设计模式-手写jdk动态代理

话不多说,直接看代码。注意我们没用jdk的。

1、首先创建一个代理接口

public interface InvocationHandler {
	Object invoke(Object proxy, Method method, Object[] args) throws Throwable;
}

2、生产代理对象

  public class Proxy {

    /**
     * 生产代理对象
     * @param clazz
     * @param h
     * @return
     * @throws Exception
     */
	public static Object newProxyInstance(Class clazz,InvocationHandler h) throws Exception{
        //代理类类名
        String cname = clazz.getName().substring(clazz.getName().lastIndexOf(".")+1) + "$Proxy0";
        //手写代理类源码
        StringBuilder source = getSource(clazz, h, cname);
        //产生代理类的java文件
		String filename = Thread.currentThread().getContextClassLoader().getResource("").getPath()
                + clazz.getPackage().getName().replaceAll("\\.", "/") +"/"+cname+".java";
        System.out.println(filename);
        //把源码写入到文件中
		File file = new File(filename);
		FileUtil.writeStringToFile(file, source.toString());
		//编译
		//拿到编译器
		JavaCompiler complier = ToolProvider.getSystemJavaCompiler();
		//文件管理者
		StandardJavaFileManager fileMgr =
				complier.getStandardFileManager(null, null, null);
		//获取文件
		Iterable units = fileMgr.getJavaFileObjects(filename);
		//编译任务
		CompilationTask t = complier.getTask(null, fileMgr, null, null, null, units);
		//进行编译
		t.call();
		fileMgr.close();
		//load 到内存
		ClassLoader cl = ClassLoader.getSystemClassLoader();
		Class<?> c = cl.loadClass(clazz.getPackage().getName() + "."+cname);
		//获取构造函数Constructor
		Constructor<?> ctr = c.getConstructor(h.getClass());
		return ctr.newInstance(h);
	}

    /**
     * 手写代理类源码
     * @param clazz
     * @param h
     * @param cname
     * @return
     */
    private static StringBuilder getSource(Class clazz, InvocationHandler h, String cname) {
        //调用处理接口
        String handler = h.getClass().getName();
        //换行符号
        String line = "\r\n";
        String space = " ";
        //代理类源码
        StringBuilder source = new StringBuilder();
        //包声明
        source.append("package" + space + clazz.getPackage().getName() + ";").append(line);
        //获取类的名称
        source.append(Modifier.toString(clazz.getModifiers()) + space + "class" + space + cname + space);
        //继承接口
        source.append("implements" + space);
        Class[] interfaces = clazz.getInterfaces();
        for (int i = 0; i < interfaces.length; i++) {
            source.append(interfaces[i].getName());
            if (i != interfaces.length - 1) {
                source.append(",");
            }
        }
        source.append("{").append(line);
        //声明变量
        source.append("private " + handler + " h;").append(line);
        //构造方法
        source.append("public " + cname + "(" + handler + " h){").append(line);
        source.append("this.h=h;").append(line).append("}").append(line);
        //实现所有方法
        Method[] methods = clazz.getDeclaredMethods();
        for (Method method : methods) {
            //获取方法返回类型
            Class returnType = method.getReturnType();
            //获取方法上的所有注释
            Annotation[] annotations = method.getDeclaredAnnotations();
            for (Annotation annotation : annotations) {
                //打印注释类型
                source.append("@" + annotation.annotationType().getName()).append(line);
            }
            //打印方法声明
            source.append(Modifier.toString(method.getModifiers()) + " " + returnType.getName() + " " + method.getName() + "(");
            //获取方法的所有参数
            Parameter[] parameters = method.getParameters();
            //参数字符串
            StringBuilder args = new StringBuilder();
            for (int i = 0; i < parameters.length; i++) {
                //参数的类型,形参(全是arg123..)
                source.append(parameters[i].getType().getName() + " " + parameters[i].getName());
                args.append(parameters[i].getName());
                if (i != parameters.length - 1) {
                    source.append(",");
                    args.append(",");
                }
            }
            source.append("){").append(line);
            //方法逻辑
            source.append("Object obj=null; \n try {").append(line);
            source.append("Class[] args = new Class[]{" + args + "};").append(line);
            source.append(Method.class.getName()+" method = " + clazz.getName() + ".class.getMethod(\"" + method.getName() + "\",args);").append(line);
            source.append("obj = h.invoke(this,method,args);").append(line);
            source.append("} catch (Exception e) {\n" + "e.printStackTrace();\n" + "}catch (Throwable throwable) {\n" +
                    "throwable.printStackTrace();\n" + "}").append(line);
            //方法结束
            source.append("return (obj!=null)?("+returnType.getName()+")obj:null;\n}").append(line);
        }
        //类结束
        source.append("}");
        return source;
    }
}

3、有一个工具类

public class FileUtil {

    public static void writeStringToFile(File file, String str){
        try {
            BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file)));
            bufferedWriter.write(str);
            bufferedWriter.flush();
            bufferedWriter.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

4、以上就是自己编写的jdk动态代理,我们来测试下

1)提供一个业务接口
public interface Moveable {
	String move();
}

2)实现这个业务
public class Car implements Moveable {
	@Override
	public String move() {
		try {
			Thread.sleep(new Random().nextInt(1000));
			System.out.println("汽车行驶中....");
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		return "success";
	}
}
3)生成代理对象

public class TimeHandler implements InvocationHandler {

    private Object target;

    public TimeHandler(Object target) {
        super();
        this.target = target;
    }

    @Override
    public Object invoke(Object object, Method method, Object[] args) throws InvocationTargetException, IllegalAccessException {
        long starttime = System.currentTimeMillis();
        System.out.println("开始记录时间");
        Object o = method.invoke(target,args);
        long endtime = System.currentTimeMillis();
        System.out.println("耗时:" + (endtime - starttime) + "毫秒!");
        return o;
    }

}

4)调用
 /**
     * 测试类
     * 1、声明一段源码,源码动态产生动态代理
     * 2、源码产生java文件,对java文件进行编译
     * 3、得到编译文件  调用编译任务 生产class文件
     * 4、把class文件load到内存之中,产生代理类对象返回
     */
    public static void main(String[] args) throws Exception {
        Car car = new Car();
        InvocationHandler h = new TimeHandler(car);
        //通过反射获取该类中的方法,初始化构造函数
        Moveable m = (Moveable) Proxy.newProxyInstance(Car.class, h);
        String s = m.move();
        System.out.println(s);
    }

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