How to dynamically map JSON array of key values to sub-object using Jackson?

Question

Say we have a JSON structure that looks like this:

{
 "field1": "val1",
 "field2": "v2",
 "f3": "v3",
 "f4": "v4",
 "arrayOfStuff": [
  {
   "f5": "v5",
   ....
   "f10": "v10"
  }
 ],
 "attributes": [
  {"att1": "att1"},
  {"att2": "attr2"},
  {"att3": "att3"}
 ],
 "options": [
  "ignoreMismatchFile"
 ]
}

And our matching java class looks like:

public class Message {
   @IsUniqueId
   private String field1; //
   private String field2;
   private String field3;
   private String field4;
   private List<AnotherObject> f5;
   @JsonProperty("attributes")
   private LinkedHashMap<String, String> attributes;
   private List<String> options;
   ....
}

The parsing code looks like:

protected Message loadSavedMessageAsMessageObject(String path) throws IOException {
    File file = ResourceUtils.getFile(path);
    if (file.exists()) {
        ObjectMapper mapper = this.getObjectMapper();
        return mapper.readValue(file, Message.class);
    }

    return null;
}

We tried different ways of accomplishing this, originally we tried to have attributes as private List<MessageAttribute> attributes; but that has not worked either (we switched to the Map based on Another answer - doesn't work)

Our goal is to keep Attributes a dynamic, not hard coded list of attributes.

This is how the MessageAttribute class looked like:

public class MessageAttribute {
    private String key;
    private String value;

    public String getKey() {
        return key;
    }

    public void setKey(String key) {
        this.key = key;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
}

The exception we currently get is:

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.LinkedHashMap` out of START_OBJECT token
at [Source: (File); line: 32, column: 3] (through reference chain: com.org.Message["attributes"])

have you considered the idea of writing a Custom Deserializer — mehdi maick
– mehdi maick, Commented Feb 1, 2019 at 19:46

Ryuzaki L · Accepted Answer · 2019-02-01 21:06:43Z

2

Corresponding Message POJO to above JSON is in wrong format, i made couple of changes attributes should be List of Map and list of AnotherObject should point to arrayOfStuff

public class Message {
 @IsUniqueId
 private String field1; //
 private String field2;
 private String field3;
 private String field4;
 private List<AnotherObject> arrayOfStuff;  //or you can have List<Map<String,String>> arrayOfStuff
 @JsonProperty("attributes")
 private List<LinkedHashMap<String, String>> attributes; // this is list of map objects
 private List<String> options;
  ....
  }

edited Feb 1, 2019 at 21:06

answered Feb 1, 2019 at 19:48

Ryuzaki L

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1 Comment

Carmageddon Over a year ago

Thank you! With this answer, figured out we had the JSON wrong, so instead of double wrapping changed the attributes to be a single object with many dynamic fields, works :)

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