Spring Boot: 编写一个 Hello World 应用（Java & Maven）

本文介绍如何使用 Spring Boot CLI 快速创建一个 Web 应用，编写一个非常简单的 “Hello World”，使用 Maven 构建并运行起来。

1. 介绍

内容简介： 一个简单的 Spring Boot Web 应用示例
语言框架： Java、Spring Boot、Spring MVC
难度级别： L1
阅读时间： 10 分钟

2. 工具准备

Java SDK : 8.0+Spring Boot CLI : 2.1.2Maven : 3.6.0STS : 4.0Curl / HTTPPie

3. 实现步骤

3.1. 创建项目

首先，通过 Spring CLI 创建一个空白工程： Hello World 应用。

$ spring init --name hello-world --artifactId spring-boot-hello-world \ --groupId org.springdev.guides --package-name org.springdev.guides.helloworld \ --language java --build maven \ --dependencies web,devtools --extract

3.2. 打开项目

打开 STS，点击菜单 File Import，选择导入向导 Maven 下的 Existing Maven Projects，在下一步中选择刚刚创建的工程目录，确定后导入到 STS 中。

3.3. 项目结构

此时创建的新工程目录结构如下:

├── mvnw ├── mvnw.cmd ├── pom.xml └── src ├── main │ ├── java │ │ └── org │ │ └── springdev │ │ └── guides │ │ └── helloworld │ │ └── HelloWorldApplication.java │ └── resources │ ├── application.properties │ ├── static │ └── templates └── test └── java └── org └── springdev └── guides └── helloworld └── HelloWorldApplicationTests.java

在工程根目录打开 pom.xml，其内容如下：

4.0.0 org.springframework.boot spring-boot-starter-parent 2.1.2.RELEASE org.springdev.guides spring-boot-hello-world 0.0.1-SNAPSHOT hello-world Demo project for Spring Boot 1.8 org.springframework.boot spring-boot-starter-web org.springframework.boot spring-boot-devtools runtime org.springframework.boot spring-boot-starter-test test org.springframework.boot spring-boot-maven-plugin 代码说明如下：
Spring Boot 版本使用 2.1.2.RELEASE；项目的起步依赖：web、devtools、test；Spring Boot 插件，用于打包和运行应用。

在 Package Explorer 中打开应用主程序文件： HelloWorldApplication.java，可以看到这个文件代码非常简单。

package org.springdev.guides.helloworld; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class HelloWorldApplication { public static void main(String[] args) { SpringApplication.run(HelloWorldApplication.class, args); } }

3.4. 编写代码

3.4.1. 编写 Controller

接下来我们开始编写 Controller。在 src/main/java/org/springdev/guides/helloworld/ 目录中新增一个 HelloController.java，内容如下：

package org.springdev.guides.helloworld; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; @RestController public class HelloController { @GetMapping("/hello") public String hello() { return "Hello, World!"; } }

代码说明如下：

Spring MVC 提供了@RestController注解，这是一个 REST 接口类；设置 Get 请求，请求地址为/hello；响应成功，并返回内容为：Hello, World!。

3.5. 单元测试

3.5.1. 编写测试用例

package org.springdev.guides.helloworld; ... @RunWith(SpringRunner.class) @SpringBootTest @AutoConfigureMockMvc public class HelloControllerTests { @Autowired private MockMvc mockMvc; @Test public void hello() throws Exception { this.mockMvc.perform(get("/hello")) .andDo(print()) .andExpect(status().isOk()) .andExpect(content().string("Hello, World!")); } }

代码说明如下：

Spring Boot 提供了@SpringBootTest注解，该注解简化了 Spring Boot 应用的测试，提供了对应 spring-test 中@ContextConfiguration的功能，用于创建ApplicationContext； 自动配置MockMvc实例，用于模拟执行请求/hello；验证响应状态码为200，表示成功；验证返回内容为：Hello, World!。

3.5.2. 执行单元测试

mvn test

运行结果

2019-01-14 19:40:11.860 INFO 71447 --- [ main] o.s.g.helloworld.HelloControllerTests : Started HelloControllerTests in 1.902 seconds (JVM running for 2.661) MockHttpServletRequest: HTTP Method = GET Request URI = /hello Parameters = {} Headers = [] Body = null Session Attrs = {} Handler: Type = org.springdev.guides.helloworld.HelloController Method = public java.lang.String org.springdev.guides.helloworld.HelloController.hello() Async: Async started = false Async result = null Resolved Exception: Type = null ModelAndView: View name = null View = null Model = null FlashMap: Attributes = null MockHttpServletResponse: Status = 200 Error message = null Headers = [Content-Type:"text/plain;", Content-Length:"13"] Content type = text/plain;charset=UTF-8 Body = Hello, World! Forwarded URL = null Redirected URL = null Cookies = [] [INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 2.653 s - in org.springdev.guides.helloworld.HelloControllerTests 2019-01-14 19:40:12.159 INFO 71447 --- [ Thread-4] o.s.s.concurrent.ThreadPoolTaskExecutor : Shutting down ExecutorService 'applicationTaskExecutor' [INFO] [INFO] Results: [INFO] [INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0 [INFO] [INFO] ------------------------------------------------------------------------ [INFO] BUILD SUCCESS [INFO] ------------------------------------------------------------------------ [INFO] Total time: 5.106 s [INFO] Finished at: 2019-01-14T19:40:12+08:00 [INFO] ------------------------------------------------------------------------

4. 构建运行

选中工程，然后打开菜单 Run Run as Spring Boot App，应用就开始启动了，可以在控制台看到启动应用的日志。

或者，在控制台下执行命令:

mvn spring-boot:run

运行结果如下：

. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.1.2.RELEASE) 2019-01-14 19:47:13.422 INFO 71332 --- [ restartedMain] o.s.g.helloworld.HelloWorldApplication : Starting HelloWorldApplication on Michaels-MBP.lan with PID 71332 (/Users/rain/Development/springdev/guides/spring/spring-boot-hello-world/complete/target/classes started by rain in /Users/rain/Development/springdev/guides/spring/spring-boot-hello-world/complete) 2019-01-14 19:47:13.426 INFO 71332 --- [ restartedMain] o.s.g.helloworld.HelloWorldApplication : No active profile set, falling back to default profiles: default 2019-01-14 19:47:13.481 INFO 71332 --- [ restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : Devtools property defaults active! Set 'spring.devtools.add-properties' to 'false' to disable 2019-01-14 19:47:13.482 INFO 71332 --- [ restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : For additional web related logging consider setting the 'logging.level.web' property to 'DEBUG' 2019-01-14 19:47:14.790 INFO 71332 --- [ restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http) 2019-01-14 19:47:14.825 INFO 71332 --- [ restartedMain] o.apache.catalina.core.StandardService : Starting service [Tomcat] 2019-01-14 19:47:14.826 INFO 71332 --- [ restartedMain] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.14] 2019-01-14 19:47:14.837 INFO 71332 --- [ restartedMain] o.a.catalina.core.AprLifecycleListener : The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [/Users/rain/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.] 2019-01-14 19:47:14.911 INFO 71332 --- [ restartedMain] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2019-01-14 19:47:14.911 INFO 71332 --- [ restartedMain] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1429 ms 2019-01-14 19:47:15.113 INFO 71332 --- [ restartedMain] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor' 2019-01-14 19:47:15.289 INFO 71332 --- [ restartedMain] o.s.b.d.a.OptionalLiveReloadServer : LiveReload server is running on port 35729 2019-01-14 19:47:15.359 INFO 71332 --- [ restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '' 2019-01-14 19:47:15.364 INFO 71332 --- [ restartedMain] o.s.g.helloworld.HelloWorldApplication : Started HelloWorldApplication in 2.346 seconds (JVM running for 2.746)

5. 测试验证

打开浏览器，访问地址： http://localhost:8080/hello 会看到下图所示的界面：

或者，通过 curl 来验证：

$ curl -v http://localhost:8080/hello * Trying ::1... * TCP_NODELAY set * Connected to localhost (::1) port 8080 (#0) > GET /hello HTTP/1.1 > Host: localhost:8080 > User-Agent: curl/7.54.0 > Accept: */* > < HTTP/1.1 200 < Content-Type: text/plain;charset=UTF-8 < Content-Length: 13 < Date: Mon, 14 Jan 2019 11:47:50 GMT < * Connection #0 to host localhost left intact Hello, World!

或者，通过 HTTPie 验证：

$ http :8080/hello HTTP/1.1 200 Content-Length: 13 Content-Type: text/plain;charset=UTF-8 Date: Mon, 14 Jan 2019 11:47:24 GMT Hello, World!

6. 小结

恭喜，你已经学会使用 Spring Boot CLI 创建一个 Spring Boot Web 简单应用，并且使用 Maven 构建运行起来。

7. 源码下载

原文： Spring Guides

源码： springdev-guides/spring-boot-hello-world

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