/*
* 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.commons.jxpath;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Properties;
/**
* Defines a factory API that enables applications to obtain a
* {@link JXPathContext} instance. To acquire a JXPathContext, first call the
* static {@link #newInstance} method of JXPathContextFactory.
* This method returns a concrete JXPathContextFactory.
* Then call {@link #newContext} on that instance. You will rarely
* need to perform these steps explicitly: usually you can call one of the
* <code>JXPathContex.newContext</code> methods, which will perform these steps
* for you.
*
* @see JXPathContext#newContext(Object)
* @see JXPathContext#newContext(JXPathContext,Object)
*
* @author Dmitri Plotnikov
* @version $Revision: 670727 $ $Date: 2008-06-23 15:10:38 -0500 (Mon, 23 Jun 2008) $
*/
public abstract class JXPathContextFactory {
/** The default property */
public static final String FACTORY_NAME_PROPERTY =
"org.apache.commons.jxpath.JXPathContextFactory";
/** The default factory class */
private static final String DEFAULT_FACTORY_CLASS =
"org.apache.commons.jxpath.ri.JXPathContextFactoryReferenceImpl";
/** Avoid reading all the files when the findFactory
method is called the second time ( cache the result of
finding the default impl )
*/
private static String factoryImplName = null;
/**
* Create a new JXPathContextFactory.
*/
protected JXPathContextFactory () {
}
/**
* Obtain a new instance of a <code>JXPathContextFactory</code>.
* This static method creates a new factory instance.
* This method uses the following ordered lookup procedure to determine
* the <code>JXPathContextFactory</code> implementation class to load:
* <ul>
* <li>
* Use the <code>org.apache.commons.jxpath.JXPathContextFactory</code>
* system property.
* </li>
* <li>
* Alternatively, use the JAVA_HOME (the parent directory where jdk is
* installed)/lib/jxpath.properties for a property file that contains the
* name of the implementation class keyed on
* <code>org.apache.commons.jxpath.JXPathContextFactory</code>.
* </li>
* <li>
* Use the Services API (as detailed in the JAR specification), if
* available, to determine the classname. The Services API will look
* for a classname in the file
* <code>META- INF/services/<i>org.apache.commons.jxpath.
* JXPathContextFactory</i></code> in jars available to the runtime.
* </li>
* <li>
* Platform default <code>JXPathContextFactory</code> instance.
* </li>
* </ul>
*
* Once an application has obtained a reference to a
* <code>JXPathContextFactory</code> it can use the factory to
* obtain JXPathContext instances.
*
* @return JXPathContextFactory
* @exception JXPathContextFactoryConfigurationError if the implementation
* is not available or cannot be instantiated.
*/
public static JXPathContextFactory newInstance() {
if (factoryImplName == null) {
factoryImplName =
findFactory(FACTORY_NAME_PROPERTY, DEFAULT_FACTORY_CLASS);
}
JXPathContextFactory factoryImpl;
try {
Class clazz = Class.forName(factoryImplName);
factoryImpl = (JXPathContextFactory) clazz.newInstance();
}
catch (ClassNotFoundException cnfe) {
throw new JXPathContextFactoryConfigurationError(cnfe);
}
catch (IllegalAccessException iae) {
throw new JXPathContextFactoryConfigurationError(iae);
}
catch (InstantiationException ie) {
throw new JXPathContextFactoryConfigurationError(ie);
}
return factoryImpl;
}
/**
* Creates a new instance of a JXPathContext using the
* currently configured parameters.
* @param parentContext parent context
* @param contextBean Object bean
* @return JXPathContext
* @exception JXPathContextFactoryConfigurationError if a JXPathContext
* cannot be created which satisfies the configuration requested
*/
public abstract JXPathContext newContext(
JXPathContext parentContext,
Object contextBean);
// -------------------- private methods --------------------
// This code is duplicated in all factories.
// Keep it in sync or move it to a common place
// Because it's small probably it's easier to keep it here
/** Temp debug code - this will be removed after we test everything
*/
private static boolean debug = false;
static {
try {
debug = System.getProperty("jxpath.debug") != null;
}
catch (SecurityException se) { //NOPMD
// This is ok
}
}
/**
* Private implementation method - will find the implementation
* class in the specified order.
* @param property Property name
* @param defaultFactory Default implementation, if nothing else is found
*
* @return class name of the JXPathContextFactory
*/
private static String findFactory(String property, String defaultFactory) {
// Use the factory ID system property first
try {
String systemProp = System.getProperty(property);
if (systemProp != null) {
if (debug) {
System.err.println(
"JXPath: found system property" + systemProp);
}
return systemProp;
}
}
catch (SecurityException se) { //NOPMD
// Ignore
}
// try to read from $java.home/lib/xml.properties
try {
String javah = System.getProperty("java.home");
String configFile =
javah
+ File.separator
+ "lib"
+ File.separator
+ "jxpath.properties";
File f = new File(configFile);
if (f.exists()) {
Properties props = new Properties();
FileInputStream fis = new FileInputStream(f);
try {
props.load(fis);
}
finally {
if (fis != null) {
try {
fis.close();
}
catch (IOException e) { //NOPMD
//swallow
}
}
}
String factory = props.getProperty(property);
if (factory != null) {
if (debug) {
System.err.println(
"JXPath: found java.home property " + factory);
}
return factory;
}
}
}
catch (IOException ex) {
if (debug) {
ex.printStackTrace();
}
}
String serviceId = "META-INF/services/" + property;
// try to find services in CLASSPATH
try {
ClassLoader cl = JXPathContextFactory.class.getClassLoader();
InputStream is = null;
if (cl == null) {
is = ClassLoader.getSystemResourceAsStream(serviceId);
}
else {
is = cl.getResourceAsStream(serviceId);
}
if (is != null) {
if (debug) {
System.err.println("JXPath: found " + serviceId);
}
BufferedReader rd =
new BufferedReader(new InputStreamReader(is));
String factory = null;
try {
factory = rd.readLine();
}
finally {
try {
rd.close();
}
catch (IOException e) { //NOPMD
//swallow
}
}
if (factory != null && !"".equals(factory)) {
if (debug) {
System.err.println(
"JXPath: loaded from services: " + factory);
}
return factory;
}
}
}
catch (Exception ex) {
if (debug) {
ex.printStackTrace();
}
}
return defaultFactory;
}
}
|