SpringMvc Json (使用Jackson演示)

8.1、什么是JSON？

• JSON(JavaScript Object Notation, JS 对象标记) 是一种轻量级的数据交换格式，目前使用特别广泛。
• 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。

在 JavaScript 语言中，一切都是对象。因此，任何JavaScript 支持的类型都可以通过 JSON 来表示，例如字符串、数字、对象、数组等。看看他的要求和语法格式：

• 对象表示为键值对，数据由逗号分隔
• 花括号保存对象
• 方括号保存数组

代码演示

- 引入jackson依赖

<dependency>
    <groupId>com.fasterxml.jackson.coregroupId>
    <artifactId>jackson-databindartifactId>
    <version>2.9.8version>
dependency>

- 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>

- springmvc-servlet.xml
这里注意一下，需要先解决json中文乱码问题

    <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>

springmvc-servlet完整配置

<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
       http://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd
">
    
    <context:component-scan base-package="com.xu.controller"/>
    
    <mvc:default-servlet-handler/>
    
    <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>

    <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>
beans>

业务代码
为了简化我们的操作，我们先封装一个工具类jsonUtils

package com.xu.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) throws JsonProcessingException {
        return getJson(object,"yyyy-MM-dd HH:mm:ss");
    }
    public static String getJson(Object object,String dataFormat) throws JsonProcessingException {
        ObjectMapper mapper=new ObjectMapper();
        //不使用时间戳方式
        mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        //自定义时间格式
        SimpleDateFormat sdf=new SimpleDateFormat(dataFormat);
        mapper.setDateFormat(sdf);
        return mapper.writeValueAsString(object);
    }
}

我们要做的是将时间转化json字符串，将user类集合转化为json字符串

• 实体类User

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

• JsonDemo

import java.util.ArrayList;
import java.util.Date;
import java.util.List;

@RestController//不走视图解析器
@RequestMapping(produces = "application/json")
public class JsonDemo {
    @RequestMapping("/json1")
    public String json1() throws JsonProcessingException {
        List<User> userList=new ArrayList<>();
        userList.add( new User("小王1",18,"女"));
        userList.add( new User("小王2",19,"女"));
        userList.add( new User("小王3",20,"女"));
        userList.add( new User("小王4",21,"女"));
        return  jsonUtils.getJson(userList);
    }
    @RequestMapping("/json2")
    public String json2() throws JsonProcessingException {
        Date date=new Date();
        return  jsonUtils.getJson(date);
    }
}

可以看出经过我们的封装之后业务代码变得十分简单