主要实现功能：浏览器发送/hello请求，服务器接受请求并处理，输出hello world字符串。

1.新建maven项目

2.pom.xml中加入starter和相关依赖

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.4.RELEASE</version>
        <!--<relativePath/> &lt;!&ndash; lookup parent from repository &ndash;&gt;-->
    </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>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

3.编写一个主程序，启动Springboot应用

helloworlddemo.java

package com.yzl;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

//来标注一个主程序类，说明这是一个SpringBoot应用
@SpringBootApplication
public class helloworlddemo {
    public static void main(String[] args) {
        //spring应用启动起来
        SpringApplication.run(helloworlddemo.class,args);
    }
}

4.编写Controller

package com.yzl.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;


@Controller
public class HelloController {
    @ResponseBody
    @RequestMapping("/hello")
    public  String hello (){

        return "HELLO WORLD";
    }
}

5.启动主程序

浏览器通过http://localhost:8080/hello访问,输出：

HELLO WORLD