Spring Controller无法解析HttpClient发送的JSON：无法构造LinkedHashMap实例

场景说明 #

使用java.net.http.HttpClient向Spring控制器发送JSON对象，控制器以Map<String, Object>接收请求体。JSON格式合法，Postman发送可正常接收，但HttpClient发送时出现解析错误。

待发送的JSON内容：

{"fruit": "Apple", "color": "Red"}

原客户端请求代码 #

ObjectMapper mapper = new ObjectMapper();
mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
String jsonString = mapper.writeValueAsString(body);

HttpRequest request = HttpRequest.newBuilder()
    .uri(new URI(url))
    .header("content-type", "application/json")
    .POST(BodyPublishers.ofString(jsonString))
    .build();
HttpResponse<String> response = client.send(request, BodyHandlers.ofString());

Spring控制器代码 #

@PostMapping(value = "/config/addDocument", consumes = {"application/json"})
public void addDocument(@RequestBody Map<String, Object> document)

报错信息 #

HttpMessageNotReadableException: JSON parse error: Cannot construct instance of `java.util.LinkedHashMap` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('{"fruit": "Apple", "color": "Red"}'); nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `java.util.LinkedHashMap` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('{"fruit": "Apple", "color": "Red"}')
 at [Source: (org.springframework.util.StreamUtils$NonClosingInputStream); line: 1, column: 1]]

补充信息 #

• 客户端为java.net.http.HttpClient，通过HttpClient.newHttpClient()实例化
• 使用Spring Boot Starter Web 2.7.5版本

解决方法 #

将输入的JSON字符串先反序列化为Map，再重新序列化为JSON字符串后发送，即可解决问题。修改后的代码如下：

ObjectMapper mapper = new ObjectMapper();
Map<String, Object> map = mapper.readValue(body, Map.class);
String jsonString = mapper.writeValueAsString(map);

HttpRequest request = HttpRequest.newBuilder()
    .uri(new URI(url))
    .header("content-type", "application/json")
    .POST(HttpRequest.BodyPublishers.ofString(jsonString))
    .build();
HttpResponse<String> response = client.send(request, BodyHandlers.ofString());

内容的提问来源于stack exchange，提问作者Yoh