Commons JXPath example source code file (JXPathContextFactory.java)

This example Commons JXPath source code file (JXPathContextFactory.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons JXPath tags/keywords

bufferedreader, file, io, ioexception, ioexception, jxpath, jxpathcontext, jxpathcontextfactory, jxpathcontextfactory, jxpathcontextfactoryconfigurationerror, nopmd, nopmd, properties, string, string, util

The Commons JXPath JXPathContextFactory.java source code

/*
 * 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 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.
     * This static method creates a new factory instance.
     * This method uses the following ordered lookup procedure to determine
     * the <code>JXPathContextFactory implementation class to load:
     * <ul>
     * <li>
     * Use  the <code>org.apache.commons.jxpath.JXPathContextFactory
     * 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.
     * </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/org.apache.commons.jxpath.
     * JXPathContextFactory</i> in jars available to the runtime.
     * </li>
     * <li>
     * Platform default <code>JXPathContextFactory instance.
     * </li>
     * </ul>
     *
     * Once an application has obtained a reference to a
     * <code>JXPathContextFactory 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;
    }
}