaded configuration file. These properties can be altered using several setter methods, but they are not modified by `save()` and `load()` methods. If XML documents contain relative paths to other documents (for example to a DTD), these references are resolved based on the path set for this configuration.

By inheriting from `AbstractConfiguration` this class provides some extended functionality, for example interpolation of property values. Like in `PropertiesConfiguration` property values can contain delimiter characters (the comma ',' per default) and are then split into multiple values. This works for XML attributes and text content of elements as well. The delimiter can be escaped by a backslash. As an example consider the following XML fragment:

     <config>
       <array>10,20,30,40</array>
       <scalar>3\,1415</scalar>
       <cite text="To be or not to be\, this is the question!"/>
     </config>

Here the content of the `array` element will be split at the commas, so the `array` key will be assigned 4 values. In the `scalar` property and the `text` attribute of the `cite` element the comma is escaped, so that no splitting is performed.

The configuration API allows setting multiple values for a single attribute, for example something like the following is legal (assuming that the default expression engine is used):

     XMLConfiguration config = new XMLConfiguration();
     config.addProperty("test.dir[@name]", "C:\\Temp\\");
     config.addProperty("test.dir[@name]", "D:\\Data\\");

However, in XML such a constellation is not supported; an attribute can appear only once for a single element. Therefore, an attempt to save a configuration which violates this condition will throw an exception.

Like other `Configuration` implementations, `XMLConfiguration` uses a `ListDelimiterHandler` object for controlling list split operations. Per default, a list delimiter handler object is set which disables this feature. XML has a built-in support for complex structures including list properties; therefore, list splitting is not that relevant for this configuration type. Nevertheless, by setting an alternative `ListDelimiterHandler` implementation, this feature can be enabled. It works as for any other concrete `Configuration` implementation.

Whitespace in the content of XML documents is trimmed per default. In most cases this is desired. However, sometimes whitespace is indeed important and should be treated as part of the value of a property as in the following example:

       <indent>    </indent>

Per default the spaces in the `indent` element will be trimmed resulting in an empty element. To tell `XMLConfiguration` that spaces are relevant the `xml:space` attribute can be used, which is defined in the XML specification. This will look as follows:

       <indent xml:space="preserve">    </indent>

The value of the `indent` property will now contain the spaces.

`XMLConfiguration` implements the `FileBasedConfiguration` interface and thus can be used together with a file-based builder to load XML configuration files from various sources like files, URLs, or streams.

Like other `Configuration` implementations, this class uses a `Synchronizer` object to control concurrent access. By choosing a suitable implementation of the `Synchronizer` interface, an instance can be made thread-safe or not. Note that access to most of the properties typically set through a builder is not protected by the `Synchronizer`. The intended usage is that these properties are set once at construction time through the builder and after that remain constant. If you wish to change such properties during life time of an instance, you have to use the `lock()` and `unlock()` methods manually to ensure that other threads see your changes.

More information about the basic functionality supported by `XMLConfiguration` can be found at the user's guide at Basic features and AbstractConfiguration. There is also a separate chapter dealing with XML Configurations in special.

Since:
  1.0

- ## Nested Class Summary

  ## Nested classes/interfaces inherited from class org.apache.commons.configuration2.BaseHierarchicalConfiguration

  `BaseHierarchicalConfiguration.BuilderVisitor`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `XMLConfiguration()`
  Creates a new instance of `XMLConfiguration`.
  `XMLConfiguration(HierarchicalConfiguration<ImmutableNode> c)`
  Creates a new instance of `XMLConfiguration` and copies the content of the passed in configuration into this object.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected DocumentBuilder`
  `createDocumentBuilder()`
  Creates the `DocumentBuilder` to be used for loading files.
  `protected Transformer`
  `createTransformer()`
  Creates and initializes the transformer used for save operations.
  `Document`
  `getDocument()`
  Gets the XML document this configuration was loaded from.
  `DocumentBuilder`
  `getDocumentBuilder()`
  Gets the `DocumentBuilder` object that is used for loading documents.
  `EntityResolver`
  `getEntityResolver()`
  Gets the EntityResolver.
  `String`
  `getPublicID()`
  Gets the public ID of the DOCTYPE declaration from the loaded XML document.
  `protected String`
  `getRootElementNameInternal()`
  Gets the name of the root element.
  `String`
  `getSystemID()`
  Gets the system ID of the DOCTYPE declaration from the loaded XML document.
  `void`
  `initFileLocator(FileLocator loc)`
  Passes the current `FileLocator` to this object.
  `boolean`
  `isSchemaValidation()`
  Returns the value of the schemaValidation flag.
  `boolean`
  `isValidating()`
  Returns the value of the validating flag.
  `void`
  `read(InputStream in)`
  Loads the configuration from the given input stream.
  `void`
  `read(Reader in)`
  Loads the configuration from the given reader.
  `void`
  `read(Element element)`
  Loads the configuration from the given XML DOM Element.
  `void`
  `setDocumentBuilder(DocumentBuilder documentBuilder)`
  Sets the `DocumentBuilder` object to be used for loading documents.
  `void`
  `setEntityResolver(EntityResolver resolver)`
  Sets a new EntityResolver.
  `void`
  `setPublicID(String publicID)`
  Sets the public ID of the DOCTYPE declaration.
  `void`
  `setRootElementName(String name)`
  Sets the name of the root element.
  `void`
  `setSchemaValidation(boolean schemaValidation)`
  Sets the value of the schemaValidation flag.
  `void`
  `setSystemID(String systemID)`
  Sets the system ID of the DOCTYPE declaration.
  `void`
  `setValidating(boolean validating)`
  Sets the value of the validating flag.
  `void`
  `validate()`
  Validate the document against the Schema.
  `void`
  `write(Writer writer)`
  Saves the configuration to the specified writer.
  `void`
  `write(Writer writer, Transformer transformer)`
  Saves the configuration to the specified writer.

  ### Methods inherited from class org.apache.commons.configuration2.BaseHierarchicalConfiguration

  `childConfigurationsAt, childConfigurationsAt, cloneNodeModel, configurationAt, configurationAt, configurationsAt, configurationsAt, createSubConfigurationForTrackedNode, getNodeModel, getSubConfigurationNodeSelector, getSubConfigurationParentModel, immutableChildConfigurationsAt, immutableConfigurationAt, immutableConfigurationAt, immutableConfigurationsAt, initSubConfigurationForThisParent, interpolatedConfiguration, subnodeConfigurationChanged, subset`

  ### Methods inherited from class org.apache.commons.configuration2.AbstractHierarchicalConfiguration

  `addNodes, addNodesInternal, addPropertyDirect, addPropertyInternal, clearInternal, clearPropertyDirect, clearTree, clearTreeInternal, clone, containsKeyInternal, containsValueInternal, fetchNodeList, getExpressionEngine, getKeysInternal, getKeysInternal, getKeysInternal, getMaxIndex, getMaxIndexInternal, getModel, getPropertyInternal, getRootElementName, isEmptyInternal, nodeDefined, nodeKey, resolveAddKey, resolveKey, resolveNodeKey, resolveUpdateKey, setExpressionEngine, setPropertyInternal, sizeInternal, toString`

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

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

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

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

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

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

  ### Methods inherited from interface org.apache.commons.configuration2.Configuration

  `addProperty, clear, clearProperty, getInterpolator, installInterpolator, setInterpolator, setProperty, subset`

  ### Methods inherited from interface org.apache.commons.configuration2.ImmutableConfiguration

  `containsKey, containsValue, entrySet, forEach, get, get, getArray, getArray, getBigDecimal, getBigDecimal, getBigInteger, getBigInteger, getBoolean, getBoolean, getBoolean, getByte, getByte, getByte, getCollection, getCollection, getDouble, getDouble, getDouble, getDuration, getDuration, getEncodedString, getEncodedString, getEnum, getEnum, getFloat, getFloat, getFloat, getInt, getInt, getInteger, getKeys, getKeys, getKeys, getList, getList, getList, getList, getLong, getLong, getLong, getProperties, getProperty, getShort, getShort, getShort, getString, getString, getStringArray, immutableSubset, isEmpty, size`

  ### Methods inherited from interface org.apache.commons.configuration2.sync.SynchronizerSupport

  `getSynchronizer, lock, setSynchronizer, unlock`

- ## Constructor Details

  - ### XMLConfiguration

    public XMLConfiguration()
    Creates a new instance of `XMLConfiguration`.

  - ### XMLConfiguration

    public XMLConfiguration(HierarchicalConfiguration<ImmutableNode> c)
    Creates a new instance of `XMLConfiguration` and copies the content of the passed in configuration into this object. Note that only the data of the passed in configuration will be copied. If, for instance, the other configuration is a `XMLConfiguration`, too, things like comments or processing instructions will be lost.
    Parameters:
      `c` - the configuration to copy.
    Since:
      1.4

- ## Method Details

  - ### createDocumentBuilder

    protected DocumentBuilder createDocumentBuilder() throws ParserConfigurationException
    Creates the `DocumentBuilder` to be used for loading files. This implementation checks whether a specific `DocumentBuilder` has been set. If this is the case, this one is used. Otherwise a default builder is created. Depending on the value of the validating flag this builder will be a validating or a non validating `DocumentBuilder`.
    Returns:
      the `DocumentBuilder` for loading configuration files.
    Throws:
      `ParserConfigurationException` - if an error occurs.
    Since:
      1.2

  - ### createTransformer

    protected Transformer createTransformer() throws ConfigurationException
    Creates and initializes the transformer used for save operations. This base implementation initializes all of the default settings like indentation mode and the DOCTYPE. Derived classes may overload this method if they have specific needs.
    Returns:
      the transformer to use for a save operation.
    Throws:
      `ConfigurationException` - if an error occurs.
    Since:
      1.3

  - ### getDocument

    public Document getDocument()
    Gets the XML document this configuration was loaded from. The return value is null if this configuration was not loaded from a XML document.
    Returns:
      the XML document this configuration was loaded from.

  - ### getDocumentBuilder

    public DocumentBuilder getDocumentBuilder()
    Gets the `DocumentBuilder` object that is used for loading documents. If no specific builder has been set, this method returns null.
    Returns:
      the `DocumentBuilder` for loading new documents.
    Since:
      1.2

  - ### getEntityResolver

    public EntityResolver getEntityResolver()
    Gets the EntityResolver.
    Returns:
      The EntityResolver.
    Since:
      1.7

  - ### getPublicID

    public String getPublicID()
    Gets the public ID of the DOCTYPE declaration from the loaded XML document. This is null if no document has been loaded yet or if the document does not contain a DOCTYPE declaration with a public ID.
    Returns:
      the public ID.
    Since:
      1.3

  - ### getRootElementNameInternal

    protected String getRootElementNameInternal()
    Gets the name of the root element. If this configuration was loaded from a XML document, the name of this document's root element is returned. Otherwise it is possible to set a name for the root element that will be used when this configuration is stored.
    Overrides:
      `getRootElementNameInternal` in class `AbstractHierarchicalConfiguration<ImmutableNode>`
    Returns:
      the name of the root element.

  - ### getSystemID

    public String getSystemID()
    Gets the system ID of the DOCTYPE declaration from the loaded XML document. This is null if no document has been loaded yet or if the document does not contain a DOCTYPE declaration with a system ID.
    Returns:
      the system ID.
    Since:
      1.3

  - ### initFileLocator

    public void initFileLocator(FileLocator loc)
    Passes the current `FileLocator` to this object. Note that this `FileLocator` object is only temporarily valid for the following invocation of `read()` or `write(`. Depending on the state of the `FileHandler` and which of its methods was called, the object may not be fully initialized. For instance, if the `FileHandler`'s `load(InputStream)` method was called, no file information is available, and all methods of the `FileLocator` will return null. Stores the passed in locator for the upcoming IO operation.
    Specified by:
      `initFileLocator` in interface `FileLocatorAware`
    Parameters:
      `loc` - the current `FileLocator`

  - ### isSchemaValidation

    public boolean isSchemaValidation()
    Returns the value of the schemaValidation flag.
    Returns:
      the schemaValidation flag.
    Since:
      1.7

  - ### isValidating

    public boolean isValidating()
    Returns the value of the validating flag.
    Returns:
      the validating flag.
    Since:
      1.2

  - ### read

    public void read(Element element) throws ConfigurationException
    Loads the configuration from the given XML DOM Element.

    This method can be used to initialize the configuration from an XML element in a document that has already been parsed. This is especially useful if the configuration is only a part of a larger XML document.

    Parameters:
      `element` - the input element.
    Throws:
      `ConfigurationException` - if an error occurs.
    Since:
      2.14.0

  - ### read

    public void read(InputStream in) throws ConfigurationException, IOException
    Loads the configuration from the given input stream. This is analogous to `read(Reader)`, but data is read from a stream. Note that this method will be called most time when reading an XML configuration source. By reading XML documents directly from an input stream, the file's encoding can be correctly dealt with.
    Specified by:
      `read` in interface `InputStreamSupport`
    Parameters:
      `in` - the input stream.
    Throws:
      `ConfigurationException` - if an error occurs.
      `IOException` - if an IO error occurs.

  - ### read

    public void read(Reader in) throws ConfigurationException, IOException
    Loads the configuration from the given reader. Note that the `clear()` method is not called, so the properties contained in the loaded file will be added to the current set of properties.
    Specified by:
      `read` in interface `FileBased`
    Parameters:
      `in` - the reader.
    Throws:
      `ConfigurationException` - if an error occurs.
      `IOException` - if an IO error occurs.

  - ### setDocumentBuilder

    public void setDocumentBuilder(DocumentBuilder documentBuilder)
    Sets the `DocumentBuilder` object to be used for loading documents. This method makes it possible to specify the exact document builder. So an application can create a builder, configure it for its special needs, and then pass it to this method.
    Parameters:
      `documentBuilder` - the document builder to be used; if undefined, a default builder will be used.
    Since:
      1.2

  - ### setEntityResolver

    public void setEntityResolver(EntityResolver resolver)
    Sets a new EntityResolver. Setting this will cause RegisterEntityId to have no effect.
    Parameters:
      `resolver` - The EntityResolver to use.
    Since:
      1.7

  - ### setPublicID

    public void setPublicID(String publicID)
    Sets the public ID of the DOCTYPE declaration. When this configuration is saved, a DOCTYPE declaration will be constructed that contains this public ID.
    Parameters:
      `publicID` - the public ID.
    Since:
      1.3

  - ### setRootElementName

    public void setRootElementName(String name)
    Sets the name of the root element. This name is used when this configuration object is stored in an XML file. Note that setting the name of the root element works only if this configuration has been newly created. If the configuration was loaded from an XML file, the name cannot be changed and an `UnsupportedOperationException` exception is thrown. Whether this configuration has been loaded from an XML document or not can be found out using the `getDocument()` method.
    Parameters:
      `name` - the name of the root element.

  - ### setSchemaValidation

    public void setSchemaValidation(boolean schemaValidation)
    Sets the value of the schemaValidation flag. This flag determines whether DTD or Schema validation should be used. This flag is evaluated only if no custom `DocumentBuilder` was set. If set to true the XML document must contain a schemaLocation definition that provides resolvable hints to the required schemas.
    Parameters:
      `schemaValidation` - the validating flag.
    Since:
      1.7

  - ### setSystemID

    public void setSystemID(String systemID)
    Sets the system ID of the DOCTYPE declaration. When this configuration is saved, a DOCTYPE declaration will be constructed that contains this system ID.
    Parameters:
      `systemID` - the system ID.
    Since:
      1.3

  - ### setValidating

    public void setValidating(boolean validating)
    Sets the value of the validating flag. This flag determines whether DTD/Schema validation should be performed when loading XML documents. This flag is evaluated only if no custom `DocumentBuilder` was set.
    Parameters:
      `validating` - the validating flag.
    Since:
      1.2

  - ### validate

    public void validate() throws ConfigurationException
    Validate the document against the Schema.
    Throws:
      `ConfigurationException` - if the validation fails.

  - ### write

    public void write(Writer writer) throws ConfigurationException, IOException
    Saves the configuration to the specified writer.
    Specified by:
      `write` in interface `FileBased`
    Parameters:
      `writer` - the writer used to save the configuration.
    Throws:
      `ConfigurationException` - if an error occurs.
      `IOException` - if an IO error occurs.

  - ### write

    public void write(Writer writer, Transformer transformer) throws ConfigurationException
    Saves the configuration to the specified writer.
    Parameters:
      `writer` - the writer used to save the configuration.
      `transformer` - How to transform this configuration.
    Throws:
      `ConfigurationException` - if an error occurs.
    Since:
      2.7.0