Spring中Ordered接口简介

一.前言

        Spring中提供了一个Ordered接口。Ordered接口，顾名思义，就是用来排序的。

        Spring是一个大量使用策略设计模式的框架，这意味着有很多相同接口的实现类，那么必定会有优先级的问题。

        于是，Spring就提供了Ordered这个接口，来处理相同接口实现类的优先级问题。

 

二.Ordered接口介绍

        首先，我们来看下Ordered接口的定义：

package org.springframework.core;

public abstract interface Ordered
{
  public static final int HIGHEST_PRECEDENCE = Integer.MIN_VALUE;
  public static final int LOWEST_PRECEDENCE = Integer.MAX_VALUE;
  
  public abstract int getOrder();
}

        只有1个方法：getOrder()；  2个变量：最高级(数值最小)和最低级(数值最大)。

        OrderComparator类：实现了Comparator的一个比较器。

        提供了3个静态排序方法：sort(List<?> list)、sort(Object[] array)、sortIfNecessary(Object value)。根据OrderComparator对数组和集合进行排序。

        sortIfNecessary方法内部会判断value参数是Object[]还是List类型，然后使用Object[]参数的sort方法和List参数的sort方法进行排序。

        我们看下这个比较器的compare方法：

public int compare(Object o1, Object o2)
{
  return doCompare(o1, o2, null);
}

private int doCompare(Object o1, Object o2, OrderSourceProvider sourceProvider) {
  boolean p1 = o1 instanceof PriorityOrdered;
  boolean p2 = o2 instanceof PriorityOrdered;
  if ((p1) && (!p2)) {
    return -1;
  }
  if ((p2) && (!p1)) {
    return 1;
  }
  

  int i1 = getOrder(o1, sourceProvider);
  int i2 = getOrder(o2, sourceProvider);
  return i1 > i2 ? 1 : i1 < i2 ? -1 : 0;
}

private int getOrder(Object obj, OrderSourceProvider sourceProvider)
{
  Integer order = null;
  if (sourceProvider != null) {
    Object orderSource = sourceProvider.getOrderSource(obj);
    if ((orderSource != null) && (orderSource.getClass().isArray())) {
      Object[] sources = ObjectUtils.toObjectArray(orderSource);
      for (Object source : sources) {
        order = findOrder(source);
        if (order != null) {
          break;
        }
      }
    }
    else {
      order = findOrder(orderSource);
    }
  }
  return order != null ? order.intValue() : getOrder(obj);
}

protected int getOrder(Object obj)
{
  Integer order = findOrder(obj);
  return order != null ? order.intValue() : Integer.MAX_VALUE;
}

        PriorityOrdered是个接口，继承自Ordered接口，未定义任何方法。

package org.springframework.core;

public abstract interface PriorityOrdered
  extends Ordered
{}

这段代码的逻辑：

        1.若对象o1是Ordered接口类型，o2是PriorityOrdered接口类型，那么o2的优先级高于o1

        2.若对象o1是PriorityOrdered接口类型，o2是Ordered接口类型，那么o1的优先级高于o2

        3.其他情况，若两者都是Ordered接口类型或两者都是PriorityOrdered接口类型，调用Ordered接口的getOrder方法得到order值，order值越大，优先级越小

简单概括就是：

        OrderComparator比较器进行排序的时候，若2个对象中有一个对象实现了PriorityOrdered接口，那么这个对象的优先级更高。若2个对象都是PriorityOrdered或Ordered接口的实现类，那么比较Ordered接口的getOrder方法得到order值，值越低，优先级越高。

 

三.Ordered接口在Spring中的使用

        以SpringMVC为例，举例Ordered接口的运用。

<mvc:annotation-driven/>

        这段配置在*-dispatcher.xml中定义的话，那么SpringMVC默认会注入RequestMappingHandlerAdapter和RequestMappingHandlerMapping这两个类。

        关于这部分的内容，请参考楼主的另外一篇博客：http://bijian1013.iteye.com/blog/2310236

        既然SpringMVC以及默认为我们注入了RequestMappingHandlerAdapter和RequestMappingHandlerMapping这两个类，我们是否可以再次配置这两个类？答案当然是可以的。

RequestMappingHandlerMapping:

<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping">
  <property name="interceptors">
    <bean class="package.interceptor.XXInterceptor"/>
  </property>  
  <property name="order" value="-1"/>
</bean>

RequestMappingHandlerAdapter:

<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
  <property name="messageConverters">
    <list>
      <bean class="org.springframework.http.converter.ByteArrayHttpMessageConverter"/>
      <bean class="org.springframework.http.converter.StringHttpMessageConverter">
        <property name="supportedMediaTypes">
          <list>
            <value>text/plain;charset=UTF-8</value>
          </list>
        </property>
      </bean>
      <bean class="org.springframework.http.converter.ByteArrayHttpMessageConverter"/>
      <bean class="org.springframework.http.converter.ResourceHttpMessageConverter"/>
      <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter"/>
      <bean class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter">
        <constructor-arg ref="marshaller"/>
      </bean>
    </list>
  </property>  
  <property name="customArgumentResolvers">
    <bean class="org.format.demo.support.resolve.FormModelMethodArgumentResolver"/>
  </property>
  <property name="webBindingInitializer">
    <bean class="org.format.demo.support.binder.MyWebBindingInitializer"/>
  </property>
  <property name="order" value="-1"/>
</bean>

        当我们配置了annotation-driven以及这两个bean的时候。Spring容器就有了2个RequestMappingHandlerAdapter和2个RequestMappingHandlerMapping。

        DispatcherServlet内部有HandlerMapping(RequestMappingHandlerMapping是其实现类)集合和HandlerAdapter(RequestMappingHandlerAdapter是其实现类)集合。

private List<HandlerMapping> handlerMappings;

private List<HandlerAdapter> handlerAdapters;

        我们看下这两个集合的初始化代码：

private void initHandlerMappings(ApplicationContext context)
{
this.handlerMappings = null;

if (this.detectAllHandlerMappings)
{

  Map<String, HandlerMapping> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
  if (!matchingBeans.isEmpty()) {
    this.handlerMappings = new ArrayList(matchingBeans.values());
    
    AnnotationAwareOrderComparator.sort(this.handlerMappings);
  }
}
else {
  try {
    HandlerMapping hm = (HandlerMapping)context.getBean("handlerMapping", HandlerMapping.class);
    this.handlerMappings = Collections.singletonList(hm);
  }
  catch (NoSuchBeanDefinitionException localNoSuchBeanDefinitionException) {}
}

private void initHandlerAdapters(ApplicationContext context)
{
  this.handlerAdapters = null;
  
  if (this.detectAllHandlerAdapters)
  {

    Map<String, HandlerAdapter> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
    if (!matchingBeans.isEmpty()) {
      this.handlerAdapters = new ArrayList(matchingBeans.values());
      
      AnnotationAwareOrderComparator.sort(this.handlerAdapters);
    }
  }
  else {
    try {
      HandlerAdapter ha = (HandlerAdapter)context.getBean("handlerAdapter", HandlerAdapter.class);
      this.handlerAdapters = Collections.singletonList(ha);
    }
    catch (NoSuchBeanDefinitionException localNoSuchBeanDefinitionException) {}
  }
  
  if (this.handlerAdapters == null) {
    this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
    if (this.logger.isDebugEnabled()) {
      this.logger.debug("No HandlerAdapters found in servlet '" + getServletName() + "': using default");
    }
  }
}

        很明显使用了AnnotationAwareOrderComparator（OrderComparator的子类）比较器进行了排序。

        下面我们看下annotation-driven代码配置的RequestMappingHandlerMapping和RequestMappingHandlerAdapter。

WebMvcConfigurationSupport.java

@Bean
public RequestMappingHandlerMapping requestMappingHandlerMapping()
{
  RequestMappingHandlerMapping handlerMapping = createRequestMappingHandlerMapping();
  handlerMapping.setOrder(0);
  handlerMapping.setInterceptors(getInterceptors());
  handlerMapping.setContentNegotiationManager(mvcContentNegotiationManager());
  handlerMapping.setCorsConfigurations(getCorsConfigurations());
  
  PathMatchConfigurer configurer = getPathMatchConfigurer();
  if (configurer.isUseSuffixPatternMatch() != null) {
    handlerMapping.setUseSuffixPatternMatch(configurer.isUseSuffixPatternMatch().booleanValue());
  }
  if (configurer.isUseRegisteredSuffixPatternMatch() != null) {
    handlerMapping.setUseRegisteredSuffixPatternMatch(configurer.isUseRegisteredSuffixPatternMatch().booleanValue());
  }
  if (configurer.isUseTrailingSlashMatch() != null) {
    handlerMapping.setUseTrailingSlashMatch(configurer.isUseTrailingSlashMatch().booleanValue());
  }
  if (configurer.getPathMatcher() != null) {
    handlerMapping.setPathMatcher(configurer.getPathMatcher());
  }
  if (configurer.getUrlPathHelper() != null) {
    handlerMapping.setUrlPathHelper(configurer.getUrlPathHelper());
  }
  
  return handlerMapping;
}

@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter()
{
  List<HandlerMethodArgumentResolver> argumentResolvers = new ArrayList();
  addArgumentResolvers(argumentResolvers);
  
  List<HandlerMethodReturnValueHandler> returnValueHandlers = new ArrayList();
  addReturnValueHandlers(returnValueHandlers);
  
  RequestMappingHandlerAdapter adapter = new RequestMappingHandlerAdapter();
  adapter.setContentNegotiationManager(mvcContentNegotiationManager());
  adapter.setMessageConverters(getMessageConverters());
  adapter.setWebBindingInitializer(getConfigurableWebBindingInitializer());
  adapter.setCustomArgumentResolvers(argumentResolvers);
  adapter.setCustomReturnValueHandlers(returnValueHandlers);
  
  if (jackson2Present) {
    List<RequestBodyAdvice> requestBodyAdvices = new ArrayList();
    requestBodyAdvices.add(new JsonViewRequestBodyAdvice());
    adapter.setRequestBodyAdvice(requestBodyAdvices);
    
    List<ResponseBodyAdvice<?>> responseBodyAdvices = new ArrayList();
    responseBodyAdvices.add(new JsonViewResponseBodyAdvice());
    adapter.setResponseBodyAdvice(responseBodyAdvices);
  }
  
  AsyncSupportConfigurer configurer = new AsyncSupportConfigurer();
  configureAsyncSupport(configurer);
  
  if (configurer.getTaskExecutor() != null) {
    adapter.setTaskExecutor(configurer.getTaskExecutor());
  }
  if (configurer.getTimeout() != null) {
    adapter.setAsyncRequestTimeout(configurer.getTimeout().longValue());
  }
  adapter.setCallableInterceptors(configurer.getCallableInterceptors());
  adapter.setDeferredResultInterceptors(configurer.getDeferredResultInterceptors());
  
  return adapter;
}

        RequestMappingHandlerMapping默认会设置order属性为0，RequestMappingHandlerAdapter没有设置order属性。

        我们进入RequestMappingHandlerMapping和RequestMappingHandlerAdapter代码里面看看它们的order属性是如何定义的。

public abstract class AbstractHandlerMethodAdapter
  extends WebContentGenerator
  implements HandlerAdapter, Ordered
{
  private int order = Integer.MAX_VALUE;

        AbstractHandlerMethodAdapter是RequestMappingHandlerAdapter的父类。

public abstract class AbstractHandlerMapping
  extends WebApplicationObjectSupport
  implements HandlerMapping, Ordered
{
  private int order = Integer.MAX_VALUE;

        AbstractHandlerMapping是RequestMappingHandlerMapping的父类。

        我们看到，RequestMappingHandlerMapping和RequestMappingHandlerAdapter没有设置order属性的时候，order属性的默认值都是Integer.MAX_VALUE，即优先级最低。 

 

PS：

        如果配置了<mvc:annotation-driven />，又配置了自定义的RequestMappingHandlerAdapter，并且没有设置RequestMappingHandlerAdapter的order值，那么这2个RequestMappingHandlerAdapter的order值都是Integer.MAX_VALUE。那么谁的优先级高呢？

        答案： 谁先定义的，谁优先级高。 <mvc:annotation-driven />配置在自定义的RequestMappingHandlerAdapter配置之前，那么<mvc:annotation-driven />配置的RequestMappingHandlerAdapter优先级高，反之自定义的RequestMappingHandlerAdapter优先级高。

        如果配置了<mvc:annotation-driven />，又配置了自定义的RequestMappingHandlerMapping，并且没有设置RequestMappingHandlerMapping的order值。那么<mvc:annotation-driven />配置的RequestMappingHandlerMapping优先级高，因为<mvc:annotation-driven />内部会设置RequestMappingHandlerMapping的order，即0。

        在多个视图解释器中，也运用到了Ordered接口。如下所示：

DispatcherServlet.java

private void initViewResolvers(ApplicationContext context)
{
  this.viewResolvers = null;
  
  if (this.detectAllViewResolvers)
  {

    Map<String, ViewResolver> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
    if (!matchingBeans.isEmpty()) {
      this.viewResolvers = new ArrayList(matchingBeans.values());
      
      AnnotationAwareOrderComparator.sort(this.viewResolvers);
    }
  }
  else {
    try {
      ViewResolver vr = (ViewResolver)context.getBean("viewResolver", ViewResolver.class);
      this.viewResolvers = Collections.singletonList(vr);
    }
    catch (NoSuchBeanDefinitionException localNoSuchBeanDefinitionException) {}
  }
  
  if (this.viewResolvers == null) {
    this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);
    if (this.logger.isDebugEnabled()) {
      this.logger.debug("No ViewResolvers found in servlet '" + getServletName() + "': using default");
    }
  }
}

 

四.总结

        了解了Spring中Ordered接口的意义，并从实践中分析了这个接口的运用。

        这个Ordered接口也是楼主研究SpringMVC配置多个视图解析器的时候发现的，以前的时候没怎么注意，一直认为自定义配置的RequestMappingHandlerAdapter优先级会高一点，会覆盖<mvc:annotation-driven />配置的RequestMappingHandlerAdapter。 如今已明白优先级的问题。

 

文章来源：http://www.cnblogs.com/fangjian0423/p/spring-Ordered-interface.html