New article: Dependency Injection and Unit Testing

[Ulf Dittmer]

The current issue of the JavaRanch Journal has an article by Christophe Verré about Dependency Injection and Unit Testing. You can check it out here, and if you have comments or question, feel free to post them in this thread.

[qunfeng wang]

public class FarmServlet extends ActionServlet {
 
public void doAction( ServletData servletData ) throws Exception {
String species = servletData.getParameter("species");
String buildingID = servletData.getParameter("buildingID");
if ( Str.usable( species ) && Str.usable( buildingID ) ) {
FarmEJBRemote remote = FarmEJBUtil.getHome().create();
remote.addAnimal( species , buildingID );
}
}
}

public class FarmServlet extends ActionServlet {
private FarmEJBRemote remote;
 
public void setRemote(FarmEJBRemote remote) {
this.remote = remote;
}
    
public void doAction( ServletData servletData ) throws Exception {
String species = servletData.getParameter("species");
String buildingID = servletData.getParameter("buildingID");
if ( Str.usable( species ) && Str.usable( buildingID ) ) {
remote.addAnimal( species , buildingID );
}
}
}
 

You have already noticed that FarmServlet is tightly coupled to the FarmEJBRemote instance, which was retrieved via a call to "FarmEJBUtil.getHome().create()". It makes it very hard to test. When unit testing, we don't want to use any database. We don't want to access an EJB server either. That would make unit tests both difficult to execute and slow. So in order to unit test the FarmServlet class smoothly, we'd better make it loosely coupled. To remove the tight dependency between FarmServlet and FarmEJBRemote, we could use a setter based injection:

In the second one, it still depends on FarmEJBRemote, doesn't it?

[Frank Carver]

It looks like "FarmServlet is tightly coupled to the FarmEJBRemote instance" should maybe be "FarmServlet is tightly coupled to the FarmEJBUtil class".

Does that make more sense?