SpringBoot使用CommandLineRunner或ApplicationRunner接口创建bean

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