Jackson asText vs textValue

Its such a simple thing but its enough to make your mind boggle. I recently spent some time working on a legacy code base, and as expected it followed the norm of having no test cases and no documentation. The bug that was reported was that when the UI form opens up and some fields which are supposed to be empty had the value null in them.

Debugging

As usual, the debugging process started and we started looking at the returned value from the database and what was getting saved in the database. The code was splattered with if and else conditions. One of the things that caught our attention was a series of if statements written in the form of .

if (jsonNode.get(Constants.CATEGORY) != null) {
        category = jsonNode.get(Constants.CATEGORY).textValue();
     }

We knew that these values were getting displayed as “null” in the UI, so it was time to write a quick unit test .

package com.sample;

import static org.junit.Assert.assertEquals;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.junit.Test;

public class JsonNodeTest {

  @Test
  public void testValues(){
    ObjectMapper mapper = new ObjectMapper();
    TestEntity fromValue = new TestEntity(2016, null);
    JsonNode node = mapper.valueToTree(fromValue);

    assertEquals(2016, node.get("id").intValue());
    assertEquals(null, node.get("name").textValue());

    //assertEquals(null, node.get("name").asText()); Throws assertion error
    assertEquals("null", node.get("name").asText());

  }


  @Data
  @AllArgsConstructor
  @NoArgsConstructor
  public class TestEntity {
    private int id;
    private String name;
  }
}

The culprit was caught. While saving to the database, we were doing a conversion of asText() . The javadocs of asText() points out

Method that will return a valid String representation of the container value, if the node is a value node.

So null is returned as “null”. (with the double quotes like a string)

JsonNode also exposes the textValue() method. This also returns the textual value if and only if it is a valid textual jsonNode. A null jsonNode is returned as null. The javadocs for textvalue() also state that

Does NOT do any conversions for non-String value nodes;for non-String values (ones for which {@link #isTextual} returns false) null will be returned.

We quickly changed a bunch of code which was calling the asText() method to call the textValue() method and voila! no more null on the UI.