debug GWT on tomcat using eclipse

Question

I'm using GWT 2.4 and have a ton of code already written. I understand the Jetty server that comes with the GWT plugin has very tight control over the jars that can be used in a project to mimic app engine as closely as possible. I need to deploy to tomcat 7. I modified my project in eclipse and "blessed" it as a dynamic web project so I can export...WAR and upload it to my QA and production tomcat.

I need help with getting the app to run (and debug) on an embedded tomcat (like an honest dynamic web project would). I already have tomcat setup in eclipse and I have my CAS server web app deployed to it.

I've ready tons of either old or confusing posts here and elsewhere. Basically, I'm looking for the same debugging environment I would get with the packaged Jetty server, but on my own tomcat configured with WTP in eclipse...so I can mimic my production environment (just like Jetty mimics app engine)

any help is appreciated.

Answer 1

It should probably a little bit easier, but it's possible. Here's how I do it:

1. Setting up the web server

• Using the JavaEE edition of Eclipse, I set up the Tomcat 7.0 server adapter, and define an environment in Preferences > Server > Runtime Environments
• File > New > Project... > Web/Dynamic Web Project
  • Select the target runtime I set up in the first step
  • Important: In Context Root, enter /
• I create an HTML file and a Servlet, and then try running the setup using Debug As > Debug On Server

2. Adding the GWT code server

• Project > Properties > Google > Web Toolkit > Use Google Web Toolkit
• Important: I always need to change the order in the Java Build Path (Project > Properties > Java Build Path > Order and Export), see http://code.google.com/p/google-web-toolkit/issues/detail?id=4479 - gwt-dev.jar must be pretty much on top of the path.
• Project > Properties > Google > Web Application: War directory = "WebContent", also check "Launch and deploy from this directory"
• I create some sample GWT content (I create a sample GWT project, and copy most of it over)
• I try to GWT compile the project. This shows me, if I got the build path order right - otherwise, the compiler fails early with "java.lang.NoSuchFieldError: warningThreshold".
• Debug As > Web Application - just to create a debug configuration. Stop the debug. Edit the debug configuration (Run > Debug Configurations...), deselect "Run built-in server". Start the debug again.

Now, finally, I can debug both the server and the client part (I still need to click two Debug icons to start both!) I can manage the client side from the "Development Mode" view, and the server side from the "Servers" view. At the end of the day, it works great, and using the "Automatically publish when resources change" feature (Servers view > myServerName > Open > Publishing), sometimes even better than with the integrated Jetty.

Answer 2

At first thought, I don't really see why you would be facing a problem. Perhaps, the way Eclipse is laid out is too confusing and daunting.

On my Eclipse, I had been using the default jetty as the server during GWT debug. However, there were some problems which would not be caught by jetty when deployed on Tomcat or JBoss.

And when I added Tomcat or JBoss instances to Eclipse and added my app to those server instances, the debugging worked straight away. Are you missing one piece of vital, but simple info?

Let me presume that the following would fill in your missing link ...

1. Locating/adding your server instance:

   On Package Explorer (or Project Explorer, either one) in Eclipse, you would see, besides your personal projects, a "servers" project. Under it is are configuration nodes listing all your Tomcat instances.

   If you cannot see the "servers" node in Package Explorer, it probably is due to your working set filter. (And if you don't know what working sets are ... I guess you would need to beef up on your dexterity in Eclipse).

   If you don't already have a Tomcat instance, you simply right click on the "servers" project to add a new server (Package Explorer -> New -> Server ...). You would be asked the location of your Tomcat home. And your desired port number of the server instance. Of course, you would have to ensure that the port number will not clash with the port used by any other inet operation on your box.

2. Configuring the port number a 2nd time

   On the server instance node in Package Explorer, you would find the file you should edit to set the port number to match the one you specified when creating the new Tomcat instance. If you don't know which file to edit, you would need to read up on the Tomcat version you created to find out which file contains the port number config.

   You need to config the port a 2nd time because the 1st time tells Eclipse where and at what port to expect the server instance to be running. The 2nd time is to configure the server instance itself.

3. Adding your app to the server

   However, the nodes in "servers" project only allow you to configure your Tomcat instances. There is yet another view called the "server view" to further configure your tomcat instance. You need to enable Server view from Window->Show View->Server->Servers.

   Right click on the server instance in the "Server View" to add your app.

4. Running debug off the Maven generated target.

   There are times you wish to debug the war structure to figure out which jars are missing in the war. And incrementally remove jars from your war to figure out the jars that are already supplied by the server. Since JBoss supplies many of the jars already, you would have to figure out if your development jars are of the versions as those expected by JBoss.

   You would create another Eclipse project in your workspace and make an Eclipse folder softlink in your 2nd project to point to the Maven generated target of your first project. And you specify target/{maven generated webapp directory} as the webapp directory of your 2nd project. What I mean by "maven generated webapp directory" is the unzipped intermediate directory generated by Maven (used by Maven to generate the zipped war file).

   This is the cleanest way to debug production war if you could faithfully replicate the production tomcat/jboss server on your Eclipse development box.

5. If you prefer JBoss.

   Somehow, JBoss config node is not listed in the "Servers" node in Package/Project Explorers. You would need to go to your JBoss installation directory to edit them.

6. Remote debugging.

   If you wanted to debug the app on your production box, or on a server sitting on another box, you would have to start that tomcat instance under debug. You should read up on that. You have to specify the debug port.

   Then in Eclipse, at Run->Debug Configuration->Remote Java Application, you specify the app and the debug port.

   The first time you debug, Eclipse "may not know" where the source files are, especially if your app has multiple project dependencies. (Why can't Eclipse search the source files from my list of projects?) Anyway, you have to specify where to find your source files. And then when your debugging traverses into another project dependency, you would have to over-write the location of the source files.

So, voila! That is how I got my debugging working. I advise you to avoid remote debugging as much as possible unless you need to diagnose production problems. Unless you are doing remote debugging, do not attempt to deploy the war to local server, but simply depend on associating the project to the server instance.

Eclipse is too confusing

I know Eclipse is too confusing and you have to wade thro its features. You just have to bear with it. Eclipse menus & views are apparently optimized for plugin-programmer-centric not user-centric.

For example, why would I go to "help" to install new software? I used to expect that "Help->Install new software" to be an instructional manual to installing new software.

It beats (and annoys me) that the Eclipse team did not combine the operations together so that I could add apps to a server instance at Package Explorer. Why not? As a user I would expect to see only a single entry point to configuring my servers.

To alleviate the confusion, I like encouraging people to download and install Springsource's version of Eclipse (STS). It's the same Eclipse, except that STS has the essential parts installed and has a dashboard pointing to compatibly installable plugins. Tomcat is preinstalled as VMware tc Server. And the views are correctly config'd to show the server instances. And the correct workable Eclipse-Maven bridging plugin is pre-installed.