How to Return a JSON Response from a Java Servlet

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In this blog post, we'll create a simple web application and explore how to return a JSON response from a Java Servlet. We'll use the latest versions of the relevant libraries and tools to ensure our example is up-to-date.

Returning a JSON response from a Java Servlet is a common task, especially in RESTful web services.

Development Steps

1. Create a Maven Web Application
2. Add Maven Dependencies
3. Create a Java POJO Entity - User.java
4. Create Servlet and Return JSON Response - UserServlet.java
5. Demo

Tools and Technologies Used

• Java 11 or later
• Servlet 6.1.0
• GSON 2.8.8
• IDE - Eclipse
• Maven 3.6 +

Step 1: Create a Maven Web Application

Let's create a simple Maven web application in Eclipse IDE using this guide.

Refer to the following project structure for your reference:

Step 2: Add Maven Dependencies

Add the latest release of the required dependencies to your pom.xml file:

 <dependency> <groupId>jakarta.servlet</groupId> <artifactId>jakarta.servlet-api</artifactId> <version>6.1.0</version> <scope>provided</scope> </dependency> <dependency> <groupId>com.google.code.gson</groupId> <artifactId>gson</artifactId> <version>2.8.8</version> </dependency> </dependencies> 

Step 3: Create a Java POJO Entity - User.java

Let’s create a User entity, which will later be returned from the Servlet as JSON:

package net.javaguides.servlet; import java.util.Date; public class User { private long id; private String firstName; private String lastName; private String emailId; private Date createdAt; private String createdBy; private Date updatedAt; private String updatedBy; public long getId() { return id; } public void setId(long id) { this.id = id; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getEmailId() { return emailId; } public void setEmailId(String emailId) { this.emailId = emailId; } public Date getCreatedAt() { return createdAt; } public void setCreatedAt(Date createdAt) { this.createdAt = createdAt; } public String getCreatedBy() { return createdBy; } public void setCreatedBy(String createdBy) { this.createdBy = createdBy; } public Date getUpdatedAt() { return updatedAt; } public void setUpdatedAt(Date updatedAt) { this.updatedAt = updatedAt; } public String getUpdatedBy() { return updatedBy; } public void setUpdatedBy(String updatedBy) { this.updatedBy = updatedBy; } } 

Step 4: Create Servlet and Return JSON Response - UserServlet.java

A quick sample for converting an object to JSON representation with Gson would be:

String userJsonString = new Gson().toJson(user); 

For producing a JSON response, the content type should be application/json:

PrintWriter out = response.getWriter(); response.setContentType("application/json"); response.setCharacterEncoding("UTF-8"); out.print(userJsonString); out.flush(); 

Now, let’s create UserServlet that returns a JSON response:

package net.javaguides.servlet; import java.io.IOException; import java.io.PrintWriter; import java.util.Date; import jakarta.servlet.annotation.WebServlet; import jakarta.servlet.http.HttpServlet; import jakarta.servlet.http.HttpServletRequest; import jakarta.servlet.http.HttpServletResponse; import com.google.gson.Gson; /** * Class demonstrates how to return JSON from a servlet using Gson API. */ @WebServlet(name = "UserServlet", urlPatterns = "/userServlet") public class UserServlet extends HttpServlet { private static final long serialVersionUID = 1L; private Gson gson = new Gson(); @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException { User user = new User(); user.setId(100L); user.setFirstName("Ramesh"); user.setLastName("Fadatare"); user.setCreatedAt(new Date()); user.setCreatedBy("Admin"); user.setEmailId("ramesh@gmail.com"); user.setUpdatedAt(new Date()); user.setUpdatedBy("Admin"); String userJsonString = this.gson.toJson(user); PrintWriter out = response.getWriter(); response.setContentType("application/json"); response.setCharacterEncoding("UTF-8"); out.print(userJsonString); out.flush(); } } 

Step 5: Demo

Deploy this web application in the Tomcat server and access it at: http://localhost:8080/servlet-json-example/userServlet.

Conclusion

In this tutorial, we have learned how to create a simple web application and return a JSON response from a Java Servlet using the Gson library. This approach is useful for building RESTful APIs where JSON is the standard format for data exchange.

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