The @WebServletannotation is used to declare a servlet. The annotated class must extend the javax.servlet.http.HttpServlet class.

Syntax of @WebServlet Annotation:

@WebServlet(
    attribute1=value1,
    attribute2=value2,
    ...
)
public class TheServlet extends javax.servlet.http.HttpServlet {
    // servlet code...
}

Attributes of @WebServlet Annotation:

NOTE: the attributes displayName, description, smallIcon and largeIcon are primarily used by tools, IDEs or servlet containers, they do not affect operation of the servlet.

Some Examples with @WebServlet Annotation:

• A servlet is annotated with only the URL pattern:

  import java.io.IOException;
  
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  @WebServlet("/processForm")
  public class MyServlet extends HttpServlet {
  	public void doGet(HttpServletRequest request, HttpServletResponse response)
  			throws IOException {
  		response.getWriter().println("Hello");
  	}
  }

  Here the servlet MyServlet is mapped to the URL pattern /processForm. When accessing this servlet, it will return a “Hello” message.

• A servlet is annotated with multiple URL patterns:

  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  
  @WebServlet(urlPatterns = {"/sendFile", "/uploadFile"})
  public class UploadServlet extends HttpServlet {
  	// implement servlet doPost() and doGet()...
  }

  Here the servlet UploadServlet can be accessed through two URL patterns: /sendFile and /uploadFile.

• Declare a servlet with additional information:
  

  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  
  @WebServlet(
  		name = "MyOwnServlet",
  		description = "This is my first annotated servlet",
  		urlPatterns = "/processServlet"
  )
  public class MyServlet extends HttpServlet {
  	// implement servlet doPost() and doGet()...
  }

   

  Here we specify name and description for the servlet class MyServlet. 

• Declare a servlet with some init parameters:
  

  import java.io.IOException;
  import java.io.PrintWriter;
  
  import javax.servlet.annotation.WebInitParam;
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  @WebServlet(
  		urlPatterns = "/imageUpload",
  		initParams =
  		{
  			@WebInitParam(name = "saveDir", value = "D:/FileUpload"),
  			@WebInitParam(name = "allowedTypes", value = "jpg,jpeg,gif,png")
  		}
  )
  public class ImageUploadServlet extends HttpServlet {
  
  	public void doGet(HttpServletRequest request, HttpServletResponse response)
  			throws IOException {
  		String saveDir = getInitParameter("saveDir");
  		String fileTypes = getInitParameter("allowedTypes");
  
  		PrintWriter writer = response.getWriter();
  
  		writer.println("saveDir = " + saveDir);
  		writer.println("fileTypes = " + fileTypes);
  	}
  }

   

  Here we declare the ImageUploadServletmapped by the URL pattern /imageUpload and specify two init parameters saveDir and allowedTypes. The doGet() method retrieves values of these parameters and prints them out to the client.

• Declare a servlet with asynchronous operation mode and load-on-startup order:

import javax.servlet.ServletConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;

@WebServlet(
		urlPatterns = "/myController",
		loadOnStartup = 1,
		asyncSupported = true
)
public class StartupServlet extends HttpServlet {
	
	public void init(ServletConfig config) {
		System.out.println("My servlet has been initialized");
	}
	
	// implement servlet doPost() and doGet()...
}

Here we declare the servlet StartupServlet with loadOnStartup = 1 which means that this servlet is initialized automatically by the servlet container when the server is being started (the message in the init() method will be printed). We also specify the servlet supports asynchronous mode.

Related Java Servlet Annotations:

• @WebFilter annotation
• @WebListener annotation
• @WebInitParam annotation
• @HandlesTypes annotation
• @MultipartConfig annotation
• @ServletSecurity, @HttpMethodContraint and @HttpConstraint annotations

Other Java Servlet Tutorials:

• Java Servlet Quick Start for beginners (XML)
• Java Servlet for beginners (annotations)
• Java Servlet and JSP Hello World Tutorial with Eclipse, Maven and Apache Tomcat
• Handling HTML form data with Java Servlet
• Java File Download Servlet Example

About the Author:

Nam Ha Minh is certified Java programmer (SCJP and SCWCD). He began programming with Java back in the days of Java 1.4 and has been passionate about it ever since. You can connect with him on Facebook and watch his Java videos on YouTube.