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Liferay implements several communication mechanisms across portlets including those specified by the JSR-286 standard: public render parameters and events. Public render parameters are easy to use and can be quite powerful. Some Liferay portlets provide a configuration UI to help you get the most out of this communication mechanism. To access this UI, open your portlet’s configuration window by clicking on the gear icon and selecting Configuration. Then click on the Communication tab.


Figure 4.10: You can configure portlets to communicate with each other using public render parameters.

The screenshot above is for the Wiki portlet, which has six public render parameters: categoryId, nodeId, nodeName, resetCur, tag, title. For each of these parameters, you can configure the portlet to ignore the values coming from other portlets to read the value from another parameter.

Why might it be useful to ignore the values for certain parameters that come from other portlets? Consider a common use case for the Wiki portlet. The Wiki portlet is often used along with the Tags Navigation portlet so that when a user clicks on a tag of the latter, the Wiki portlet shows a list of pages with that tag. In some cases, an administrator may want the Wiki portlet to always show the front page independently of any tag navigation done through other portlets. This can be achieved by checking the Ignore checkbox so that the values of the parameter coming from those other portlets are ignored.

Reading the value of a parameter from another portlet is an advanced but very powerful option that allows portlets to communicate with each other even if their developers didn’t intend them to. For example, imagine that the Wiki portlet is being used to publish information about certain countries. Imagine further that there’s another portlet that allows browsing countries for administrative reasons. The second portlet has a public render parameter called country with the name of the country. We’d like the Wiki to show the information from the country that’s selected in the administration portlet. This can be achieved by setting the value of the title parameter of the Wiki portlet to be read from the country parameter of the administration portlet. Cool, isn’t it?

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