Servlets and JSP

JSPs are Actually Servlets

JSPs are actually servlets. Container will convert all jsp files as servlets before executing it. By default, the JSP is compiled into a servlet and then loaded the first time it is accessed. This might cause a small delay for the first request, but there won’t be any delay in subsequent requests. You may also precompile JSPs before adding them into JARs. Certain application servers might even provide tools for doing so.

How can you suppress direct access to a JSP file and allow only programmatic access?

Answer

I can suppress direct access to a JSP file and want users to go only through a registered name and a servlet mapping in web.xml. I can place the JSP page under WEB- INF and configure it in the web.xml file.

JSP Elements Overview

A JSP page can be said to be divided into two types of contents, which are template text and JSP elements. Template text is any non-java lines like html, comments, javascript, css etc. that are directly sent to the client without any processing. Java code is embedded into JSP pages using scripting elements and these elements will be processed and not directly rendered to the output like template text.

 

JSP elements can be mainly divided into 3 categories:

The JSP Life Cycle Events

JSPs are actually servlets, as you have already seen. Container will convert all jsp files into servlets before executing them. JSPs just provide an easy way to create components containing non-java code.

Once a JSP page is created and deployed, container will do some life cycle events, which also includes calling some of its methods similar to servlet life cycle events.

 

Introduction to Java Server Pages (JSPs)

JavaServer Pages (JSP) is a technology that helps software developers create dynamically generated web pages based on HTML, Javascript, CSS, XML, or other web technologies.

Irrespective of the server side technology like servlet, JSP, ASP or PHP, programming language independent web technologies like html, javascript, css etc. are finally sent to client by default as client can only understand these web technologies like html, javascript, css etc. by default and not any server side technologies.

[Demo] Deploying Using Web Fragments (web-fragment.xml) Using Eclipse Feature

Web fragments are xml files that will have part of the configurations of a web.xml. There can be many web fragments, and when the application is deployed container will combine all the fragments and will treat it like a single web.xml. Similar to annotations, now developers can write web fragments for their modules and application assemblers would not have to add them to the web.xml file. We can override annotation behavior with a web fragment or web.xml.

Deploying using Web Fragments (web-fragment.xml)

Annotations were introduced to reduce the burden of Application assemblers who would otherwise have to combine every developer’s configuration details into the web.xml file. Thus annotations allow for pluggability of the code by allowing developers to specify configurations on their own classes and hence application assemblers would not have to add them to the web.xml file. We can still use web.xml to override any of the configuration given by an annotation.

[Demo] Multipart File Upload in Servlet 3.0 Using Multipart Config - Errors and Exceptions

Methods related to getPart will throw IOException if an I/O error occurred during the retrieval of the Part components of this request, ServletException if this request is not of type multipart/form-data or IllegalStateException if the request body is larger than maxRequestSize, or any Part in the request is larger than maxFileSize.

[Demo] Multipart File Upload in Servlet 3.0 Using Multipart Config

Java EE introduced built in support for handling multipart MIME file uploads in Servlet 3.0 (Java EE 6). If you enable this functionality on a servlet, the container will make additional methods available on an HttpServletRequest to get all parts available on a request and also to get one of those parts passing in its name. We will see a demo of the multipart file upload in Servlet 3.0 using multipart config.

Multipart File Upload in Servlet 3.0 Using Multipart Config

Java EE introduced built in support for handling multipart MIME file uploads in Servlet 3.0 (Java EE 6). Web servers based on PHP and ASP.NET have provided this functionality for some time now, saving having to use other third party libraries for the multipart “heavy lifting”.

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