动态ClassLoader

代码来源  http://www.oschina.net/code/snippet_54100_3353
加载原理  http://vivisidea.iteye.com/blog/662620

package libra.law.util;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;

public class DynamicClassLoader extends ClassLoader {

public DynamicClassLoader(ClassLoader parent) {
   super(parent);
}

@SuppressWarnings("unchecked")
public Class loadClass(String classPath, String className)
    throws ClassNotFoundException {
   try {
    String url = classPathParser(classPath)
      + classNameParser(className);
    System.out.println(url);
    URL myUrl = new URL(url);
    URLConnection connection = myUrl.openConnection();
    InputStream input = connection.getInputStream();
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    int data = input.read();
    while (data != -1) {
     buffer.write(data);
     data = input.read();
    }
    input.close();
    byte[] classData = buffer.toByteArray();
    return defineClass(noSuffix(className), classData, 0,
      classData.length);
   } catch (MalformedURLException e) {
    e.printStackTrace();
   } catch (IOException e) {
    e.printStackTrace();
   }
   return null;
}

private String pathParser(String path) {
   return path.replaceAll("\\\\", "/");
}

private String classPathParser(String path) {
   String classPath = pathParser(path);
   if (!classPath.startsWith("file:")) {
    classPath = "file:" + classPath;
   }
   if (!classPath.endsWith("/")) {
    classPath = classPath + "/";
   }
   return classPath;
}

private String classNameParser(String className) {
   return className.substring(0, className.lastIndexOf(".")).replaceAll(
     "\\.", "/")
     + className.substring(className.lastIndexOf("."));
}

private String noSuffix(String className) {
   return className.substring(0, className.lastIndexOf("."));
}

public static void main(String[] arguments) throws Exception {
   String classPath = "C:\\Documents and Settings\\Administrator\\Workspaces\\MyEclipse7.5\\lhsp\\web\\WEB-INF\\classes";
   String className = "libra.law.util.Test.class";
   new DynamicClassLoader(DynamicClassLoader.class.getClassLoader())
     .loadClass(classPath, className).newInstance();
}
}