《Java知识应用》模式实现Java 动态代理

Posted 2021-03-05 加速丨世界

动态代理说明：将你提供的接口改造成和你这个类有关的代理对象。

Java动态代理案例和原理：https://www.cnblogs.com/jssj/p/11771408.html

我们无法像JVM一样不需要生成Java文件直接生成字节码。我们模拟就通过手工生成java,然后编译成Class文件来实现。

模式案例：

package demo.knowledgepoints.invocationhandler;

public interface MyInvocationHandler {
    public Object invoke();
}

package demo.knowledgepoints.invocationhandler;

public class MyInvocationHandlerImpl implements MyInvocationHandler {

    @Override
    public Object invoke() {
        System.out.println("===== MyInvocationHandlerImpl =====");
        return null;
    }
}

package demo.knowledgepoints.invocationhandler;

public interface MyService {
    public void query();
}

package demo.knowledgepoints.invocationhandler;

public class BinServvice implements MyService {
    @Override
    public void query() {
        System.out.println("===== start BinServvice =======");
    }
}

package demo.knowledgepoints.invocationhandler;

public class TaoService implements MyService {
    @Override
    public void query() {
        System.out.println("========= start TaoService ========");
    }
}

package demo.knowledgepoints.invocationhandler;

import javax.tools.JavaCompiler;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;

public class MyProxy {

    public static void main(String[] args) {
        try {
            MyInvocationHandler myInvocationHandler = new MyInvocationHandlerImpl();

            MyService myService = (MyService) MyProxy.getInstance(new BinServvice(),myInvocationHandler);
            myService.query();

            System.out.println("================================================");

            myService = (MyService) MyProxy.getInstance(new TaoService(),myInvocationHandler);
            myService.query();
        } catch (Exception e) {
            //
        }
    }

    public static Object getInstance(Object target, MyInvocationHandler myInvocationHandler) throws IOException, ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
        Class clazz = target.getClass().getInterfaces()[0];
        Class myInvocationHandlerClazz = myInvocationHandler.getClass().getInterfaces()[0];
        String interfaceName = clazz.getSimpleName();   //获取接口名称。
        String content = "";
        String line = "\\n";//换行
        String tab = "\\t";//tab
        /****组装一个类start ***/
        String packageContent = "package demo.knowledgepoints.invocationhandler;" + line;
        String importContent = "import " + clazz.getName() + ";" + line
                              +"import " + myInvocationHandlerClazz.getName() + ";" + line;
        String clazzFirstLineContent = "public class $ProxyMy implements " + interfaceName + "{" + line;
        String myInvocationHandlerName= myInvocationHandlerClazz.getSimpleName();
        String filedContent = tab + "private " + interfaceName + " target;" + line
                + tab + "private " + myInvocationHandlerName + " myInvocationHandler;" + line;
        String constructorContent = tab + "public $ProxyMy (" + interfaceName + " target,"+myInvocationHandlerName+" myInvocationHandler){" + line
                + tab + tab + "this.target =target;"
                + line + tab + tab + "this.myInvocationHandler = myInvocationHandler;"
                + line + tab + "}" + line;


        String methodContent = "";
        /**获取传入接口中的全部方法***/
        Method[] methods = clazz.getDeclaredMethods();
        /**循环组装接口中的各个方法**/
        for (Method method : methods) {
            //返回值类型
            String returnTypeName = method.getReturnType().getSimpleName();
            //方法名称
            String methodName = method.getName();
            // 参数类型的数组（int,String等）
            Class args[] = method.getParameterTypes();
            String argsContent = "";
            String paramsContent = "";
            int flag = 0;
            for (Class arg : args) {
                //String
                String temp = arg.getSimpleName();
                //String
                //String p0
                argsContent += temp + " p" + flag + ",";
                //p0
                paramsContent += "p" + flag + ",";
                flag++;
            }
            if (argsContent.length() > 0) {
                argsContent = argsContent.substring(0, argsContent.lastIndexOf(",") - 1);
                paramsContent = paramsContent.substring(0, paramsContent.lastIndexOf(",") - 1);
            }

            methodContent += tab + "public " + returnTypeName + " " + methodName + "(" + argsContent + ") {" + line
                    + tab + tab + "myInvocationHandler.invoke();" + line
                    + tab + tab + "target." + methodName + "(" + paramsContent + ");" + line
                    + tab + "}" + line;

        }
        content += packageContent + importContent + clazzFirstLineContent + filedContent + constructorContent + methodContent + "}";
        /****组装一个类end ***/

        /****将上述组装的类写入文件中***/
        File file = new File("d:\\\\Study\\\\AcceleateWorld\\\\study\\\\MyProcedure\\\\src\\\\demo\\\\knowledgepoints\\\\invocationhandler\\\\$ProxyMy.java");
        try {
            if (!file.exists()) {
                file.createNewFile();
            }
            FileWriter fw = new FileWriter(file);
            fw.write(content);
            fw.flush();
            fw.close();
        } catch (Exception e) {

        }
        /***使用JavaCompiler对象需要安装JDK，只有JAR无法使用**/
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        StandardJavaFileManager fileMgr = compiler.getStandardFileManager(null, null, null);
        Iterable units = fileMgr.getJavaFileObjects(file);
        JavaCompiler.CompilationTask t = compiler.getTask(null, fileMgr, null, null, null, units);
        t.call();
        fileMgr.close();

        /***将对象new出来读取到内存中***/
        URL[] urls = new URL[]{new URL("file:d:\\\\Study\\\\AcceleateWorld\\\\study\\\\MyProcedure\\\\src\\\\\\\\")};
        URLClassLoader urlClassLoader = new URLClassLoader(urls);
        Class cls = urlClassLoader.loadClass("demo.knowledgepoints.invocationhandler.$ProxyMy");
        Class[] classes = new Class[]{clazz,myInvocationHandlerClazz};
        Constructor constructor = cls.getConstructor(classes);
        Object o  = constructor.newInstance(target,myInvocationHandler);
        return  o;
    }
}

运行效果：

生成的代理java文件和Class文件：