java web-12.3JSON解析器

Myth丶恋晨 2023-02-11 13:29 1阅读 0赞

## JSON数据和java对象的相互转换 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTc5NTA0OQ_size_16_color_FFFFFF_t_70]  
**0.JSON解析器**  
常见的解析器：Jsonlib，Gson，fastjson，jackson

**1.JSON转为java对象**  
**(1)使用步骤：**  
a.导入jackson的相关jar包  
b.创建jackson核心对象，ObjectMapper  
c.调用ObjectMapper的相关方法进行转换

1.readValue(json字符串数据，Class)

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTc5NTA0OQ_size_16_color_FFFFFF_t_70 1]  
**2.java对象转换JSON**  
**(1)使用步骤：**  
a.导入jackson的相关jar包  
b.创建jackson核心对象，ObjectMapper  
c.调用ObjectMapper的相关方法进行转换

转换方法：
     1.writeValue(参数1，obj)
     参数1：
    File:将obj对象转换为json字符串，并保存到指定的文件中
    Writer：将obj对象转换为json字符串，并将json数据填充到字符输出流中
    OutputStream：将obj对象转换为Json字符串，并将json数据填充到字节输出流中
    2.writeValueAsString(obj):将对象转为json字符串

**示例**

//java对象转为json字符串
        @Test
        public void test1() throws IOException { 
            //1、创建person对象
            Person p = new Person();
            p.setName("张三");
            p.setAge(23);
            p.setGender("男");
            //创建jackson的核心对象，ObjectMapper
            ObjectMapper mapper = new ObjectMapper();
            //3.转换
            String json = mapper.writeValueAsString(p);
            System.out.println(json);
            //将数据写到d盘文件中
            //mapper.writeValue(new File("D://a.txt"),p);
            //将数据关联到writer中
            mapper.writeValue(new FileWriter("d://b/.txt"),p);
        }

**(2)细节：**  
1.@JsonIgnore：排除属性![在这里插入图片描述][20200523232016684.png]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTc5NTA0OQ_size_16_color_FFFFFF_t_70 2]  
2.@JsonFormat：属性值的格式化  
![在这里插入图片描述][20200523232140862.png]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTc5NTA0OQ_size_16_color_FFFFFF_t_70 3]  
**(3)复杂java对象转换**  
1.List：数组  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTc5NTA0OQ_size_16_color_FFFFFF_t_70 4]  
2.Map：与对象格式一致  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTc5NTA0OQ_size_16_color_FFFFFF_t_70 5]  
**案例**  
需求：校验用户名是否存在  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTc5NTA0OQ_size_16_color_FFFFFF_t_70 6]  
注意：  
1.服务器响应的数据，在客户端 使用时，要想当做json数据格式使用  
（1）`$.get(type)`:将最后一个参数type指定为json  
（2）在服务器端设置MIME类型

response.setContentType("application/json;charset=utf-8");

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[20200523232016684.png]: https://img-blog.csdnimg.cn/20200523232016684.png
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[20200523232140862.png]: https://img-blog.csdnimg.cn/20200523232140862.png
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