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Servlets

Server-Sent Events (SSE) is part of HTML5. SSE is a simple, undirectional communication from server to browser. It allows server to push data to client once a connection is established. The entire point of SSE is to make it easy for the server to push messages to the browser, once the browser has first established a connection to the server. These messages are of the form "field: value" with...
on May 21, 2014
javax.servlet.http.HttpSession provides a way to identify an user across multiple HTTP requests and to store user specified information. In other words, it provides a support of stateful communications with the stateless HTTP protocol. For security and memory management, sessions need to be invalidated at a certain time. There are two related methods in HttpSession. HttpSession.invalidate() By...
on Aug 29, 2013
Expression Language (EL) was first introduced as part of JSTL 1.0, was then moved JSP 2.0 and was unified with JSF 1.2 in JSP 2.1. In Java EE 7, EL is a new separate JSR, JSR 341. Many new features are introduced in EL 3.0. This blog shows how to use new following new features of EL 3.0: Standalone environment Lambda expression (section 1.20 of EL 3.0 spec) The new operator ; to separate...
on Jul 1, 2013
Asynchronous operation was introduced in Servlet 3.0. ServletRequest#startAsync is used to put the request into asynchronous mode. A thread need to be created implicitly or explicitly (see here for an example). Servlet 3.1, JSR 340 includes clarifications in asynchronous area. Besides Servlet 3,1, Concurreny Utilities for Java EE 1.0, JSR 236 is introduced in Java EE 7. JSR 236 provides a...
on Jun 6, 2013
Update: In Servlet 3.0, the behavior of using response is undefined after invoking #complete or #dispatch. In Servlet 3.1, it is clarified that AsyncContext#getResponse will throw IllegalStateException. The blog has been updated for this. Asynchronous operation is supported in Servlet 3.0. I have discussed startAsync in my previous blog, startAsync in Servlet 3.0. In this blog, I will discuss...
on May 14, 2013

Programming

Java API for WebSocket is a new JSR to Java EE 7. It provides a stardard Java API for creating WebSocket applications. This gives web applications the ability to push data. In Java EE 6 samples, we added a chat room sample to illustrate how to use of Servlet 3.0 asynchronous operation. In that sample, the servlet code did the following: keep track of AsyncContext in a Queue create a thread to...
on Aug 13, 2013

Security

Servlet 3.1 Specification (JSR 340) is almost ready for the release. Several new security features have been added in this version of Servlet specification. In this blog, I will explain one of the security features, namely deny-uncovered-http-methods. Let us take a look at a simple security-constraint in web.xml as follows: <web-app xmlns="http://www.w3.org/2001/XMLSchema" ...
on Apr 19, 2013
Servlet 3.1 was in Public Review in Janurary 2013. And it is in Proposed Final Draft now. Most of the new features are related to security. In this following, I will highlight features since Servlet 3.1 Public Review: add new API javax.servlet.http.Part#getSubmittedFileName add new API javax.servlet.ServletContext#getVirtualServerNameThis API allows a JASPIC module to be registered in a Servlet...
on Mar 18, 2013

JSR

Update: One should not use response in AsyncListener#onComplete. Only print debug in this example. Servlet 3.1 (JSR 340) is almost ready for the release. One of the new features is the support for non-blocking IO. ReadListener and WriteListener are introduced to allow non-blocking processing in Servlet. Non-blocking IO can only be used in async (defined in Servlet 3.0) or the upgrade mode. We can...
on Apr 16, 2013