What is the significance of url-pattern in web.xml and how to configure servlet?

Question

I have manually configured web.xml for my application. Now, I'm facing issues while running my application. I'm trying to access my servlet from my jsp page. But, it is throwing error as page not found.

The servlets are placed under below folder location

<application folder>/WEB-INF/classes/<package>

So, what should be the entries for servlets in url-pattern and servlet-mapping. So that, servlet can be accessible through URL.

Answer 1

url-pattern is used in web.xml to map your servlet to specific URL. Please see below xml code, similar code you may find in your web.xml configuration file.

<servlet>
    <servlet-name>AddPhotoServlet</servlet-name>  //servlet name
    <servlet-class>upload.AddPhotoServlet</servlet-class>  //servlet class
</servlet>
 <servlet-mapping>
    <servlet-name>AddPhotoServlet</servlet-name>   //servlet name
    <url-pattern>/AddPhotoServlet</url-pattern>  //how it should appear
</servlet-mapping>

If you change url-pattern of AddPhotoServlet from /AddPhotoServlet to /MyUrl. Then, AddPhotoServlet servlet can be accessible by using /MyUrl. Good for the security reason, where you want to hide your actual page URL.

Java Servlet url-pattern Specification:

1. A string beginning with a '/' character and ending with a '/*' suffix is used for path mapping.
2. A string beginning with a '*.' prefix is used as an extension mapping.
3. A string containing only the '/' character indicates the "default" servlet of the application. In this case the servlet path is the request URI minus the context path and the path info is null.
4. All other strings are used for exact matches only.

Reference : Java Servlet Specification

You may also read this Basics of Java Servlet