org.apache.xerces.dom.CoreDOMImplementationImpl Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.xerces.dom;
import java.lang.ref.SoftReference;
import org.apache.xerces.impl.RevalidationHandler;
import org.apache.xerces.impl.dtd.XMLDTDLoader;
import org.apache.xerces.parsers.DOMParserImpl;
import org.apache.xerces.util.XMLChar;
import org.apache.xerces.xni.grammars.XMLGrammarDescription;
import org.apache.xml.serialize.DOMSerializerImpl;
import org.w3c.dom.DOMException;
import org.w3c.dom.DOMImplementation;
import org.w3c.dom.Document;
import org.w3c.dom.DocumentType;
import org.w3c.dom.Element;
import org.w3c.dom.ls.DOMImplementationLS;
import org.w3c.dom.ls.LSInput;
import org.w3c.dom.ls.LSOutput;
import org.w3c.dom.ls.LSParser;
import org.w3c.dom.ls.LSSerializer;
/**
* The DOMImplementation class is description of a particular
* implementation of the Document Object Model. As such its data is
* static, shared by all instances of this implementation.
*
* The DOM API requires that it be a real object rather than static
* methods. However, there's nothing that says it can't be a singleton,
* so that's how I've implemented it.
*
* This particular class, along with CoreDocumentImpl, supports the DOM
* Core and Load/Save (Experimental). Optional modules are supported by
* the more complete DOMImplementation class along with DocumentImpl.
*
* @xerces.internal
*
* @version $Id: CoreDOMImplementationImpl.java 826681 2009-10-19 14:15:37Z mrglavas $
* @since PR-DOM-Level-1-19980818.
*/
public class CoreDOMImplementationImpl
implements DOMImplementation, DOMImplementationLS {
//
// Data
//
// validator pools
private static final int SIZE = 2;
private SoftReference schemaValidators[] = new SoftReference[SIZE];
private SoftReference xml10DTDValidators[] = new SoftReference[SIZE];
private SoftReference xml11DTDValidators[] = new SoftReference[SIZE];
private int freeSchemaValidatorIndex = -1;
private int freeXML10DTDValidatorIndex = -1;
private int freeXML11DTDValidatorIndex = -1;
private int schemaValidatorsCurrentSize = SIZE;
private int xml10DTDValidatorsCurrentSize = SIZE;
private int xml11DTDValidatorsCurrentSize = SIZE;
private SoftReference xml10DTDLoaders[] = new SoftReference[SIZE];
private SoftReference xml11DTDLoaders[] = new SoftReference[SIZE];
private int freeXML10DTDLoaderIndex = -1;
private int freeXML11DTDLoaderIndex = -1;
private int xml10DTDLoaderCurrentSize = SIZE;
private int xml11DTDLoaderCurrentSize = SIZE;
// Document and doctype counter. Used to assign order to documents and
// doctypes without owners, on an demand basis. Used for
// compareDocumentPosition
private int docAndDoctypeCounter = 0;
// static
/** Dom implementation singleton. */
static final CoreDOMImplementationImpl singleton = new CoreDOMImplementationImpl();
//
// Public methods
//
/** NON-DOM: Obtain and return the single shared object */
public static DOMImplementation getDOMImplementation() {
return singleton;
}
//
// DOMImplementation methods
//
/**
* Test if the DOM implementation supports a specific "feature" --
* currently meaning language and level thereof.
*
* @param feature The package name of the feature to test.
* In Level 1, supported values are "HTML" and "XML" (case-insensitive).
* At this writing, org.apache.xerces.dom supports only XML.
*
* @param version The version number of the feature being tested.
* This is interpreted as "Version of the DOM API supported for the
* specified Feature", and in Level 1 should be "1.0"
*
* @return true iff this implementation is compatible with the specified
* feature and version.
*/
public boolean hasFeature(String feature, String version) {
boolean anyVersion = version == null || version.length() == 0;
// check if Xalan implementation is around and if yes report true for supporting
// XPath API
// if a plus sign "+" is prepended to any feature name, implementations
// are considered in which the specified feature may not be directly
// castable DOMImplementation.getFeature(feature, version). Without a
// plus, only features whose interfaces are directly castable are considered.
if ((feature.equalsIgnoreCase("+XPath"))
&& (anyVersion || version.equals("3.0"))) {
try {
Class xpathClass = ObjectFactory.findProviderClass(
"org.apache.xpath.domapi.XPathEvaluatorImpl",
ObjectFactory.findClassLoader(), true);
// Check if the DOM XPath implementation implements
// the interface org.w3c.dom.XPathEvaluator
Class interfaces[] = xpathClass.getInterfaces();
for (int i = 0; i < interfaces.length; i++) {
if (interfaces[i].getName().equals(
"org.w3c.dom.xpath.XPathEvaluator")) {
return true;
}
}
} catch (Exception e) {
return false;
}
return true;
}
if (feature.startsWith("+")) {
feature = feature.substring(1);
}
return (
feature.equalsIgnoreCase("Core")
&& (anyVersion
|| version.equals("1.0")
|| version.equals("2.0")
|| version.equals("3.0")))
|| (feature.equalsIgnoreCase("XML")
&& (anyVersion
|| version.equals("1.0")
|| version.equals("2.0")
|| version.equals("3.0")))
|| (feature.equalsIgnoreCase("XMLVersion")
&& (anyVersion
|| version.equals("1.0")
|| version.equals("1.1")))
|| (feature.equalsIgnoreCase("LS")
&& (anyVersion
|| version.equals("3.0")))
|| (feature.equalsIgnoreCase("ElementTraversal")
&& (anyVersion
|| version.equals("1.0")));
} // hasFeature(String,String):boolean
/**
* Introduced in DOM Level 2.
*
* Creates an empty DocumentType node.
*
* @param qualifiedName The qualified name of the document type to be created.
* @param publicID The document type public identifier.
* @param systemID The document type system identifier.
* @since WD-DOM-Level-2-19990923
*/
public DocumentType createDocumentType( String qualifiedName,
String publicID, String systemID) {
// REVISIT: this might allow creation of invalid name for DOCTYPE
// xmlns prefix.
// also there is no way for a user to turn off error checking.
checkQName(qualifiedName);
return new DocumentTypeImpl(null, qualifiedName, publicID, systemID);
}
final void checkQName(String qname){
int index = qname.indexOf(':');
int lastIndex = qname.lastIndexOf(':');
int length = qname.length();
// it is an error for NCName to have more than one ':'
// check if it is valid QName [Namespace in XML production 6]
if (index == 0 || index == length - 1 || lastIndex != index) {
String msg =
DOMMessageFormatter.formatMessage(
DOMMessageFormatter.DOM_DOMAIN,
"NAMESPACE_ERR",
null);
throw new DOMException(DOMException.NAMESPACE_ERR, msg);
}
int start = 0;
// Namespace in XML production [6]
if (index > 0) {
// check that prefix is NCName
if (!XMLChar.isNCNameStart(qname.charAt(start))) {
String msg =
DOMMessageFormatter.formatMessage(
DOMMessageFormatter.DOM_DOMAIN,
"INVALID_CHARACTER_ERR",
null);
throw new DOMException(DOMException.INVALID_CHARACTER_ERR, msg);
}
for (int i = 1; i < index; i++) {
if (!XMLChar.isNCName(qname.charAt(i))) {
String msg =
DOMMessageFormatter.formatMessage(
DOMMessageFormatter.DOM_DOMAIN,
"INVALID_CHARACTER_ERR",
null);
throw new DOMException(
DOMException.INVALID_CHARACTER_ERR,
msg);
}
}
start = index + 1;
}
// check local part
if (!XMLChar.isNCNameStart(qname.charAt(start))) {
// REVISIT: add qname parameter to the message
String msg =
DOMMessageFormatter.formatMessage(
DOMMessageFormatter.DOM_DOMAIN,
"INVALID_CHARACTER_ERR",
null);
throw new DOMException(DOMException.INVALID_CHARACTER_ERR, msg);
}
for (int i = start + 1; i < length; i++) {
if (!XMLChar.isNCName(qname.charAt(i))) {
String msg =
DOMMessageFormatter.formatMessage(
DOMMessageFormatter.DOM_DOMAIN,
"INVALID_CHARACTER_ERR",
null);
throw new DOMException(DOMException.INVALID_CHARACTER_ERR, msg);
}
}
}
/**
* Introduced in DOM Level 2.
*
* Creates an XML Document object of the specified type with its document
* element.
*
* @param namespaceURI The namespace URI of the document
* element to create, or null.
* @param qualifiedName The qualified name of the document
* element to create.
* @param doctype The type of document to be created or null.
*
* When doctype is not null, its
* Node.ownerDocument attribute is set to
* the document being created.
* @return Document A new Document object.
* @throws DOMException WRONG_DOCUMENT_ERR: Raised if doctype has
* already been used with a different document.
* @since WD-DOM-Level-2-19990923
*/
public Document createDocument(
String namespaceURI,
String qualifiedName,
DocumentType doctype)
throws DOMException {
if (doctype != null && doctype.getOwnerDocument() != null) {
String msg =
DOMMessageFormatter.formatMessage(
DOMMessageFormatter.DOM_DOMAIN,
"WRONG_DOCUMENT_ERR",
null);
throw new DOMException(DOMException.WRONG_DOCUMENT_ERR, msg);
}
CoreDocumentImpl doc = createDocument(doctype);
// If namespaceURI and qualifiedName are null return a Document with no document element.
if (qualifiedName != null || namespaceURI != null) {
Element e = doc.createElementNS(namespaceURI, qualifiedName);
doc.appendChild(e);
}
return doc;
}
protected CoreDocumentImpl createDocument(DocumentType doctype) {
return new CoreDocumentImpl(doctype);
}
/**
* DOM Level 3 WD - Experimental.
*/
public Object getFeature(String feature, String version) {
if (singleton.hasFeature(feature, version)) {
if ((feature.equalsIgnoreCase("+XPath"))) {
try {
Class xpathClass = ObjectFactory.findProviderClass(
"org.apache.xpath.domapi.XPathEvaluatorImpl",
ObjectFactory.findClassLoader(), true);
// Check if the DOM XPath implementation implements
// the interface org.w3c.dom.XPathEvaluator
Class interfaces[] = xpathClass.getInterfaces();
for (int i = 0; i < interfaces.length; i++) {
if (interfaces[i].getName().equals(
"org.w3c.dom.xpath.XPathEvaluator")) {
return xpathClass.newInstance();
}
}
} catch (Exception e) {
return null;
}
} else {
return singleton;
}
}
return null;
}
// DOM L3 LS
/**
* DOM Level 3 LS CR - Experimental.
* Create a new LSParser. The newly constructed parser may
* then be configured by means of its DOMConfiguration
* object, and used to parse documents by means of its parse
* method.
* @param mode The mode argument is either
* MODE_SYNCHRONOUS or MODE_ASYNCHRONOUS, if
* mode is MODE_SYNCHRONOUS then the
* LSParser that is created will operate in synchronous
* mode, if it's MODE_ASYNCHRONOUS then the
* LSParser that is created will operate in asynchronous
* mode.
* @param schemaType An absolute URI representing the type of the schema
* language used during the load of a Document using the
* newly created LSParser. Note that no lexical checking
* is done on the absolute URI. In order to create a
* LSParser for any kind of schema types (i.e. the
* LSParser will be free to use any schema found), use the value
* null.
*
Note: For W3C XML Schema [XML Schema Part 1]
* , applications must use the value
* "http://www.w3.org/2001/XMLSchema". For XML DTD [XML 1.0],
* applications must use the value
* "http://www.w3.org/TR/REC-xml". Other Schema languages
* are outside the scope of the W3C and therefore should recommend an
* absolute URI in order to use this method.
* @return The newly created LSParser object. This
* LSParser is either synchronous or asynchronous
* depending on the value of the mode argument.
*
Note: By default, the newly created LSParser
* does not contain a DOMErrorHandler, i.e. the value of
* the "
* error-handler" configuration parameter is null. However, implementations
* may provide a default error handler at creation time. In that case,
* the initial value of the "error-handler" configuration
* parameter on the new created LSParser contains a
* reference to the default error handler.
* @exception DOMException
* NOT_SUPPORTED_ERR: Raised if the requested mode or schema type is
* not supported.
*/
public LSParser createLSParser(short mode, String schemaType)
throws DOMException {
if (mode != DOMImplementationLS.MODE_SYNCHRONOUS || (schemaType !=null &&
!"http://www.w3.org/2001/XMLSchema".equals(schemaType) &&
!"http://www.w3.org/TR/REC-xml".equals(schemaType))) {
String msg =
DOMMessageFormatter.formatMessage(
DOMMessageFormatter.DOM_DOMAIN,
"NOT_SUPPORTED_ERR",
null);
throw new DOMException(DOMException.NOT_SUPPORTED_ERR, msg);
}
if (schemaType != null
&& schemaType.equals("http://www.w3.org/TR/REC-xml")) {
return new DOMParserImpl(
"org.apache.xerces.parsers.DTDConfiguration",
schemaType);
}
else {
// create default parser configuration validating against XMLSchemas
return new DOMParserImpl(
"org.apache.xerces.parsers.XIncludeAwareParserConfiguration",
schemaType);
}
}
/**
* DOM Level 3 LS CR - Experimental.
* Create a new LSSerializer object.
* @return The newly created LSSerializer object.
*
Note: By default, the newly created
* LSSerializer has no DOMErrorHandler,
* i.e. the value of the "error-handler" configuration
* parameter is null. However, implementations may
* provide a default error handler at creation time. In that case, the
* initial value of the "error-handler" configuration
* parameter on the new created LSSerializer contains a
* reference to the default error handler.
*/
public LSSerializer createLSSerializer() {
try {
Class serializerClass = ObjectFactory.findProviderClass(
"org.apache.xml.serializer.dom3.LSSerializerImpl",
ObjectFactory.findClassLoader(), true);
return (LSSerializer) serializerClass.newInstance();
}
catch (Exception e) {}
// Fall back to Xerces' deprecated serializer if
// the Xalan based serializer is unavailable.
return new DOMSerializerImpl();
}
/**
* DOM Level 3 LS CR - Experimental.
* Create a new empty input source.
* @return The newly created input object.
*/
public LSInput createLSInput() {
return new DOMInputImpl();
}
//
// Protected methods
//
/** NON-DOM: retrieve validator. */
synchronized RevalidationHandler getValidator(String schemaType, String xmlVersion) {
if (schemaType == XMLGrammarDescription.XML_SCHEMA) {
// create new validator - we should not attempt
// to restrict the number of validation handlers being
// requested
while (freeSchemaValidatorIndex >= 0) {
// return first available validator
SoftReference ref = schemaValidators[freeSchemaValidatorIndex];
RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
if (holder != null && holder.handler != null) {
RevalidationHandler val = holder.handler;
holder.handler = null;
--freeSchemaValidatorIndex;
return val;
}
schemaValidators[freeSchemaValidatorIndex--] = null;
}
return (RevalidationHandler) (ObjectFactory
.newInstance(
"org.apache.xerces.impl.xs.XMLSchemaValidator",
ObjectFactory.findClassLoader(),
true));
}
else if(schemaType == XMLGrammarDescription.XML_DTD) {
// return an instance of XML11DTDValidator
if ("1.1".equals(xmlVersion)) {
while (freeXML11DTDValidatorIndex >= 0) {
// return first available validator
SoftReference ref = xml11DTDValidators[freeXML11DTDValidatorIndex];
RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
if (holder != null && holder.handler != null) {
RevalidationHandler val = holder.handler;
holder.handler = null;
--freeXML11DTDValidatorIndex;
return val;
}
xml11DTDValidators[freeXML11DTDValidatorIndex--] = null;
}
return (RevalidationHandler) (ObjectFactory
.newInstance(
"org.apache.xerces.impl.dtd.XML11DTDValidator",
ObjectFactory.findClassLoader(),
true));
}
// return an instance of XMLDTDValidator
else {
while (freeXML10DTDValidatorIndex >= 0) {
// return first available validator
SoftReference ref = xml10DTDValidators[freeXML10DTDValidatorIndex];
RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
if (holder != null && holder.handler != null) {
RevalidationHandler val = holder.handler;
holder.handler = null;
--freeXML10DTDValidatorIndex;
return val;
}
xml10DTDValidators[freeXML10DTDValidatorIndex--] = null;
}
return (RevalidationHandler) (ObjectFactory
.newInstance(
"org.apache.xerces.impl.dtd.XMLDTDValidator",
ObjectFactory.findClassLoader(),
true));
}
}
return null;
}
/** NON-DOM: release validator */
synchronized void releaseValidator(String schemaType, String xmlVersion,
RevalidationHandler validator) {
if (schemaType == XMLGrammarDescription.XML_SCHEMA) {
++freeSchemaValidatorIndex;
if (schemaValidators.length == freeSchemaValidatorIndex) {
// resize size of the validators
schemaValidatorsCurrentSize += SIZE;
SoftReference newarray[] = new SoftReference[schemaValidatorsCurrentSize];
System.arraycopy(schemaValidators, 0, newarray, 0, schemaValidators.length);
schemaValidators = newarray;
}
SoftReference ref = schemaValidators[freeSchemaValidatorIndex];
if (ref != null) {
RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
if (holder != null) {
holder.handler = validator;
return;
}
}
schemaValidators[freeSchemaValidatorIndex] = new SoftReference(new RevalidationHandlerHolder(validator));
}
else if (schemaType == XMLGrammarDescription.XML_DTD) {
// release an instance of XML11DTDValidator
if ("1.1".equals(xmlVersion)) {
++freeXML11DTDValidatorIndex;
if (xml11DTDValidators.length == freeXML11DTDValidatorIndex) {
// resize size of the validators
xml11DTDValidatorsCurrentSize += SIZE;
SoftReference [] newarray = new SoftReference[xml11DTDValidatorsCurrentSize];
System.arraycopy(xml11DTDValidators, 0, newarray, 0, xml11DTDValidators.length);
xml11DTDValidators = newarray;
}
SoftReference ref = xml11DTDValidators[freeXML11DTDValidatorIndex];
if (ref != null) {
RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
if (holder != null) {
holder.handler = validator;
return;
}
}
xml11DTDValidators[freeXML11DTDValidatorIndex] = new SoftReference(new RevalidationHandlerHolder(validator));
}
// release an instance of XMLDTDValidator
else {
++freeXML10DTDValidatorIndex;
if (xml10DTDValidators.length == freeXML10DTDValidatorIndex) {
// resize size of the validators
xml10DTDValidatorsCurrentSize += SIZE;
SoftReference [] newarray = new SoftReference[xml10DTDValidatorsCurrentSize];
System.arraycopy(xml10DTDValidators, 0, newarray, 0, xml10DTDValidators.length);
xml10DTDValidators = newarray;
}
SoftReference ref = xml10DTDValidators[freeXML10DTDValidatorIndex];
if (ref != null) {
RevalidationHandlerHolder holder = (RevalidationHandlerHolder) ref.get();
if (holder != null) {
holder.handler = validator;
return;
}
}
xml10DTDValidators[freeXML10DTDValidatorIndex] = new SoftReference(new RevalidationHandlerHolder(validator));
}
}
}
/** NON-DOM: retrieve DTD loader */
synchronized final XMLDTDLoader getDTDLoader(String xmlVersion) {
// return an instance of XML11DTDProcessor
if ("1.1".equals(xmlVersion)) {
while (freeXML11DTDLoaderIndex >= 0) {
// return first available DTD loader
SoftReference ref = xml11DTDLoaders[freeXML11DTDLoaderIndex];
XMLDTDLoaderHolder holder = (XMLDTDLoaderHolder) ref.get();
if (holder != null && holder.loader != null) {
XMLDTDLoader val = holder.loader;
holder.loader = null;
--freeXML11DTDLoaderIndex;
return val;
}
xml11DTDLoaders[freeXML11DTDLoaderIndex--] = null;
}
return (XMLDTDLoader) (ObjectFactory
.newInstance(
"org.apache.xerces.impl.dtd.XML11DTDProcessor",
ObjectFactory.findClassLoader(),
true));
}
// return an instance of XMLDTDLoader
else {
while (freeXML10DTDLoaderIndex >= 0) {
// return first available DTD loader
SoftReference ref = xml10DTDLoaders[freeXML10DTDLoaderIndex];
XMLDTDLoaderHolder holder = (XMLDTDLoaderHolder) ref.get();
if (holder != null && holder.loader != null) {
XMLDTDLoader val = holder.loader;
holder.loader = null;
--freeXML10DTDLoaderIndex;
return val;
}
xml10DTDLoaders[freeXML10DTDLoaderIndex--] = null;
}
return new XMLDTDLoader();
}
}
/** NON-DOM: release DTD loader */
synchronized final void releaseDTDLoader(String xmlVersion, XMLDTDLoader loader) {
// release an instance of XMLDTDLoader
if ("1.1".equals(xmlVersion)) {
++freeXML11DTDLoaderIndex;
if (xml11DTDLoaders.length == freeXML11DTDLoaderIndex) {
// resize size of the DTD loaders
xml11DTDLoaderCurrentSize += SIZE;
SoftReference [] newarray = new SoftReference[xml11DTDLoaderCurrentSize];
System.arraycopy(xml11DTDLoaders, 0, newarray, 0, xml11DTDLoaders.length);
xml11DTDLoaders = newarray;
}
SoftReference ref = xml11DTDLoaders[freeXML11DTDLoaderIndex];
if (ref != null) {
XMLDTDLoaderHolder holder = (XMLDTDLoaderHolder) ref.get();
if (holder != null) {
holder.loader = loader;
return;
}
}
xml11DTDLoaders[freeXML11DTDLoaderIndex] = new SoftReference(new XMLDTDLoaderHolder(loader));
}
// release an instance of XMLDTDLoader
else {
++freeXML10DTDLoaderIndex;
if (xml10DTDLoaders.length == freeXML10DTDLoaderIndex) {
// resize size of the DTD loaders
xml10DTDLoaderCurrentSize += SIZE;
SoftReference [] newarray = new SoftReference[xml10DTDLoaderCurrentSize];
System.arraycopy(xml10DTDLoaders, 0, newarray, 0, xml10DTDLoaders.length);
xml10DTDLoaders = newarray;
}
SoftReference ref = xml10DTDLoaders[freeXML10DTDLoaderIndex];
if (ref != null) {
XMLDTDLoaderHolder holder = (XMLDTDLoaderHolder) ref.get();
if (holder != null) {
holder.loader = loader;
return;
}
}
xml10DTDLoaders[freeXML10DTDLoaderIndex] = new SoftReference(new XMLDTDLoaderHolder(loader));
}
}
/** NON-DOM: increment document/doctype counter */
protected synchronized int assignDocumentNumber() {
return ++docAndDoctypeCounter;
}
/** NON-DOM: increment document/doctype counter */
protected synchronized int assignDocTypeNumber() {
return ++docAndDoctypeCounter;
}
/**
* DOM Level 3 LS CR - Experimental.
*
* Create a new empty output destination object where
* LSOutput.characterStream,
* LSOutput.byteStream, LSOutput.systemId,
* LSOutput.encoding are null.
* @return The newly created output object.
*/
public LSOutput createLSOutput() {
return new DOMOutputImpl();
}
/**
* A holder for RevalidationHandlers. This allows us to reuse
* SoftReferences which haven't yet been cleared by the garbage
* collector.
*/
static final class RevalidationHandlerHolder {
RevalidationHandlerHolder(RevalidationHandler handler) {
this.handler = handler;
}
RevalidationHandler handler;
}
/**
* A holder for XMLDTDLoaders. This allows us to reuse SoftReferences
* which haven't yet been cleared by the garbage collector.
*/
static final class XMLDTDLoaderHolder {
XMLDTDLoaderHolder(XMLDTDLoader loader) {
this.loader = loader;
}
XMLDTDLoader loader;
}
} // class DOMImplementationImpl