java动态代理作用及源码分析

时间:2021-7-4 作者:qvyue

一、理解

  • 静态代理:静态代理是在编译时就将接口、实现类、代理类一股脑儿全部手动完成
  • 动态代理:在程序运行期间根据需要动态的创建代理类及其实例,来完成具体的功能

二、应用场景

  • 参考装饰器模式,在已有的方法中进行再次封装,实现新增功能
  • AOP面向切面编程思想

三、实现代码

在了解了动态代理之前,我们先通过最简单的例子看静态代理是如何实现的。
先定义一个接口

package about_proxy.static_proxy;

/**
 * Created by solie_h on 2018/2/7.
 */
public interface Subject {

    public void doSomething();

}

完成一个该接口的实现类,并实现doSomething方法

package about_proxy.static_proxy;

/**
 * Created by solie_h on 2018/2/7.
 */
public class RealSubject implements Subject {

    @Override
    public void doSomething() {

        System.out.println("call doSomething()");

    }
}

假如这时有需求,需要改写doSomething方法,再方法执行前后增加日志打印功能,并计算该功能耗时,可是其中实现逻辑复杂,不想修改原有代码,这时我们新建一个代理类,在其中实现我们需要的功能。

package about_proxy.static_proxy;

/**
 * Created by solie_h on 2018/2/7.
 */
public class SubjectProxy implements Subject {

    Subject subimpl = new RealSubject();

    @Override
    public void doSomething() {
        System.out.println("我们先做点什么");
        subimpl.doSomething();
        System.out.println("我们再做点什么");

    }
}

这个时候我们就可以利用新的代理类来实现新的需求,而不用修改源代码。下面完成测试类

package about_proxy.static_proxy;

/**
 * Created by solie_h on 2018/2/7.
 */
public class TestStaticProxy {

    public static void main(String args[]) {
//        Subject sub = new RealSubject();
        Subject sub = new SubjectProxy();
        sub.doSomething();
    }
}

好啦,这时候我们已经完成了需求人员的要求了。可是这个时候,老板又跳出来,说我想测试一下工程中多个类中方法的耗时。
干!我要新建多少个代理类啊。
这个时候动态代理就应运而生了。首先我们还是定义接口

package about_proxy.dynamic_proxy;

/**
 * Created by solie_h on 2018/2/7.
 */
public interface Subject {
    public void doSomething();
}

然后定义实现类

package about_proxy.dynamic_proxy;

/**
 * Created by solie_h on 2018/2/7.
 */
public class RealSubject implements Subject {
    @Override
    public void doSomething() {
        System.out.println("call doSomething()");
    }
}

上面我们就完成了准备工作,接下来实现动态代理

package about_proxy.dynamic_proxy;

import org.omg.CORBA.portable.InvokeHandler;
import sun.rmi.runtime.Log;

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

/**
 * Created by solie_h on 2018/2/7.
 */
public class ProxyHandler implements InvocationHandler {

    private Object tar;


    public Object bind(Object tar)
    {
        this.tar = tar;
        //绑定该类实现的所有接口,取得代理类
        return Proxy.newProxyInstance(tar.getClass().getClassLoader(), tar.getClass().getInterfaces(), this);
    }



    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        Object result = null;
        //这里就可以进行所谓的AOP编程了
        //在调用具体函数方法前,执行功能处理
        System.out.println("start time:"+System.currentTimeMillis());
        result = method.invoke(tar,args);
        //在调用具体函数方法后,执行功能处理
        System.out.println("end time:"+System.currentTimeMillis());
        return result;

    }
}

最后再测试类中使用动态代理

package about_proxy.dynamic_proxy;

/**
 * Created by solie_h on 2018/2/7.
 */
public class TestDynamicProxy {

    public static void main(String args[]){
//        Subject sub = new RealSubject();
        ProxyHandler proxy = new ProxyHandler();
        //绑定该类实现的所有接口
        Subject sub = (Subject) proxy.bind(new RealSubject());
        sub.doSomething();
    }
}

这样我们就可以在一个ProxyHandler实现多个代理类的功能(本demo只使用了一个动态代理),但是只创建了一个实体类。是如何实现的呢?动态代理其实为我们在运行期间动态生成了多个代理类,下面我们通过源码来了解一下jdk中是如何操作的。

四、原理简析

我们可以debug一下demo,当工程执行到doSomething()方法时进入了ProxyHandler类中的invoke方法,以实现了我们在真正的doSomething()方法前后增加了自己想要的功能。
为什么会进入invoke中呢?
在上述demo的main方法中调用了ProxyHandler的bind方法,

Subject sub = (Subject) proxy.bind(new RealSubject());

其实是调用了Proxy类的静态方法newProxyInstance()

Proxy.newProxyInstance(tar.getClass().getClassLoader(), tar.getClass().getInterfaces(), this);

这里便是生成代理的关键了,我们继续跟进查看内部关键

@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,Class>[] interfaces, 
InvocationHandler h) throws IllegalArgumentException
    {
        Objects.requireNonNull(h);

        final Class>[] intfs = interfaces.clone();
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
        }

        /*
         * 获取代理类。
         */
        Class> cl = getProxyClass0(loader, intfs);

        /*
         * 使用指定的invocationHandler调用构造方法
         */
        try {
            if (sm != null) {
                checkNewProxyPermission(Reflection.getCallerClass(), cl);
            }
            //调用代理对象的构造函数(代理对象的构造函数$Proxy0(InvocationHandler h),通过字节码反编译可以查看生成的代理类)  
            final Constructor> cons = cl.getConstructor(constructorParams);
            final InvocationHandler ih = h;
            if (!Modifier.isPublic(cl.getModifiers())) {
                AccessController.doPrivileged(new PrivilegedAction() {
                    public Void run() {
                        cons.setAccessible(true);
                        return null;
                    }
                });
            }
            //生成代理类的实例,并把MyInvocationHander的实例作为构造函数参数传入  
            return cons.newInstance(new Object[]{h});
        } catch (IllegalAccessException|InstantiationException e) {
            throw new InternalError(e.toString(), e);
        } catch (InvocationTargetException e) {
            Throwable t = e.getCause();
            if (t instanceof RuntimeException) {
                throw (RuntimeException) t;
            } else {
                throw new InternalError(t.toString(), t);
            }
        } catch (NoSuchMethodException e) {
            throw new InternalError(e.toString(), e);
        }
    }

我们继续看是如何获取代理类的,跟入Class> cl = getProxyClass0(loader, intfs)方法

   /**
    * Generate a proxy class.  Must call the checkProxyAccess method
    * to perform permission checks before calling this.
    */
    private static Class> getProxyClass0(ClassLoader loader,
                                           Class>... interfaces) {
        //实现接口的最大数量 65535) {
            throw new IllegalArgumentException("interface limit exceeded");
        }

        // If the proxy class defined by the given loader implementing
        // the given interfaces exists, this will simply return the cached copy;
        // otherwise, it will create the proxy class via the ProxyClassFactory
        //调用了get方法
        return proxyClassCache.get(loader, interfaces);
    }

继续跟入proxyClassCache.get(loader, interfaces);

    /**
     * @param key       上面传入的loader,类加载器
     * @param parameter 上面方法传入的interfaces,接口数组
     */
    public V get(K key, P parameter) {
        Objects.requireNonNull(parameter);

        expungeStaleEntries();

        Object cacheKey = CacheKey.valueOf(key, refQueue);

        // lazily install the 2nd level valuesMap for the particular cacheKey
        ConcurrentMap> valuesMap = map.get(cacheKey);
        if (valuesMap == null) {
            ConcurrentMap> oldValuesMap
                = map.putIfAbsent(cacheKey,
                                  valuesMap = new ConcurrentHashMap());
            if (oldValuesMap != null) {
                valuesMap = oldValuesMap;
            }
        }

        // create subKey and retrieve the possible Supplier stored by that
        // subKey from valuesMap
        Object subKey = Objects.requireNonNull(subKeyFactory.apply(key, parameter));
        Supplier supplier = valuesMap.get(subKey);
        Factory factory = null;

        while (true) {
            if (supplier != null) {
                // supplier might be a Factory or a CacheValue instance
                // 返回的value是通过该方法调用的
                V value = supplier.get();
                if (value != null) {
                    return value;
                }
            }
            // else no supplier in cache
            // or a supplier that returned null (could be a cleared CacheValue
            // or a Factory that wasn't successful in installing the CacheValue)

            // lazily construct a Factory
            if (factory == null) {
                factory = new Factory(key, parameter, subKey, valuesMap);
            }

            if (supplier == null) {
                supplier = valuesMap.putIfAbsent(subKey, factory);
                if (supplier == null) {
                    // successfully installed Factory
                    supplier = factory;
                }
                // else retry with winning supplier
            } else {
                if (valuesMap.replace(subKey, supplier, factory)) {
                    // successfully replaced
                    // cleared CacheEntry / unsuccessful Factory
                    // with our Factory
                    supplier = factory;
                } else {
                    // retry with current supplier
                    supplier = valuesMap.get(subKey);
                }
            }
        }
    }

我们继续查看supplier.get()方法,该方法的实现在WeakCache的内部类Factory中,代码如下

        @Override
        public synchronized V get() { // serialize access
            // re-check
            Supplier supplier = valuesMap.get(subKey);
            if (supplier != this) {
                // something changed while we were waiting:
                // might be that we were replaced by a CacheValue
                // or were removed because of failure ->
                // return null to signal WeakCache.get() to retry
                // the loop
                return null;
            }
            // else still us (supplier == this)

            // create new value
            V value = null;
            try {
                // 这里又通过valueFactory.apply(key, parameter)得到value进行返回
                value = Objects.requireNonNull(valueFactory.apply(key, parameter));
            } finally {
                if (value == null) { // remove us on failure
                    valuesMap.remove(subKey, this);
                }
            }
            // the only path to reach here is with non-null value
            assert value != null;

            // wrap value with CacheValue (WeakReference)
            CacheValue cacheValue = new CacheValue(value);

            // try replacing us with CacheValue (this should always succeed)
            if (valuesMap.replace(subKey, this, cacheValue)) {
                // put also in reverseMap
                reverseMap.put(cacheValue, Boolean.TRUE);
            } else {
                throw new AssertionError("Should not reach here");
            }

            // successfully replaced us with new CacheValue -> return the value
            // wrapped by it
            return value;
        }
    }

继续跟踪valueFactory.apply(key, parameter)方法,该方法的实现在Proxy的内部类ProxyClassFactory中

@Override
        public Class> apply(ClassLoader loader, Class>[] interfaces) {

            Map, Boolean> interfaceSet = new IdentityHashMap(interfaces.length);
            for (Class> intf : interfaces) {
                /*
                 * 确保该loader加载的此类(intf)
                 */
                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");
                }
                /*
                 * 确保是一个接口
                 */
                if (!interfaceClass.isInterface()) {
                    throw new IllegalArgumentException(
                        interfaceClass.getName() + " is not an interface");
                }
                /*
                 * 确保接口没重复
                 */
                if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) {
                    throw new IllegalArgumentException(
                        "repeated interface: " + interfaceClass.getName());
                }
            }

            String proxyPkg = null;     // package to define proxy class in
            int accessFlags = Modifier.PUBLIC | Modifier.FINAL;

            /*
             * 验证所有非公共的接口在同一个包内;公共的就无需处理.
             */
            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 + ".";
            }

            /*
             * 为代理类生成一个名字,防止重复
             */
            long num = nextUniqueNumber.getAndIncrement();
            String proxyName = proxyPkg + proxyClassNamePrefix + num;

            /*
             * 具体生成代理类的方法又在该方法中实现
             */
            byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
                proxyName, interfaces, accessFlags);
            try {
                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());
            }
        }
    }

再跟踪ProxyGenerator.generateProxyClass(proxyName, interfaces, accessFlags)

public static byte[] generateProxyClass(final String name, Class>[] interfaces, int accessFlags) {
        ProxyGenerator gen = new ProxyGenerator(name, interfaces, accessFlags);
        //真正生成字节码的方法
        final byte[] classFile = gen.generateClassFile();
        //如果saveGeneratedFiles为true 则生成字节码文件,所以在开始我们要设置这个参数
        //当然,也可以通过返回的bytes自己输出
        if (saveGeneratedFiles) {
            java.security.AccessController.doPrivileged( new java.security.PrivilegedAction() {
                public Void run() {
                    try {
                        int i = name.lastIndexOf('.');
                        Path path;
                        if (i > 0) {
                            Path dir = Paths.get(name.substring(0, i).replace('.', File.separatorChar));
                            Files.createDirectories(dir);
                            path = dir.resolve(name.substring(i+1, name.length()) + ".class");
                        } else {
                            path = Paths.get(name + ".class");
                        }
                        Files.write(path, classFile);
                        return null;
                    } catch (IOException e) {
                        throw new InternalError( "I/O exception saving generated file: " + e);
                    }
                }
            });
        }
        return classFile;
    }

继续跟生成自己码的代码,这里便是最终的生成方法了

private byte[] generateClassFile() {
  /* ============================================================
   * Step 1: Assemble ProxyMethod objects for all methods to generate proxy dispatching code for.
   * 步骤1:为所有方法生成代理调度代码,将代理方法对象集合起来。
   */
  //增加 hashcode、equals、toString方法
  addProxyMethod(hashCodeMethod, Object.class);
  addProxyMethod(equalsMethod, Object.class);
  addProxyMethod(toStringMethod, Object.class);
  //增加接口方法
  for (Class> intf : interfaces) {
   for (Method m : intf.getMethods()) {
    addProxyMethod(m, intf);
   }
  }

  /*
   * 验证方法签名相同的一组方法,返回值类型是否相同;意思就是重写方法要方法签名和返回值一样
   */
  for (List sigmethods : proxyMethods.values()) {
   checkReturnTypes(sigmethods);
  }

  /* ============================================================
   * Step 2: Assemble FieldInfo and MethodInfo structs for all of fields and methods in the class we are generating.
   * 为类中的方法生成字段信息和方法信息
   */
  try {
   //增加构造方法
   methods.add(generateConstructor());
   for (List sigmethods : proxyMethods.values()) {
    for (ProxyMethod pm : sigmethods) {
     // add static field for method's Method object
     fields.add(new FieldInfo(pm.methodFieldName,
       "Ljava/lang/reflect/Method;",
       ACC_PRIVATE | ACC_STATIC));
     // generate code for proxy method and add it
     methods.add(pm.generateMethod());
    }
   }
   //增加静态初始化信息
   methods.add(generateStaticInitializer());
  } catch (IOException e) {
   throw new InternalError("unexpected I/O Exception", e);
  }

  if (methods.size() > 65535) {
   throw new IllegalArgumentException("method limit exceeded");
  }
  if (fields.size() > 65535) {
   throw new IllegalArgumentException("field limit exceeded");
  }

  /* ============================================================
   * Step 3: Write the final class file.
   * 步骤3:编写最终类文件
   */
  /*
   * Make sure that constant pool indexes are reserved for the following items before starting to write the final class file.
   * 在开始编写最终类文件之前,确保为下面的项目保留常量池索引。
   */
  cp.getClass(dotToSlash(className));
  cp.getClass(superclassName);
  for (Class> intf: interfaces) {
   cp.getClass(dotToSlash(intf.getName()));
  }

  /*
   * Disallow new constant pool additions beyond this point, since we are about to write the final constant pool table.
   * 设置只读,在这之前不允许在常量池中增加信息,因为要写常量池表
   */
  cp.setReadOnly();

  ByteArrayOutputStream bout = new ByteArrayOutputStream();
  DataOutputStream dout = new DataOutputStream(bout);

  try {
   // u4 magic;
   dout.writeInt(0xCAFEBABE);
   // u2 次要版本;
   dout.writeShort(CLASSFILE_MINOR_VERSION);
   // u2 主版本
   dout.writeShort(CLASSFILE_MAJOR_VERSION);

   cp.write(dout);    // (write constant pool)

   // u2 访问标识;
   dout.writeShort(accessFlags);
   // u2 本类名;
   dout.writeShort(cp.getClass(dotToSlash(className)));
   // u2 父类名;
   dout.writeShort(cp.getClass(superclassName));
   // u2 接口;
   dout.writeShort(interfaces.length);
   // u2 interfaces[interfaces_count];
   for (Class> intf : interfaces) {
    dout.writeShort(cp.getClass(
      dotToSlash(intf.getName())));
   }
   // u2 字段;
   dout.writeShort(fields.size());
   // field_info fields[fields_count];
   for (FieldInfo f : fields) {
    f.write(dout);
   }
   // u2 方法;
   dout.writeShort(methods.size());
   // method_info methods[methods_count];
   for (MethodInfo m : methods) {
    m.write(dout);
   }
   // u2 类文件属性:对于代理类来说没有类文件属性;
   dout.writeShort(0); // (no ClassFile attributes for proxy classes)

  } catch (IOException e) {
   throw new InternalError("unexpected I/O Exception", e);
  }

  return bout.toByteArray();
 }

上面对源码一顿分析,接下来我们将demo中调用bind方法中Proxy.newProxyInstance(tar.getClass().getClassLoader(), tar.getClass().getInterfaces(), this)动态生成的代理类打印出来,修改我们的demo

package about_proxy.dynamic_proxy;

import sun.misc.ProxyGenerator;

import java.io.FileOutputStream;
import java.io.IOException;

/**
 * Created by solie_h on 2018/2/7.
 */
public class TestDynamicProxy {

    public static void main(String args[]){
//        Subject sub = new RealSubject();
        ProxyHandler proxy = new ProxyHandler();
        //绑定该类实现的所有接口
        Subject sub = (Subject) proxy.bind(new RealSubject());
        // 将动态生成的代理类打印出来
        // 这里需要修改为你需要输出的路径
        String path = "请修改路径/TestProxy.class";
        byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy0",RealSubject.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();
            }
        }
        sub.doSomething();

    }

}

将生成的TestProxy.class文件反编译,这里给不熟悉反编译操作的同学提供一个在线反编译工具:http://www.javadecompilers.com/

import about_proxy.dynamic_proxy.Subject;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

public final class $Proxy0
  extends Proxy
  implements Subject
{
  private static Method m1;
  private static Method m3;
  private static Method m2;
  private static Method m0;
  
  public $Proxy0(InvocationHandler paramInvocationHandler)
  {
    super(paramInvocationHandler);
  }
  
  public final boolean equals(Object paramObject)
  {
    try
    {
      return ((Boolean)h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final void doSomething()
  {
    try
    {
      h.invoke(this, m3, null);
      return;
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final String toString()
  {
    try
    {
      return (String)h.invoke(this, m2, null);
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final int hashCode()
  {
    try
    {
      return ((Integer)h.invoke(this, m0, null)).intValue();
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  static
  {
    try
    {
      m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
      m3 = Class.forName("about_proxy.dynamic_proxy.Subject").getMethod("doSomething", new Class[0]);
      m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
      m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
      return;
    }
    catch (NoSuchMethodException localNoSuchMethodException)
    {
      throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
    }
    catch (ClassNotFoundException localClassNotFoundException)
    {
      throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
    }
  }
}

我们先来看该类的构造方法

 public $Proxy0(InvocationHandler paramInvocationHandler)
  {
    super(paramInvocationHandler);
  }

传入参数为InvocationHandler,这就是为什么动态代理类在调用接口中方法时会走到自定义的InvocationHandler中的invoke方法。
super(paramInvocationHandler),是调用父类Proxy的构造方法。而父类又持有protected InvocationHandler h的实例,参考Proxy的构造方法:

  protected Proxy(InvocationHandler h) {
        Objects.requireNonNull(h);
        this.h = h;
    }

在继续看反编译出来文件的静态代码块

static
  {
    try
    {
      m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
      m3 = Class.forName("about_proxy.dynamic_proxy.Subject").getMethod("doSomething", new Class[0]);
      m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
      m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
      return;
    }
    catch (NoSuchMethodException localNoSuchMethodException)
    {
      throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
    }
    catch (ClassNotFoundException localClassNotFoundException)
    {
      throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
    }
  }

我们在接口中定义的方法doSomething通过反射得到的名字是m3,我们继续查看文件中实现的doSomething()方法

  public final void doSomething()
  {
    try
    {
      h.invoke(this, m3, null);
      return;
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

这里调用代理对象的doSomething方法,直接就调用了InvocationHandler中的invoke方法,并把m3传了进去。
this.h.invoke(this, m3, null);
其余的equals、toString、hashCode也是同样的道理。
到这里就很明了了,所有的动态代理流程也清晰了。

五、总结

JDK是动态生成代理类,并通过调用解析器,执行接口实现的方法的原理已经一目了然。动态代理加上反射,是很多框架的基础。期待下一章节实现根据动态代理与反射实现的android的注入框架原理解析。

个人见解,若有错误之处,欢迎指出更正

文章中demo放置在github
https://github.com/loosaSH/java-Proxy

参考文章:
1、Java帝国之动态代理(用故事形式讲解动态代理的出现及原理)
2、知乎-Java 动态代理作用是什么?
3、简书-动态代理
4、JDK8动态代理源码分析

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