参考资料
大话设计模式
设计模式之禅
http://c.biancheng.net/view/1326.html
定义
- 代理模式为其他对象提供一种代理，用来控制对于这个对象的访问
- 在客户类和目标类之间起到中介作用
- 结构型设计模式
类图
- 房产中介
- 快递小哥
- 黄牛党
使用场景
- 保护目标对象
- 增强目标对象的功能
静态代理
显示声明被代理的对象
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("开始交往");
}
}编译期就清楚了
有点类似于装饰者模式
动态代理
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，开始交往");
}
private void before() {
System.out.println("我是媒婆，已经收集到你的需求，开始物色");
}
}问题
好像动态代理和静态代理没有区别
- 动态代理编译期确认的，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，现在已经确认你的需求");
System.out.println("开始物色");
}
private void after(){
System.out.println("OK的话，准备办事");
}
}深入了解代理模式一般$开头的类都是动态代理的类
JDK的动态代理
通过反编译来查看字节码文件
public static void generator() {
byte[] bytes = ProxyGenerator.generateProxyClass("$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安装步骤可以参考https://blog.csdn.net/qing_gee/article/details/86510704
也可以直接放到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());
}
}
}关键代码
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
动态生成源码.java文件
- 自己手动拼代码
Java文件输出到磁盘，保存为文件$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);
自己的类加载器
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采用继承的方式，重写父类的方法
- JDK采用的方式，要求代理的目标对象一定要实现一个接口
思想：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，调用也更加安全
- CGLIB要求目标类不能有final的方法，final方法不能被代理
- 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
Spring
AOP
BeanPostProcessor核心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动态代理
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动态代理
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
我们在Spring中可以使用声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接口就能够调用，不需要写实现类
Mapper接口
创建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);
}
}当前获取代理对象通过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，可以看到通过Proxy#newProxyInstance来生成的代理对象，也就是走的JDK的动态代理
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方法
所以Mapper接口有要求，不能是final类并且方法不能是final的，并且方法不能重载
Spring Cloud Feign
如果了解过Spring Cloud Feign应该可以知道可以在对应的接口上面加FeignClient那么在调用的时候就会帮我们自动负载均衡
@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);肯定是做了代理，那么我们查看代码探究一下Spring Cloud Feign是如何做的
创建FeignClientFactoryBean
org.springframework.cloud.openfeign.FeignClientsRegistrar#registerFeignClient
可以看到
BeanDefinitionBuilder definition = BeanDefinitionBuilder .genericBeanDefinition(FeignClientFactoryBean.class);
创建了一个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();
}可以看到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;
}可以看到也是通过JDK的动态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);
}会通过方法来分发做负载均衡
总结优点
- 能把代理对象和真实被调用的目标对象分离
- 降低了系统的耦合度，易于扩展
- 能够保护目标对象
- 增强目标对象的功能
缺点
- 系统类数目增加
- 客户端和目标对象之间增加了代理对象，请求处理速度会变慢，增加了系统的复杂度
Spring中的代理选择原则
- Bean中有实现接口的时候，Spring会使用JDK的动态代理
- Bean没有实现接口的时候，Spring会选择CGLIB
- Spring可以通过配置强制使用CGLIB,只需在Spring的配置文件中加入这个代码
<aop:aspectj-autoproxy proxy-target-class="true">
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