JAVA-获取 JDK 动态代理生成的 Class 文件

可指定路径

import sun.misc.ProxyGenerator;

import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

interface Dao {
    void save();
}

class DaoImpl implements Dao {
    @Override
    public void save() {
        System.out.println("save...");
    }
}

public class DynamicProxyTest {

    /**
     * 保存 JDK 动态代理生产的类
     * @param filePath 保存路径，默认在项目路径下生成 $Proxy0.class 文件
     */
    private static void saveProxyFile(String... filePath) {
        if (filePath.length == 0) {
            System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
        } else {
            FileOutputStream out = null;
            try {
                byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy0", DaoImpl.class.getInterfaces());
                out = new FileOutputStream(filePath[0] + "$Proxy0.class");
                out.write(classFile);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                try {
                    if (out != null) {
                        out.flush();
                        out.close();
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) throws Exception {
        saveProxyFile();

        Object target = new DaoImpl();

        /**
         * loader：业务对象的类加载器
         * interfaces：业务对象实现的所有接口
         * public static Class<?> getProxyClass(ClassLoader loader, Class<?>... interfaces)
         */
        Class<?> proxyClass = Proxy.getProxyClass(DaoImpl.class.getClassLoader(), DaoImpl.class.getInterfaces());
        InvocationHandler handler = new InvocationHandler() {
            /**
             * @param proxy 代理对象
             * @param method 代理的方法对象
             * @param args 方法调用时参数
             */
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                Object result = null;
                if (method.getName().equals("save")) {
                    System.out.println("before...");
                    result = method.invoke(target, args);
                    System.out.println("after...");
                }
                return result;
            }
        };
        Dao userDao = (Dao) proxyClass.getConstructor(InvocationHandler.class).newInstance(handler);
        userDao.save();
    }
}

生成的代理类，方法调用会经过 InvocationHandler 对象

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

final class $Proxy0 extends Proxy implements Dao {
    private static Method m1;
    private static Method m3;
    private static Method m2;
    private static Method m0;

    public $Proxy0(InvocationHandler var1) throws  {
        super(var1);
    }

    public final boolean equals(Object var1) throws  {
        try {
            return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final void save() throws  {
        try {
            super.h.invoke(this, m3, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final String toString() throws  {
        try {
            return (String)super.h.invoke(this, m2, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final int hashCode() throws  {
        try {
            return (Integer)super.h.invoke(this, m0, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m3 = Class.forName("javabase.dynamic.Dao").getMethod("save");
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

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https://rejoy.iteye.com/blog/1627405

https://blog.csdn.net/lh513828570/article/details/74078773

https://blog.csdn.net/bestkilly/article/details/82141802