SpringMVC原理分析 | JSON、Jackson、FastJson

男娘i 2024-04-22 19:01 5阅读 0赞

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> 
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> 
> 🌐Hello World ！

--------------------

### JSON ###

> JSON（`JavaScript`Object 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 #####

##### JSON对象 ——> JavaScript对象 #####

#### 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.core</groupId>
>                 <artifactId>jackson-databind</artifactId>
>                 <version>2.14.0-rc3</version>
>             </dependency>
>             <dependency>
>                 <groupId>org.projectlombok</groupId>
>                 <artifactId>lombok</artifactId>
>                 <version>1.18.24</version>
>        </dependency>
>     </dependencies>
> 
>  *  配置核心配置文件：web.xml
> 
>     <?xml version="1.0" encoding="UTF-8"?>
>     <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>SpringMVC</servlet-name>
>             <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
>             
>             <init-param>
>                 <param-name>contextConfigLocation</param-name>
>                 <param-value>classpath:springmvc-servlet.xml</param-value>
>             </init-param>
>             
>             <load-on-startup>1</load-on-startup>
>         </servlet>
>         <servlet-mapping>
>             <servlet-name>SpringMVC</servlet-name>
>             <url-pattern>/</url-pattern>
>         </servlet-mapping>
>         
>         
>         <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>
>         
>     </web-app>
> 
>  *  映射文件配置：springmvc-servlet.xml映射文件
> 
>     <?xml version="1.0" encoding="UTF-8"?>
>     <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.alibaba</groupId>
>             <artifactId>fastjson</artifactId>
>             <version>2.0.18</version>
>         </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 ####

<table> 
 <thead> 
  <tr> 
   <th>Java对象——&gt;Json字符串</th> 
   <th>JSON.toJSONString(Object,object);</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>Json字符串——&gt;Java对象</td> 
   <td>JSON.parseObject(String str, Class objectClass);</td> 
  </tr> 
  <tr> 
   <td>Java对象——&gt;Json对象</td> 
   <td>JSON.parseObject(String str, Class objectClass);</td> 
  </tr> 
  <tr> 
   <td>Java对象——&gt;Json对象</td> 
   <td>JSON.toJSON(Object javaObject);</td> 
  </tr> 
  <tr> 
   <td>Json对象——&gt;Java对象</td> 
   <td>JSON.toJavaObject(JSON json, Class clazz);</td> 
  </tr> 
 </tbody> 
</table>

@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)
    */

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[wei_shuo]: https://blog.csdn.net/weixin_62765017
[wei_shuo 1]: https://bbs.csdn.net/forums/wei_shuo_study
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