Java™ Application Development on Linux - Dator

148Chapter 5The Sun Microsystems Java Software <strong>Development</strong> Kita very simplistic naming/lookup system. Clients must know where to find theregistry with the resources they need.RMI is very useful for problems of a certain scale, but it is not, in and ofitself, sufficient for high-volume, highly available, mission-critical enterprisesystems. 22 But that is what J2EE and EJB are for. We’ll deal with those inPart V later in the book.5.9THE JAVA DEBUGGERHow can you stand using the SDK? It doesn’t even have a debugger!Wrong. It has a debugger. It just has an extremely basic command-linedebugger. Example 5.16 shows the output of its help.Again, we are not going to document everything here. That’s what theonline Sun Microsystems Java SDK documentation is for. Instead, we will usethe debugger to step through the execution of our simple application and showyou some of the debugger’s basic operations.There are two ways to invoke jdb. One is to attach it to an already runningJVM that has been started with remote debugging enabled. See the Java SDKdocumentation for details on that method. Here we’ll show you the simplercase of invoking the program locally by running the application directly underthe debugger.The basic invocation is:$ jdbYou may optionally name the class whose main() is to be executed underthe debugger, but we usually use the run from inside the debugger itself to dothis. Remember that if you want to be able to view local variables in the debugger,you must have compiled your class or classes with the -g option of javac.In the rest of this section, we will examine an actual debug session. Wewill run our single-class application, FetchURL, and use it to retrieve theindex.html file from the Web server on the laptop on which this chapter isbeing written. To refresh your memory, remember that the source code forFetchURL is at Example 3.30. Example 5.17 is what that file looks like.22. If that sentence did not cause you to get “buzzword bingo,” then you aren’t trying.