Spring框架中的11种设计模式（设计模式之美）

适配器模式

例如Controller的三种实现方式：

@Controller注解
实现Controller接口 + xml配置文件:配置DemoController与URL的对应关系
实现Servlet接口 + xml配置文件:配置DemoController类与URL的对应关系

不同的Controller如何调用呢？可以通过适配器模式。

java">terface HandlerAdapter {boolean supports(Object var1);ModelAndView handle(HttpServletRequest var1, HttpServletResponse var2, Object var3) throws Exception;long getLastModified(HttpServletRequest var1, Object var2);
}// 对应实现Controller接口的Controller
public class SimpleControllerHandlerAdapter implements HandlerAdapter {public SimpleControllerHandlerAdapter() {}public boolean supports(Object handler) {return handler instanceof Controller;}public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {return ((Controller)handler).handleRequest(request, response);}public long getLastModified(HttpServletRequest request, Object handler) {return handler instanceof LastModified ? ((LastModified)handler).getLastModified(request) : -1L;}
}// 对应实现Servlet接口的Controller
public class SimpleServletHandlerAdapter implements HandlerAdapter //AnnotationMethodHandlerAdapter对应通过注解实现的Controller，

策略模式

Spring AOP是通过动态代理来实现的。Spring支持两种动态代理实现方式，一种是JDK提供的动态代理实现方式，另一种是Cglib提供的动态代理实现方式。Spring会在运行时动态地选择不同的动态代理实现方式：策略模式包含三部分，策略的定义、创建和使用。

java">public interface AopProxy {Object getProxy();Object getProxy(ClassLoader var1);
}public interface AopProxyFactory {AopProxy createAopProxy(AdvisedSupport var1) throws AopConfigException;
}public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {public DefaultAopProxyFactory() {}public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {if (!config.isOptimize() && !config.isProxyTargetClass() && !this.hasNoUserSuppliedProxyInterfaces(config)) {return new JdkDynamicAopProxy(config);} else {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.");} else {return (AopProxy)(!targetClass.isInterface() && !Proxy.isProxyClass(targetClass) ? new ObjenesisCglibAopProxy(config) : new JdkDynamicAopProxy(config));}}}//用来判断用哪个动态代理实现方式private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {Class<?>[] ifcs = config.getProxiedInterfaces();return ifcs.length == 0 || ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0]);}
}

组合模式

Spring Cache提供了一套抽象的Cache接口。使用它我们能够统一不同缓存实现（Redis、Google Guava…）的不同的访问方式。Spring中针对不同缓存实现的不同缓存访问类，都依赖这个接口，比如：EhCacheCache、GuavaCache、NoOpCache、RedisCache、JCacheCache、ConcurrentMapCache、CaffeineCache。Cache接口的源码如下所示：

java">public interface Cache {String getName();Object getNativeCache();Cache.ValueWrapper get(Object var1);<T> T get(Object var1, Class<T> var2);<T> T get(Object var1, Callable<T> var2);void put(Object var1, Object var2);Cache.ValueWrapper putIfAbsent(Object var1, Object var2);void evict(Object var1);void clear();public static class ValueRetrievalException extends RuntimeException {private final Object key;public ValueRetrievalException(Object key, Callable<?> loader, Throwable ex) {super(String.format("Value for key '%s' could not be loaded using '%s'", key, loader), ex);this.key = key;}public Object getKey() {return this.key;}}public interface ValueWrapper {Object get();}
}