What does portlet programming in java can offer to us?

even i do search in google, and read some of the article, but i still not clear what portlet in java can do for us (english is not my native language, sometime is hard to totally understand what people wrote)

i was discussing with my friend between java and php.

most of the php forum, they allow user to install forum plug-in on the fly within the forum system. some of the forum system even have a plugin list in the backend, the list is displaying all the plugin offer from that forum system, after clicking install, the system will download all the file need and install into the local forum system. just like we purchase iphone app from app store

while in java, we all know if we want to add any functionality into a web application, we have to recompile build the war again, and deploy onto the server container. Seems it is not possible to do things like php did.

however,　there is a application JIRA, seems it was writen in java technology, and they allow their user to do things justs like the php application i descrip above.

and i happened to know the te开发者_运维知识库rm "portlet", both spring and apache have such kind of project as well. Spring Portlet MVC and Apache Jetspeed

so does it real those portlet framework can offer us to build web application like those php forum did???

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If you want to add feature to application written in ANY language you can either change the application and deploy it again OR you can use the plugin system(if the application has one)

JIRA has the plugin system so adding features is easy. But it's using its own proprietary plugin system. So if you write a Jira plugin it will work only in Jira. You cannot use it for example in Bugzilla or Trac.

Portlet is just plugin with standardized API. Main motivation is the ability to write portlet which will work on portal servers from multiple vendors. This goal is often hard-to-reach to be honest. But true is it at least simplify the porting.

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Liferay is a very powerful and popular open source portlet container implementation wich implements both JSR 168 and JSR 286 portlet standards. If offers a plugin-like deployment system.

Available new portlets are listed in a marketplace like manner and can be downloaded and installed by clicking a single button. You can drag and drop them after installation on your pages and they are available immediately.

By default, Liferay connects to liferay.com portlet repository and displays all portlets available there, but it is very easy to set up your own repository (e.g. corporate) and host portlets on your own.

There is an online demo available and you can download and install it in just a few steps.