Exception in thread main com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException while conv-CodePudding

I am trying to read a string from a text file and want to map it to a bean class but I am getting an unusual exception from jackson library.

I have a made a POJO named Question.java that has all the values that I have to read from the text file.

    private String Code;
    private String QuestionCode;
    private String Description;
    private String Type;
    private String LastUpdated;

I have main class where I read the string from the text file and try to map it to Question class

public class QuestionParser {
    
    public static void main(String[] args) throws IOException {
        
        BufferedReader reader = new BufferedReader(new FileReader("Sample.txt"));
        StringBuilder stringBuilder = new StringBuilder();
        String line = null;
        String ls = System.getProperty("line.separator");
        while ((line = reader.readLine()) != null) {
            stringBuilder.append(line);
            stringBuilder.append(ls);
        }
        
        stringBuilder.deleteCharAt(stringBuilder.length() - 1);
        reader.close();
        
        String content = stringBuilder.toString();
        System.out.println(content);
        String sample = content.replaceAll("\\\\", " ");
        
        ObjectMapper mapper = new ObjectMapper();
        
        Question question = mapper.readValue(sample, Question.class);
        System.out.println(question);
        
        
    }

}

The Sample.txt looks like

{\"Code\":\"60\",
\"QuestionCode\":\"7000\",
\"Description\":\"What is your favorite movie?\",
\"Type\":\"R\",
\"LastUpdated\":\"2015-05-21\"
}

After all this when I run the code it gives me below exception

Exception in thread "main" com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "Code " (class Question), not marked as ignorable (5 known properties: "type", "questionCode", "description", "code", "lastUpdated"])

  at [Source: (String)"{ "Code ": "60 ",

  "QuestionCode ": "7000 ",

  "Description ": "What is your favorite movie? ",

  "Type ": "R ",

  "LastUpdated ": "2015-05-21 "

 }

 "; line: 1, column: 13] (through reference chain: Question["Code "])

    at com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:61)

    at com.fasterxml.jackson.databind.DeserializationContext.handleUnknownProperty(DeserializationContext.java:1127)

    at com.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:1984)

    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1701)

    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1679)

    at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:319)

    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:176)

    at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:322)

    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4620)

    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3575)

    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3543)

    at QuestionParser.main(QuestionParser.java:33)

CodePudding user response：

You're defining and reading the file incorrectly. JSON is not line-delimited, so don't read it as lines

JSON should look like this, for example, no backslashes...

(file extension should ideally be .json as well, but doesn't matter except for your text editor)

{
  "Code": "60",
  "QuestionCode":"7000"
}

Also, the Java field names should be annotated or exactly match the JSON fields; Java fields should be lower-case. You could also remove the quotes in the JSON values if you wanted to use integers or other datatypes than strings

public class Question {

 public Question() { }

 @JsonProperty("Code")
 private String code;

 // getters and setters
}

Then you can open that using the ObjectMapper directly

ObjectMapper om = new ObjectMapper();
// File should be in `src/main/resources` folder of a Java project
InputStream is = QuestionParser.class.getResourceAsStream("/questions.json");
Question q = om.readValue(is, Question.class);

CodePudding user response：

Your replace is creating all the issues. String sample = content.replaceAll("\\\\", " "); is adding an additional whitespace to every JSON key. Please use the following code instead:

public class QuestionParser {
    public static void main(String[] args) throws IOException {
        
        BufferedReader reader = new BufferedReader(new FileReader("Sample.txt"));
        StringBuilder stringBuilder = new StringBuilder();
        String line = null;
        String ls = System.getProperty("line.separator");
        while ((line = reader.readLine()) != null) {
            stringBuilder.append(line);
            stringBuilder.append(ls);
        }
        
        stringBuilder.deleteCharAt(stringBuilder.length() - 1);
        reader.close();
        
        String content = stringBuilder.toString();
        System.out.println(content);
        String sample = content.replaceAll("\\\\", "");
        
        ObjectMapper mapper = new ObjectMapper();
        
        Question question = mapper.readValue(sample, Question.class);
        System.out.println(question);    
    }
}

Mind the changed line: String sample = content.replaceAll("\\\\", "");.

Additionally, as @Jens already mentioned, follow Java conventions and follow camelcase for Java property name. Having said this, please also change your Question to:

public class Question {
    private String code;
    private String questionCode;
    private String description;
    private String type;
    private String lastUpdated;

    //getters & setters
}

Finally, you also need to adjust your JSON as follows:

{\"code\":\"60\",
\"questionCode\":\"7000\",
\"description\":\"What is your favorite movie?\",
\"type\":\"R\",
\"lastUpdated\":\"2015-05-21\"
}

UPDATE

Assuming you can't change the JSON file you are trying to read you would need to use @JsonProperty annotation in your Question class to "glue" the properties together. In this case, JSON would still look as you added in the question:

{\"Code\":\"60\",
\"QuestionCode\":\"7000\",
\"Description\":\"What is your favorite movie?\",
\"Type\":\"R\",
\"LastUpdated\":\"2015-05-21\"
}

But your Question class would have a bunch of @JsonProperty annotations (you can read more about it at https://fasterxml.github.io/jackson-annotations/javadoc/2.8/com/fasterxml/jackson/annotation/JsonProperty.html):

public class Question {
    @JsonProperty("Code")
    private String code;

    @JsonProperty("QuestionCode")
    private String questionCode;

    @JsonProperty("Description")
    private String description;

    @JsonProperty("Type")
    private String type;

    @JsonProperty("LastUpdated")
    private String lastUpdated;

    //getters & setters
}

CodePudding user response：

After parsing your string contains variable Code like "Code " with whitespace. You should fix replace logic or use annotation.

@JsonProperty("Code ")
private String Code;