Java动态代理-白红宇

Java动态代理

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发布时间：2019-06-11

本文共 8082 字，大约阅读时间需要 26 分钟。

最近看了Feign的远程调用代理这部分的代码，尝试的自己写了一下。

调用模型图：

1.ProxyMethod注解，判断方法是否需要做代理。

/** * 代理方法注解 */@java.lang.annotation.Target(METHOD)@Retention(RUNTIME)public @interface ProxyMethod {    public String value();}

2.启动类，idService是生成的代理类。

public class StartApplication {    public static void main(String[] args) {        // 创建代理        IdService idService = ProxyUtil.newInstance(new Target.HardCodedTarget<>(IdService.class));        // 执行代理方法        Integer id = idService.getId();        System.out.println(id);    }}

3.IdService服务类

public interface IdService {    @ProxyMethod("getId")    public Integer getId();}

4.类代理

/** * 代理 * @param 
     
       */public interface Target
      
        {    public Class
       
         type();    public static class HardCodedTarget
        
          implements Target
         
           {        private Class
          
            type; public HardCodedTarget(Class
           
             type) { this.type = type; } @Override public Class
            
              type() { return type; } }}

5.代理工具类

/** * 代理工具类 */public class ProxyUtil {    public static 
     
       T newInstance(Target
      
        target) {        Map
       
         nameToHandler = MethodHandler.FactoryMethodHandler.apply(target);        Map
        
          methodToHandler = new LinkedHashMap
         
          ();        for (Method method : target.type().getMethods()) {            if (method.getDeclaringClass() == Object.class) {                continue;            } else if (isDefault(method)) {                MethodHandler.DefaultMethodHandler handler = new MethodHandler.DefaultMethodHandler(method);                methodToHandler.put(method, handler);            } else {                System.out.println("ProxyUtil.newInstance.Method:" + method.getName());                methodToHandler.put(method, nameToHandler.get(configKey(target.type(), method)));            }        }        InvocationHandler handler = new DefaultInvocationHandler(target, methodToHandler);        @SuppressWarnings("unchecked")        T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(), new Class
          []{target.type()}, handler);        return proxy;    }    public static String configKey(Class
           targetType, Method method) {        StringBuilder builder = new StringBuilder();        builder.append(targetType.getSimpleName());        builder.append('#').append(method.getName()).append('(');        for (Type param : method.getGenericParameterTypes()) {            builder.append(getRawType(param)).append(',');        }        if (method.getParameterTypes().length > 0) {            builder.deleteCharAt(builder.length() - 1);        }        return builder.append(')').toString();    }    public static String getRawType(Type param) {        return param.getTypeName();    }    /**     * Identifies a method as a default instance method.     */    public static boolean isDefault(Method method) {        // Default methods are public non-abstract, non-synthetic, and non-static instance methods        // declared in an interface.        // method.isDefault() is not sufficient for our usage as it does not check        // for synthetic methods.  As a result, it picks up overridden methods as well as actual default methods.        final int SYNTHETIC = 0x00001000;        return ((method.getModifiers() & (Modifier.ABSTRACT | Modifier.PUBLIC | Modifier.STATIC | SYNTHETIC)) ==                Modifier.PUBLIC) && method.getDeclaringClass().isInterface();    }    /**     * 自定义方法代理     */    public static class DefaultInvocationHandler implements InvocationHandler {        private final Target
           target;        private final Map
          
            dispatch; public DefaultInvocationHandler(Target
            target, Map
           
             dispatch) { this.target = target; this.dispatch = dispatch; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { if ("equals".equals(method.getName())) { try { Object otherHandler = args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null; return equals(otherHandler); } catch (IllegalArgumentException e) { return false; } } else if ("hashCode".equals(method.getName())) { return hashCode(); } else if ("toString".equals(method.getName())) { return toString(); } return dispatch.get(method).invoke(args); } @Override public boolean equals(Object obj) { if (obj instanceof DefaultInvocationHandler) { DefaultInvocationHandler other = (DefaultInvocationHandler) obj; return target.equals(other.target); } return false; } @Override public int hashCode() { return target.hashCode(); } @Override public String toString() { return target.toString(); } }}

6.代理方法处理类

public interface MethodHandler {    Object invoke(Object[] argv) throws Throwable;    public static class DefaultMethodHandler implements MethodHandler {        private final MethodHandle unboundHandle;        private MethodHandle handle;        public DefaultMethodHandler(Method defaultMethod) {            try {                Class
      declaringClass = defaultMethod.getDeclaringClass();                Field field = MethodHandles.Lookup.class.getDeclaredField("IMPL_LOOKUP");                field.setAccessible(true);                MethodHandles.Lookup lookup = (MethodHandles.Lookup) field.get(null);                this.unboundHandle = lookup.unreflectSpecial(defaultMethod, declaringClass);            } catch (NoSuchFieldException ex) {                throw new IllegalStateException(ex);            } catch (IllegalAccessException ex) {                throw new IllegalStateException(ex);            }        }        /**         * Bind this handler to a proxy object.  After bound, DefaultMethodHandler#invoke will act as if it was called         * on the proxy object.  Must be called once and only once for a given instance of DefaultMethodHandler         */        public void bindTo(Object proxy) {            if (handle != null) {                throw new IllegalStateException("Attempted to rebind a default method handler that was already bound");            }            handle = unboundHandle.bindTo(proxy);        }        /**         * Invoke this method.  DefaultMethodHandler#bindTo must be called before the first         * time invoke is called.         */        @Override        public Object invoke(Object[] argv) throws Throwable {            if (handle == null) {                throw new IllegalStateException("Default method handler invoked before proxy has been bound.");            }            return handle.invokeWithArguments(argv);        }    }    public static class FactoryMethodHandler {        public static Map
     
       apply(Target
       target) {            System.out.println("初始化代理>>>");            Map
      
        result = new LinkedHashMap
       
        ();            Class
         targetType = target.type();            for (Method method : targetType.getMethods()) {                if (method.getDeclaringClass() == Object.class ||                        (method.getModifiers() & Modifier.STATIC) != 0 ||                        ProxyUtil.isDefault(method)) {                    continue;                }                result.put(ProxyUtil.configKey(targetType, method), new ProxyMethodHandler(method));            }            return result;        }    }    public static class ProxyMethodHandler implements MethodHandler {        private Method method;        public ProxyMethodHandler(Method method) {            this.method = method;        }        @Override        public Object invoke(Object[] argv) throws Throwable {            System.out.println("执行代理方法>>>");            ProxyMethod proxyMethod = method.getAnnotation(ProxyMethod.class);            if (null != proxyMethod) {                if ("getId".equals(proxyMethod.value())) {                    return 1;                }            }            return null;        }    }}