由于输入结束 Jackson 解析器，没有要映射的内容

我从服务器 {"status":"true","msg":"success"}得到这个响应

我尝试使用 Jackson 解析器库来解析这个 json 字符串，但是不知怎么的，我遇到了映射-异常声明

com.fasterxml.jackson.databind.JsonMappingException: No content to map due to end-of-input
at [Source: java.io.StringReader@421ea4c0; line: 1, column: 1]

为什么我们会有这种例外？

如何理解是什么导致了这个异常？

我尝试使用以下方法进行解析:

StatusResponses loginValidator = null;


ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(Feature.AUTO_CLOSE_SOURCE, true);


try {
String res = result.getResponseAsString();//{"status":"true","msg":"success"}
loginValidator = objectMapper.readValue(result.getResponseAsString(), StatusResponses.class);
} catch (Exception e) {
e.printStackTrace();
}

StatusResponse 类

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({ "status","msg" })
public class StatusResponses {


@JsonProperty("status")
public String getStatus() {
return status;
}


@JsonProperty("status")
public void setStatus(String status) {
this.status = status;
}


@JsonProperty("msg")
public String getMessage() {
return message;
}


@JsonProperty("msg")
public void setMessage(String message) {
this.message = message;
}


@JsonProperty("status")
private String status;


@JsonProperty("msg")
private String message;


private Map<String, Object> additionalProperties = new HashMap<String, Object>();


@JsonGetter
public Map<String, Object> getAdditionalProperties() {
return additionalProperties;
}


@JsonSetter
public void setAdditionalProperties(Map<String, Object> additionalProperties) {
this.additionalProperties = additionalProperties;
}
}
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For one, @JsonProperty("status") and @JsonProperty("msg") should only be there only when declaring the fields, not on the setters and geters.

In fact, the simplest way to parse this would be

@JsonAutoDetect  //if you don't want to have getters and setters for each JsonProperty
public class StatusResponses {


@JsonProperty("status")
private String status;


@JsonProperty("msg")
private String message;


}
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最佳答案 
import com.fasterxml.jackson.core.JsonParser.Feature;
import com.fasterxml.jackson.databind.ObjectMapper;


StatusResponses loginValidator = null;


ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(Feature.AUTO_CLOSE_SOURCE, true);


try {
String res = result.getResponseAsString();//{"status":"true","msg":"success"}
loginValidator = objectMapper.readValue(res, StatusResponses.class);//replaced result.getResponseAsString() with res
} catch (Exception e) {
e.printStackTrace();
}

Don't know how it worked and why it worked? :( but it worked

小开

I could fix this error. In my case, the problem was at client side. By mistake I did not close the stream that I was writing to server. I closed stream and it worked fine. Even the error sounds like server was not able to identify the end-of-input.

OutputStream out = new BufferedOutputStream(urlConnection.getOutputStream());
out.write(jsonstring.getBytes());
out.close() ; //This is what I did
小开

I had a similar error today and the issue was the content-type header of the post request. Make sure the content type is what you expect. In my case a multipart/form-data content-type header was being sent to the API instead of application/json.

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In my case I was reading the stream in a jersey RequestEventListener I created on the server side to log the request body prior to the request being processed. I then realized that this probably resulted in the subsequent read to yield no string (which is what is passed over when the business logic is run). I verified that to be the case.

So if you are using streams to read the JSON string be careful of that.

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In my case the problem was caused by my passing a null InputStream to the ObjectMapper.readValue call:

ObjectMapper objectMapper = ...
InputStream is = null; // The code here was returning null.
Foo foo = objectMapper.readValue(is, Foo.class)

I am guessing that this is the most common reason for this exception.

小开

A simple fix could be Content-Type: application/json

You are probably making a REST API call to get the response.

Mostly you are not setting Content-Type: application/json when you the request. Content-Type: application/x-www-form-urlencoded will be chosen which might be causing this exception.

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I know this is weird but when I changed GetMapping to PostMapping for both client and server side the error disappeared.

Both client and server are Spring boot projects.

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The problem for me was that I read the response twice as follows:

System.out.println(response.body().string());
getSucherResponse = objectMapper.readValue(response.body().string(), GetSucherResponse.class);

However, the response can only be read once as it is a stream.

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I got this error when sending a GET request with postman. The request required no parameters. My mistake was I had a blank line in the request body.

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This error is sometimes (often?) hiding the real problem: a failure condition could be causing the content to be incorrect, which then fails to deserialize.

In my case, today, I was making HTTP calls and (foolishly) omitted to check the HTTP status code before trying to unmarshal the body of the response => my real problem was actualy that I had some authentication error, which caused a 401 Unauthorized to be sent back to me, with an empty body. Since I was unmarshalling that empty body directly without checking anything, I was getting this No content to map due to end-of-input, without getting any clue about the authentication issue.

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In my case I had race condition between 2 threads trying to write and read the file simultaneously. I added the "synchronized" keyword on my methods which writes and reads to the file and the error is gone.

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Please Don't overthink this issue, simply handle the null pointer exception here as your response is received null and you will get your solution.


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