SpringMVC原理分析 | JSON、Jackson、FastJson
wei_shuo的个人主页
wei_shuo的学习社区
Hello World ！
JSON
JSON（
JavaScriptObject Notation，JS对象简谱）是一种轻量级的数据交换格式。它基于ECMAScript（European Computer Manufacturers Association，欧洲计算机协会制定的js规范）的一个子集，采用完全独立于编程语言的文本格式来存储和表示数据。简洁和清晰的层次结构使得 JSON 成为理想的数据交换语言。 易于人阅读和编写，同时也易于机器解析和生成，并有效地提升网络传输效率
特点：
- 对象表示键值对，数据由逗号分隔
- 花括号保存对象{}
- 方括号保存数据[]
语法格式：
{"name":"wei_shuo"} {"age":"3"} {"sex":"男"}
JSON & JavaScript对象相互转换
JavaScript对象 ——> JSON对象
<script type="text/javascript">
//编写一个JavaScript对象
var user = {
name: "wei_shuo",
age: 18,
sex: "男"
};
//将JavaScript对象转换为JSON对象
let json = JSON.stringify(user);
console.log(json);
</script>
JSON对象 ——> JavaScript对象
<script type="text/javascript">
//编写一个JavaScript对象
var user = {
name: "wei_shuo",
age: 18,
sex: "男"
};
//将JSON对象对象转换为JavaScript对象
let obj = JSON.parse(json);
console.log(obj)
</script>
var、let、const | 全局、函数、块级作用域
函数作用域：var
块级作用域：let、const
全局作用域：函数之外，使用var进行定义，在全局中都能使用的变量，称为
全局变量,全局变量对应的作用域就是全局作用域函数作用域：函数之内，使用var进行定义，只能在该函数中使用的变量，称为
函数变量（局部变量），局部变量对应的作用域就是函数作用域（局部作用域）块级作用域：ES6中，可以通过关键词let来定义变量，通过let定义的变量，只能在当前代码块（以 { } 为界限）中使用，对应的作用域为
块级作用域
Jackson
Jackson 是用来解析 JSON 的框架是一种数据格式，用来在客户端和服务器之间，或系统组件之间交换数据
环境搭建
- pom.xml中导包：导入Jackson和lambok的jar包
<dependencies> <dependency> <groupId>com.fasterxml.jackson.coregroupId> <artifactId>jackson-databindartifactId> <version>2.14.0-rc3version> dependency> <dependency> <groupId>org.projectlombokgroupId> <artifactId>lombokartifactId> <version>1.18.24version> dependency> dependencies>
- 配置核心配置文件：web.xml
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0"> <servlet> <servlet-name>SpringMVCservlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServletservlet-class> <init-param> <param-name>contextConfigLocationparam-name> <param-value>classpath:springmvc-servlet.xmlparam-value> init-param> <load-on-startup>1load-on-startup> servlet> <servlet-mapping> <servlet-name>SpringMVCservlet-name> <url-pattern>/url-pattern> servlet-mapping> <filter> <filter-name>encodingfilter-name> <filter-class>org.springframework.web.filter.CharacterEncodingFilterfilter-class> <init-param> <param-name>encodingparam-name> <param-value>utf-8param-value> init-param> filter> <filter-mapping> <filter-name>encodingfilter-name> <url-pattern>/url-pattern> filter-mapping> web-app>
- 映射文件配置：springmvc-servlet.xml映射文件
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xmlns:mvc="http://www.springframework.org/schema/mvc" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc https://www.springframework.org/schema/mvc/spring-mvc.xsd"> <context:component-scan base-package="com.wei.controller"/> <mvc:annotation-driven/> <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver" id="internalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> bean> beans>
- User类
@Data @AllArgsConstructor @NoArgsConstructor public class User { private String name; private int age; private String sex; }
- UserController类
@Controller public class UserController { //produces = "application/json;charset=utf-8" : 解决JSON对象乱码问题 @RequestMapping(value = "/j1",produces = "application/json;charset=utf-8") @ResponseBody //@ResponseBody不会通过视图解析器，会直接返回一个字符串 public String json1() throws JsonProcessingException { //使用jackson包，创建ObjectMapper对象 ObjectMapper mapper = new ObjectMapper(); //创建对象 User user = new User("wei_shuo",18,"男"); String str = mapper.writeValueAsString(user); return str; } }
JSON乱码解决
注解方式
//produces = "application/json;charset=utf-8" : 解决JSON对象乱码问题
@RequestMapping(value = "/j1",produces = "application/json;charset=utf-8")
Spring配置方式
<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>
返回JSON对象
- @Controller：代码通过视图解析器
- @RequestMapping：处理请求地址映射
- @ResponseBody：@ResponseBody不会通过视图解析器，会直接返回一个字符串，同@Controller注解同时使用
- @RestController：直接返回一个字符串
- JSON返回普通对象
//代码通过视图解析器 @Controller public class UserController { //produces = "application/json;charset=utf-8" : 解决JSON对象乱码问题 @RequestMapping(value = "/j1") @ResponseBody //@ResponseBody不会通过视图解析器，会直接返回一个字符串 public String json1() throws JsonProcessingException { //使用jackson包，创建ObjectMapper对象 ObjectMapper mapper = new ObjectMapper(); //创建对象 User user = new User("wei_shuo",18,"男"); String str = mapper.writeValueAsString(user); return str; } }
- JSON返回集合对象
//直接返回一个字符串 @RestController public class UserController { @RequestMapping("/j2") public String json2() throws JsonProcessingException { //使用jackson包，创建ObjectMapper对象 ObjectMapper mapper = new ObjectMapper(); //创建集合对象 ArrayList<User> userList = new ArrayList<>(); //创建对象 User user1 = new User("wei_shuo",18,"男"); User user2 = new User("tian_tain",19,"男"); User user3 = new User("wu_wu",14,"男"); User user4 = new User("qi_qi",25,"男"); userList.add(user1); userList.add(user2); userList.add(user3); userList.add(user4); String str = mapper.writeValueAsString(userList); return str; } }
- JSON返回时间对象
@RestController public class UserController { @RequestMapping("/j3") public String json3() throws JsonProcessingException { //使用jackson包，创建ObjectMapper对象 ObjectMapper mapper = new ObjectMapper(); //创建时间对象 Date date = new Date(); //自定义日期格式 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); String format = sdf.format(date); String str = mapper.writeValueAsString(format); return str; // "2022-11-19 18:08:43" } }
- 编写utils工具类返回时间对象（JsonUtils类）
package com.wei.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 JsonUtils { public static String getJson(Object object){ return getJson(object,"yyyy-MM-dd HH:mm:ss"); } public static String getJson(Object object,String dateFormat){ //使用jackson包，创建ObjectMapper对象 ObjectMapper mapper = new ObjectMapper(); //不使用时间戳的方式 mapper.configure(SerializationFeature.WRITE_DATE_KEYS_AS_TIMESTAMPS,false); //自定义日期的格式 SimpleDateFormat sdf = new SimpleDateFormat(dateFormat); mapper.setDateFormat(sdf); try { return mapper.writeValueAsString(object); } catch (JsonProcessingException e) { e.printStackTrace(); } return null; } }
- UserController类
//直接返回一个字符串 @RestController public class UserController { @RequestMapping("/j1") public String json2() throws JsonProcessingException { //创建集合对象 ArrayList<User> userList = new ArrayList<>(); //创建对象 User user1 = new User("wei_shuo",18,"男"); User user2 = new User("tian_tain",19,"男"); User user3 = new User("wu_wu",14,"男"); User user4 = new User("qi_qi",25,"男"); userList.add(user1); userList.add(user2); userList.add(user3); userList.add(user4); return JsonUtils.getJson(userList); } @RequestMapping("/j2") public String json3() throws JsonProcessingException { //创建时间对象 Date date = new Date(); return JsonUtils.getJson(date,"yyyy-MM-dd HH:mm:ss"); } }
FastJson
Fastjson是一个Java语言编写的高性能功能完善的JSON库。它采用一种“假定有序快速匹配”的算法，把JSON Parse的性能提升到极致，是目前Java语言中最快的JSON库。Fastjson接口简单易用，已经被广泛使用在缓存序列化、协议交互、Web输出、Android客户端等多种应用场景
环境搭建
- 导入pom.xml依赖
<dependencies> <dependency> <groupId>com.alibabagroupId> <artifactId>fastjsonartifactId> <version>2.0.18version> dependency> dependencies>
- 使用FastJson
@RestController public class UserController { @RequestMapping("/j1") public String json1() throws JsonProcessingException { //创建集合对象 ArrayList<User> userList = new ArrayList<>(); //创建对象 User user1 = new User("wei_shuo",18,"男"); User user2 = new User("tian_tain",19,"男"); User user3 = new User("wu_wu",14,"男"); User user4 = new User("qi_qi",25,"男"); userList.add(user1); userList.add(user2); userList.add(user3); userList.add(user4); String s = JSON.toJSONString(userList); return s; } }
Java <——> Json相互转换
| Java对象——>Json字符串 | JSON.toJSONString(Object,object); |
|---|---|
| Json字符串——>Java对象 | JSON.parseObject(String str, Class objectClass); |
| Java对象——>Json对象 | JSON.parseObject(String str, Class objectClass); |
| Java对象——>Json对象 | JSON.toJSON(Object javaObject); |
| Json对象——>Java对象 | JSON.toJavaObject(JSON json, Class clazz); |
@RestController
public class UserController {
@RequestMapping("/j1")
public String json1() throws JsonProcessingException {
//创建集合对象
ArrayList<User> userList = new ArrayList<>();
//创建对象
User user1 = new User("wei_shuo", 18, "男");
User user2 = new User("tian_tain", 19, "男");
User user3 = new User("wu_wu", 14, "男");
User user4 = new User("qi_qi", 25, "男");
userList.add(user1);
userList.add(user2);
userList.add(user3);
userList.add(user4);
System.out.println("Java对象——>Json字符串");
String str1 = JSON.toJSONString(userList);
System.out.println("JSON字符串：" + str1);
System.out.println("=================");
String str2 = JSON.toJSONString(user1);
System.out.println("JSON字符串：" + str2);
System.out.println("=================");
System.out.println("Json字符串——>Java对象");
User Json_TO_Java1 = JSON.parseObject(str2, User.class);
System.out.println("Java对象：" + Json_TO_Java1);
System.out.println("Java对象——>Json对象");
JSONObject jsonObject = (JSONObject) JSON.toJSON(user1);
System.out.println("Json对象：" + jsonObject.getString("name"));
System.out.println("Json对象——>Java对象");
User Json_TO_Java2 = JSON.toJavaObject(jsonObject, User.class);
System.out.println("Java对象：" + Json_TO_Java2);
return "Hello";
}
}
/*
输出结果：
Java对象——>Json字符串
JSON字符串：[{"age":18,"name":"wei_shuo","sex":"男"},{"age":19,"name":"tian_tain","sex":"男"},{"age":14,"name":"wu_wu","sex":"男"},{"age":25,"name":"qi_qi","sex":"男"}]
=================
JSON字符串：{"age":18,"name":"wei_shuo","sex":"男"}
=================
Json字符串——>Java对象
Java对象：User(name=wei_shuo, age=18, sex=男)
Java对象——>Json对象
Json对象：wei_shuo
Json对象——>Java对象
Java对象：User(name=wei_shuo, age=18, sex=男)
*/
结语：创作不易，如果觉得博主的文章赏心悦目，还请——
点赞收藏⭐️评论