Question

Good day!

I am reading Head First Servlets and JSP and it says that 99% of servlets make use of the HttpServlet. What is the other 1%? And it says that in the real world, 99.9% of all servlets override either that doGet() or doPost() method. What is the other 0.1%? Or it isn’t worth mentioning that’s why the book didn’t mention it?

Thank you.

Answer 1

The 1% doesn’t make use of abstract HttpServlet class. So they use Servlet interface without extending HttpServlet.

Currently in the Java EE API, there’s only one other Servlet which does that: the FacesServlet which is the core controller behind the Java EE provided MVC framework JavaServer Faces (JSF). JSF enables you to skip all the tedious process and the boilerplate code which is necessary to gather, convert and validate parameters, update the model values and invoke specific action methods.

But at the time of writing this book, the author likely didn’t realize that. As of now, JSF certainly doesn’t account for only 1%. In theory it’s possible to implement Servlet for other protocols than HTTP, like FTP. This is not provided by the standard Java EE API, but there are some 3rd party "FtpServlet" classes out. And I believe some Portlet APIs also use a non-HttpServlet class (they just implement Servlet and don’t extend HttpServlet).

As to the HTTP methods, next to HTTP GET and POST there are also HEAD, PUT, OPTIONS, etc. But I think 0.1% is heavily underestimated. The HEAD is definitely much more often used, think of servletcontainer’s own DefaultServlet (like as Tomcat has). The HEAD plays an important role in browser cache requests. But when it comes to "homegrown" servlets, then it are indeed GET and POST which gets the lone attention.

See also:

• What is the difference between JSP, Servlets and JSF?