How To Test Servlet Using Postman

Testing Servlets with Postman: A Comprehensive Guide

Servlet testing is an essential part of web application development. Postman, a powerful API testing tool, can be instrumental in efficiently testing your servlets. This guide provides a comprehensive overview of how to use Postman to test servlets, encompassing various aspects and practical examples.

Setting Up Your Environment

Before diving into testing, you need a suitable environment. Ensure you have the following:

Java Development Kit (JDK): Download and install the JDK appropriate for your operating system. You’ll need it to compile and run your Servlet code.
Servlet Container (e.g., Tomcat): You’ll need a servlet container to host and execute your servlets. You can download and install Apache Tomcat, a popular choice, from https://tomcat.apache.org/
Postman: Download and install Postman from https://www.postman.com/. It offers both a desktop app and a web-based version.
IDE (Optional): An IDE like Eclipse, IntelliJ IDEA, or NetBeans can help you write and manage your servlet code.

Creating a Simple Servlet

Let’s start with a basic servlet to demonstrate testing. The following Java code defines a servlet that responds to HTTP GET requests:

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class GreetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head><title>Greetings!</title></head>");
        out.println("<body>");
        out.println("<h1>Hello from the Servlet!</h1>");
        out.println("</body>");
        out.println("</html>");
    }
}

Deploying the Servlet

Deploy your servlet in your chosen servlet container (Tomcat in this example).

Create a web application: Create a directory structure inside Tomcat’s “webapps” folder (e.g., “myWebApp”).
Compile the servlet: Compile GreetServlet.java using the JDK.
Place the servlet class: Move the compiled GreetServlet.class file into the WEB-INF/classes directory inside your web application folder.
Create web.xml (optional): Create a web.xml file in the WEB-INF directory to define theservlet mapping (if not using annotations).

Sample web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
     version="3.1">

  <servlet>
    <servlet-name>GreetServlet</servlet-name>
    <servlet-class>GreetServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>GreetServlet</servlet-name>
    <url-pattern>/greet</url-pattern>
  </servlet-mapping>

</web-app>

Start Tomcat: Start your Tomcat server.

Now your Servlet is deployed and ready to be tested using Postman.

Testing Servlet with Postman

Sending an HTTP Request

Open Postman: Launch the Postman application.
Create a new request: Click on “New” or ”+“.
Set the request details:
- HTTP Method: Select “GET” as the HTTP method for our servlet.
- URL: Enter the complete URL to access your servlet. The URL format would be something like http://localhost:8080/myWebApp/greet (adjust the port number and web application name if necessary).
Send Request: Click the “Send” button in Postman.

Analyzing the Response

Postman will display the response from the servlet. You can check:

Status Code: The HTTP status code (e.g., 200 OK) will indicate if the request was successful.
Response Headers: The response headers provide additional information.
Response Body: The content returned by the servlet will be shown here. In our example, you should see the HTML output containing “Hello from the Servlet!” .

Testing Different HTTP Methods

You can test your servlet for different HTTP methods (POST, PUT, DELETE) in Postman. Simply change the request method on the Postman interface.

Testing with Parameters

Scenario: Adding a Name Parameter

Let’s modify our servlet to handle a parameter:

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class GreetServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        String name = request.getParameter("name");
        out.println("<!DOCTYPE html>");
        out.println("<html>");
        out.println("<head><title>Greetings!</title></head>");
        out.println("<body>");
        if (name != null) {
            out.println("<h1>Hello " + name + "!</h1>");
        } else {
            out.println("<h1>Hello!</h1>");
        }
        out.println("</body>");
        out.println("</html>");
    }
}

Send a GET request with parameters: Go back to Postman. In the URL section, append a query parameter: http://localhost:8080/myWebApp/greet?name=John.
Send Request and Analyze: Send the request. The response will now say “Hello John!”

Testing with Authentication

If your servlet needs authentication (e.g., using Basic Auth, API keys, etc.), you can configure this directly within Postman:

Authorization Tab: In Postman, click on the “Authorization” tab.
Select Type: Choose the authentication type (e.g., Basic Auth, API Key).
Provide Credentials: Enter your authentication credentials as required.

Testing with JSON Data

Scenario: Sending JSON data to a POST Servlet

Let’s assume you have a POST servlet that accepts JSON data. You’ll need a way to send JSON data from Postman.

Create your Servlet: In Java, create a servlet that handles POST requests and parses the JSON data. You can use libraries like Gson or Jackson to handle JSON serialization and deserialization.
Create POST request in Postman: In Postman, switch the “GET” method to “POST”.
Send JSON data: In the “Body” tab, choose “raw” and select “JSON” for the format. Enter your JSON data.

Example JSON:

{
  "name": "Jane Doe",
  "age": 30
}

Analyze the response: Send the request. Your server should process the JSON data and return a response. Analyze the response in Postman.

Additional Considerations

Error Handling: Test for potential errors that your servlet might encounter (e.g., invalid inputs, missing parameters).
Load Testing: Postman can be integrated with tools like Newman for performance and load testing.
Pre-request Scripts: Postman allows you to use JavaScript-based pre-request scripts to automate data manipulation before sending a request.
Post-request Scripts: You can use post-request scripts in Postman to assert the correctness of responses.

By following these steps, you can effectively test your servlets using Postman to ensure their functionality and reliability.