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93 lines
2.7 KiB
93 lines
2.7 KiB
1 year ago
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title: 关于Spring里类的私有字段的一些坑
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author: lensfrex
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cover: 'https://oss-img.ciduid.top/blog/covers/cover(10).jpg'
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tags:
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- Java
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- 笔记
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categories: []
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date: 2022-07-11 15:42:00
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---
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封面：https://www.pixiv.net/artworks/98234187
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---
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话先说在前头：
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> 记得写上getter/setter方法
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---
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我们写统一响应类一般会这么写：
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``` java
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package net.lensfrex.dscape.domain.response;
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public class Response<T> {
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private final int code;
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private final String message;
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private final T data;
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public Response(int code, String message, T data) {
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this.code = code;
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this.message = message;
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this.data = data;
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}
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public static<T> Response<T> success(T data) {
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return new Response<>(20000, "success", data);
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}
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public static Response<Object> error(int code, String message) {
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return new Response<>(code, message, null);
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}
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}
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```
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在controller里边如果是这样写：
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```java
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@RestController
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@RequestMapping("/user")
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public class User {
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@PostMapping(value = "/login" , produces = "application/json")
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public Response<LoginResponseData> result(@RequestBody String body) {
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LoginResponseData loginResponseData = new LoginResponseData();
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loginResponseData.setRole(0);
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loginResponseData.setUid("uuid");
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loginResponseData.setAccessToken("token");
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loginResponseData.setExpired(120202002);
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loginResponseData.setRefreshToken("refreshToken");
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return Response.success(loginResponseData);
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}
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}
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```
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当我们发起请求的时候，会出现这样的问题：
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``` json
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{
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"timestamp": "2022-07-11T07:49:09.656+00:00",
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"status": 500,
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"error": "Internal Server Error",
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"path": "/user/login"
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}
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```
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程序会打出这样的日志：
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`2022-07-11 15:49:09.652 WARN 14728 --- [tp1298557761-40] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotWritableException: No converter for [class net.lensfrex.dscape.domain.response.Response] with preset Content-Type 'null']`
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也就是说没法把这个类给转换成json
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这是因为在Spring MVC里面将实体Bean转换成json时，是通过对应字段的getter来获取到其值的。我们这里并没有为其提供相应的getter方法，所以没法获取到字段的值，因为所有字段都是`private`，所以得到的也都是`null`，也就没法转成json，产生错误。
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因此在编写统一返回类的时候应当要注意带上getter方法。
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> 番外：
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>
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> 如果想让值为`null`的字段不参与序列化，则在这个类标注上`@JsonInclude(JsonInclude.Include.NON_NULL)`，这样，在json输出的时候，这个null字段就会消失，在json中不会有这个key
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