完整的是在扩展篇之动态代理,但还是单独把这部分内容拿出来了,主要自己模拟了JDK动态代理的Prxoy.newProxyInstance(),生成我们的一个代理类
我们自己来写一个JDK动态代理

public interface NbInvocationHandler {
    public void invoke(Object o,Method m);
}

先看我们的测试类

public class MProxyTest {
    public static void main(String[] args) throws Exception {
        ITarget target = new MyTarget();
        MInvocationImpl mInvocation = new MInvocationImpl(target);
        ITarget o = (ITarget) MProxy.newProxyInstance(ITarget.class, mInvocation);
        o.hello();
    }
}

public class MProxy {

    public  static  Object  newProxyInstance(Class Interfaces,NbInvocationHandler h) throws Exception {
        File file = generateJava(Interfaces,h);
        compilerJava(file);
        MyClassLoader classLoader = new MyClassLoader();
        Class cl = classLoader.loadClass("com.yjm.proxy.$Proxy0");
        Constructor<?> constructor = cl.getConstructor(NbInvocationHandler.class);

        return  constructor.newInstance(h);
    }
 
    public static File generateJava(Class Interfaces,NbInvocationHandler h) throws Exception {
        String rt="\r\n";
        String methodStr="";
        for (Method method : Interfaces.getMethods()) {
            methodStr += "@Override" + rt +
                    "public void " + method.getName() + "() {" + rt +
                    "try{" + rt +
                    "Method method = " + Interfaces.getName() + ".class.getMethod(\""
                    + method.getName() + "\");" + rt +
                    "h.invoke(this,method);" + rt +
                    "}catch(Exception e){e.printStackTrace();}" + rt +
                    "}";
        }


        String source = "package com.yjm.proxy;" + rt +
                "import java.lang.reflect.Method;" + rt +
                "import com.yjm.proxy.NbInvocationHandler;" + rt +
                "public class $Proxy0 implements " + Interfaces.getName() + "{" + rt +
                "private NbInvocationHandler h;" + rt +
                "public $Proxy0(NbInvocationHandler h) {" + rt +
                "super();" + rt +
                "this.h = h;" + rt +
                "}" + rt +
                methodStr + rt +
                "}";

        File dir = new File(MyClassLoader.sourecPath);
        if (!dir.exists()) {
            dir.mkdirs();
        }

        File file = new File(dir, "$Proxy0.java");
        FileWriter writer = new FileWriter(file);

        try {
            writer.write(source);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            writer.flush();
            writer.close();
        }

        return file;
    }
    public static void compilerJava(File file) throws Exception {
        JavaCompiler javaCompiler = ToolProvider.getSystemJavaCompiler();
        StandardJavaFileManager javaFileManager = javaCompiler.getStandardFileManager((DiagnosticListener)null, (Locale)null, (Charset)null);

        try {
            Iterable it = javaFileManager.getJavaFileObjects(file);
            File dir = new File(MyClassLoader.classPath);
            if (!dir.exists()) {
                dir.mkdirs();
            }

            JavaCompiler.CompilationTask task = javaCompiler.getTask((Writer)null, javaFileManager, (DiagnosticListener)null, Arrays.asList("-d", MyClassLoader.classPath), (Iterable)null, it);
            task.call();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            javaFileManager.close();
        }

    }
}

自定义了我们的类加载器 用于加载我们生成的.class文件

public class MyClassLoader extends ClassLoader {
    public static  final  String classPath = System.getProperty("user.dir")+"/temp/class";
    public static  final  String sourecPath = System.getProperty("user.dir")+"/temp/source";

    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        byte [] data = loadByte(name);
        return defineClass(name,data,0,data.length);
    }
    public  byte[] loadByte(String name){
        try {
            name = name.replaceAll("\\.", "/");
            FileInputStream fileInputStream = new FileInputStream(classPath+"/"+name+".class");
            int len = fileInputStream.available();
            byte [] data = new byte[len];
            fileInputStream.read(data);
            fileInputStream.close();
            return  data;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return  null;
    }
}

public class MInvocationImpl implements NbInvocationHandler{
    private ITarget target;

    public MInvocationImpl(ITarget target) {
        this.target = target;
    }

    public void invoke(Object o, Method m) throws Exception {
        System.out.println("执行前");
        m.invoke(target);
        System.out.println("执行后");
    }
}

我们打断点看一下运行结果

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