DDevelopment & Design

Implementing graph editor in JavaFX using MVC like approach

JavaFX has very good SVG support, embedded into language runtime. This makes it interesting choice for implementing custom UI components, which includes graph editors. In this article, I show how to create a simple graph editor, using MVC like approach and XML serialization via XStream. Example can be found here:

Launch JNLP,Browse on GitHub. Application brings graph editing functionality and maximum network flow computation using Ford Fulkerson algorithm Architecture is divided into Model, View and Controller. I made a slight upgrade to classic understanding of MVC. Classic View was responsible for displaying data only. Here, View consists also of UI parts, which include editable labels or combo boxes. Also, in Classic MVC, Model was responsible for refreshing View after Model changes by sending events to registered views. Here, Controller is responsible for refreshing View after Model changes and Model is just a plain POJO structure. I found such approach easier to implement. Model consists of Three Java classes (non JavaFX), which represent structure of a graph: MNode, MShape, MConnection. Separating those classes from UI gives benefit of easier serialization. In this case using XStream::toXML(model) does the job. Sample output is like this: View consists of corresponding UI implementations for Model elements, which are UINode, UILine, UIShape. Here, UINode is connected to MNode through model property. This is Bridge Pattern like approach for splitting class hierarchy of nodes into two. UINode classes refer to controller to perform user input actions, like delete node. Controller implements user action logic. This includes add, delete, and drag node. It is also responsible for refreshing UI after model changes. In order to do that easily, it uses Weak Hash Map, which keys are Model nodes and values are UI Nodes. Update function is like this: Because of Weak Hash Map, removing nodes from Model leads to removing corresponding UI elements from map automaticly. JavaFX SVG support and Layouts make it easy to render quite good looking nodes and connections.

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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?