How to debug Google App Engine servlets?

Question

I am new to App Engine and I am testing some sample Java web applications. I was not able to figure out how to debug a java web application project in eclipse.

When I start the debug configuration, the set-top box server, which is part of the SDK, starts, and I can access my page from the browser. But none of my breakpoints in servlets hit. Is there any configuration for debugging?

Answer 1

Assuming you installed Google Plugin for Eclipse , this should be simple:

Run menu -> Debug As -> Web Application 

This, of course, runs your application on a web server inside the Eclipse debugger. See Starting a project for more details.

Answer 2

Check if there is a “skip all breakpoints” option selected in breakpoint mode.

Answer 3

For those trying to debug the Google App Engine using Eclipse but without using the GAE Eclipse plugin , I wrote a detailed answer here: Dev workflow for the application engine + modules + maven

As already mentioned, here is a copy of the answer:

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I use a similar structure with a slight difference. The top level directory has war and ear, and then they contain their specific pom.xml. I use Eclipse for debugging, and I can deploy “most of the time”, and I don’t use the Eclipse plugin, which (I

understand) is what you want. Directory structure

 . |-- pom.xml |-- README.md |-- my-ear | |-- devpid | |-- pom.xml | `-- src | `-- main | `-- application | `-- META-INF `-- my-war |-- build | `-- classes | |-- main | | |-- java | | `-- webapp | `-- test | `-- java |-- pom.xml `-- src |-- main | |-- java | | `-- com | `-- webapp | |-- css | |-- favicon.ico | |-- index.html | |-- js | |-- test.html | `-- WEB-INF `-- test `-- java 

Instruments

• Eclipse Luna without the Google App Engine (or SDK) plugin
• Maven 3.2.1
• Google App Engine SDK 1.9.6

Dev Workflow

• If you already have the source code, keep it in another place and generate the skeleton using the mvn appengine command.
• Start the first cut using the simple Hello World, using only the maven command and the mvn appengine: devserver command.
• After that create an eclipse project.
• Import the eclipse project into the Maven project. He will see banks through Maven. I will not write this answer to the moon, because it takes too many settings. In Luna, this works automatically.
• The step above will create three projects: the upper level, the ear and the war with pom.xml - OK.
• In eclipse, specify the output directory as the war / target directory. This is a step that enables hot deployment.

• In maven ear / pom.xml add xArgs for the appengine plugin to work in debug mode.

   <plugin> <groupId>com.google.appengine</groupId> <artifactId>appengine-maven-plugin</artifactId> <version>${appengine.target.version}</version> <configuration> <jvmFlags> <jvmFlag>-Xdebug</jvmFlag> <jvmFlag>-Xrunjdwp:transport=dt_socket,address=1044,server=y,suspend=n</jvmFlag> </jvmFlags> <disableUpdateCheck>true</disableUpdateCheck> </configuration> </plugin> 

• Pay attention to suspend = n.

• Launch the application engine from an external eclipse using mvn appengine: devserver from the ear directory. I use this command: `mvn appengine: devserver> ~ / .logs / .appengine.devserver.logs and echo $!

  devpid` Call this terminal 1.

• The advantage of this method is that your console is not captured by Eclipse, so you can use the tool of your choice to view it, such as multitail, etc. I use this simple tail command: tail -f ~/.logs/.appengine.devserver.logs | sed 's/INFO/^[[0;34m&^[[0m/g;s/ERROR/^[[0;31m&^[[0m/g;s/WARN\|WARNING/^[[0;35m&^[[0m/g;s/SEVERE\|FATAL/^[[0;31;47m&^[[0m/g' tail -f ~/.logs/.appengine.devserver.logs | sed 's/INFO/^[[0;34m&^[[0m/g;s/ERROR/^[[0;31m&^[[0m/g;s/WARN\|WARNING/^[[0;35m&^[[0m/g;s/SEVERE\|FATAL/^[[0;31;47m&^[[0m/g' The above command is difficult to enter. Each case ^ [actually Ctrl + V Esc - it's worth trying to type it once. But this, of course, is subjective and up to you.
• In Eclipse, create a debug profile for your project under a remote Java application - select the project settings for the war and socket connections.

This step is available on the Internet in many places, here is the image nonetheless

11. Open another terminal, Terminal 2 in the military directory and keep it open to run mvn compile install when you need to.
12. You are good to go. You should be able to integrate the source code by simply pasting it in the right place. You should also be able to use standard debugging methods. Eclipse will compile the location on the right and devserver will detect everything is in order. If Eclipse throws a warning, ignore it.
13. This works most of the time. Sometimes you save something that breaks the compilation of the entire project, or changes the name of a function, is called from a pre-compiled class, or simply changes the web.xml that loads at startup. Of course, then a hot deployment will not work.
14. In this case, stop the debug removal within the eclipse, complete your tasks, run mvn compile install from terminal 2. Devserver will automatically detect it.
15. Basically, I almost don't need to touch the tail running in terminal 1. Devserver does not need to reboot.
16. If I do not change web.xml or refactoring, I do not need to run mvn compile install from the outside.

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My reason for providing a list of windows (Eclipse, Terminal 1, and Terminal 2) is to show that Alt + Tab is actually faster than Shift + F7 from inside the eclipse. This is subjective and, of course, up to you.