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Commons Beanutils example source code file (ClassReloader.java)

This example Commons Beanutils source code file (ClassReloader.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 Beanutils tags/keywords

bytearrayoutputstream, bytearrayoutputstream, class, class, classloader, classreloader, classreloader, filenotfoundexception, inputstream, io, ioexception, string, string

The Commons Beanutils ClassReloader.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.beanutils.converters;

import java.io.InputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

/**
 * A special classloader useful for testing j2ee-like scenarios.
 * 
 * <p>In some tests we want to be able to emulate "container" frameworks,
 * where code runs in a hierarchy of classloaders, and certain classes may
 * be loaded by various classloaders in the hierarchy.</p>
 *
 * <p>Normally this is done by having certain jars or class-file-directories
 * in the classpath of some classloaders but not others. This is quite 
 * difficult difficult to integrate with the build process for the unit
 * tests though; compiling certain classes and having the output go into
 * places that is not in the default classpath for the unit tests would be
 * a major pain.</p>
 *
 * <p>So this class takes a sneaky alternative approach: it can grab any class
 * already loaded by a parent classloader and <i>reload that class via this
 * classloader. The effect is exactly as if a class (or jar file) had been
 * present in the classpath for a container's "shared" classloader <i>and
 * been present in the component-specific classpath too, without any messing
 * about with the way unit test code is compiled or executed.
 */

public class ClassReloader extends ClassLoader {
    public ClassReloader(ClassLoader parent) {
        super(parent);
    }
    
    /**
     * Given a class already in the classpath of a parent classloader,
     * reload that class via this classloader.
     */
    public Class reload(Class clazz) throws FileNotFoundException, IOException {
        String className = clazz.getName();
        String classFile = className.replace('.', '/') + ".class";
        InputStream classStream = getParent().getResourceAsStream(classFile);
        
        if (classStream == null) {
            throw new FileNotFoundException(classFile);
        }
        
        byte[] buf = new byte[1024];
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        for(;;) {
            int bytesRead = classStream.read(buf);
            if (bytesRead == -1)
                break;
            baos.write(buf, 0, bytesRead);
        }
        classStream.close();
        
        byte[] classData = baos.toByteArray();
        
        // now we have the raw class data, let's turn it into a class
        Class newClass = defineClass(className, classData, 0, classData.length);
        resolveClass(newClass);
        return newClass;
    }
}

Other Commons Beanutils examples (source code examples)

Here is a short list of links related to this Commons Beanutils ClassReloader.java source code file:

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