Spring核心接口之Ordered

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2017/12/16 19:34
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一、Ordered接口介绍

Spring中提供了一个Ordered接口。从单词意思就知道Ordered接口的作用就是用来排序的。

Spring框架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接口分析

1、Ordered接口的定义:

public interface Ordered {

/**

 * Useful constant for the highest precedence value.

 * @see java.lang.Integer#MIN_VALUE

 */

int HIGHEST_PRECEDENCE = Integer.MIN_VALUE;

 

/**

 * Useful constant for the lowest precedence value.

 * @see java.lang.Integer#MAX_VALUE

 */

int LOWEST_PRECEDENCE = Integer.MAX_VALUE;

 

/**

 * Get the order value of this object.

 * <p>Higher values are interpreted as lower priority. As a consequence,

 * the object with the lowest value has the highest priority (somewhat

 * analogous to Servlet {@code load-on-startup} values).

 * <p>Same order values will result in arbitrary sort positions for the

 * affected objects.

 * @return the order value

 * @see #HIGHEST_PRECEDENCE

 * @see #LOWEST_PRECEDENCE

 */

int getOrder();

 

}

 

该接口卡只有1个方法getOrder()及 2个变量HIGHEST_PRECEDENCE最高级(数值最小)和LOWEST_PRECEDENCE最低级(数值最大)。

 

2、OrderComparator类:实现了Comparator接口的一个比较器。

public class OrderComparator implements Comparator<Object> {

/**

 * Shared default instance of OrderComparator.

 */

public static final OrderComparator INSTANCE = new OrderComparator();

 

public int compare(Object o1, Object o2) {

boolean p1 = (o1 instanceof PriorityOrdered);

boolean p2 = (o2 instanceof PriorityOrdered);

if (p1 && !p2) {

return -1;

}

else if (p2 && !p1) {

return 1;

}

 

// Direct evaluation instead of Integer.compareTo to avoid unnecessary object creation.

int i1 = getOrder(o1);

int i2 = getOrder(o2);

return (i1 < i2) ? -1 : (i1 > i2) ? 1 : 0;

}

 

/**

 * Determine the order value for the given object.

 * <p>The default implementation checks against the {@link Ordered}

 * interface. Can be overridden in subclasses.

 * @param obj the object to check

 * @return the order value, or {@code Ordered.LOWEST_PRECEDENCE} as fallback

 */

protected int getOrder(Object obj) {

return (obj instanceof Ordered ? ((Ordered) obj).getOrder() : Ordered.LOWEST_PRECEDENCE);

}

 

/**

 * Sort the given List with a default OrderComparator.

 * <p>Optimized to skip sorting for lists with size 0 or 1,

 * in order to avoid unnecessary array extraction.

 * @param list the List to sort

 * @see java.util.Collections#sort(java.util.List, java.util.Comparator)

 */

public static void sort(List<?> list) {

if (list.size() > 1) {

Collections.sort(list, INSTANCE);

}

}

 

/**

 * Sort the given array with a default OrderComparator.

 * <p>Optimized to skip sorting for lists with size 0 or 1,

 * in order to avoid unnecessary array extraction.

 * @param array the array to sort

 * @see java.util.Arrays#sort(Object[], java.util.Comparator)

 */

public static void sort(Object[] array) {

if (array.length > 1) {

Arrays.sort(array, INSTANCE);

}

}

}

 

提供了2个静态排序方法:sort(List<?> list)用来排序list集合、sort(Object[] array)用来排序Object数组

可以下OrderComparator类的public int compare(Object o1, Object o2)方法,可以看到另外一个类PriorityOrdered,这个方法的逻辑解析如下:

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

简单来说就是:

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、Spring中使用Ordered接口在的例子

在spring配置文件中添加:<mvc:annotation-driven/>,那么SpringMVC默认会注入RequestMappingHandlerAdapter和RequestMappingHandlerMapping这两个类。 既然SpringMVC已经默认为我们注入了RequestMappingHandlerAdapter和RequestMappingHandlerMapping这两个类,如果再次配置这两个类,将会出现什么效果呢?

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。

//RequestMappingHandlerMapping集合

private List<HandlerMapping> handlerMappings;

//HandlerAdapter集合

private List<HandlerAdapter> handlerAdapters;

在仔细看下DispatcherServlet类的private void initHandlerMappings(ApplicationContext context)方法可以看到如下代码:

//detectAllHandlerMappings默认为true

if (this.detectAllHandlerMappings) {

// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.

Map<String, HandlerMapping> matchingBeans =

BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);

if (!matchingBeans.isEmpty()) {

this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());

// We keep HandlerMappings in sorted order.

//进行排序

AnnotationAwareOrderComparator.sort(this.handlerMappings);

}

}

AnnotationAwareOrderComparator继承了OrderComparator类

 

再看下<mvc:annotation-driven/>配置的RequestMappingHandlerMapping和RequestMappingHandlerAdapter

@Bean

public RequestMappingHandlerAdapter requestMappingHandlerAdapter()方法

@Bean

public RequestMappingHandlerMapping requestMappingHandlerMapping()方法 分析代码可以知道:RequestMappingHandlerMapping默认会设置order属性为0,RequestMappingHandlerAdapter没有设置order属性。

 

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

RequestMappingHandlerMapping

// Ordered.LOWEST_PRECEDENCE只为Integer.MAX_VALUE

public abstract class AbstractHandlerMapping extends WebApplicationObjectSupport

implements HandlerMapping, Ordered {

private int order = Integer.MAX_VALUE; 

 

AbstractHandlerMapping是RequestMappingHandlerMapping的父类。

 

RequestMappingHandlerAdapter

public abstract class AbstractHandlerMethodAdapter extends WebContentGenerator implements HandlerAdapter, Ordered {

// Ordered.LOWEST_PRECEDENCE只为Integer.MAX_VALUE

private int order = Ordered.LOWEST_PRECEDENCE;

 

AbstractHandlerMethodAdapter是RequestMappingHandlerAdapter的父类。 可以看到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。 

总结: 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为0。

 

四、应用

1、定义接口

import java.util.Map;

import org.springframework.core.Ordered;

 

public interface Filter extends Ordered{

public void doFiler(Map<String, String> prams);

 

}

 

2、实现接口

import java.util.Map;

@Component

public class LogFilter implements Filter {

private int order =1;

public int getOrder() {

return order;

}

public void setOrder(int order) {

this.order = order;

}

public void doFiler(Map<String, String> prams) {

System.out.println("打印日志");

}

}

 

import java.util.Map;

@Component

public class PowerLogFilter implements Filter {

private int order =2;

public int getOrder() {

return order;

}

public void setOrder(int order) {

this.order = order;

}

public void doFiler(Map<String, String> prams) {

System.out.println("权限控制");

}

}

 

3、测试进行排序

public static void main(String[] args) throws Exception {

String config = Test.class.getPackage().getName().replace('.', '/') + "/bean.xml";

       ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(config);

       context.start();

       Map<String, Filter> filters = context.getBeansOfType(Filter.class);

System.out.println(filters.size());

       List<Filter> f= new ArrayList<Filter>(filters.values());

       OrderComparator.sort(f);

       for(int i=0; i<f.size(); i++){

        Map<String, String> params = new HashMap<String, String>();

        f.get(i).doFiler(params);

       }

}

 

4、配置文件

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:context="http://www.springframework.org/schema/context"

xmlns:aop="http://www.springframework.org/schema/aop" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"

xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd

http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd

http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd

http://code.alibabatech.com/schema/dubbo http://code.alibabatech.com/schema/dubbo/dubbo.xsd">

 

<context:component-scan base-package="com" />

 

</beans>

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参考:http://www.wang1314.com/doc/topic-1568135-1.html

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