Package org.apache.commons.configuration

Class XMLConfiguration

java.lang.Object

org.apache.commons.configuration.event.EventSource

org.apache.commons.configuration.AbstractConfiguration

org.apache.commons.configuration.HierarchicalConfiguration

org.apache.commons.configuration.AbstractHierarchicalFileConfiguration

org.apache.commons.configuration.XMLConfiguration

All Implemented Interfaces:

Configuration, ConfigurationErrorListener, ConfigurationListener, FileConfiguration, FileSystemBased, Reloadable, EntityRegistry, org.xml.sax.EntityResolver

Direct Known Subclasses:

DefaultConfigurationBuilder, HierarchicalXMLConfiguration

public class XMLConfiguration
extends AbstractHierarchicalFileConfiguration
implements org.xml.sax.EntityResolver, EntityRegistry

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\\");
 

Because in XML such a constellation is not directly supported (an attribute can appear only once for a single element), the values are concatenated to a single value. If delimiter parsing is enabled (refer to the AbstractConfiguration.setDelimiterParsingDisabled(boolean) method), the current list delimiter character will be used as separator. Otherwise the pipe symbol ("|") will be used for this purpose. No matter which character is used as delimiter, it can always be escaped with a backslash. A backslash itself can also be escaped with another backslash. Consider the following example fragment from a configuration file:

 <directories names="C:\Temp\\|D:\Data\"/>
 

Here the backslash after Temp is escaped. This is necessary because it would escape the list delimiter (the pipe symbol assuming that list delimiter parsing is disabled) otherwise. So this attribute would have two values.

Note: You should ensure that the delimiter parsing disabled property is always consistent when you load and save a configuration file. Otherwise the values of properties can become corrupted.

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 FileConfiguration interface and thus provides full support for loading XML documents from different sources like files, URLs, or streams. A full description of these features can be found in the documentation of AbstractFileConfiguration.

Note:Configuration objects of this type can be read concurrently by multiple threads. However if one of these threads modifies the object, synchronization has to be performed manually.

Since:

commons-configuration 1.0

Version:

$Id: XMLConfiguration.java 1534429 2013-10-22 00:45:36Z henning $

Author:

Jörg Schaible

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.commons.configuration.AbstractHierarchicalFileConfiguration

AbstractHierarchicalFileConfiguration.FileConfigurationDelegate

Nested classes/interfaces inherited from class org.apache.commons.configuration.HierarchicalConfiguration

HierarchicalConfiguration.BuilderVisitor, HierarchicalConfiguration.Node, HierarchicalConfiguration.NodeVisitor

Field Summary

Fields inherited from class org.apache.commons.configuration.AbstractConfiguration

END_TOKEN, EVENT_ADD_PROPERTY, EVENT_CLEAR, EVENT_CLEAR_PROPERTY, EVENT_READ_PROPERTY, EVENT_SET_PROPERTY, START_TOKEN

Fields inherited from class org.apache.commons.configuration.HierarchicalConfiguration

EVENT_ADD_NODES, EVENT_CLEAR_TREE, EVENT_SUBNODE_CHANGED

Constructor Summary

Constructors

Constructor	Description
XMLConfiguration()	Creates a new instance of XMLConfiguration.
XMLConfiguration(java.io.File file)	Creates a new instance of XMLConfiguration.
XMLConfiguration(java.lang.String fileName)	Creates a new instance ofXMLConfiguration.
XMLConfiguration(java.net.URL url)	Creates a new instance of XMLConfiguration.
XMLConfiguration(HierarchicalConfiguration 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
void	addNodes(java.lang.String key, java.util.Collection<? extends ConfigurationNode> nodes)	Adds a collection of nodes directly to this configuration.
void	clear()	Removes all properties from this configuration.
java.lang.Object	clone()	Creates a copy of this object.
protected AbstractHierarchicalFileConfiguration.FileConfigurationDelegate	createDelegate()	Creates the file configuration delegate for this object.
protected org.w3c.dom.Document	createDocument()	Creates a DOM document from the internal tree of configuration nodes.
protected javax.xml.parsers.DocumentBuilder	createDocumentBuilder()	Creates the DocumentBuilder to be used for loading files.
protected HierarchicalConfiguration.Node	createNode(java.lang.String name)	Creates a new node object.
protected javax.xml.transform.Transformer	createTransformer()	Creates and initializes the transformer used for save operations.
org.w3c.dom.Document	getDocument()	Returns the XML document this configuration was loaded from.
javax.xml.parsers.DocumentBuilder	getDocumentBuilder()	Returns the DocumentBuilder object that is used for loading documents.
org.xml.sax.EntityResolver	getEntityResolver()	Returns the EntityResolver.
java.lang.String	getPublicID()	Returns the public ID of the DOCTYPE declaration from the loaded XML document.
java.util.Map<java.lang.String,java.net.URL>	getRegisteredEntities()	Returns a map with the entity IDs that have been registered using the registerEntityId() method.
java.lang.String	getRootElementName()	Returns the name of the root element.
java.lang.String	getSystemID()	Returns the system ID of the DOCTYPE declaration from the loaded XML document.
void	initProperties(org.w3c.dom.Document document, boolean elemRefs)	Initializes this configuration from an XML document.
boolean	isAttributeSplittingDisabled()	Returns the flag whether attribute splitting is disabled.
boolean	isSchemaValidation()	Returns the value of the schemaValidation flag.
boolean	isValidating()	Returns the value of the validating flag.
void	load(java.io.InputStream in)	Loads the configuration from the given input stream.
void	load(java.io.Reader in)	Load the configuration from the given reader.
void	registerEntityId(java.lang.String publicId, java.net.URL entityURL)	Registers the specified DTD URL for the specified public identifier.
org.xml.sax.InputSource	resolveEntity(java.lang.String publicId, java.lang.String systemId)	Deprecated. Use getEntityResolver().resolveEntity()
void	save(java.io.Writer writer)	Saves the configuration to the specified writer.
void	setAttributeSplittingDisabled(boolean attributeSplittingDisabled)	Sets a flag whether attribute splitting is disabled.
void	setDocumentBuilder(javax.xml.parsers.DocumentBuilder documentBuilder)	Sets the DocumentBuilder object to be used for loading documents.
void	setEntityResolver(org.xml.sax.EntityResolver resolver)	Sets a new EntityResolver.
void	setPublicID(java.lang.String publicID)	Sets the public ID of the DOCTYPE declaration.
void	setRootElementName(java.lang.String name)	Sets the name of the root element.
void	setSchemaValidation(boolean schemaValidation)	Sets the value of the schemaValidation flag.
void	setSystemID(java.lang.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.

Methods inherited from class org.apache.commons.configuration.AbstractConfiguration

addErrorLogListener, addProperty, append, clearPropertyDirect, copy, createInterpolator, getBigDecimal, getBigDecimal, getBigInteger, getBigInteger, getBoolean, getBoolean, getBoolean, getByte, getByte, getByte, getDefaultListDelimiter, getDelimiter, getDouble, getDouble, getDouble, getFloat, getFloat, getFloat, getInt, getInt, getInteger, getInterpolator, getList, getList, getListDelimiter, getLogger, getLong, getLong, getLong, getProperties, getProperties, getShort, getShort, getShort, getString, getString, getStringArray, getSubstitutor, interpolate, interpolate, interpolateHelper, isDelimiterParsingDisabled, isScalarValue, isThrowExceptionOnMissing, resolveContainerStore, setDefaultListDelimiter, setDelimiter, setDelimiterParsingDisabled, setListDelimiter, setLogger, setThrowExceptionOnMissing

Methods inherited from class org.apache.commons.configuration.AbstractHierarchicalFileConfiguration

addPropertyDirect, clearProperty, clearTree, configurationChanged, configurationError, containsKey, fetchNodeList, getBasePath, getDelegate, getEncoding, getFile, getFileName, getFileSystem, getKeys, getKeys, getProperty, getReloadingStrategy, getReloadLock, getURL, isAutoSave, isEmpty, load, load, load, load, load, refresh, reload, resetFileSystem, save, save, save, save, save, save, setAutoSave, setBasePath, setDelegate, setEncoding, setFile, setFileName, setFileSystem, setProperty, setReloadingStrategy, setURL, subnodeConfigurationChanged

Methods inherited from interface org.apache.commons.configuration.Configuration

addProperty, getBigDecimal, getBigDecimal, getBigInteger, getBigInteger, getBoolean, getBoolean, getBoolean, getByte, getByte, getByte, getDouble, getDouble, getDouble, getFloat, getFloat, getFloat, getInt, getInt, getInteger, getList, getList, getLong, getLong, getLong, getProperties, getShort, getShort, getShort, getString, getString, getStringArray, subset

Methods inherited from class org.apache.commons.configuration.event.EventSource

addConfigurationListener, addErrorListener, clearConfigurationListeners, clearErrorListeners, createErrorEvent, createEvent, fireError, fireEvent, getConfigurationListeners, getErrorListeners, isDetailEvents, removeConfigurationListener, removeErrorListener, setDetailEvents

Methods inherited from class org.apache.commons.configuration.HierarchicalConfiguration

clearNode, clearNode, clearReferences, configurationAt, configurationAt, configurationsAt, createAddPath, createSubnodeConfiguration, createSubnodeConfiguration, fetchAddNode, findLastPathNode, findPropertyNodes, getDefaultExpressionEngine, getExpressionEngine, getMaxIndex, getRoot, getRootNode, interpolatedConfiguration, nodeDefined, nodeDefined, removeNode, removeNode, setDefaultExpressionEngine, setExpressionEngine, setRoot, setRootNode, subset

Methods inherited from class java.lang.Object

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

Constructor Detail

XMLConfiguration

public XMLConfiguration()

Creates a new instance of XMLConfiguration.

XMLConfiguration

public XMLConfiguration(HierarchicalConfiguration 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

XMLConfiguration

public XMLConfiguration(java.lang.String fileName)
                 throws ConfigurationException

Creates a new instance ofXMLConfiguration. The configuration is loaded from the specified file

Parameters:

fileName - the name of the file to load

Throws:

ConfigurationException - if the file cannot be loaded

XMLConfiguration

public XMLConfiguration(java.io.File file)
                 throws ConfigurationException

Creates a new instance of XMLConfiguration. The configuration is loaded from the specified file.

Parameters:

file - the file

Throws:

ConfigurationException - if an error occurs while loading the file

XMLConfiguration

public XMLConfiguration(java.net.URL url)
                 throws ConfigurationException

Creates a new instance of XMLConfiguration. The configuration is loaded from the specified URL.

Parameters:

url - the URL

Throws:

ConfigurationException - if loading causes an error

Method Detail

getRootElementName

public java.lang.String getRootElementName()

Returns 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.

Returns:

the name of the root element

setRootElementName

public void setRootElementName(java.lang.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

getDocumentBuilder

public javax.xml.parsers.DocumentBuilder getDocumentBuilder()

Returns 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

setDocumentBuilder

public void setDocumentBuilder(javax.xml.parsers.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

getPublicID

public java.lang.String getPublicID()

Returns 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

setPublicID

public void setPublicID(java.lang.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

getSystemID

public java.lang.String getSystemID()

Returns 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

setSystemID

public void setSystemID(java.lang.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

isValidating

public boolean isValidating()

Returns the value of the validating flag.

Returns:

the validating flag

Since:

1.2

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

isSchemaValidation

public boolean isSchemaValidation()

Returns the value of the schemaValidation flag.

Returns:

the schemaValidation flag

Since:

1.7

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

setEntityResolver

public void setEntityResolver(org.xml.sax.EntityResolver resolver)

Sets a new EntityResolver. Setting this will cause RegisterEntityId to have no effect.

Parameters:

resolver - The EntityResolver to use.

Since:

1.7

getEntityResolver

public org.xml.sax.EntityResolver getEntityResolver()

Returns the EntityResolver.

Returns:

The EntityResolver.

Since:

1.7

isAttributeSplittingDisabled

public boolean isAttributeSplittingDisabled()

Returns the flag whether attribute splitting is disabled.

Returns:

the flag whether attribute splitting is disabled

Since:

1.6

See Also:

setAttributeSplittingDisabled(boolean)

setAttributeSplittingDisabled

public void setAttributeSplittingDisabled(boolean attributeSplittingDisabled)

Sets a flag whether attribute splitting is disabled.

The Configuration API allows adding multiple values to an attribute. This is problematic when storing the configuration because in XML an attribute can appear only once with a single value. To solve this problem, per default multiple attribute values are concatenated using a special separator character and split again when the configuration is loaded. The separator character is either the list delimiter character (see AbstractConfiguration.setListDelimiter(char)) or the pipe symbol ("|") if list delimiter parsing is disabled.

In some constellations the splitting of attribute values can have undesired effects, especially if list delimiter parsing is disabled and attributes may contain the "|" character. In these cases it is possible to disable the attribute splitting mechanism by calling this method with a boolean value set to false. If attribute splitting is disabled, the values of attributes will not be processed, but stored as configuration properties exactly as they are returned by the XML parser.

Note that in this mode multiple attribute values cannot be handled correctly. It is possible to create a XMLConfiguration object, add multiple values to an attribute and save it. When the configuration is loaded again and attribute splitting is disabled, the attribute will only have a single value, which is the concatenation of all values set before. So it lies in the responsibility of the application to carefully set the values of attributes.

As is true for the AbstractConfiguration.setDelimiterParsingDisabled(boolean) method, this method must be called before the configuration is loaded. So it can't be used together with one of the constructors expecting the specification of the file to load. Instead the default constructor has to be used, then setAttributeSplittingDisabled(false) has to be called, and finally the configuration can be loaded using one of its load() methods.

Parameters:

attributeSplittingDisabled - true for disabling attribute splitting, false for enabling it

Since:

1.6

See Also:

AbstractConfiguration.setDelimiterParsingDisabled(boolean)

getDocument

public org.w3c.dom.Document getDocument()

Returns 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

clear

public void clear()

Removes all properties from this configuration. If this configuration was loaded from a file, the associated DOM document is also cleared.

Specified by:

clear in interface Configuration

Overrides:

clear in class HierarchicalConfiguration

initProperties

public void initProperties(org.w3c.dom.Document document,
                           boolean elemRefs)

Initializes this configuration from an XML document.

Parameters:

document - the document to be parsed

elemRefs - a flag whether references to the XML elements should be set

createDocumentBuilder

protected javax.xml.parsers.DocumentBuilder createDocumentBuilder()
                                                           throws javax.xml.parsers.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:

javax.xml.parsers.ParserConfigurationException - if an error occurs

Since:

1.2

createDocument

protected org.w3c.dom.Document createDocument()
                                       throws ConfigurationException

Creates a DOM document from the internal tree of configuration nodes.

Returns:

the new document

Throws:

ConfigurationException - if an error occurs

createNode

protected HierarchicalConfiguration.Node createNode(java.lang.String name)

Creates a new node object. This implementation returns an instance of the XMLNode class.

Overrides:

createNode in class HierarchicalConfiguration

Parameters:

name - the node's name

Returns:

the new node

load

public void load(java.io.InputStream in)
          throws ConfigurationException

Loads the configuration from the given input stream.

Specified by:

load in interface FileConfiguration

Overrides:

load in class AbstractHierarchicalFileConfiguration

Parameters:

in - the input stream

Throws:

ConfigurationException - if an error occurs

load

public void load(java.io.Reader in)
          throws ConfigurationException

Load 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 actual set of properties.

Specified by:

load in interface FileConfiguration

Parameters:

in - An InputStream.

Throws:

ConfigurationException - if an error occurs

save

public void save(java.io.Writer writer)
          throws ConfigurationException

Saves the configuration to the specified writer.

Specified by:

save in interface FileConfiguration

Parameters:

writer - the writer used to save the configuration

Throws:

ConfigurationException - if an error occurs

validate

public void validate()
              throws ConfigurationException

Validate the document against the Schema.

Throws:

ConfigurationException - if the validation fails.

createTransformer

protected javax.xml.transform.Transformer createTransformer()
                                                     throws javax.xml.transform.TransformerException

Creates and initializes the transformer used for save operations. This base implementation initializes all of the default settings like indention 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:

javax.xml.transform.TransformerException - if an error occurs

Since:

1.3

clone

public java.lang.Object clone()

Creates a copy of this object. The new configuration object will contain the same properties as the original, but it will lose any connection to a source document (if one exists). This is to avoid race conditions if both the original and the copy are modified and then saved.

Overrides:

clone in class HierarchicalConfiguration

Returns:

the copy

createDelegate

protected AbstractHierarchicalFileConfiguration.FileConfigurationDelegate createDelegate()

Creates the file configuration delegate for this object. This implementation will return an instance of a class derived from FileConfigurationDelegate that deals with some specialties of XMLConfiguration.

Overrides:

createDelegate in class AbstractHierarchicalFileConfiguration

Returns:

the delegate for this object

addNodes

public void addNodes(java.lang.String key,
                     java.util.Collection<? extends ConfigurationNode> nodes)

Adds a collection of nodes directly to this configuration. This implementation ensures that the nodes to be added are of the correct node type (they have to be converted to XMLNode if necessary).

Overrides:

addNodes in class AbstractHierarchicalFileConfiguration

Parameters:

key - the key where the nodes are to be added

nodes - the collection with the new nodes

Since:

1.5

registerEntityId

public void registerEntityId(java.lang.String publicId,
                             java.net.URL entityURL)

Registers the specified DTD URL for the specified public identifier.

XMLConfiguration contains an internal EntityResolver implementation. This maps PUBLICID's to URLs (from which the resource will be loaded). A common use case for this method is to register local URLs (possibly computed at runtime by a class loader) for DTDs. This allows the performance advantage of using a local version without having to ensure every SYSTEM URI on every processed XML document is local. This implementation provides only basic functionality. If more sophisticated features are required, using setDocumentBuilder(DocumentBuilder) to set a custom DocumentBuilder (which also can be initialized with a custom EntityResolver) is recommended.

Note: This method will have no effect when a custom DocumentBuilder has been set. (Setting a custom DocumentBuilder overrides the internal implementation.)

Note: This method must be called before the configuration is loaded. So the default constructor of XMLConfiguration should be used, the location of the configuration file set, registerEntityId() called, and finally the load() method can be invoked.

Specified by:

registerEntityId in interface EntityRegistry

Parameters:

publicId - Public identifier of the DTD to be resolved

entityURL - The URL to use for reading this DTD

Throws:

java.lang.IllegalArgumentException - if the public ID is undefined

Since:

1.5

resolveEntity

@Deprecated
public org.xml.sax.InputSource resolveEntity(java.lang.String publicId,
                                             java.lang.String systemId)
                                      throws org.xml.sax.SAXException

Deprecated. Use getEntityResolver().resolveEntity()

Resolves the requested external entity. This is the default implementation of the EntityResolver interface. It checks the passed in public ID against the registered entity IDs and uses a local URL if possible.

Specified by:

resolveEntity in interface org.xml.sax.EntityResolver

Parameters:

publicId - the public identifier of the entity being referenced

systemId - the system identifier of the entity being referenced

Returns:

an input source for the specified entity

Throws:

org.xml.sax.SAXException - if a parsing exception occurs

Since:

1.5

getRegisteredEntities

public java.util.Map<java.lang.String,java.net.URL> getRegisteredEntities()

Returns a map with the entity IDs that have been registered using the registerEntityId() method.

Specified by:

getRegisteredEntities in interface EntityRegistry

Returns:

a map with the registered entity IDs