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

Need to make a quick json fixes – JSONPath for rescue

From time to time I have a need to do some fixes in my json data. In a world of flat files I do this with grep/sed/awk tool chain. How to handle it for JSON? Searching for a solution I came across the JSONPath. It quite mature tool (from 2007) but I haven't hear about it so I decided to share my experience with others.

First of all you can try it without pain online: http://jsonpath.curiousconcept.com/. Full syntax is described at http://goessner.net/articles/JsonPath/



But also you can download python binding and run it from command line:
$ sudo apt-get install python-jsonpath-rw
$ sudo apt-get install python-setuptools
$ sudo easy_install -U jsonpath

After that you can use inside python or with simple cli wrapper:
#!/usr/bin/python
import sys, json, jsonpath

path = sys.argv[1]

result = jsonpath.jsonpath(json.load(sys.stdin), path)
print json.dumps(result, indent=2)

… you can use it in your shell e.g. for json:
{
"store": {
"book": [
      {
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
      },
      {
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
      },
      {
"category": "fiction",
"author": "Herman Melville",
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"price": 8.99
      },
      {
"category": "fiction",
"author": "J. R. R. Tolkien",
"title": "The Lord of the Rings",
"isbn": "0-395-19395-8",
"price": 22.99
      }
    ],
"bicycle": {
"color": "red",
"price": 19.95
    }
  }
}

You can print only book nodes with price lower than 10 by:
$ jsonpath '$..book[?(@.price

Result:
[
  {
"category": "reference",
"price": 8.95,
"title": "Sayings of the Century",
"author": "Nigel Rees"
  },
  {
"category": "fiction",
"price": 8.99,
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"author": "Herman Melville"
  }
]

Have a nice JSON hacking!From time to time I have a need to do some fixes in my json data. In a world of flat files I do this with grep/sed/awk tool chain. How to handle it for JSON? Searching for a solution I came across the JSONPath. It quite mature tool (from 2007) but I haven't hear about it so I decided to share my experience with others.