在spring boot应用中，我们可以在程序启动之前执行任何任务。为了达到这个目的，我们需要使用CommandLineRunner或ApplicationRunner接口创建bean，spring boot会自动监测到它们。这两个接口都有一个run()方法，在实现接口时需要覆盖该方法，并使用@Component注解使其成为bean。CommandLineRunner和ApplicationRunner的作用是相同的。不同之处在于CommandLineRunner接口的run()方法接收String数组作为参数，而ApplicationRunner接口的run()方法接收ApplicationArguments对象作为参数。当程序启动时，我们传给main()方法的参数可以被实现CommandLineRunner和ApplicationRunner接口的类的run()方法访问。我们可以创建多个实现CommandLineRunner和ApplicationRunner接口的类。为了使他们按一定顺序执行，可以使用@Order注解或实现Ordered接口。
CommandLineRunner和ApplicationRunner接口的run()方法在SpringApplication完成启动时执行。启动完成之后，应用开始运行。CommandLineRunner和ApplicationRunner的作用是在程序开始运行前执行任务或记录信息。
下面展示了如何在程序中使用CommandLineRunner和ApplicationRunner。
Maven配置
pom.xml
<?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.concretepage</groupId>
<artifactId>spring-boot-demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>spring-demo</name>
<description>Spring Boot Demo Project</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.2.RELEASE</version>
</parent>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
CommandLineRunner
CommandLineRunner是个接口，有一个run()方法。为了使用CommandLineRunner我们需要创建一个类实现该接口并覆盖run()方法。使用@Component注解实现类。当SpringApplication.run()启动spring boot程序时，启动完成之前，CommandLineRunner.run()会被执行。CommandLineRunner的run()方法接收启动服务时传过来的参数。
run(String... args)
参数为String数组。
CommandLineRunnerBean.java
package com.concretepage.bean;
import java.util.Arrays;
import java.util.stream.Collectors;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;
@Component
public class CommandLineRunnerBean implements CommandLineRunner {
private static final Logger logger = LoggerFactory.getLogger(CommandLineRunnerBean.class);
public void run(String... args) {
String strArgs = Arrays.stream(args).collect(Collectors.joining("|"));
logger.info("Application started with arguments:" + strArgs);
}
}
MyApplication.java
package com.concretepage;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import com.concretepage.service.HelloService;
@SpringBootApplication
public class MyApplication {
private static final Logger logger = LoggerFactory.getLogger(MyApplication.class);
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(MyApplication.class, args);
HelloService service = context.getBean(HelloService.class);
logger.info(service.getMessage());
}
}
我们也可以创建一个service。一旦Spring boot启动完成service就会执行。这意味着SpringApplication.run()执行完成后service的方法就会执行。
HelloService.java
package com.concretepage.service;
import org.springframework.stereotype.Service;
@Service
public class HelloService {
public String getMessage(){
return "Hello World!";
}
}
现在使用带有参数的可执行jar运行程序。spring-boot-demo-0.0.1-SNAPSHOT.jar为生成的jar文件。执行命令如下：
java -jar spring-boot-demo-0.0.1-SNAPSHOT.jar data1 data2 data3
输出结果为：
2017-03-19 13:38:38.909 INFO 1036 --- [ main] c.c.bean.CommandLineRunnerBean : Application started with arguments:data1|data2|data3
2017-03-19 13:38:38.914 INFO 1036 --- [ main] com.concretepage.MyApplication : Started MyApplication in 1.398 seconds (JVM running for 1.82)
2017-03-19 13:38:38.915 INFO 1036 --- [ main] com.concretepage.MyApplication : Hello World!
ApplicationRunner
ApplicationRunner和CommandLineRunner的作用相同。在SpringApplication.run()完成spring boot启动之前，ApplicationRunner的run()方法会被执行。
run(ApplicationArguments args)
可以看到，CommandLineRunner.run()接收String数组作为参数，而ApplicationRunner.run()接收ApplicationArguments作为参数。这些参数是启动spring boot程序时传给main()方法的。
ApplicationRunnerBean.java
package com.concretepage.bean;
import java.util.Arrays;
import java.util.stream.Collectors;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.stereotype.Component;
@Component
public class ApplicationRunnerBean implements ApplicationRunner {
private static final Logger logger = LoggerFactory.getLogger(ApplicationRunnerBean.class);
@Override
public void run(ApplicationArguments arg0) throws Exception {
String strArgs = Arrays.stream(arg0.getSourceArgs()).collect(Collectors.joining("|"));
logger.info("Application started with arguments:" + strArgs);
}
}
创建可执行jar包并使用如下参数运行：
java -jar spring-boot-demo-0.0.1-SNAPSHOT.jar data1 data2 data3
输出结果为：
2017-03-19 16:26:06.952 INFO 5004 --- [ main] c.c.bean.ApplicationRunnerBean : Application started with arguments:data1|data2|data3
2017-03-19 16:26:06.956 INFO 5004 --- [ main] com.concretepage.MyApplication : Started MyApplication in 1.334 seconds (JVM running for 1.797)
2017-03-19 16:26:06.957 INFO 5004 --- [ main] com.concretepage.MyApplication : Hello World!
CommandLineRunner和ApplicationRunner的执行顺序
在spring boot程序中，我们可以使用不止一个实现CommandLineRunner和ApplicationRunner的bean。为了有序执行这些bean的run()方法，可以使用@Order注解或Ordered接口。例子中我们创建了两个实现CommandLineRunner接口的bean和两个实现ApplicationRunner接口的bean。我们使用@Order注解按顺序执行这四个bean。
CommandLineRunnerBean1.java
@Component
@Order(1)
public class CommandLineRunnerBean1 implements CommandLineRunner {
public void run(String... args) {
System.out.println("CommandLineRunnerBean 1");
}
}
ApplicationRunnerBean1.java
@Component
@Order(2)
public class ApplicationRunnerBean1 implements ApplicationRunner {
@Override
public void run(ApplicationArguments arg0) throws Exception {
System.out.println("ApplicationRunnerBean 1");
}
}
CommandLineRunnerBean2.java
@Component
@Order(3)
public class CommandLineRunnerBean2 implements CommandLineRunner {
public void run(String... args) {
System.out.println("CommandLineRunnerBean 2");
}
}
ApplicationRunnerBean2.java
@Component
@Order(4)
public class ApplicationRunnerBean2 implements ApplicationRunner {
@Override
public void run(ApplicationArguments arg0) throws Exception {
System.out.println("ApplicationRunnerBean 2");
}
}
输出结果为：
CommandLineRunnerBean 1
ApplicationRunnerBean 1
CommandLineRunnerBean 2
ApplicationRunnerBean 2
