简介
- JSON(JavaScript Object Notation, JS 对象简谱) 是一种轻量级的数据交换格式。形式和键值对很相似，但是它返回的是键值对的字符串形式
- 形式：以一对大括号包裹，里面是键值对。
jackson的使用
前期工作
在springmvc-servlet.xml引入jackson依赖
<!-- JSON解决乱码-->
<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>
JSON还引入了处理中文乱码的过滤器，在web.xml配置
<!-- SpringMVC自带的解决中文乱码-->
<filter>
<filter-name>encoding</filter-name>
<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>utf-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>encoding</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
创建实体类User.java
package pojo;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
private int id;
private String name;
private int age;
}
主要使用过程
业务控制类的编写，这里我写了四个测试，分别对应四种情况，仔细阅读
package controller;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;
import pojo.User;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
//@Controller和@ResponseBody搭配使用，不会走视图解析器，会返回一个字符串
// 也可以把@Controller和@ResponseBody去掉， 在类上写@RestController ,效果一样
@Controller
//@RestController
public class Usercontroller {
@ResponseBody
@RequestMapping("/j1")
public String json1() throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
User user = new User(1,"xiaomi",3);
String str = mapper.writeValueAsString(user);
return str;
}
@ResponseBody
@RequestMapping("/j2")
public String json2() throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
List<User> userList = new ArrayList<User>();
User user1 = new User(1,"小米",13);
User user2 = new User(2,"小明",23);
User user3 = new User(3,"小虎",15);
User user4 = new User(4,"小兰",16);
User user5 = new User(5,"小红",19);
userList.add(user1);
userList.add(user2);
userList.add(user3);
userList.add(user4);
userList.add(user5);
String str = mapper.writeValueAsString(userList);
return str;
}
@ResponseBody
@RequestMapping("/j3")
public String json3() throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
//ObjectMapper解析时间，默认格式为时间戳
Date date = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
return mapper.writeValueAsString(sdf.format(date));
}
@ResponseBody
@RequestMapping("/j4")
public String json4() throws JsonProcessingException {
//不使用时间戳
ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);
Date date = new Date();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
mapper.setDateFormat(sdf);
return mapper.writeValueAsString(date);
}
}
其中，
- @Controller和@ResponseBody搭配使用，不会走视图解析器，会返回一个字符串
- 也可以把@Controller和@ResponseBody去掉， 在类上写@RestController ,效果一样，也会返回一个字符串
引入一种思想
在我上面所写的业务控制类，看起来是不是重复的代码有点多，这时候，我们就可以把他们提取出来，成为一种工具类！！！
参考工具类：
package utils;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import java.text.SimpleDateFormat;
public class JsonUtil {
public static String getJson(Object object){
return getJson(object,"yyyy-MM-dd HH:mm:ss");
}
public static String getJson(Object object,String dateFormat){
ObjectMapper mapper = new ObjectMapper();
SimpleDateFormat sdf = new SimpleDateFormat(dateFormat);
mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);
mapper.setDateFormat(sdf);
try {
return mapper.writeValueAsString(object);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
return null;
}
}
工具类提取出来后，业务控制类就可以变为：
package controller;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;
import pojo.User;
import utils.JsonUtil;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
@RestController
@RequestMapping("/uc2")
public class Usercontroller2 {
@RequestMapping("/j1")
public String json1() {
User user = new User(1, "xiaomi", 3);
return JsonUtil.getJson(user);
}
@RequestMapping("/j2")
public String json2() {
List<User> userList = new ArrayList<User>();
User user1 = new User(1, "小米", 13);
User user2 = new User(2, "小明", 23);
User user3 = new User(3, "小虎", 15);
User user4 = new User(4, "小兰", 16);
User user5 = new User(5, "小红", 19);
userList.add(user1);
userList.add(user2);
userList.add(user3);
userList.add(user4);
userList.add(user5);
return JsonUtil.getJson(userList);
}
@RequestMapping("/j3")
public String json3() {
Date date = new Date();
return JsonUtil.getJson(date);
}
}
结果是一样的，注意体会工具类的思想！！！
