【SpringBoot】SpringBoot 事件监听机制（十六）

　　本例介绍SpringBoot的事件监听机制及使用

　　主要有ApplicationContextInitializer（上下文初始化器）、SpringApplicationRunListener（Spring应用运行监听器）、ApplicationRunner（启动加载类）、CommandLineRunner（启动加载类）

　　关于调用流程参考【SpringBoot】SpringBoot 启动原理（十五）

ApplicationContextInitializer（上下文初始化器）

　　1、新建一个SpringBoot Web项目

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.test</groupId>
    <artifactId>test-springboot-runner</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.8.RELEASE</version>
    </parent>

    <properties>

        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

    </dependencies>


    <!-- SpringBoot打包插件，可以将代码打包成一个可执行的jar包 -->
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

　　2、新建HelloApplicationContextInitializer类，实现ApplicationContextInitializer接口，如下：

package com.test.springboot.listener;

import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;

public class HelloApplicationContextInitializer implements ApplicationContextInitializer {
    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        System.out.println("====HelloApplicationContextInitializer======initialize：" + applicationContext);
    }
}

　　3、将HelloApplicationContextInitializer加入SpringBoot中，在resources目录下新建文件META-INF/spring.factories，添加一下内容

# Initializers
org.springframework.context.ApplicationContextInitializer=
com.test.springboot.listener.HelloApplicationContextInitializer

　　4、启动SpringBoot程序，查看控制台

　　　　

SpringApplicationRunListener（Spring应用运行监听器）

　　1、在SpringBoot Web项目中，新建HelloSpringApplicationRunListener类，实现SpringApplicationRunListener接口

package com.test.springboot.listener;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringApplicationRunListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.env.ConfigurableEnvironment;

public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {

    public HelloSpringApplicationRunListener(SpringApplication application, String[] args) {

    }

    @Override
    public void starting() {
        System.out.println("===HelloSpringApplicationRunListener===starting");
    }

    @Override
    public void environmentPrepared(ConfigurableEnvironment environment) {
        System.out.println("===os.name：" + environment.getSystemProperties().get("os.name") );
        System.out.println("===HelloSpringApplicationRunListener===environmentPrepared");
    }

    @Override
    public void contextPrepared(ConfigurableApplicationContext context) {
        System.out.println("===HelloSpringApplicationRunListener===contextPrepared");
    }

    @Override
    public void contextLoaded(ConfigurableApplicationContext context) {
        System.out.println("===HelloSpringApplicationRunListener===contextLoaded");
    }

    @Override
    public void started(ConfigurableApplicationContext context) {
        System.out.println("===HelloSpringApplicationRunListener===started");
    }

    @Override
    public void running(ConfigurableApplicationContext context) {
        System.out.println("===HelloSpringApplicationRunListener===running");
    }

    @Override
    public void failed(ConfigurableApplicationContext context, Throwable exception) {
        System.out.println("===HelloSpringApplicationRunListener===failed");
    }
}

　　　　注意：HelloSpringApplicationRunListener必须添加构造方法，否则会包如下错误

　　　　

　　　　HelloSpringApplicationRunListener的构造方法编写，可以参考SpringApplicationRunListener的其他实现类，如：EventPublishingRunListener

public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {

    private final SpringApplication application;

    private final String[] args;

    private final SimpleApplicationEventMulticaster initialMulticaster;

    public EventPublishingRunListener(SpringApplication application, String[] args) {
        this.application = application;
        this.args = args;
        this.initialMulticaster = new SimpleApplicationEventMulticaster();
        for (ApplicationListener<?> listener : application.getListeners()) {
            this.initialMulticaster.addApplicationListener(listener);
        }
    }

    ...

}

　　2、将HelloSpringApplicationRunListener加入SpringBoot中，在resources目录下新建文件META-INF/spring.factories，添加一下内容

# Run Listeners
org.springframework.boot.SpringApplicationRunListener=
com.test.springboot.listener.HelloSpringApplicationRunListener

　　3、测试启动SpringBoot程序，查看控制台

　　　　

ApplicationRunner（启动加载类）

　　1、在SpringBoot Web项目中，新建HelloApplicationRunner类，实现接口 ApplicationRunner

@Component
public class HelloApplicationRunner implements ApplicationRunner {
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("===HelloApplicationRunner===run");
    }
}

　　2、需要在HelloApplicationRunner类上加上注解@Component

　　3、启动SpringBoot项目，查看是否在启动时，调用了run方法

　　　　

CommandLineRunner（启动加载类）

　　1、在SpringBoot Web项目中，新建HelloCommandLineRunner类，实现接口 CommandLineRunner

@Component
public class HelloCommandLineRunner implements CommandLineRunner {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("===HelloCommandLineRunner===run：" + Arrays.asList(args));
    }
}

　　2、需要在HelloCommandLineRunner类上加上注解@Component

　　3、启动SpringBoot项目，查看是否在启动时，调用了run方法

　　　　

　　4、同时注入ApplicationRunner和CommandLineRunner，ApplicationRunner先回调，CommandLineRunner再回调