Creating a Java Web App Servlet in Visual Studio Code

Would you like to add a Java Http Servlet to your Java web app project? This guide will cover doing just that. 

Rewind - Create a Java Project First

If you missed the Create a Java Project in VS Code, check it out first. 

3 Steps

It takes three easy steps to wire up an HttpServlet.

1. Adding the HttpServlet dependency
2. Add a Java HttpServlet class
3. Map an endpoint to the HttpServlet class.

Add the Dependency to your Project

In a Maven project add the dependency below. In a Java standard project, download the jar and add it to the build path. Check the latest version out here.

<dependencies>
    <dependency>
	    <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>4.0.1</version>
        <scope>provided</scope>
    </dependency>
</dependencies>  
  

Add the Http Servlet Class 

Create an HttpServlet and add it to your source path. This example only shows how to handle a get request. You can handle other request methods too, such as: doDelete, doHead, doOptions, doPost, doPut, and doTrace.

package com.brandondonnelson;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ApiServlet extends HttpServlet {
  
  private static final long serialVersionUID = 1L;

  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
      
      response.setContentType("text/html");

      PrintWriter out = response.getWriter();
      out.println("./api works. Try ./api/getMessage");
   }

}

Add the Http Servlet Endpoint to the web.xml

A servlet can be configured in more than one way. In this way, it must be stated in the web.xml server instructions and mapped to an endpoint, like ./api. If you notice, the ./api endpoint is bound to the ApiServlet, so when the path is dialed up http://something.tld/api, it will run the servlet doGet path. 

<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">

  <display-name>My App</display-name>

  <servlet>
    <servlet-name>ApiServlet</servlet-name>
    <servlet-class>com.brandondonnelson.ApiServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ApiServlet</servlet-name>
    <url-pattern>/api</url-pattern>
  </servlet-mapping>

</web-app>
  

Load the HttpServlet

Now that everything is configured. Load the page. 

• Open the servlet by going to: http://domain.tld/api

Video Tutorial

See the debugging a servlet in action in this video.