Servlet 3 initialisation parameter annotation @WebInitParam

We will show how you can use the servlet 3 initialisation parameter annotation @WebInitParam to inject initialisation parameters in our servlet. We can configure our servlet entirely with annotations which means no more web.xml which is awesome.

Project structure

+--src
|   +--main
|       +--java
|           +--com
|               +--memorynotfound
|                   |--ExampleServlet.java
|       |--resources
|       |--webapp
pom.xml

Maven Dependency

<dependencies>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
        <scope>provided</scope>
    </dependency>
</dependencies>

Servlet 3 initialisation parameter annotation

The @WebInitParam annotation is used to specify init parameters for a servlet or filter. The servlet 3 initialisation parameter takes a required name and value. You can add a description but this is rather informative. In the initialisation method init() we can get our init parameter using the servletConfig.getInitParameter() method.

package com.memorynotfound;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
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;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(
        value = "/example",
        initParams = {
                @WebInitParam(name = "email", value = "[email protected]", description = "Email from webmaster"),
                @WebInitParam(name = "phone", value = "xxxx/xx.xx.xx", description = "Phone webmaster")
        },
        description = "Servlet 3 initialisation parameter annotation example: @WebInitParam")
public class ExampleServlet extends HttpServlet{

    private String email, phone;

    @Override
    public void init(ServletConfig config) throws ServletException {
        email = config.getInitParameter("email");
        phone = config.getInitParameter("phone");
    }

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html");
        PrintWriter out = resp.getWriter();
        out.write("<h2>Servlet 3 initialisation parameter annotation example: @WebInitParam</h2>");
        out.write("<p><strong>E-mail: </strong>" + email + "</p>");
        out.write("<p><strong>Phone: </strong>" + phone + "</p>");
    }

}

Demo

URL: localhost:8080/init-param/example

References

• Servlet 3 API specification

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