Json

JSON

1.前端的JSON对象

//编写一个js对象
var user = {
    name : "东",
    age:18,
    sex:"男"
};
//将js对象转化为json对象
var s = JSON.stringify(user);

//将json对象转换为js对象
var obj = JSON.parse(s);

2.controller生成JSON对象

• 首先需要导包

  <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
  <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>2.11.0</version>
  </dependency>
  

• 有一个pojo类

  @Data
  @AllArgsConstructor
  @NoArgsConstructor
  public class User {
      private String name;
      private int age;
      private String sex;
  }
  

• 在controller生成json

  @Controller
  //@RestController
  //RestController所有的返回值都不走视图解析器
  public class UserController {
      @RequestMapping("/j1")
     @ResponseBody
     //不会走视图解析器,会直接返回字符串
      public String json1() throws JsonProcessingException {
          User user = new User("东", 12, "男");
          //jackson, objectMapper
          ObjectMapper mapper = new ObjectMapper();
          //将对象转化为字符串
          String s = mapper.writeValueAsString(user);
          return s;
      };
  }
  

3.解决乱码

• 通过produces设置

  @RequestMapping(value = "/j1",produces = "application/json;charset=utf-8")
  

• 通过spring配置文件

  <!--  解决JSON乱码  -->
      <mvc:annotation-driven>
          <mvc:message-converters>
              <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>
  

4.JSON对象中有多个java对象

@RequestMapping(value = "/j2")
@ResponseBody
 public String json2() throws JsonProcessingException {
    ObjectMapper mapper = new ObjectMapper();
    List<User> users = new ArrayList<User>();
    User user1 = new User("东1", 12, "男");
     User user2 = new User("东2", 13, "男");
     User user3 = new User("东3", 14, "男");
     User user4 = new User("东4", 15, "男");
     User user5 = new User("东5", 16, "男");
     users.add(user1);
     users.add(user2);
     users.add(user3);
     users.add(user4);
     users.add(user5);
     String s = mapper.writeValueAsString(users);
     return s;
 };

5.JSON返回时间对象

• 使用java方法

 @RequestMapping(value = "/j3")
    @ResponseBody
    public String json3() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        Date date = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        String s = mapper.writeValueAsString(sdf.format(date));
        return s;
    };

• 使用mapper object,String da

@RequestMapping(value = "/j3")
@ResponseBody
public String json3() throws JsonProcessingException {
    ObjectMapper mapper = new ObjectMapper();
    mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);
    Date date = new Date();
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    mapper.setDateFormat(sdf);
    String s = mapper.writeValueAsString(date);
    return s;
};

• 自己创建工具类

public class JsonUtils {
    public  static String getJson(Object object){
        return getJson(object,"yyyy-MM-dd HH:mm:ss");
    }

    public static String getJson(Object object, String dateFormat){
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(dateFormat);
        objectMapper.setDateFormat(simpleDateFormat);
        try {
            return objectMapper.writeValueAsString(object);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        return null;
    }
}

6.使用fastjson

• 导包

  <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>1.2.70</version>
  </dependency>