SpringMVC-相关知识：JSON

Posted 2023-03-19 jiaxing-java

JSON

前后端分离时代：

后端部署后端，提供接口

＋

建立连接（json）

＋

前端独立部署，负责渲染后端的数据

<script type="text/javascript">
  // 编写一个JavaScript对象
  var user = 
    name:"秦疆",
    age : 3,
    sex:"男"
  

  // 将js对象转化为JSON对象（字符串）
  var json  = JSON.stringify(name:\'秦疆\',age:3,sex:\'男\')
  // // 将JSON对象（字符串）转化为js对象
  var obj = JSON.parse(\'"name":"秦疆","age":3,"sex":"男"\')

  console.log(user)
  console.log(json) // "name":"秦疆","age":3,"sex":"男"
  console.log(obj) // age: 3 \\n name: "秦疆" \\n sex: "男"

</script>

1、Jackson的使用

1. 导入依赖

   <dependency>
       <groupId>com.fasterxml.jackson.core</groupId>
       <artifactId>jackson-databind</artifactId>
       <version>2.12.7.1</version>
   </dependency>
   

2. 配置解决乱码问题

   <!--配置注解驱动-->
   <mvc:annotation-driven>
       <mvc:message-converters register-defaults="true">
           <bean class="org.springframework.http.converter.StringHttpMessageConverter">
               <constructor-arg value="UTF-8"/>
           </bean>
           <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
               <property name="objectMapper">
                   <bean class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
                       <property name="failOnEmptyBeans" value="false"/>
                   </bean>
               </property>
           </bean>
       </mvc:message-converters>
   </mvc:annotation-driven>
   

3. 在Controller类中创建一个ObjectMapper对象，把实体类的对象转换成String

   @Controller
   public class UserController 
   
       @RequestMapping("j1")
       @ResponseBody  // 增加了这个注解，就不会走视图解析器，会直接返回一个字符串
       public String json1() throws JsonProcessingException 
   
           // jackson ObjectMapper
           ObjectMapper mapper = new ObjectMapper();
   
           // 创建一个对象
           User user = new User("长江七号",3,"男");
   
           String s = mapper.writeValueAsString(user);
   
           return s;
       
   
   
   

   • 或者把类上的注解改成@RestController，使它其中的所有方法都会返回JSON字符串

   @RestController
   public class UserController 
   
       @RequestMapping("j1")
       public String json1() throws JsonProcessingException 
   
           // jackson ObjectMapper
           ObjectMapper mapper = new ObjectMapper();
   
           // 创建一个对象
           User user = new User("长江七号",3,"男");
   
           String s = mapper.writeValueAsString(user);
   
           return s;
       
   
   
   

2、fastjson的使用

1. 导入依赖

   <dependency>
       <groupId>com.alibaba</groupId>
       <artifactId>fastjson</artifactId>
       <version>2.0.25</version>
   </dependency>
   

2. 新建类并在其中测试

   @RequestMapping("j4")
   public String json4() 
       List<User> userList = new ArrayList<>();
   
       // 创建一个对象
       User user1 = new User("长江1七号",3,"男");
       User user2 = new User("长江2七号",3,"男");
       User user3 = new User("长江3七号",3,"男");
       User user4 = new User("长江4七号",3,"男");
   
       userList.add(user1);
       userList.add(user2);
       userList.add(user3);
       userList.add(user4);
   
       System.out.println("*********Java对象转JSON字符串*********");
       String str1 = JSON.toJSONString(userList);
       System.out.println("JSON.toJSONString(list) ==>" + str1);
       String str2 = JSON.toJSONString(user1);
       System.out.println("JSON.toJSONString(user1) ==>" + str2);
   
       System.out.println("\\n*********JSON字符串转Java对象*********");
       User jp_user1 = JSON.parseObject(str2,User.class);
       System.out.println("JSON.parseObject(str2,User.class) ==>" + jp_user1);
   
       System.out.println("\\n*********Java对象转JSON对象*********");
       JSONObject jsonObject1 = (JSONObject) JSON.toJSON(user2);
       System.out.println("(JSONObject) JSON.toJSON(user2) ==>" + jsonObject1.getString("name"));
   
       System.out.println("\\n*********JSON对象转Java对象*********");
       User to_java_user = JSON.toJavaObject(jsonObject1,User.class);
       System.out.println("JSON.toJavaObject(jsonObject1,User.class) ==>" + to_java_user);
   
       return "hello";
   
   

由阿里巴巴团队开发，大多方法见名知意