关于spring:设计模式代理模式

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代理模式

参考资料

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…

定义

  • 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

类图

生存中的代理模式

  • 房产中介
  • 快递小哥
  • 黄牛党

应用场景

  • 爱护指标对象
  • 加强指标对象的性能

案例

动态代理

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

动静代理

JDK

  • 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

cglibProxy

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

深刻理解代理模式

JDK 的动静代理

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;
}

手写

  1. 动静生成源码.java 文件

    1. 本人手动拼代码
  2. 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();
  3. 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();
  4. 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();
  5. 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 和 DJK 的区别

  • 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

常见的动静代理

Spring

AOP

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);
    }
  }
}

事物

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

缓存

org.springframework.cache.interceptor.CacheInterceptor#invoke

  • Cacheable
  • `CacheConfig
  • CacheEvict
  • CachePut
  • Caching
  • EnableCaching

Mybatis

为什么通过 Mapper 接口就可能调用,不须要写实现类

Mapper 接口

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

Spring Cloud Feign

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

创立 FeignClientFactoryBean

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

初始化生成代理对象

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);
}

生成代理

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

总结

长处

  • 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

毛病

  • 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

Spring 中的代理抉择准则

  1. Bean 中有实现接口的时候,Spring 会应用 JDK 的动静代理
  2. Bean 没有实现接口的时候,Spring 会抉择CGLIB
  3. 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

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