Servlet 3.0 was released as part of Java EE 6 and made huge changes
focused at ease-of-use. The idea was to leverage the latest language
features such as annotations and generics and modernize how Servlets
can be written. The web.xml was made as optional as possible. Servet
3.1 (JSR 340),
scheduled to be part of Java EE 7, is an incremental release
focusing on couple of key features and some clarifications in the
specification.
The main features of Servlet 3.1 are explained below:
Non-blocking I/O - Servlet 3.0 allowed asynchronous request
processing but only traditional I/O was permitted. This can
restrict scalability of your applications. Non-blocking I/O
allow to build scalable applications. TOTD
#188 provide more details about how non-blocking I/O can
be done using Servlet 3.1.
HTTP protocol
upgrade mechanism - Section
14.42 in the HTTP 1.1 specification (RFC 2616)
defines an
upgrade mechanism that allows to transition from HTTP
1.1 to some other, incompatible protocol. The capabilities and
nature of the application-layer communication after the protocol
change is entirely dependent upon the new protocol chosen. After
an
upgrade is negotiated between the client and the server, the
subsequent requests use the new chosen protocol for message
exchanges. A typical example is how WebSocket protocol is
upgraded from HTTP as described in Opening
Handshake section of RFC 6455.
The decision to
upgrade is made in Servlet.service
method. This is achieved by adding a new method: HttpServletRequest.
upgrade
and two new interfaces: javax.servlet.http.HttpUpgradeHandler
and javax.servlet.http.WebConnection.
TyrusHttpUpgradeHandler shows how WebSocket protocol
upgrade is done in Tyrus
(Reference Implementation for Java API for WebSocket).
Security enhancements
Applying run-as security roles to #init and #destroy methods
Session
fixation attack by adding HttpServletRequest.changeSessionId
and a new interface HttpSessionIdListener. You
can listen for any session id changes using these methods.
Default security semantic for non-specified HTTP method in <security-constraint>
Clarifying the semantics if a parameter is specified in the
URI and payload
Miscellaneous
ServletResponse.reset clears any data that
exists in the buffer as well as the status code, headers. In
addition, Servlet 3.1 will also clears the state of calling getServletOutputStream
or getWriter.
ServletResponse.setCharacterEncoding: Sets the
character encoding (MIME charset) of the response being sent
to the client, for example, to UTF-8.
Relative protocol URL can be specified in HttpServletResponse.sendRedirect.
This will allow a URL to be specified without a scheme. That
means instead of specifying
"http://anotherhost.com/foo/bar.jsp" as a redirect address,
"//anotherhost.com/foo/bar.jsp" can be specified. In this case
the scheme of the corresponding request will be used.
Clarification in HttpServletRequest.getPart
and .getParts without multipart configuration.
Clarification that ServletContainerInitializer
is independent of metadata-complete and is
instantiated per web application.
A complete replay of What's
New in Servlet 3.1: An Overview from JavaOne 2012 can be seen
here (click on CON6793_mp4_6793_001 in Media).
Each feature will be added to the JSR subject to EG approval. You
can share your feedback to
[email protected].
Here are some more references for you:
Servlet
3.1 Public Review Candidate Downloads
Servlet
3.1 PR Candidate Spec
Servlet
3.1 PR Candidate Javadocs
Servlet
Specification Project
JSR
Expert Group Discussion Archive
Java
EE 7 Specification Status
Several features have already been integrated in GlassFish
4 Promoted Builds. Have you tried any of them ?
Here are some other Java EE 7 primers published so far:
Concurrency
Utilities for Java EE (JSR 236)
Collaborative
Whiteboard using WebSocket in GlassFish 4 (TOTD #189)
Non-blocking
I/O using Servlet 3.1 (TOTD #188)
What's
New in EJB 3.2 ?
JPA
2.1 Schema Generation (TOTD #187)
WebSocket
Applications using Java (JSR 356)
Jersey
2 in GlassFish 4 (TOTD #182)
WebSocket
and Java EE 7 (TOTD #181)
Java
API for JSON Processing (JSR 353)
JMS
2.0 Early Draft (JSR 343)
And of course, more on their way! Do you want to see any particular
one first ?
