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 (e.g. 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, e.g. 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, e.g. 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

  • 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(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