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