Convert the Java Objects to JSON using Jackson API and vice versa

JSON Stand for JavaScript Object Notation. It is mostly used for transmitting the data in web applications. JSON is highly recommended to transfer data between a server and web application. To convert a Java object into JSON, the JACKSON API can be used:

In below example, Java object is converted into the JSON using the Jackson API:

Steps1: Add jar files of Jackson in the Maven project 

Add Jackson dependencies in pom.xml file as below:

<dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.5.3</version>
</dependency>

or Add below JARs manually to the Project's build path as external JARs:

jackson-core-asl-1.9.11.jar
jackson-mapper-asl-1.9.11.jar
jackson-xc-1.9.11.jar

Above are the Jackson API JARs which converts the Java Objects(POJO) to JSON and vice versa.


Steps2:  Create a POJO (Plain Old Java Object) to be converted into JSON

The POJO class:
============

public class KeyValuePair {

public String key;
public String value;

// The getters and setters
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;
}

}

Steps 3: Create a Java class for converting the JSON into KeyValuePair object. Below program converts the JSON into Java objects using ObjectMapper class of Jackson API.

import org.codehaus.jackson.map.ObjectMapper;

public class TestProgram {
public static void main(String[] args) {

String inputJson="{\"key\":\"Hello\", \"value\":\"World\"}";

ObjectMapper mapper = new ObjectMapper();

try {
KeyValuePair kv = mapper.readValue(inputJson, KeyValuePair.class);

System.out.println(kv.getKey());
System.out.println(kv.getValue());

} catch(Exception e) {
e.printStackTrace();
}

  }
}

Output: (The Java Objects)
Hello
World


To convert the KeyValuePair POJO to JSON, we will use the following methods of Jackson API:

ObjectMapper Obj = new ObjectMapper();
try {
ObjectWriter ow = Obj.writer().withDefaultPrettyPrinter();
String jsonStr = ow.writeValueAsString(kv);
         
// Displaying JSON String
            System.out.println(jsonStr);
         
        }catch (IOException e) {
            e.printStackTrace();
        }
    }

Output: (The JSON string)
{
  "key": "Hello",
  "value": "World"
}


Pankaj