jakeson的使用

先导入jakeson的包

 <dependencies>
        <!--将字符串转换成JSON格式-->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.13.1</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.10</version>
        </dependency>
    </dependencies>

配置web.xml文件

<?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">
    <!--1.注册servlet-->
    <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，进行关联-->
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc-servlet.xml</param-value>
        </init-param>
        <!-- 启动顺序，数字越小，启动越早 -->
        <load-on-startup>1</load-on-startup>
    </servlet>
 
    <!--所有请求都会被springmvc拦截 -->
    <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>

配置springmvc-servlet.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">
 
    <!-- 自动扫描指定的包，下面所有注解类交给IOC容器管理 -->
    <context:component-scan base-package="com.Google.controller"/>
    <!-- 视图解析器 -->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"
          id="internalResourceViewResolver">
        <!-- 前缀 -->
        <property name="prefix" value="/WEB-INF/jsp/" />
        <!-- 后缀 -->
        <property name="suffix" value=".jsp" />
    </bean>
 
</beans>

编写实体类

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private String name;
    private int age;
    private String Sex;
}

编写Controller，传递一个对象

package com.Google.controller;
 
import com.Google.pojo.User;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;
//@Controller
@RestController//这个注解不会走视图解析器，会直接返回一个字符串
public class jsonController {
    @RequestMapping("/j1")
    //@ResponseBody//这个注解配合@Controller一起使用达到RestController的效果
    public String json1() throws JsonProcessingException {
        //
        ObjectMapper mapper = new ObjectMapper();
        User user = new User("Spring", 2, "女");
        String str = mapper.writeValueAsString(user);
        return str;
    }
}

后端一般就是传字符串给前端，所以以后一般直接使用RestController

这里没有配置传输JSON乱码问题

可以使用RequestMapping

//produces:指定响应体返回类型和编码
@RequestMapping(value = "/json1",produces = "application/json;charset=utf-8")

最好就是同一处理(在spring中处理)

    <!--配合Jakeson，解决JSON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>

传递一个数组

//传递一个数组
    @RequestMapping("/j2")
    public String json2() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        List<User> users = new ArrayList<>();
        User user = new User("Spring", 2, "女");
        User user1 = new User("Spring", 2, "女");
        User user2 = new User("Spring", 2, "女");
        User user3 = new User("Spring", 2, "女");
        users.add(user);
        users.add(user1);
        users.add(user2);
        users.add(user3);
        return mapper.writeValueAsString(users);
    }

传递一个时间对象

//传递一个时间对象
    @RequestMapping("/j3")
    public String json3() throws JsonProcessingException {
        Date date = new Date();
        return new ObjectMapper().writeValueAsString(date);
    }

时间对象返回的结果是一个时间戳

我们需要更改一下它的格式

1、使用java纯代码

//传递一个时间对象
    @RequestMapping("/j3")
    public String json3() throws JsonProcessingException {
        Date date = new Date();
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy:MM:dd HH:mm:ss");
        String format = dateFormat.format(date);
        return new ObjectMapper().writeValueAsString(format);
    }

结果

2、使用jackson取消timestamps形式 ， 自定义时间格式

 @RequestMapping("/j3")
    public String json3() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        //将时间戳的方式关闭
        mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        Date date = new Date();
        //自定义时间格式
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy:MM:dd HH:mm:ss");
        mapper.setDateFormat(dateFormat);
        return mapper.writeValueAsString(date);
    }

结果

可以将重复使用的代码包装成一个类，来实现代码的复用(编写这类代码，思想很重要啊)

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) {
       ObjectMapper mapper = new ObjectMapper();
       //不使用时间差的方式
       mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
       //自定义日期格式对象
       SimpleDateFormat sdf = new SimpleDateFormat(dateFormat);
       //指定日期格式
       mapper.setDateFormat(sdf);
       try {
           return mapper.writeValueAsString(object);
      } catch (JsonProcessingException e) {
           e.printStackTrace();
      }
       return null;
  }
}