目录

• 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
• 使用spring 3.x 和spring 4.x 的例子

SpringBoot开机启动与@Order注解

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 ...");
    }
}

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 ...");
    }
}

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：

@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

package com.javapapers.spring3.autowire.collection;
public interface Ranks {  
}

RankOne.java

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

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

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

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

<?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

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。

@Component
@Order(1)
public class RankOne implements Ranks{
private String rank = "RankOne";    
    public String toString(){
        return this.rank;
    }
}

输出结果如下：

[RankOne, RankTwo, RankThree]

参考文章： http://javapapers.com/spring/spring-order-annotation/

以上为个人经验，希望能给大家一个参考，也希望大家多多支持自由互联。

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