DDevelopment & Design

Red Black Tree Visualization using HTML5 Canvas and GWT

I created a sample app that demonstrates HTML5 Canvas usage from Java through GWT. I think GWT is an excellent tool for migrating desktop apps into Web nowadays, especially for Java developers. So it’s worth giving it a try. Google has made significant progress on migrating desktop apps into Web during the last year. They propagated trend for HTML5 support and Javascript JIT compilers among modern browsers. So it’s possible to run Quake 2 or CAD software directly in browser at decent speed. Red Black Tree is a balanced BST tree. Details are described on Wikipedia. You can run this sample app directly on appspot (it works on iPhone too :-) ) Sample code can be found here: Browse on GitHub. Let’s start from initialization. First, we need to create Canvas element and add it to HTML. getContext2D is called to obtain drawing context. We register a timer to redraw frames frequently: So doUpdate is called every 50 ms and whenever redrawFrame is set to true, it redraws Canvas contents. In autoplay mode, we call processFrame in while loop. So whenever redraw procedure takes too long, we will process frames without redrawing them. This won’t slow down animation on low resources. Then, we need to draw a tree. We use drawTree procedure, which is recursive and draws nodes along with contents and connections between them: The best part is that we can do regular Java unit tests on Red Black tree to verify the correctness of implementation:

— Previous article

TouK sponsorem Warsjawa 2011

Next article —

SoapUI ext libs and its weirdness

You May Also Like
DDevelopment & Design

Grails with Spock unit test + IntelliJ IDEA = No thread-bound request found

During my work with Grails project using Spock test in IntelliJ IDEA I've encountered this error:

java.lang.IllegalStateException: No thread-bound request found: Are you referring to request attributes outside of an actual web request, or processing a request outside of the originally receiving thread? If you are actually operating within a web request and still receive this message, your code is probably running outside of DispatcherServlet/DispatcherPortlet: In this case, use RequestContextListener or RequestContextFilter to expose the current request.
 at org.springframework.web.context.request.RequestContextHolder.currentRequestAttributes(RequestContextHolder.java:131)
 at org.codehaus.groovy.grails.plugins.web.api.CommonWebApi.currentRequestAttributes(CommonWebApi.java:205)
 at org.codehaus.groovy.grails.plugins.web.api.CommonWebApi.getParams(CommonWebApi.java:65)
... // and few more lines of stacktrace ;)

It occurred when I tried to debug one of test from IDEA level. What is interesting, this error does not happen when I'm running all test using grails test-app for instance.

So what was the issue? With little of reading and tip from Tomek Kalkosiński (http://refaktor.blogspot.com/) it turned out that our test was missing @TestFor annotation and adding it solved all problems.

This annotation, according to Grails docs (link), indicates Spock what class is being tested and implicitly creates field with given type in test class. It is somehow strange as problematic test had explicitly and "manually" created field with proper controller type. Maybe there is a problem with mocking servlet requests?