FileSysClassLoader

package com.javabook.classloader;
import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import com.javabook.classloader.service.api.ISimpleService;
/**
 * @author Summer Lu
 * @email gmluyang@gmail.com
 * @date 2014-8-25
 *
 */
public class FileSysClassLoader extends ClassLoader {
    /**
     * classPath
     */
    private String classPath;
    /**
     * @param classPath
     */
    public FileSysClassLoader(String classPath) {
        this.classPath = classPath;
    }
    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        byte[] classData = getClassData(name);
        if (classData == null) {
            throw new ClassNotFoundException();
        } else {
            return defineClass(name, classData, 0, classData.length);
        }
    }
    /**
     * @param className
     * @return
     */
    private byte[] getClassData(String className) {
        String path = classNameToPath(className);
        try {
            // io
            InputStream  is = new BufferedInputStream( new FileInputStream(path) );
            // os
            OutputStream os = new ByteArrayOutputStream();
            // buffer
            int bufferSize = 4096;
            byte[] buffer = new byte[bufferSize];
            // read/write
            int bytesNumRead = 0;
            while ((bytesNumRead = is.read(buffer)) != -1) {
                os.write(buffer, 0, bytesNumRead);
            }
            // flush
            os.flush();
            // toByteArray
            return ((ByteArrayOutputStream)os).toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
    /**
     * @param className
     * @return
     */
    private String classNameToPath(String className) {
        return classPath + File.separatorChar + className.replace('.', File.separatorChar) + ".class";
    }
    /**
     * @param args
     */
    public static void main(String[] args) {
        try {
            // File
            String file = "C:\\mybin\\";
            // fileSystemClassLoader
            FileSysClassLoader fileSysClassLoader = new FileSysClassLoader(file);
            // ----------------------------------------------------------------------------------------------------
            // SimpleServiceLowerCaseImpl        
            // ----------------------------------------------------------------------------------------------------
            // simpleServiceLowerCaseImpl
            String simpleServiceLowerCaseImpl = "com.javabook.classloader.service.impl.SimpleServiceLowerCaseImpl";
            // simpleServiceLowerCaseImplClass2
            Class<?> simpleServiceLowerCaseImplClass2 = fileSysClassLoader.loadClass(simpleServiceLowerCaseImpl);
            System.out.println(    simpleServiceLowerCaseImplClass2.getClassLoader() + " -> " + simpleServiceLowerCaseImplClass2.getName());
            ISimpleService simpleServiceLowerCaseImpl2 = (ISimpleService) simpleServiceLowerCaseImplClass2.newInstance();
            System.out.println(simpleServiceLowerCaseImpl2.calculate("Abc"));
            // ----------------------------------------------------------------------------------------------------
            // SimpleServiceUpperCaseImpl        
            // ----------------------------------------------------------------------------------------------------
            System.out.println();
            // simpleServiceUpperCaseImpl
            String simpleServiceUpperCaseImpl = "com.javabook.classloader.service.impl.SimpleServiceUpperCaseImpl";        
            Class<?> simpleServiceUpperCaseImplClass2 = fileSysClassLoader.loadClass(simpleServiceUpperCaseImpl);
            System.out.println(    simpleServiceUpperCaseImplClass2.getClassLoader() + " -> " + simpleServiceUpperCaseImplClass2.getName());
            ISimpleService simpleServiceUpperCaseImpl2 = (ISimpleService) simpleServiceUpperCaseImplClass2.newInstance();
            System.out.println(simpleServiceUpperCaseImpl2.calculate("Abc"));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Console

com.javabook.classloader.FileSysClassLoader@74a14482 -> com.javabook.classloader.service.impl.SimpleServiceLowerCaseImpl
com.javabook.classloader.service.impl.SimpleServiceLowerCaseImpl:abc

com.javabook.classloader.FileSysClassLoader@74a14482 -> com.javabook.classloader.service.impl.SimpleServiceUpperCaseImpl
com.javabook.classloader.service.impl.SimpleServiceUpperCaseImpl:ABC