package com.example.demo;

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

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

package com.example.demo.controler;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
//注解的解释参考下面
@RestController
public class HelloControler {　　//映射路径定义为hello
    @RequestMapping("/hello")
    public String hello() {

        return "hello world!";
    }
}

@Open Declaration   org.springframework.web.bind.annotation.RestController
@Controller
@ResponseBody
@Target(value={TYPE})
@Retention(value=RUNTIME)
@Documented

A convenience annotation that is itself annotated with @Controller and @ResponseBody. 

Types that carry this annotation are treated as controllers where @RequestMapping methods assume @ResponseBody semantics by default. 

NOTE: @RestController is processed if an appropriate HandlerMapping-HandlerAdapter pair is configured such as the RequestMappingHandlerMapping-RequestMappingHandlerAdapterpair which are the default in the MVC Java config and the MVC namespace.
Since:4.0Author:Rossen StoyanchevSam Brannen

package com.example.demo.controler;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.request.MockMvcRequestBuilders;

import static org.hamcrest.Matchers.equalTo;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

@RunWith(SpringRunner.class)
@SpringBootTest//配置注入MockMvc
@AutoConfigureMockMvc
public class HelloControlerTest {
　　

　　//因为使用的时MVC框架
    @Autowired
    private MockMvc mockmvc;
    @Test
    public void testHello() throws Exception {　　　　　//构建MVC的请求，get方法，接受的媒体类型（JSON），断言预期返回（），期望返回内容（字符串和“hello world!”匹配）
        mockmvc.perform(MockMvcRequestBuilders.get("/hello").accept(org.springframework.http.MediaType.APPLICATION_JSON))
        .andExpect(status().isOk())
        .andExpect(content().string(equalTo("hello world!")));
    }

}