基于SpringBoot开机启动与@Order注解_Java教程

SpringBoot开机启动与@Order注解

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									package com.example.zcw.runner;

									import lombok.extern.slf4j.Slf4j;

									import org.springframework.boot.ApplicationArguments;

									import org.springframework.boot.ApplicationRunner;

									import org.springframework.core.annotation.Order;

									import org.springframework.stereotype.Component;

									/**

									 * @Classname BootApplicationRunner

									 * @Description TODO

									 * @Date 2020/3/6 13:06

									 * @Created by zhaocunwei

									 */

									@Order(2)

									@Slf4j

									@Component

									public class BootApplicationRunner implements ApplicationRunner {

									    @Override

									    public void run(ApplicationArguments args) throws Exception {

									        log.info("This is BootApplicationRunner ...");

									    }

									}

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									package com.example.zcw.runner;

									import lombok.extern.slf4j.Slf4j;

									import org.springframework.boot.CommandLineRunner;

									import org.springframework.core.annotation.Order;

									import org.springframework.stereotype.Component;

									/**

									 * @Classname BootCommandLineRunner

									 * @Description TODO

									 * @Date 2020/3/6 13:09

									 * @Created by zhaocunwei

									 */

									@Order(1)

									@Slf4j

									@Component

									public class BootCommandLineRunner implements CommandLineRunner {

									    @Override

									    public void run(String... args) throws Exception {

									        log.info("This is BootCommandLineRunner ...");

									    }

									}

基于SpringBoot开机启动与@Order注解

spring @Order标记

@Order标记定义了组件的加载顺序

@Order标记从spring 2.0出现，但是在spring 4.0之前，@Order标记只支持AspectJ的切面排序。spring 4.0对@Order做了增强，它开始支持对装载在诸如Lists和Arrays容器中的自动包装（auto-wired）组件的排序。

在spring内部，对基于spring xml的应用，spring使用OrderComparator类来实现排序。对基于注解的应用，spring采用AnnotationAwareOrderComparator来实现排序。

@Order 标记定义如下：

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									@Retention(value=RUNTIME)

									@Target(value={TYPE,METHOD,FIELD})

									@Documented

									public @interface Order

这个标记包含一个value属性。属性接受整形值。如：1,2 等等。值越小拥有越高的优先级。

下面让我们来看一个

使用spring 3.x 和spring 4.x 的例子

Ranks.java

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									package com.javapapers.spring3.autowire.collection;

									public interface Ranks {  

									}

RankOne.java

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									package com.javapapers.spring3.autowire.collection;

									import org.springframework.core.annotation.Order;

									import org.springframework.stereotype.Component;

									@Component

									public class RankOne implements Ranks{

									 private String rank = "RankOne";

									 public String toString(){

									  return this.rank;

									 } 

									}

RankTwo.java

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									package com.javapapers.spring3.autowire.collection;

									import org.springframework.core.annotation.Order;

									import org.springframework.stereotype.Component;

									@Component

									public class RankTwo implements Ranks{

									 private String rank = "RankTwo";

									 public String toString(){

									  return this.rank;

									 }

									}

RankThree.java

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									package com.javapapers.spring3.autowire.collection;

									import org.springframework.core.annotation.Order;

									import org.springframework.stereotype.Component;

									@Component

									public class RankThree implements Ranks{

									 private String rank = "RankThree";

									 public String toString(){

									  return this.rank;

									 }

									}

Results.java

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									Component to hold student ranks in a collection as shown below.

									package com.javapapers.spring3.autowire.collection;

									import java.util.List;

									import org.springframework.beans.factory.annotation.Autowired;

									import org.springframework.stereotype.Component;

									@Component

									public class Results {

									  @Autowired

									  private List ranks ;

									  @Override

									  public String toString(){

									   return ranks.toString();

									  }

									}

beans.xml

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									<?xml version="1.0" encoding="UTF-8"?>

									<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

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

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

									 xsi:schemaLocation="http://www.springframework.org/schema/beans 

									  http://www.springframework.org/schema/beans/spring-beans.xsd

									  http://www.springframework.org/schema/context 

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

									  <context:annotation-config />

									  <context:component-scan base-package="com.javapapers.spring3"/> 

									</beans>

RanksClient.java

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									package com.javapapers.spring3.autowire.collection;

									import org.springframework.context.ApplicationContext;

									import org.springframework.context.support.ClassPathXmlApplicationContext;

									public class RanksClient {

									 public static void main(String[] args) {

									  ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");

									  Results results = (Results)context.getBean("results");

									  System.out.println(results);

									 }

									}

输出结果：

[RankOne, RankThree, RankTwo]

从结果可以看出，结果是没有顺序的。因为spring 3.x不支持对自动包装组件的排序。

接下来，我升级spring的版本至4.x，并对RanOne,RankTwo和RankThree加上order标记，值做相应的调整。

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									@Component

									@Order(1)

									public class RankOne implements Ranks{

									private String rank = "RankOne";    

									    public String toString(){

									        return this.rank;

									    }

									}