Jackson

从JSON转Java对象

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Jackson是目前比较好的一个json解析工具，当然还有阿里巴巴的fastjson等等

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.15.2</version>
</dependency>

配置web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
         version="5.0">
    <!-- 1. 注册 DispatchServlet -->
    <servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <!-- 通过初始化参数指定 Springmvc 配置文件的位置和名称 -->
        <init-param>
            <!-- contextConfigLocation 为固定值 -->
            <param-name>contextConfigLocation</param-name>
            <!-- 使用classpath: 表示从类路径查找配置文件，例如maven工程中的src/main/resource -->
            <param-value>classpath:springmvc.xml</param-value>
        </init-param>
        <!-- 将前端控制器 DispatcherServlet 的初始化时间提前到服务器启动时 -->
        <load-on-startup>1</load-on-startup>
    </servlet>
    <!-- / 匹配所有请求（不包括.jsp） -->
    <!-- /* 匹配所有请求（包括.jsp） -->
    <servlet-mapping>
        <servlet-name>springmvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
    <!--  编码过滤器  -->
    <filter>
        <filter-name>encodingFilter</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>encodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
</web-app>

配置springmvc.xml

<?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">
    <!-- 自动扫描包，让指定包下的注解生效，由IOC容器统一管理 -->
    <context:component-scan base-package="com.example.controller"/>
    <!-- 视图解析器 -->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <!-- 前缀 -->
        <property name="prefix" value="/jsp/"/>
        <!-- 后缀 -->
        <property name="suffix" value=".jsp"/>
    </bean>
    <!-- 让Spring MVC 不处理静态资源 -->
    <mvc:default-servlet-handler/>
    <!-- 开启SpringMVC注解模式 -->
    <mvc:annotation-driven/>
</beans>

任意编写一个User实体类，然后测试Controller

package com.example.dao;

public class User {
    public String name;
    public String gender;

    public Integer age;

    public User() {
    }

    public User(String name, Integer age, String gender) {
        this.name = name;
        this.gender = gender;
        this.age = age;
    }
}

package com.example.controller;

import com.example.dao.User;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
@RequestMapping("/user")
public class UserController {
    @GetMapping("/info")
    @ResponseBody
    public String info() throws JsonProcessingException {
        // 创建jackson的对象映射器ObjectMapper，用来解析数据
        ObjectMapper mapper = new ObjectMapper();
        // 创建一个对象
        User user = new User("张三", 18, "男");
        // 将我们的对象解析成为json格式
        return mapper.writeValueAsString(user);
    }
}

发现出现乱码问题，我们需要设置一下编码格式，以及返回类型：

@GetMapping(value ="/info", produces = "application/json;charset=utf-8")

统一处理编码格式

<mvc:annotation-driven>
    <mvc:message-converters>
        <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>

在类上直接使用@RestController，这样子，里面的所有方法都只会返回json字符串，不用每一个都添加@ResponseBody

package com.example.controller;

import com.example.dao.User;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@Controller
@RestController
@RequestMapping("/user")
public class UserController {
    @GetMapping("/info")
    public String info() throws JsonProcessingException {
        // 创建jackson的对象映射器ObjectMapper，用来解析数据
        ObjectMapper mapper = new ObjectMapper();
        // 创建一个对象
        User user = new User("张三", 18, "男");
        // 将我们的对象解析成为json格式
        return mapper.writeValueAsString(user);
    }
}