Liferay (s)mashup - The Beginning

Part Two - Liferay (s)mashup - Google Maps

There are many popular web services available online. From the rich set of APIs from Google and Yahoo to social sites likeTwitter and Facebook, almost all service providers make available their services in the form of an open API. These rich APIs has given rise to new kind of applications called mashups. They are basically an integration of various web APIs from different providers put together to form new kind of applications.

In this and the next series of blogs, I will show how to integrate with some of these APIs.

To make meaningful use of these APIs, let me propose a sample application where these services can be used. Let us develop a travel planning site that helps user to plan their travel dates and location. Travelling is just not about location and date. There are other factors like weather conditions, transport availabiity, political turmoil, other events clashing with date. Questions such as 'Are any of my friends travelling on that date or to that location?', 'Do I know anyone from that location I am going to?' frequently comes up. Our site will try to resolve these questions so that a probable date and location can be zeroed on.

Features of the Application
 - Display input form for receiving the source, destination, journey date and duration.
 - Show the road route of the origin and destination in Google map
 - Show weather information of origin and destination
 - Show the event happening in origin and destination on and around the journey date
 - Show news related to origin and destination
 - Moving the marker on the Google map must also update all other information in real time like weather, events, news and  the input form.

 - More services as we go along

For the first requirement, create a new portlet. In the view.jsp file, design a basic form  for the user to fill in: Origin, Destination, Journey Date and Duration.

Code Listing

<form action="<liferay-portlet:actionURL portletConfiguration="true" />" method="post" name="<portlet:namespace />fm">
    <aui:input name="origin" label="Origin" />
    <aui:input name="destination" label="Destination" />
    <aui:input name="journeyDate" label="Journey Date" />
    <aui:input name="duration" label="Duration" suffix="(in days)" />
    <input type="button" value="Search" onclick="<portlet:namespace />postPlanDetails()" />
</form>

The journeyDate is shown as a calendar when user clicks on the input field. Define it in javascript as:

AUI().ready('aui-calendar', function(A) {
    var calendar1 = new A.Calendar({
        trigger : '#<portlet:namespace />journeyDate',
        dateFormat : '%d/%m/%Y',
        setValue : true,
        selectMultipleDates : true,
        on : {
            select : function(event) {
                var normal = event.date.normal;
                var detailed = event.date.detailed;
                var formatted = event.date.formatted;
            }
        }
}).render();

A.on('mousedown', function() {
    A.CalendarManager.hideAll();
}, document);

});

The postPlanDetails() javascript function is defined as follows:

function <portlet:namespace />postPlanDetails() {
    var origin = document.<portlet:namespace />fm.<portlet:namespace />origin.value;
    var dest = document.<portlet:namespace />fm.<portlet:namespace />destination.value;
    var journeyDate = document.<portlet:namespace />fm.<portlet:namespace />journeyDate.value;
    var duration = document.<portlet:namespace />fm.<portlet:namespace />duration.value;

    Liferay.fire('planTravel', {
        origin : origin,
        destination : dest,
        journeyDate : journeyDate,
        duration : duration
    });

}

The code in bold above functions publishes the 4 parameters as an event using Liferay client side Inter Portlet Communication. For more details on IPC, see Portlet to Portlet Communication.

This portlet also receives the 'directionsChanged' event from the Google Maps portlet. We will discuss this in the next blog.

Liferay.on('directionsChanged',
    function(event) {
        document.<portlet:namespace />fm.<portlet:namespace />origin.value = event.origin;
        document.<portlet:namespace />fm.<portlet:namespace />destination.value = event.destination;
});

Speeding up page loading

Developing fast loading pages is a complex task. Some have even defined it as an art. Large companies have dedicated professionals or hire external consultants to audit their applications for speed and responsiveness.

Here I provide some simple tips to speed up page loading in Liferay. Liferay also provides some in built features for fast page loading. Whenever available, Liferay support will be shown for each tip.

Tip 1: Sharing script and css files across portlets

For each script and css file included in a page, the browser makes separate requests to fetch them. This takes time. If the same file is included many times, the browser only makes requests the first time and for subsequent access, it picks from the cache. Therefore, common javascript code should be placed in a single file and this file should be included in all portlets that need it.

To share scripts across portlets, use the <header-portlet-javascript> tag or <footer-portlet-javascript> tag in the liferay-portlet.xml file. Similarly, use <header-portlet-css> tag or the <footer-portlet-css> tag in the liferay-portlet.xml file.

Tip 2: Lazy loading of scripts

Sometimes, scripts are not immediately needed after page load but only after user takes some action. To prevent such scripts being loaded on page load, we can load in the background after the page has loaded. There are two ways for lazy loading. One, the script is added to the <head> tag and the other is to add it to the <body> tag.

Adding to head tag:
function loadScript() {
    var script = document.createElement("script");
    script.type = "text/javascript";
    script.src = "";
    var head = document.getElementsByTagName("head")[0];
    head.appendChild(script);
}

window.onload = loadScript;

The function loadScript() above creates a dynamic script tag and adds it to the first head tag available. It registers this function to be called on load of the page.

Adding to body tag:

function loadScript() {
    var script = document.createElement("script");
    script.type = "text/javascript";
    script.src = "";
    document.body.appendChild(script);
}

window.onload = loadScript;

The function loadScript() above creates a dynamic script tag and adds it to the body. It registers this function to be called on load of the page.

Tip 3: Minimize script, stylesheet and html output

Whitespace and comments in script file or html pages takes up bandwith and so slows down page load. While comments and whitespaces are necessary for development, in production they should be removed. It would be nice to not to change the source code for production while still be able to remove the comments and whitespaces. A simple technique for this would be to use server side comments in jsp files and not to use html or javascript comments. Whitespaces cannot be handled this way.
Liferay provides a minifier process that strips down both whitespaces and comments from script and css files. The minifier also shortens function and variable names to make the script even smaller. To enable the minifier, set the option in the portlet-ext.properties file.

com.liferay.portal.servlet.filters.minifier.MinifierFilter=true

Another option Liferay provides is to load packed (compressed) versions of Liferay scripts and css. Enable it using

javascript.fast.load=true

By default, both the options are true. Make sure, they are not false on production systems.

Tip 4: Specify image and table width and height

If the browser can immediately determine the height and/or width of images and tables, it will be able to display a web page without having to reflow the content. This not only speeds the display of the page but prevents annoying changes in a page's layout when the page completes loading. For this reason, height and width should be specified for images and tables, whenever possible.