动态加载class文件

1.参考老外：

public class ClassPathUpdater {

    /** Used to find the method signature. */

    private static final Class[] PARAMETERS = new Class[] { URL.class };



    /** Class containing the private addURL method. */

    private static final Class CLASS_LOADER = URLClassLoader.class;



    /**

     * Adds a new path to the classloader. If the given string points to a file,

     * then that file's parent file (i.e., directory) is used as the directory

     * to add to the classpath. If the given string represents a directory, then

     * the directory is directly added to the classpath.

     * 

     * @param s

     * The directory to add to the classpath (or a file, which will

     * relegate to its directory).

     */

    public static void add(String s) throws IOException, NoSuchMethodException,

            IllegalAcces***ception, InvocationTargetException {

        add(new File(s));

    }



    /**

     * Adds a new path to the classloader. If the given file object is a file,

     * then its parent file (i.e., directory) is used as the directory to add to

     * the classpath. If the given string represents a directory, then the

     * directory it represents is added.

     * 

     * @param f

     * The directory (or enclosing directory if a file) to add to the

     * classpath.

     */

    public static void add(File f) throws IOException, NoSuchMethodException,

            IllegalAcces***ception, InvocationTargetException {

        f = f.isDirectory() ? f : f.getParentFile();

        add(f.toURI().toURL());

    }



    /**

     * Adds a new path to the classloader. The class must point to a directory,

     * not a file.

     * 

     * @param url

     * The path to include when searching the classpath.

     */

    public static void add(URL url) throws IOException, NoSuchMethodException,

            IllegalAcces***ception, InvocationTargetException {

        Method method = CLASS_LOADER.getDeclaredMethod("addURL", PARAMETERS);

        method.setAccessible(true);

        method.invoke(getClassLoader(), new Object[] { url });

    }



    private static URLClassLoader getClassLoader() {

        return (URLClassLoader) ClassLoader.getSystemClassLoader();

    }

}

     ClassPathUpdater.add("E:\\workspaces\\MyDemos\\MyClass.class");
        String path = "E:\\workspaces\\MyDemos\\";
        URL url = new URL("file", null, path);
        URLClassLoader loader = new URLClassLoader(new URL[] {url});
        Class clazz = loader.loadClass("MyClass");
2.rewrite ClassLoader

static class MyClassLoader extends ClassLoader {

        @Override

        public Class<?> findClass(String name) {

            try {

                FileInputStream in = new FileInputStream(name);

                ArrayList<Byte> l = new ArrayList<Byte>();

                int c;

                while ((c = in.read()) != -1) {

                    l.add(new Byte((byte)c));

                }

                byte[] b = new byte[l.size()];

                for (int i = 0; i < l.size(); i++) {

                    b[i] = l.get(i).byteValue();

                }

                

                return defineClass(b, 0, b.length);

            } catch (Exception e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

            return null;

        }

    }

MyClassLoader mcl = new MyClassLoader();
        clazz = mcl.loadClass("E:\\workspaces\\MyDemos\\MyClass.class");