Annotations for Ignoring properties In JSON - Jackson

For my reference....

Sometimes POJOs contain properties that you do not want to write out, so you can do:

public class Value {
  public int value;
  @JsonIgnore public int internalValue;
}
and get JSON like:
{ "value" : 42 }

or, you may get properties in JSON that you just want to skip: if so, you can use:

@JsonIgnoreProperties({ "extra", "uselessValue" })
public class Value {
  public int value;
}
which would be able to handle JSON like:
{ "value" : 42, "extra" : "fluffy", "uselessValue" : -13 }

Finally, you may even want to just ignore any "extra" properties from JSON (ones for which there is no counterpart in POJO). This can be done by adding:

@JsonIgnoreProperties(ignoreUnknown=true)
public class PojoWithAny {
  public int value;
}

Reference:
http://jackson.codehaus.org/

Converting map to JSON String using Jackson API

API libraries can found here @ http://jackson.codehaus.org/

Example:

import java.util.ArrayList;
import java.util.HashMap;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class MapToJSONExample {

public static void main(String[] args) {
               
HashMap<String, String> hashMap = new HashMap<String, String>();
hashMap.put("param1", "Hyderabad");
hashMap.put("param2", "Bangalore");

ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("hello1");
arrayList.add("hello2");
arrayList.add("hello3");

Employee employee = new Employee("Kondal", "Kolipaka");

ObjectMapper mapper = new ObjectMapper();
String writeValueAsString;
try {
writeValueAsString = mapper.writeValueAsString(hashMap);
System.out.println(writeValueAsString);

writeValueAsString = mapper.writeValueAsString(arrayList);
System.out.println(writeValueAsString);

writeValueAsString = mapper.writeValueAsString(employee);
System.out.println(writeValueAsString);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
}
}

public class Employee {

private String firstName;

private String lastName;

public Employee(String firstName, String lastName) {

this.firstName = firstName;

this.lastName = lastName;

}

/**

* @return the firstName

*/

public String getFirstName() {

return firstName;

}

/**

* @return the lastName

*/

public String getLastName() {

return lastName;

}

}

Output:

{"param1":"Hyderabad","param2":"Bangalore"}

["hello1","hello2","hello3"]

{"firstName":"Kondal","lastName":"Kolipaka"}

Just to conclude, we can use writeValueAsString(Object obj) method for any bean class which can be serializable.

Say for example, if you remove getters from Employee class, it will be throwing JsonMappingException.

No serializer found for class Employee and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationConfig.SerializationFeature.FAIL_ON_EMPTY_BEANS) )