关于spring:设计模式代理模式

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图解设计模式

大话设计模式

设计模式之禅

github 我见过最好的设计模式

http://c.biancheng.net/view/1…

代理模式为其余对象提供一种代理，用来管制对于这个对象的拜访
在客户类和指标类之间起到中介作用
结构型设计模式

房产中介
快递小哥
黄牛党

爱护指标对象
加强指标对象的性能

显示申明被代理的对象

public class ZhangLaosan implements IPerson {

  private IPerson zhangsan;

  public ZhangLaosan(IPerson person) {this.zhangsan = person;}

  public void findLove() {System.out.println("张老三开始物色");
    person.findLove();
    System.out.println("开始来往");
  }

}

编译期就分明了

有点相似于装璜者模式

Proxy#newProxyInstance
InvocationHandler

public class JdkMeipo implements InvocationHandler {
  private IPerson target;
  public IPerson getInstance(IPerson target){
    this.target = target;
    Class<?> clazz =  target.getClass();
    return (IPerson) Proxy.newProxyInstance(clazz.getClassLoader(),clazz.getInterfaces(),this);
  }

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {before();
    Object result = method.invoke(this.target,args);
    after();
    return result;
  }

  private void after() {System.out.println("双方同意，开始来往");
  }

  private void before() {System.out.println("我是媒婆，曾经收集到你的需要，开始物色");
  }
}

问题

如同动静代理和动态代理没有区别

动静代理编译期确认的，没有硬编码

导入依赖

<dependency>
  <groupId>cglib</groupId>
  <artifactId>cglib-nodep</artifactId>
  <version>2.2</version>
</dependency>

实现net.sf.cglib.proxy.MethodInterceptor

public class CGlibMeipo implements MethodInterceptor {public Object getInstance(Class<?> clazz) throws Exception{
    // 相当于 Proxy，代理的工具类
    Enhancer enhancer = new Enhancer();
    enhancer.setSuperclass(clazz);
    enhancer.setCallback(this);
    return enhancer.create();}

  public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {before();
    Object obj = methodProxy.invokeSuper(o,objects);
    after();
    return obj;
  }

  private void before(){System.out.println("我是媒婆，我要给你找对象，当初曾经确认你的需要");
    System.out.println("开始物色");
  }

  private void after(){System.out.println("OK 的话，筹备办事");
  }
}

个别 $ 结尾的类都是动静代理的类

通过反编译来查看字节码文件

    public static void generator() {byte[] bytes = ProxyGenerator.generateProxyClass("$proxy0", new Class[]{IPerson.class});
        FileOutputStream os = null;
        try {os = new FileOutputStream("/Users/zzy/Downloads/$proxy0.class");
            os.write(bytes);
            os.close();
            System.out.println("print success");

        } catch (Exception e) {e.printStackTrace();
        } finally {if (os != null) {
                try {os.close();
                } catch (IOException e) {e.printStackTrace();
                }
            }
        }
    }

反编译对应文件

jad $Proxy0.class

jad 装置步骤能够参考 https://blog.csdn.net/qing_ge…

也能够间接放到 idea 中查看

编译后的内容如下

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

import com.zzjson.pattern.proxy.dynamicproxy.jdkproxy.IPerson;
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 IPerson {
  private static Method m1;
  private static Method m4;
  private static Method m2;
  private static Method m3;
  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 findLove() throws  {
    try {super.h.invoke(this, m4, (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 void buyInsure() throws  {
    try {super.h.invoke(this, m3, (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"));
      m4 = Class.forName("com.zzjson.pattern.proxy.dynamicproxy.jdkproxy.IPerson").getMethod("findLove");
      m2 = Class.forName("java.lang.Object").getMethod("toString");
      m3 = Class.forName("com.zzjson.pattern.proxy.dynamicproxy.jdkproxy.IPerson").getMethod("buyInsure");
      m0 = Class.forName("java.lang.Object").getMethod("hashCode");
    } catch (NoSuchMethodException var2) {throw new NoSuchMethodError(var2.getMessage());
    } catch (ClassNotFoundException var3) {throw new NoClassDefFoundError(var3.getMessage());
    }
  }
}

要害代码

public final void findLove() throws  {
  try {super.h.invoke(this, m4, (Object[])null);
  } catch (RuntimeException | Error var2) {throw var2;} catch (Throwable var3) {throw new UndeclaredThrowableException(var3);
  }
}

h实际上就是代理对象

所以说实际上就是调用的

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {before();
  Object result = method.invoke(this.target,args);
  after();
  return result;
}

动静生成源码.java 文件
1. 本人手动拼代码

Java 文件输入到磁盘，保留为文件$Proxy0.java

String filePath = MyProxy.class.getResource("").getPath();
//           System.out.println(filePath);
File f = new File(filePath + "$Proxy0.java");
FileWriter fw = new FileWriter(f);
fw.write(src);
fw.flush();
fw.close();

把.java 文件编译成 $proxy0.class 文件

JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
StandardJavaFileManager manage = compiler.getStandardFileManager(null,null,null);
Iterable iterable = manage.getJavaFileObjects(f);

JavaCompiler.CompilationTask task = compiler.getTask(null,manage,null,null,null,iterable);
task.call();
manage.close();

把生成的.class 文件加载到 JVM 中

Class proxyClass =  classLoader.findClass("$Proxy0");
Constructor c = proxyClass.getConstructor(MyInvocationHandler.class);
f.delete();

返回新的代理对象
```
 return c.newInstance(h);
```

本人的类加载器

public class MyClassLoader extends ClassLoader {

  private File classPathFile;
  public MyClassLoader(){String classPath = MyClassLoader.class.getResource("").getPath();
    this.classPathFile = new File(classPath);
  }

  @Override
  protected Class<?> findClass(String name) throws ClassNotFoundException {String className = MyClassLoader.class.getPackage().getName() + "." + name;
    if(classPathFile  != null){File classFile = new File(classPathFile,name.replaceAll("\\.","/") + ".class");
      if(classFile.exists()){
        FileInputStream in = null;
        ByteArrayOutputStream out = null;
        try{in = new FileInputStream(classFile);
          out = new ByteArrayOutputStream();
          byte [] buff = new byte[1024];
          int len;
          while ((len = in.read(buff)) != -1){out.write(buff,0,len);
          }
          return defineClass(className,out.toByteArray(),0,out.size());
        }catch (Exception e){e.printStackTrace();
        }
      }
    }
    return null;
  }
}

CGLIB 采纳继承的形式，重写父类的办法
JDK 采纳的形式，要求代理的指标对象肯定要实现一个接口

思维：都是通过生成字节码，重组成一个新的类

JDK Proxy 对于用户而言，依赖性更强，调用也更加平安
CGLIB 要求指标类不能有 final 的办法，final 办法不能被代理
CGLIB 更快
- 效率更高，性能也更高，底层没有用到反射
JDK 的生成逻辑较为简单，执行效率姚笛，每次都要用反射

BeanPostProcessor 外围还是在对象后置处理器

AbstractAdvisingBeanPostProcessor#postProcessAfterInitialization`

org.springframework.aop.framework.AbstractAdvisingBeanPostProcessor#postProcessAfterInitialization

public Object postProcessAfterInitialization(Object bean, String beanName) {if (this.advisor == null || bean instanceof AopInfrastructureBean) {
    // Ignore AOP infrastructure such as scoped proxies.
    return bean;
  }

  if (bean instanceof Advised) {Advised advised = (Advised) bean;
    if (!advised.isFrozen() && isEligible(AopUtils.getTargetClass(bean))) {
      // Add our local Advisor to the existing proxy's Advisor chain...
      if (this.beforeExistingAdvisors) {advised.addAdvisor(0, this.advisor);
      }
      else {advised.addAdvisor(this.advisor);
      }
      return bean;
    }
  }

  if (isEligible(bean, beanName)) {ProxyFactory proxyFactory = prepareProxyFactory(bean, beanName);
    if (!proxyFactory.isProxyTargetClass()) {evaluateProxyInterfaces(bean.getClass(), proxyFactory);
    }
    proxyFactory.addAdvisor(this.advisor);
    customizeProxyFactory(proxyFactory);
    return proxyFactory.getProxy(getProxyClassLoader());
  }

  // No proxy needed.
  return bean;
}

最终会执行到

DefaultAopProxyFactory#createAopProxy

org.springframework.aop.framework.DefaultAopProxyFactory#createAopProxy

    public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {Class<?> targetClass = config.getTargetClass();
            if (targetClass == null) {
                throw new AopConfigException("TargetSource cannot determine target class:" +
                        "Either an interface or a target is required for proxy creation.");
            }
            if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {return new JdkDynamicAopProxy(config);
            }
            return new ObjenesisCglibAopProxy(config);
        }
        else {return new JdkDynamicAopProxy(config);
        }
    }

JDK 动静代理

public Object getProxy(@Nullable ClassLoader classLoader) {if (logger.isTraceEnabled()) {logger.trace("Creating JDK dynamic proxy:" + this.advised.getTargetSource());
  }
  Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
  findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
  return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}

对应的 InvocationHandler

org.springframework.aop.framework.JdkDynamicAopProxy#invoke

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
  Object oldProxy = null;
  boolean setProxyContext = false;

  TargetSource targetSource = this.advised.targetSource;
  Object target = null;

  try {if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {// The target does not implement the equals(Object) method itself.
      return equals(args[0]);
    }
    else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {// The target does not implement the hashCode() method itself.
      return hashCode();}
    else if (method.getDeclaringClass() == DecoratingProxy.class) {// There is only getDecoratedClass() declared -> dispatch to proxy config.
      return AopProxyUtils.ultimateTargetClass(this.advised);
    }
    else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
             method.getDeclaringClass().isAssignableFrom(Advised.class)) {
      // Service invocations on ProxyConfig with the proxy config...
      return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
    }

    Object retVal;

    if (this.advised.exposeProxy) {
      // Make invocation available if necessary.
      oldProxy = AopContext.setCurrentProxy(proxy);
      setProxyContext = true;
    }

    // Get as late as possible to minimize the time we "own" the target,
    // in case it comes from a pool.
    target = targetSource.getTarget();
    Class<?> targetClass = (target != null ? target.getClass() : null);

    // Get the interception chain for this method.
    List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

    // Check whether we have any advice. If we don't, we can fallback on direct
    // reflective invocation of the target, and avoid creating a MethodInvocation.
    if (chain.isEmpty()) {
      // We can skip creating a MethodInvocation: just invoke the target directly
      // Note that the final invoker must be an InvokerInterceptor so we know it does
      // nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
      Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
      retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
    }
    else {
      // We need to create a method invocation...
      MethodInvocation invocation =
        new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
      // Proceed to the joinpoint through the interceptor chain.
      retVal = invocation.proceed();}

    // Massage return value if necessary.
    Class<?> returnType = method.getReturnType();
    if (retVal != null && retVal == target &&
        returnType != Object.class && returnType.isInstance(proxy) &&
        !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
      // Special case: it returned "this" and the return type of the method
      // is type-compatible. Note that we can't help if the target sets
      // a reference to itself in another returned object.
      retVal = proxy;
    }
    else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
      throw new AopInvocationException("Null return value from advice does not match primitive return type for:" + method);
    }
    return retVal;
  }
  finally {if (target != null && !targetSource.isStatic()) {
      // Must have come from TargetSource.
      targetSource.releaseTarget(target);
    }
    if (setProxyContext) {
      // Restore old proxy.
      AopContext.setCurrentProxy(oldProxy);
    }
  }
}

CGLIB 动静代理

public Object getProxy(@Nullable ClassLoader classLoader) {if (logger.isTraceEnabled()) {logger.trace("Creating CGLIB proxy:" + this.advised.getTargetSource());
  }

  try {Class<?> rootClass = this.advised.getTargetClass();
    Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");

    Class<?> proxySuperClass = rootClass;
    if (rootClass.getName().contains(ClassUtils.CGLIB_CLASS_SEPARATOR)) {proxySuperClass = rootClass.getSuperclass();
      Class<?>[] additionalInterfaces = rootClass.getInterfaces();
      for (Class<?> additionalInterface : additionalInterfaces) {this.advised.addInterface(additionalInterface);
      }
    }

    // Validate the class, writing log messages as necessary.
    validateClassIfNecessary(proxySuperClass, classLoader);

    // Configure CGLIB Enhancer...
    Enhancer enhancer = createEnhancer();
    if (classLoader != null) {enhancer.setClassLoader(classLoader);
      if (classLoader instanceof SmartClassLoader &&
          ((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {enhancer.setUseCache(false);
      }
    }
    enhancer.setSuperclass(proxySuperClass);
    enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
    enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
    enhancer.setStrategy(new ClassLoaderAwareGeneratorStrategy(classLoader));

    Callback[] callbacks = getCallbacks(rootClass);
    Class<?>[] types = new Class<?>[callbacks.length];
    for (int x = 0; x < types.length; x++) {types[x] = callbacks[x].getClass();}
    // fixedInterceptorMap only populated at this point, after getCallbacks call above
    enhancer.setCallbackFilter(new ProxyCallbackFilter(this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
    enhancer.setCallbackTypes(types);

    // Generate the proxy class and create a proxy instance.
    return createProxyClassAndInstance(enhancer, callbacks);
  }
  catch (CodeGenerationException | IllegalArgumentException ex) {throw new AopConfigException("Could not generate CGLIB subclass of" + this.advised.getTargetClass() +
                                 ": Common causes of this problem include using a final class or a non-visible class",
                                 ex);
  }
  catch (Throwable ex) {// TargetSource.getTarget() failed
    throw new AopConfigException("Unexpected AOP exception", ex);
  }
}

对应的 Interceptor

org.springframework.aop.framework.CglibAopProxy.DynamicAdvisedInterceptor#intercept

public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
  Object oldProxy = null;
  boolean setProxyContext = false;
  Object target = null;
  TargetSource targetSource = this.advised.getTargetSource();
  try {if (this.advised.exposeProxy) {
      // Make invocation available if necessary.
      oldProxy = AopContext.setCurrentProxy(proxy);
      setProxyContext = true;
    }
    // Get as late as possible to minimize the time we "own" the target, in case it comes from a pool...
    target = targetSource.getTarget();
    Class<?> targetClass = (target != null ? target.getClass() : null);
    List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
    Object retVal;
    // Check whether we only have one InvokerInterceptor: that is,
    // no real advice, but just reflective invocation of the target.
    if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
      // We can skip creating a MethodInvocation: just invoke the target directly.
      // Note that the final invoker must be an InvokerInterceptor, so we know
      // it does nothing but a reflective operation on the target, and no hot
      // swapping or fancy proxying.
      Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
      retVal = methodProxy.invoke(target, argsToUse);
    }
    else {
      // We need to create a method invocation...
      retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();}
    retVal = processReturnType(proxy, target, method, retVal);
    return retVal;
  }
  finally {if (target != null && !targetSource.isStatic()) {targetSource.releaseTarget(target);
    }
    if (setProxyContext) {
      // Restore old proxy.
      AopContext.setCurrentProxy(oldProxy);
    }
  }
}

org.springframework.transaction.interceptor.TransactionInterceptor#invoke

org.springframework.transaction.interceptor.TransactionAspectSupport#invokeWithinTransaction

咱们在 Spring 中能够应用申明式事物和编程式事物

@Transactional
和编程式事物

多数据源的切换

org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource

org.springframework.cache.interceptor.CacheInterceptor#invoke

Cacheable
`CacheConfig
CacheEvict
CachePut
Caching
EnableCaching

为什么通过 Mapper 接口就可能调用，不须要写实现类

创立 MapperProxyFactory

org.apache.ibatis.binding.MapperRegistry#addMapper

  public <T> void addMapper(Class<T> type) {if (type.isInterface()) {if (hasMapper(type)) {throw new BindingException("Type" + type + "is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {knownMappers.put(type, new MapperProxyFactory<T>(type));
        // It's important that the type is added before the parser is run
        // otherwise the binding may automatically be attempted by the
        // mapper parser. If the type is already known, it won't try.
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();
        loadCompleted = true;
      } finally {if (!loadCompleted) {knownMappers.remove(type);
        }
      }
    }
  }

这一段先初始化 MapperProxyFactory，并且解析 mapper 接口上的注解

获取 Mapper

org.apache.ibatis.binding.MapperRegistry#getMapper

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
  if (mapperProxyFactory == null) {throw new BindingException("Type" + type + "is not known to the MapperRegistry.");
  }
  try {return mapperProxyFactory.newInstance(sqlSession);
  } catch (Exception e) {throw new BindingException("Error getting mapper instance. Cause:" + e, e);
  }
}

以后获取代理对象通过 MapperProxyFactory 来生成的

代理

org.apache.ibatis.binding.MapperProxyFactory#newInstance(org.apache.ibatis.binding.MapperProxy<T>)

@SuppressWarnings("unchecked")
protected T newInstance(MapperProxy<T> mapperProxy) {return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface}, mapperProxy);
}

public T newInstance(SqlSession sqlSession) {final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
  return newInstance(mapperProxy);
}

查看对应的代理，能够看到通过 Proxy#newProxyInstance 来生成的代理对象，也就是走的 JDK 的动静代理

具体的 Invocationhandler

public class MapperProxy<T> implements InvocationHandler, Serializable {

  private static final long serialVersionUID = -6424540398559729838L;
  private final SqlSession sqlSession;
  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache;

  public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {if (Object.class.equals(method.getDeclaringClass())) {
      try {return method.invoke(this, args);
      } catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);
      }
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }

}

具体的执行是执行的 MapperProxy#invoke 办法

所以 Mapper 接口有要求，不能是 final 类并且办法不能是 final 的，并且办法不能重载

如果理解过 Spring Cloud Feign 应该能够晓得能够在对应的接口下面加 FeignClient 那么在调用的时候就会帮咱们主动负载平衡

@FeignClient(value = AppConstant.APPLICATION_USER_NAME)
public interface IUserClient {
    /**
     * 获取用户信息
     *
     * @param userId 用户 id
     * @return
     */
    @GetMapping(USER_INFO_BY_ID)
    R<User> userInfoById(@RequestParam("userId") Long userId);

必定是做了代理，那么咱们查看代码探索一下 Spring Cloud Feign 是如何做的

org.springframework.cloud.openfeign.FeignClientsRegistrar#registerFeignClient

能够看到

BeanDefinitionBuilder definition = BeanDefinitionBuilder
  .genericBeanDefinition(FeignClientFactoryBean.class);

创立了一个 FeignClientFactoryBean 所以会调用他的

org.springframework.cloud.openfeign.FeignClientFactoryBean#getObject

    public Object getObject() throws Exception {return getTarget();
    }

能够看到getTarget

<T> T getTarget() {FeignContext context = applicationContext.getBean(FeignContext.class);
  Feign.Builder builder = feign(context);
// 省略
  String url = this.url + cleanPath();
  Client client = getOptional(context, Client.class);
  if (client != null) {if (client instanceof LoadBalancerFeignClient) {
      // not load balancing because we have a url,
      // but ribbon is on the classpath, so unwrap
      client = ((LoadBalancerFeignClient) client).getDelegate();}
    if (client instanceof FeignBlockingLoadBalancerClient) {
      // not load balancing because we have a url,
      // but Spring Cloud LoadBalancer is on the classpath, so unwrap
      client = ((FeignBlockingLoadBalancerClient) client).getDelegate();}
    builder.client(client);
  }
  Targeter targeter = get(context, Targeter.class);
  return (T) targeter.target(this, builder, context,
                             new HardCodedTarget<>(type, name, url));
}

调用了 targeter#target 来生成代理对象

public <T> T target(Target<T> target) {return build().newInstance(target);
}

feign.ReflectiveFeign#newInstance

public <T> T newInstance(Target<T> target) {Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
  Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
  List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();

  for (Method method : target.type().getMethods()) {if (method.getDeclaringClass() == Object.class) {continue;} else if (Util.isDefault(method)) {DefaultMethodHandler handler = new DefaultMethodHandler(method);
      defaultMethodHandlers.add(handler);
      methodToHandler.put(method, handler);
    } else {methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));
    }
  }
  InvocationHandler handler = factory.create(target, methodToHandler);
  T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(),
                                       new Class<?>[] {target.type()}, handler);

  for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {defaultMethodHandler.bindTo(proxy);
  }
  return proxy;
}

能够看到也是通过 JDK 的动静代理来生成代理对象的

InvocationHandler 如下

@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);
}

会通过办法来散发做负载平衡

能把代理对象和实在被调用的指标对象拆散
升高了零碎的耦合度，易于扩大
可能爱护指标对象
加强指标对象的性能

零碎类数目减少
客户端和指标对象之间减少了代理对象，申请处理速度会变慢，减少了零碎的复杂度

Bean 中有实现接口的时候，Spring 会应用 JDK 的动静代理
Bean 没有实现接口的时候，Spring 会抉择CGLIB
Spring 能够通过配置强制应用 CGLIB, 只需在 Spring 的配置文件中退出这个代码

<aop:aspectj-autoproxy proxy-target-class="true">

我的笔记仓库地址 gitee 快来给我点个 Star 吧

正文完

spring

发表至： spring

2021-01-04

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关于spring:设计模式代理模式

代理模式

参考资料

定义

类图

生存中的代理模式

应用场景

案例

动态代理

动静代理

JDK

cglibProxy

导入依赖

深刻理解代理模式

JDK 的动静代理

手写

本人的类加载器

CGLIb 和 DJK 的区别

常见的动静代理

Spring

AOP

AbstractAdvisingBeanPostProcessor#postProcessAfterInitialization`

DefaultAopProxyFactory#createAopProxy

JDK 动静代理

对应的 InvocationHandler

CGLIB 动静代理

对应的 Interceptor

事物

多数据源的切换

缓存

Mybatis

Mapper 接口

创立 MapperProxyFactory

获取 Mapper

代理

具体的 Invocationhandler

Spring Cloud Feign

创立 FeignClientFactoryBean

初始化生成代理对象

生成代理

总结

长处

毛病

Spring 中的代理抉择准则

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