Json Jackson

什么是Json?

json的全称为：JavaScript Object Notation，是一种轻量级的数据交互格式。它基于 ECMAScript (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。

简单来说：json就是一种在各个编程语言中流通的数据格式，负责不同编程语言中的数据传递和交互。

1.json与js对象的转换

<script>
        var user ={
            name:"liu",
            age:3,
            sex:"男"
        }
        // console.log(user);

        //js对象转json
        var json = JSON.stringify(user);
        console.log(json);

        //json 转js对象
        var object = JSON.parse(json);
        console.log(object);
    </script>

json乱码问题解决：

方法一.通过@RequestMaping的produces属性来实现，修改下代码

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

方法二.在servlet.xml中的annotation-driven中配置

<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>

jackson

1.ObjectMapper:可以将对象转换成json字符串

  public String json1() throws JsonProcessingException {
        //jackson ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        User user = new User(2,"jie",1);
        String str = mapper.writeValueAsString(user);
        return str;
    }

result:{“id”:2,“name”:“jie”,“age”:1}
2.当对象是一个Date对象时
ObjectMapper默认将其转换成时间戳形式

    @RequestMapping("j3")
    public String json3() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        Date date = new Date();
        String str = mapper.writeValueAsString(date);

        return str;
    }

修改时间格式：
方法一：利用SimpleDateFormat

    public String json3() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        Date date = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH-mm-ss");

        String str = mapper.writeValueAsString(sdf.format(date));

        return str;
    }

方法二、利用objectmapper来设置

    @RequestMapping("j4")
    public String json4() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        Date date = new Date();
        //取消设置时间戳输出
        mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);
        //设置时间输出格式
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH-mm-ss");
        mapper.setDateFormat(sdf);
        String str = mapper.writeValueAsString(date);

        return str;
    }
}

编写Utils类来实现复用

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();
        //取消设置时间戳输出
        mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS,false);
        //设置时间输出格式
        SimpleDateFormat sdf = new SimpleDateFormat(dateFormat);
        mapper.setDateFormat(sdf);

        try {
            return mapper.writeValueAsString(object);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        return null;
    }
}