JDK 동적 에이전트 절차 상세 설명(소스 코드 분석)

//   BiFunction<T, U, R>       ，      T，U       ，  R      
private static final class ProxyClassFactory
        implements BiFunction<ClassLoader, Class<?>[], Class<?>>
    {
        // prefix for all proxy class names
        //          
        private static final String proxyClassNamePrefix = "$Proxy";
        // next number to use for generation of unique proxy class names
        //             
        private static final AtomicLong nextUniqueNumber = new AtomicLong();
        @Override
        public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) {
            Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
            //      ，   
            for (Class<?> intf : interfaces) {
                /*
                 * Verify that the class loader resolves the name of this
                 * interface to the same Class object.
                 */
                Class<?> interfaceClass = null;
                try {
                    interfaceClass = Class.forName(intf.getName(), false, loader);
                } catch (ClassNotFoundException e) {
                }
                if (interfaceClass != intf) {
                    throw new IllegalArgumentException(
                        intf + " is not visible from class loader");
                }
                /*
                 * Verify that the Class object actually represents an
                 * interface.
                 */
                if (!interfaceClass.isInterface()) {
                    throw new IllegalArgumentException(
                        interfaceClass.getName() + " is not an interface");
                }
                /*
                 * Verify that this interface is not a duplicate.
                 */
                if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {
                    throw new IllegalArgumentException(
                        "repeated interface: " + interfaceClass.getName());
                }
            }
            //          
            String proxyPkg = null;     // package to define proxy class in
            //        : public ,final
            int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
            /*
             * Record the package of a non-public proxy interface so that the
             * proxy class will be defined in the same package.  Verify that
             * all non-public proxy interfaces are in the same package.
             */
            //                ；        
            //          ，     com.sun.proxy，
            //      $Proxy           
            //        non-public proxy interface ，              
            for (Class<?> intf : interfaces) {
                int flags = intf.getModifiers();
                if (!Modifier.isPublic(flags)) {
                    accessFlags = Modifier.FINAL;
                    String name = intf.getName();
                    int n = name.lastIndexOf('.');
                    String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
                    if (proxyPkg == null) {
                        proxyPkg = pkg;
                    } else if (!pkg.equals(proxyPkg)) {
                        throw new IllegalArgumentException(
                            "non-public interfaces from different packages");
                    }
                }
            }
            if (proxyPkg == null) {
                // if no non-public proxy interfaces, use com.sun.proxy package
                proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
            }

            /*
             * Choose a name for the proxy class to generate.
             */
            long num = nextUniqueNumber.getAndIncrement();
            //         ， com.sun.proxy.$Proxy0.calss
            String proxyName = proxyPkg + proxyClassNamePrefix + num;

            /*
             * Generate the specified proxy class.
             */
            //    ，         
            byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
                proxyName, interfaces, accessFlags);
            try {
                //       JVM ，             
                return defineClass0(loader, proxyName,
                                    proxyClassFile, 0, proxyClassFile.length);
            } catch (ClassFormatError e) {
                /*
                 * A ClassFormatError here means that (barring bugs in the
                 * proxy class generation code) there was some other
                 * invalid aspect of the arguments supplied to the proxy
                 * class creation (such as virtual machine limitations
                 * exceeded).
                 */
                throw new IllegalArgumentException(e.toString());
            }
        }
    }

private static List<Method> getMethods(Class<?>[] interfaces) {
        List<Method> result = new ArrayList<Method>();
        try {
            result.add(Object.class.getMethod("equals", Object.class));
            result.add(Object.class.getMethod("hashCode", EmptyArray.CLASS));
            result.add(Object.class.getMethod("toString", EmptyArray.CLASS));
        } catch (NoSuchMethodException e) {
            throw new AssertionError();
        }

        getMethodsRecursive(interfaces, result);
        return result;
    }
private static void getMethodsRecursive(Class<?>[] interfaces, List<Method> methods) {
        for (Class<?> i : interfaces) {
            getMethodsRecursive(i.getInterfaces(), methods);
            Collections.addAll(methods, i.getDeclaredMethods());
        }
    }

package com.zhb.jdk.proxy;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.Proxy;

import com.zhb.jdk.dynamicProxy.HelloworldImpl;

import sun.misc.ProxyGenerator;

/**
 * @author ZHB
 * @date 2018 8 31   11:35:07
 * @todo TODO
 */
public class DynamicProxyTest {

    public static void main(String[] args) {

        IUserService target = new UserServiceImpl();
        MyInvocationHandler handler = new MyInvocationHandler(target);
        //                （              ）
        //                （             ，                      ）
        //      invocation handler，         。           handler
        IUserService proxyObject = (IUserService) Proxy.newProxyInstance(DynamicProxyTest.class.getClassLoader(),
                target.getClass().getInterfaces(), handler);
        proxyObject.add("  ");

        String path = "D:/$Proxy0.class";
        byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy0", HelloworldImpl.class.getInterfaces());
        FileOutputStream out = null;

        try {
            out = new FileOutputStream(path);
            out.write(classFile);
            out.flush();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                out.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }
}
// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3) fieldsfirst ansi space

import com.zhb.jdk.proxy.IUserService;
import java.lang.reflect.*;

public final class $Proxy0 extends Proxy
    implements IUserService
{

    private static Method m1;
    private static Method m2;
    private static Method m3;
    private static Method m0;
    //        ，      InvocationHandler  ，
    //Proxy.newInstance                      
    public $Proxy0(InvocationHandler invocationhandler)
    {
        super(invocationhandler);
    }
     // Object       ，equals，toString， hashCode
    public final boolean equals(Object obj)
    {
        try
        {
            return ((Boolean)super.h.invoke(this, m1, new Object[] {
                obj
            })).booleanValue();
        }
        catch (Error ) { }
        catch (Throwable throwable)
        {
            throw new UndeclaredThrowableException(throwable);
        }
    }

    public final String toString()
    {
        try
        {
            return (String)super.h.invoke(this, m2, null);
        }
        catch (Error ) { }
        catch (Throwable throwable)
        {
            throw new UndeclaredThrowableException(throwable);
        }
    }
    //      
    public final void add(String s)
    {
        try
        {
            // invocation handler  invoke        
            super.h.invoke(this, m3, new Object[] {
                s
            });
            return;
        }
        catch (Error ) { }
        catch (Throwable throwable)
        {
            throw new UndeclaredThrowableException(throwable);
        }
    }

    public final int hashCode()
    {
        try
        {
            //       invoke  。
            return ((Integer)super.h.invoke(this, m0, null)).intValue();
        }
        catch (Error ) { }
        catch (Throwable throwable)
        {
            throw new UndeclaredThrowableException(throwable);
        }
    }

    //                  
    static 
    {
        try
        {
            m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] {
                Class.forName("java.lang.Object")
            });
            m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
            m3 = Class.forName("com.zhb.jdk.proxy.IUserService").getMethod("add", new Class[] {
                Class.forName("java.lang.String")
            });
            m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
        }
        catch (NoSuchMethodException nosuchmethodexception)
        {
            throw new NoSuchMethodError(nosuchmethodexception.getMessage());
        }
        catch (ClassNotFoundException classnotfoundexception)
        {
            throw new NoClassDefFoundError(classnotfoundexception.getMessage());
        }
    }
}