由于输入结束jackson解析器，没有要映射的内容

Question

我从服务器{“status”：“true”，“msg”：“success”}收到此响应

我试图使用Jackson解析器库解析这个json字符串，但是不知何故，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？

我正在尝试使用以下方式解析：

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();
}

状态响应类

@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;
    }
}

Answer 1

我可以修复此错误。就我而言，问题出在客户端。我错误地没有关闭我正在写入服务器的流。我关闭了流，它工作正常。甚至错误听起来像服务器无法识别输入结束。

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

Answer 2

在我的例子中，问题是由我向ObjectMapper.read值调用传递一个空输入流引起的：

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

我猜这是此异常的最常见原因。

Answer 3

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();
}

不知道它是如何工作的，为什么它工作？：（但它工作