14. json数据交互

在数据请求中特别是ajax中，常用到json格式。

14.1. 添加依赖

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.neuedu.mvc</groupId>
    <artifactId>p19-springmvc-json</artifactId>
    <version>1.0-SNAPSHOT</version>
    <name>p19-springmvc-json</name>
    <packaging>war</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.target>11</maven.compiler.target>
        <maven.compiler.source>11</maven.compiler.source>
        <spring.version>5.2.4.RELEASE</spring.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.0.1</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.1</version>
            <scope>provided</scope>
        </dependency>

        <!--      数据库的驱动   com.mysql.cj.jdbc.Driver-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.28</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.2.21</version>
        </dependency>


        <!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.68</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.9.1</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.3.2</version>
            </plugin>
        </plugins>
    </build>
</project>

14.3. 原生ServletAPI的形式响应json数据

@ResponseBody 返回String认为是视图 ,当想要将string直接响应给客户端 需要添加@ResponseBody

    @ResponseBody
    @GetMapping("/list")
    public String list(HttpServletResponse response){
        response.setContentType("application/json;charset=utf-8");
        List<User> users = userService.selectListEntity();
        String json = JSON.toJSONString(users);
        return json;
    }

14.4. 基础SpringMVC的机制自动的转换类型输出json

添加依赖

 <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.9.1</version>
        </dependency>

在容器中开启 注解驱动<mvc:annotation-driven/>

14.5. 控制器的方法

@ResponseBody
@GetMapping("/list")
public List list(HttpServletResponse response){

    List<User> userList = userService.selectListEntity();
    return userList;
}

@ResponseBody
@GetMapping("/getById")
public User getById(Integer id){

    User user = userService.selectByIdEntiry(id);
    return user;
}

访问后http://127.0.0.1:8080/json/user/getById?id=10的结果为json格式

{
  "userId": 10,
  "userName": "典韦使用别名",
  "gender": "男",
  "birthday": 1583910063000,
  "status": 0
}

推荐使用浏览器的一些JSON Viewer 插件 可以高亮查看 格式化之后的数据（国内访问google网站失败，建议到·https://chrome.zzzmh.cn/·下载）

14.6 @RequestBody

可以使用@RequestBody注释通过HttpMessageConverter读取请求体并将其反序列化为Object，当客户端发送的并不是传统的 form表单的键值对的时候而是 以body流的形式发送的数据 我们需要将body中的内容转换成实体类 在实体类的参数之前添加 @RequestBody注解

 @ResponseBody
    @PostMapping("/save")
    public Map save( @RequestBody   User user  ) {

        Map result = new HashMap();

        boolean success = userService.insert(user);

        result.put("success", success);
        return result;
    }