Spring使用RestTemplate返回的嵌套实体对象为空，转换json报错

项目场景：

Spring Boot项目使用RestTemplate调用接口，使用嵌套实体对象接收的返回结果

实体对象TokenUser，其中TokenUserInfo是嵌套的对象：

@Data
public class TokenUser {
 
    private Integer code;
 
    private TokenUserInfo data;
 
    private Boolean success;
}

@Data
public class TokenUserInfo {
	
    /**
     * 用户id
     */
    private String userId;
    /**
     * 用户名
     */
    private String userName;
    
}

 使用RestTemplate调用接口

HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON_UTF8);
 
HttpEntity formEntity= new HttpEntity<>(requestJson, headers);
 
TokenUser tokenUser = null;
try {
	tokenUser = restTemplate.postForObject(url, formEntity, TokenUser.class);
} catch (Exception e) {
	logger.error("调用接口出错: ", e);
}

问题描述

Spring Boot项目使用RestTemplate调用接口，使用嵌套实体对象接收的返回结果

返回的嵌套对象为null不会有问题

{
    "data": null,
    "success": true,
    "code": 200
}

但是返回的嵌套对象是''空字符串就会报错

{
    "data": "",
    "success": true,
    "code": 200
}

报错详情：

Error while extracting response for type [class com.test.dto.TokenUser] and content type [application/json;charset=UTF-8]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot construct instance of `com.test.dto.TokenUserInfo` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value (''); nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `com.test.dto.TokenUserInfo` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('')
 at [Source: (PushbackInputStream); line: 1, column: 55] (through reference chain: com.test.dto.TokenUser["data"])

原因分析：

        简单来说就是 json转化成对象失败了，失败的原因是TokenUserInfo对象中虽然有一个构造器，却是全参构造器或是无参构造器，就是缺少一个只有一个String类型参数的构造器，导致在解析 ' ' 空字符串时失败了。

解决方案：

第一种：实体类加上String类型参数的构造器

@Data
public class TokenUserInfo {
	
	/**
	 * 防止返回值是空字符串，用string来接收
	 */
	public TokenUserInfo(String userId){
		this.userId = userId;
	}
	
    /**
     * 用户id
     */
    private String userId;
    /**
     * 用户名
     */
    private String userName;
    
}

第二种：用String接收返回结果，再转json对象

HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON_UTF8);
 
HttpEntity formEntity= new HttpEntity<>(requestJson, headers);
 
TokenUser tokenUser = null;
try {
	String jsonResult = restTemplate.postForObject(url, formEntity, String.class);
	
	JSONObject userJson = JSON.parseObject(jsonResult);
	tokenUser = JSONObject.toJavaObject(userJson, TokenUser.class);
} catch (Exception e) {
	logger.error("调用接口出错: ", e);
}

我这里用的是alibaba的包

<dependency>
	<groupId>com.alibabagroupId>
	<artifactId>fastjsonartifactId>
	<version>1.2.44version>
dependency>