SpringMVC原理分析：JSON、Jackson、FastJson_Java教程

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)
*/