前往小程序,Get更优阅读体验!
立即前往
首页
学习
活动
专区
工具
TVP
发布
社区首页 >专栏 >Spring核心接口之Ordered

Spring核心接口之Ordered

作者头像
BUG弄潮儿
发布2022-06-30 14:40:28
5230
发布2022-06-30 14:40:28
举报
文章被收录于专栏:JAVA乐园

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>

本文参与 腾讯云自媒体同步曝光计划,分享自微信公众号。
原始发表:2017-12-16,如有侵权请联系 cloudcommunity@tencent.com 删除

本文分享自 BUG弄潮儿 微信公众号,前往查看

如有侵权,请联系 cloudcommunity@tencent.com 删除。

本文参与 腾讯云自媒体同步曝光计划  ,欢迎热爱写作的你一起参与!

评论
登录后参与评论
0 条评论
热度
最新
推荐阅读
相关产品与服务
容器服务
腾讯云容器服务(Tencent Kubernetes Engine, TKE)基于原生 kubernetes 提供以容器为核心的、高度可扩展的高性能容器管理服务,覆盖 Serverless、边缘计算、分布式云等多种业务部署场景,业内首创单个集群兼容多种计算节点的容器资源管理模式。同时产品作为云原生 Finops 领先布道者,主导开源项目Crane,全面助力客户实现资源优化、成本控制。
领券
问题归档专栏文章快讯文章归档关键词归档开发者手册归档开发者手册 Section 归档