使用Jackson将JSON映射到POJO

Question

I'm trying to get map a JSON to a POJO using jackson and I keep getting the following error:

> Can not deserialize instance of java.lang.String out of START_OBJECT token\n at [Source: (String)\"{\"checkstyle\

The JSON Im trying to parse is the following:

{
  "checkstyle": {
    "file": [
      {
        "name": "src\\main\\java\\com\\report\\uploader\\controller\\RandomController.java",
        "error": [
          {
            "severity": "error",
            "line": 0,
            "source": "com.puppycrawl.tools.checkstyle.checks.javadoc.JavadocPackageCheck",
            "message": "Missing package-info.java file."
          }
        ]
      }
    ],
    "version": 6.18
  }
}

For this I create the following classes:

public class Checkstyle {

    @JsonProperty("checkstyle")
    private Linter linterName;
}

public class Linter {

    @JsonProperty("file")
    private List<File> files;

    @JsonProperty("version")
    private String version;
}

public class File {

    @JsonProperty("name")
    private String name;

    @JsonProperty("error")
    private List<Error> errores;

}

public class Error {

    @JsonProperty("severity")
    private String severity;

    @JsonProperty("line")
    private int line;

    @JsonProperty("source")
    private String source;

    @JsonProperty("message")
    private String message;
}

But when I run the code I get the error mentioned above. The way I get this JSON is by converting an XML file to a JSONObject using the org.json dependency and then the JSONobject I convert it to a String.

Then I convert then I try to convert the String into my POJO the following way:

ObjectMapper mapper = new ObjectMapper();
Checkstyle checkstyle = mapper.readValue(object.toString(), Checkstyle.class);

If anyone could point me out what I'm doing wrong I would appreciate.

Answer 1

This is the line causing error in your program mapper.readValue(object.toString(), Checkstyle.class) . You have already read the json into an anonymous object , and then using its toString() representation in ObjectMapper to map to Checkstyle class, which will never work. As you already have lost the json string into java default toString representation of object: someObjectClassname@hashcodenumber .

Below are the some of the commonly used signature of readValue method to do correrct de-serialization:

readValue(InputStream in, Class c)
readValue(Reader rd, Class c)
readValue(String json, Class c)