RESTFul web service serialize non null & date field (jersey /objectmapper /contextresolver)

Yogesh

9 years ago

Given a user defined object or POJO having null fields (i.e. some fields are null).
When we are serializing object the null values gets serialized.
Moreover, suppose object contains the date field also, then date field will be serialized as timestamp value.
We will use ObjectMapper (jackson feature) to customize the serialization process.

In this post we will discuss about following:

Object having null field are serialized as null (default behavior).
- We will customize the serialization, wherein null values would not be serialized
Date field is serialized as time stamp (default behavior).
- We will serialized the date as standard date format (and not as timestamp).

1. Example – Default serialization of object (Object to JSON)

Suppose, we have EmployeeModel class having date field and some uninitialized fields.
Null fields are serialized in default object to json conversion.

EmployeeModel Class:

The parameterized constructor is not setting lastName and contact.
lastName and contact data members should be serialized as null.

package org.learn;

import java.util.Date;

public class EmployeeModel {
    public String firstName;
    public String lastName;
    public String contact;
    public int salary;
    public Date dob;
    public EmployeeModel() {} // JAXB needs this
 
    public EmployeeModel(String firstName, int salary, Date dob) {
        this.firstName = firstName;
        this.salary = salary;
        this.dob = dob;
    }
}

Default json serialized for EmployeeModel

{
firstName: "Random Name 1b09",
lastName: null,
contact: null,
salary: 8240,
dob: 1457589257128
}

2. Customize Object to JSON serialization (objectmapper contextresolver)

We have used ObjectMapper (jackson) to customize the serialization process. ObjectMapperContextResolver class (Custom Serialization using ObjectMapper and ContextResolver)

We will configure the objectMapper, date will not be serialize as timestamp (Date will be serialized in ISO format)
We will set inclusion strategy, so that null fields will not be serialized.

package org.learn;

import javax.ws.rs.ext.ContextResolver;
import javax.ws.rs.ext.Provider;

import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

@Provider
public class ObjectMapperContextResolver implements ContextResolver {

    private final ObjectMapper objectMapper = new ObjectMapper();

    public ObjectMapperContextResolver() {
    	objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
    	objectMapper.setSerializationInclusion(Include.NON_NULL);
    }

    @Override
    public ObjectMapper getContext(Class<?> type) { return objectMapper; }

}

3. RESTful Resource: Service class exposing rest interfaces using Jersey.

Resource /json will produce the EmployeeModel class as JSON
- The generated JSON will have non fields and date field in standard format.
Resource /xml will produce the EmployeeModel class as XML
- The output will be similar to JSON.

package org.learn;

import java.util.Date;
import java.util.Random;
import java.util.UUID;

import javax.ws.rs.Consumes;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;

@Path("/service")
public class Service {

	private static final String text = "status :Server is running " + "\ntime : %s";

	@GET
	@Consumes(MediaType.TEXT_PLAIN)
	public Response getText() {
		String response = String.format(text, new Date());
		return Response.status(Response.Status.OK)
				.entity(response)
				.type(MediaType.TEXT_PLAIN).build();
	}

	@GET
	@Path("/json")
	@Produces(MediaType.APPLICATION_JSON)
	public EmployeeModel getJson() {

		// ...........db operation..
		// suppose we get these value from database
		// ............
		String randomName = "Random Name " + UUID.randomUUID().toString().substring(0, 4);
		int randomSalary = new Random().nextInt((10000-6000) + 1) + 6000;

		// returns the value received from database
		return new EmployeeModel(randomName, randomSalary, new Date());
	}	
	@GET
	@Path("/xml")
	@Produces(MediaType.APPLICATION_XML)
	public EmployeeModel getXml() {
		
		// ...........db operation..
		// suppose we get these value from database
		// ............
		String randomName = "Random Name " + UUID.randomUUID().toString().substring(0, 4);
		int randomSalary = new Random().nextInt((10000-6000) + 1) + 6000;

		// returns the value received from database
		return new EmployeeModel(randomName, randomSalary, new Date());	
	}
}

4. Maven dependencies of Jersey (POM file):

<properties>
	<jdk_version>1.8</jdk_version>
	<jersey_version>2.22.1</jersey_version>
	<servlet_api_version>3.0.1</servlet_api_version>
</properties>

<dependencies>
	<dependency>
		<groupId>org.glassfish.jersey.containers</groupId>
		<artifactId>jersey-container-servlet</artifactId>
		<version>${jersey_version}</version>
	</dependency>
	<dependency>
		<groupId>org.glassfish.jersey.core</groupId>
		<artifactId>jersey-client</artifactId>
		<version>${jersey_version}</version>
	</dependency>
	<dependency>
		<groupId>org.glassfish.jersey.media</groupId>
		<artifactId>jersey-media-json-jackson</artifactId>
		<version>${jersey_version}</version>
	</dependency>

	<dependency>
		<groupId>javax.servlet</groupId>
		<artifactId>javax.servlet-api</artifactId>
		<version>${servlet_api_version}</version>
	</dependency>

</dependencies>

5. Web.xml: Filter configurations defined in web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://java.sun.com/xml/ns/javaee"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
         http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         id="WebApp_ID" version="3.0">
    <display-name>REST Web Application using Jersey Web Application</display-name>

    <servlet>
        <servlet-name>rest-server</servlet-name>
        <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
        <init-param>
            <param-name>jersey.config.server.provider.packages</param-name>
            <param-value>org.learn</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>rest-server</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>

</web-app>

6. Output: GET /json having non nulls & date field

{
firstName: "Random Name 7ea8",
salary: 8297,
dob: "2016-03-10T14:43:48.202+0000"
}

7. Output – GET /xml having non nulls & date field

<Employee>
<firstName>Random Name 72f8</firstName>
<salary>9122</salary>
<dob>2016-03-10T20:15:48.865+05:30</dob>
</Employee>