反射，代理，动态java原理

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需要两个类，用于下面的测试

package test;



public interface IProcess {

	public void process();

}

package test;

public class Process implements IProcess{
	public void process() {
		System.out.println("实际处理器开始执行！");
	}
}

反射的例子，forName方法

// 根据classname来生成对象

	@SuppressWarnings("unchecked")

	public static  U getObjectAsClassName(String className) {



		U proess = null;

		try {

			proess = (U) Class.forName(className).newInstance();

			// proess.process();

		} catch (InstantiationException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		} catch (IllegalAccessException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		} catch (ClassNotFoundException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}



		return proess;

	}

根据方法名执行方法

public static void callMehod(String methodName, Process p) {

		Method[] methods = Process.class.getMethods();



		for (Method method : methods) {

			if (method.getName().equals(methodName)) {

				// 找到方法，执行

				try {

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

				} catch (IllegalArgumentException e) {

					// TODO Auto-generated catch block

					e.printStackTrace();

				} catch (IllegalAccessException e) {

					// TODO Auto-generated catch block

					e.printStackTrace();

				} catch (InvocationTargetException e) {

					// TODO Auto-generated catch block

					e.printStackTrace();

				}

			}

		}

	}

代理，一个接口java.lang.reflect.InvocationHandler，和一个java.lang.reflect.Proxy类

Proxy用来生成生成一个代理类，InvocationHandler用于处理实际其他逻辑和调用被代理者，例子：

package test;



import java.lang.reflect.InvocationHandler;

import java.lang.reflect.Method;



/**

 * 处理器代理，这个类实现了InvocationHandler

 * 

 */

public class ProcessProxy implements InvocationHandler {

	private Object targs;

	

	public ProcessProxy(Object targs) {

		this.targs = targs;

	}

	

	@Override

	public Object invoke(Object proxy, Method method, Object[] args)

			throws Throwable {

		System.out.println("被代理对象执行前");

		Object ret = method.invoke(targs, args);

		System.out.println("被代理对象执行后");

		return ret;

	}



}

生成代理类已经代理类实例。

@SuppressWarnings("unchecked")
	public static  U getProxyProcess(Object process) {
		ProcessProxy pp = new ProcessProxy(process);

		return (U) Proxy.newProxyInstance(Process.class.getClassLoader(),
				Process.class.getInterfaces(), pp);
	}

JAVA动态技术，原理，生成一个java文件，将这个生成的java文件加载内存

// 生成动态类

	@SuppressWarnings("unchecked")

	public static IProcess makeDynamicClassObject(IProcess p) {

		String _package = "package test;\r\n";

		String classDefine = "public class DynamicClass implements IProcess {"

				+ "\r\n" + "private IProcess p;" +



				"public DynamicClass(IProcess p) {" + "this.p = p;" + "}" +



				"public void process() {"

				+ "System.out.println(\"动态生成的java类，开始执行\");" + "p.process();"

				+ "}" + "}";

		String javaSourceCode = _package + classDefine;

		String fileName = System.getProperty("user.dir")

				+ "/src/test/DynamicClass.java"; // 设置一个路径

		File javaFile = new File(fileName);



		try {

			// 写入java文件

			FileWriter outFile = new FileWriter(javaFile);

			outFile.write(javaSourceCode);

			outFile.flush();

			outFile.close();

		} catch (IOException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}

// 写入完毕，开始生成class文件（编译）

		JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

		StandardJavaFileManager fileMang = compiler.getStandardFileManager(

				null, null, Charset.forName("utf-8"));

		Iterable units = fileMang

				.getJavaFileObjects(fileName);

		CompilationTask t = compiler.getTask(null, fileMang, null, null, null,

				units);



		t.call();



		try {

			fileMang.close();

			javaFile.delete();

		} catch (IOException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}

		try {

			URLClassLoader uloader = new URLClassLoader(new URL[] { new URL(

					"file://" + System.getProperty("user.dir") + "/src/") });

			try {

　　　　　　　　//编译完成，加载

				Class c = uloader.loadClass("test.DynamicClass");

　　　　//创建实例

				return (IProcess) c.getConstructor(IProcess.class).newInstance(

						p);

			} catch (ClassNotFoundException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			} catch (IllegalArgumentException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			} catch (SecurityException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			} catch (InstantiationException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			} catch (IllegalAccessException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			} catch (InvocationTargetException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			} catch (NoSuchMethodException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			}

		} catch (MalformedURLException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}



		return null;

	}

动态加载jar的方式类似

private static class JarLoader {
		private URLClassLoader urlClassLoader;
		public JarLoader(URLClassLoader urlClassLoader) {
			this.urlClassLoader = urlClassLoader;
		}
		
		public void loadJar(URL url) throws Exception {
			Method addURL = URLClassLoader.class.getDeclaredMethod("addURL", URL.class);
			addURL.setAccessible(true);
			addURL.invoke(urlClassLoader, url);
		}
	}

private static void loadjar(JarLoader jarLoader, String path) throws MalformedURLException, Exception{
		File libdir = new File(path);
		if (libdir != null && libdir.isDirectory()) {
			
			File[] listFiles = libdir.listFiles(new FileFilter() {
				
				@Override
				public boolean accept(File file) {
					// TODO Auto-generated method stub
					return file.exists() && file.isFile() && file.getName().endsWith(".jar");
				}
			});
			
			for (File file : listFiles) {
				jarLoader.loadJar(file.toURI().toURL());
			}
			
		}else{
			System.out.println("[Console Message] Directory ["+path+"] does not exsit, please check it");
			System.exit(0);
		}
	}

public static void main(String[] args) {
		JarLoader jarLoader = new JarLoader((URLClassLoader)ClassLoader.getSystemClassLoader());

                loadjar(jarLoader, System.getProperty("user.dir")+"/lib");

}