简单的ClassLoader

package test.classloader;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.WritableByteChannel;

public class AnotherClassLoader extends ClassLoader {
private String baseDir;

public AnotherClassLoader(ClassLoader parent, String baseDir) {
super(parent);
this.baseDir = baseDir;
}

@SuppressWarnings("unchecked")
protected Class findClass(String name) throws ClassNotFoundException {
byte[] bytes = loadClassBytes(name);
Class theClass = defineClass("test.classloader.Test", bytes, 0, bytes.length);// A
if (theClass == null)
throw new ClassFormatError();
return theClass;
}

private byte[] loadClassBytes(String className)
throws ClassNotFoundException {
try {
String classFile = getClassFile(className);
FileInputStream fis = new FileInputStream(classFile);
FileChannel fileC = fis.getChannel();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
WritableByteChannel outC = Channels.newChannel(baos);
ByteBuffer buffer = ByteBuffer.allocateDirect(1024);
while (true) {
int i = fileC.read(buffer);
if (i == 0 || i == -1) {
break;
}
buffer.flip();
outC.write(buffer);
buffer.clear();
}
fis.close();
return baos.toByteArray();
} catch (IOException fnfe) {
throw new ClassNotFoundException(className);
}
}

private String getClassFile(String name) {
StringBuffer sb = new StringBuffer(baseDir);
name = name.replace('.', File.separatorChar) + ".class";
sb.append(File.separator + name);
return sb.toString();
}

protected URL findResource(String name) {
try {
System.out.println("Resource:"+name);
URL url = super.findResource(name);
if (url != null)
return url;
url = new URL("file:///" + converName(name));
// 简化处理，所有资源从文件系统中获取
return url;
} catch (MalformedURLException mue) {
return null;
}
}

private String converName(String name) {
StringBuffer sb = new StringBuffer(baseDir);
name = name.replace('.', File.separatorChar);
sb.append(File.separator + name);
return sb.toString();
}
}