Jackson not populating all properties

Question

I am working on a simple example using Jackson library to convert a json string back to Java object but I see only few properties are being set on my java object instead of all properties.

Here is my code:

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

import org.codehaus.jackson.map.ObjectMapper;

public class JsonTest {
    public static void main(String[] args) throws FileNotFoundException, IOException {

        StringBuffer buffer = new StringBuffer();       
        String data = "";
        BufferedReader reader = null;
        try {
            reader = new BufferedReader(new FileReader("path-to-sample.json"));
            while ((data = reader.readLine()) != null) {
                buffer.append(data);
            }
        } finally {
            if (reader != null) {
                reader.close(); 
            }
        }

        System.out.println(buffer.toString());

        ObjectMapper mapper = new ObjectMapper();
        Sample obj = mapper.readValue(buffer.toString(), Sample.class);


        System.out.println(obj);
    }
}

The Sample.java program looks like this:

import org.codehaus.jackson.annotate.JsonIgnoreProperties;

import com.fasterxml.jackson.annotation.JsonProperty;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Sample {

    @JsonProperty("prop_1")
    private String prop1;
    private String prop2;
    @JsonProperty("prop_3")
    private String prop3;
    private String prop4;

    // Setters & Getters for the properties.

    @Override
    public String toString() {
        return "Sample [prop1=" + prop1 + ", prop2=" + prop2 + ", prop3="
                + prop3 + ", prop4=" + prop4 + "]";
    }

}

Input json string in my file is :

{
    "prop_1": "1",
    "prop2": "2",
    "prop_3": "3",
    "prop4": "4"
}

The output of this program is :

Sample [prop1=null, prop2=2, prop3=null, prop4=4]

As per my program the prop1 and prop3 should not be null. I am not clear where I made mistake.

Update:

If I remove the @JsonProperty annotation then I am getting the exception as :

Exception in thread "main" org.codehaus.jackson.map.exc.UnrecognizedPropertyException: Unrecognized field "prop_1" (Class Sample), not marked as ignorable

This is my pom.xml file dependencies:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.6.0</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.6.0</version>
</dependency>
<dependency>
    <groupId>org.codehaus.jackson</groupId>
    <artifactId>jackson-mapper-asl</artifactId>
    <version>1.9.13</version>
</dependency>       

Answer 1

You said in your comment, that you're using Jackson in version "2.5.4", but you're importing the ObjectMapper class from the org.codehaus package. This means, that this class is from version 1.9.13 (or from an older version).

I can reproduce your problem if I mix the versions using ObjectMapper and JsonIgnoreProperties from version 1.9.13 (org.codehaus) and JsonProperty from version 2.6.0 (com.fasterxml).

Output:

Sample [prop1=null, prop2=2, prop3=null, prop4=4]

If I only use version 1.9.13 or 2.6.0, then the result is ok:

Sample [prop1=1, prop2=2, prop3=3, prop4=4]

(for both)

So I recommend to make sure that you don't mix the used libraries and I recommend to use the newest version, which is from FasterXML. But the used version is up to you.

You can download the jar file from here:

• org.codehaus.jackson v1.9.13

• com.fasterxml.jackson (core) v2.6.0

Btw about your comment:

@OldCurmudgeon, Thanks for responding. Changing the fields to public has not fixed the issue. I have removed the @JsonProperty annotation and then changed the setter methods to setProp_1 & setProp_3, it worked. So does it mean that there is an issue with @JsonProperty annotation?

Yes, you have (or hopefully had :P) a problem with that annotation: it was from a different Jackson version.

About your edit:

The link to the Jackson lib from fasterXML in the maven repository has one big advantage: it shows you which lib you should download to work with Jackson in your project.

You need:

• Jackson Databind (which also has the ObjectMapper class)
• Jackson Core
• Jackson Annotations