DDevelopment & Design

Creating charts in GWT was never so easy. (OFC GWT)

  • byRafal P
  • January 18, 2011
  • 3 minute read

In Java world there are many libaries which allow to create charts (with the most popular is JFree Chart Library). None of this libraries are however simple, powerfull and gives pretty looking charts. This is why I investigated Open Flash Chart which is library for charting written in flash. Fortunately there is a port for GWT which allows to use OFC in RIA applications. So in the next few paragraphs I will show how to use OFC GWT (this is the name of GWT port) and why this library is so amazing. Enjoy.

Starting point is OFC GWT homepage. This is the place from where porting libary (with OFC inside) could be downloaded.  I prefer to use maven  instead of downloading, so here is part of my pom.xml configured for OFC GWT. Notice that the library version is 1.3.0 but in the nearest future there will be release of new 2.0.1 version (now available in beta).

..
<br />
<repositories><br />
<repository><br />
<id> OFCGWT repo</id><br />
<url>http://logicaldoc.sourceforge.net/maven</url><br />
</repository><br />
</repositories><br />

…
<br />
<dependency><br />
<groupid>ofcgwt</groupid><br />
<artifactid>ofcgwt</artifactid><br />
<version>1.3.0</version><br />
</dependency><br />
..

Now, after the OFC GWT library is downloaded, it’s time to make some code. In OFC GWT there are many sort of charts such as: bar (horizontal, vertical), pie, scater, radar etc. All them are represented in GWT by ChartWidget class (which extends Widget). This class is a wrapper, which can be placed on any GWT panel, container just like normal GWT widget. ChartWidget renders chart on screen by communicating with OFC library by JSON.
JSON data, which describes chart to draw, have to be created by ChartData class. This is the heart of the OFC GWT port, the most important class. This class objects are used to configure title, axies, data and chart type to render. Below is the code which shows how easy is to use both above classes.

..
<br />
FlowPanel panel = new FlowPanel();

ChartWidget chart = new ChartWidget();
ChartData chartData = new ChartData(title);
chartData.setBackgroundColour(“#ffffff”);//white background
chartData.addElements(createPieChart());
chart.setSize(“350”, “350”);
chart.setJsonData(chartData.toString());

panel.add(chart);

..

Only one thing left – function which create pie chart. In OFC You can chose from various charts. All of them are easy and simmilar in use. There is a good demo app with source code in the library, where You can find out how to configure each graph. Here is my code, which creates animated and transparent pie chart without labels on graph.

<br />
private PieChart createPieChart() {<br />
PieChart pieChart = new PieChart();<br />
pieChart.setAlpha(0.3f);    //set transparency<br />
pieChart.setNoLabels(true); // w do not want labels on screen<br />
pieChart.setAnimate(true);<br />
pieChart.setGradientFill(true);<br />
pieChart.setColours("#779C00", "#0000ff");<br />
pieChart.setTooltip("#label# - #val#");<br />
pieChart.addSlices(new PieChart.Slice(30, "TV's in Poland")); //this should be passed in parameter<br />
pieChart.addSlices(new PieChart.Slice(70, "Radios in Poland"));//this should be passed in parameter<br />
return pieChart;<br />
}<br />

And thats all. This is all You need to draw pretty looking graphs. No playing with css’es or colors, no complicated building of data sets and what is the most important, not even line of server side code!

Here is the running example of OFC GWT charts, where You can see and experiment with different types and effects.

One more thing. OFC GWT is not only library to draw charts. It also allows to handle user interaction. This is done by IOnClickListener’s. More about themcould be found in OFC GWT JavaDocs.

More graph examples:

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DDevelopment & Design

Simple trick to DRY your Grails controller

Grails controllers are not very DRY. It's easy to find duplicated code fragments in default generated controller. Take a look at code sample below. It is duplicated four times in show, edit, update and delete actions:

class BookController {
def show() {
def bookInstance = Book.get(params.id)
if (!bookInstance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
return
        }
        [bookInstance: bookInstance]
    }
}

Why is it duplicated?

There is a reason for that duplication, though. If you move this snippet to a method, it can redirect to "list" action, but it can't prevent controller from further execution. After you call redirect, response status changes to 302, but after method exits, controller still runs subsequent code.

Solution

At TouK we've implemented a simple trick to resolve that situation:

  1. wrap everything with a simple withStoppingOnRender method,
  2. whenever you want to render or redirect AND stop controller execution - throw EndRenderingException.

We call it Big Return - return from a method and return from a controller at once. Here is how it works:

class BookController {
def show(Long id) {
withStoppingOnRender {
Book bookInstance = Book.get(id)
validateInstanceExists(bookInstance)
            [bookInstance: bookInstance]
        }
    }

protected Object withStoppingOnRender(Closure closure) {
try {
return closure.call()
        } catch (EndRenderingException e) {}
    }

private void validateInstanceExists(Book instance) {
if (!instance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
throw new EndRenderingException()
        }
    }
}

class EndRenderingException extends RuntimeException {}

Example usage

For simple CRUD controllers, you can use this solution and create some BaseController class for your controllers. We use withStoppingOnRender in every controller so code doesn't look like a spaghetti, we follow DRY principle and code is self-documented. Win-win-win! Here is a more complex example:

class DealerController {
@Transactional
def update() {
withStoppingOnRender {
Dealer dealerInstance = Dealer.get(params.id)
validateInstanceExists(dealerInstance)
validateAccountInExternalService(dealerInstance)
checkIfInstanceWasConcurrentlyModified(dealerInstance, params.version)
            dealerInstance.properties = params
saveUpdatedInstance(dealerInstance)
redirectToAfterUpdate(dealerInstance)
        }
    }
}