基於SpringBoot開機啟動與@Order註解

Posted on by

SpringBoot開機啟動與@Order註解

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 ...");
    }
}

在這裡插入圖片描述

spring @Order標記

@Order標記定義瞭組件的加載順序

@Order標記從spring 2.0出現，但是在spring 4.0之前，@Order標記隻支持AspectJ的切面排序。spring 4.0對@Order做瞭增強，它開始支持對裝載在諸如Lists和Arrays容器中的自動包裝（auto-wired）組件的排序。

在spring內部，對基於spring xml的應用，spring使用OrderComparator類來實現排序。對基於註解的應用，spring采用AnnotationAwareOrderComparator來實現排序。

@Order 標記定義如下：

@Retention(value=RUNTIME)
@Target(value={TYPE,METHOD,FIELD})
@Documented
public @interface Order

這個標記包含一個value屬性。屬性接受整形值。如：1,2 等等。值越小擁有越高的優先級。

下面讓我們來看一個

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);
 }
}

輸出結果：

[RankOne, RankThree, RankTwo]

從結果可以看出，結果是沒有順序的。因為spring 3.x不支持對自動包裝組件的排序。

接下來，我升級spring的版本至4.x， 並對RanOne,RankTwo和RankThree加上order標記，值做相應的調整。

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

輸出結果如下：

[RankOne, RankTwo, RankThree]

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

以上為個人經驗，希望能給大傢一個參考，也希望大傢多多支持WalkonNet。

推薦閱讀：