Develop Reference

How to debug WAR inside eclipse, NOT remote debug?

My originally question has been marked as duplicate as this question and asked to ask a new one. So here I repeat, I am not looking for a remote debug solution. What I am asking is how to debug WAR inside eclipse just as a JAVA application. Following is my original question.
I have seen many online tutorial explaining how to use eclipse to do remote debug of WAR file.
But what I want to know is how to do the debug inside eclipse just as debugging a JAVA application? I have Tomcat 7 configured in my eclipse as a server. And I have tested it with a sample servlet program successfully meaning I can set breakpoint in the source code and run into it.
My WAR application is built by gradle. I have imported the gradle project into my eclipse and build it ok inside eclipse by running gradle task inside "gradle tasks view". I added the project into the server. However, when I try to use "Debug as > Debug on Server", it fails and the breakpoint is not get hit. Anyone could share the experience to debug WAR inside eclipse?

How to hot reload Tomcat server in VSCode

I'm migrating from Eclipse IDE (+ VSCode for coding Java servlets and HTML/CSS/JS webpages, respectively) to only Visual Studio Code for its lightweight.
I have several Java extensions installed for VSCode:
Language Support for Java(TM) by Red Hat
Tomcat for Java
Debugger for Java
Eclipse has a series of settings for hot reloading:
- Automatically publish when resources change
- Refresh using native hooks or polling
while VSCode doesn't seem to have any for me.
A few things I've try to reload my Java and web code:
Restart Tomcat server
Delete and re-adding Tomcat server
Delete and regenerate .war package (not sure if this does anything, it can run well without a .war package)

Good news...
It works automatically now. With Tomcat for Java Extension (And the rest of the Java Extension Pack):
https://marketplace.visualstudio.com/items?itemName=adashen.vscode-tomcat
Just make sure your settings are like this (search for "java.autobuild" to get those two in the first results):
Very important is, that you wont see any logs in the console on the HCR (Hot Code Replacement) like it happens in Eclipse ... but you in fact will see the replaced code behavior. Just debug over the piece of code you changed, and you will see it in fact changed in the running server.
UPDATE: I've found it works better with the 'manual'(default) setting. Just clicking once in the lightning icon. (Testing in Ubuntu 18.04 LTS)
[I say it works better because if I added lines to a Class' code with the 'auto' setting it will not add that code ... only if I change code in the existing lines. But with the manual setting I just save the file, and then click the lightning icon wait ~3 seconds myself and debug over the new code ... and everything goes well!!
... This solves my coding needs(lightweight Editor/IDE with Hot-Code-Replacement in Tomcat)]
Enjoy !

This article may be helpful, I migrate from other IDE to Vscode.
According to the article, if you install Debugger for Java, it enabled Hot code replacement(HCR) and then :
You can start a debugging session and change a Java file in your development environment, and the debugger will replace the code in the JVM running your code.
Hot code replacement for java comes to visual studio code

Install “Tomcat for java” extension in VScode.
Configure the Path of Tomcat in the above extension.
Now you should be able to run tomcat in usual build -> deploy mode. Now install DCEVM, By using “java -jar installer-light.jar”. (Select “Install DCEVM as altjvm”)
Place HotSwap Agent Jar in directory of your choice.
Now In VScode right-click the Tomcat server you have created. (The one from Step 3 ) And select “Customise JVM Options”.
In the file opened, Place “-XXaltjvm=dcevm
-javaagent:/[your_directory]/hotswap-agent-1.3.1-SNAPSHOT.jar” Now Right-click the tomcat server in VScode and select “Debug WAR package”, And select the WAR file.
If everything goes well, The WAR will be start in TOMCAT in debug mode with text “HOTSWAP AGENT” in the log.
Now your every save to your file will trigger Hot Reloading.
https://medium.com/#manoj_makkuboy/hot-reload-java-8-tomcat-server-in-vscode-ba6233d632e?

finding changes eclipse makes to maven project

I have a maven project which I have downloaded from this link. When I make a couple changes to it, it runs perfectly from the command line when I type:
mvn clean install tomcat7:run-war -Dmaven.test.skip=true
in the directory to which the zip was extracted. (The only 2 changes required to make it work on the command line are to 1.) add a plugin tag for tomcat 7 in pom.xml and 2.) create a context.xml file in the webapp/META-INF folder. Everything else in the app remains the same as the github verion, and the app runs fine from the command line using the command given above and then typing the url in the browser.)
However, when I import the project into eclipse as an existing maven project, and then try to run the app, the app starts throwing errors related to not finding a couple of jars which are clearly in the repository. The app no longer compiles from the command line, or from eclipse. I even tried to run the app as a maven build from eclipse and even changed the maven instance eclipse uses to the freestanding maven that works from the command line instead of the embedded maven in eclipse, but the app still threw the same errors when I tried to run it.
But then, when I repeated the steps with a fresh copy of the app, the fresh copy runs fine from the command line, while the copy that eclipse touched does not compile by any method.
It seems that eclipse has made some changes to the app in the process of importing it as an existing maven project into eclipse. How can I locate the specific changes that eclipse has made to the app? I would like to be able to use eclipse as my IDE, but I cannot do so unless it can compile the code.

This answer was originally posted as a comment it turns out that resolved the OP's problem, and as He asked I'm turning into an answer.
First set your eclipse to use the JDK instead of the JRE. Just as a reference this configuration on Eclipse is Normally on Window->Preferences...->Java->Installed JREs:
Second (as you already did) change eclipse maven to look at installed maven that runs on the command line again.
I've encountered some problems with maven running with the JRE instead of the JDK. Try it and let me know. I will sleep now. Tomorrow I will see what happened.

how do you debug java annotation processors using intellij?

How do you debug java annotation processors using intellij?
Preferably using IDEA IntelliJ. I tried setting a breakpoint inside the processor and running but it did not break.

If you really need to debug an annotation processor, it might be better to run the annotation processor from the command line rather than within your IDE with debugging enabled and attach to that using your IDE's debugger.
If running javac directly, you can debug this by specifying the following extra parameters:
javac -J-Xdebug -J-Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000 ... (usual javac parameters go here)
If running Maven, use mvndebug instead of the standard mvn command - Maven runs the compiler in-process.
If running Ant, add the following to the ANT_OPTS environment variable before running:
-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=8000
With all these executions, the javac, Ant or Maven process will wait for you to attach your debugger before it actually starts executing. IntelliJ instructions for this are here. For Eclipse, here.

This tutorial is written for an Android project. Main module name is "app" as usual. The project contains a submodule called "annotation" which is subdependency of "app". "app" module runs annotation processing with gradle declaration
apt project(':annotation') .
SIMPLE VERSION
(run compilation from terminal and attach from IDE)
[REQUIRED] Add a new project configuration "+" -> "Remote". Check "Single instance only". All other settings are generated automatically. Leave <whole project> as the classpath. Port should be left as the default 5005.
[REQUIRED] Make sure you stop all gradle instances by calling: ./gradlew --stop
[REQUIRED] Run the command : ./gradlew --no-daemon -Dorg.gradle.debug=true :app:clean :app:compileDebugJavaWithJavac
Run the APT project configuration in debug mode as fast as possible :)
[HINT] We start with an EMPTY gradle.properties file
[HINT] DO NOT USE gradle daemon ( --no-daemon / org.gradle.daemon=false option )
[HINT] Run gradle in debug mode ( org.gradle.debug=true option )
[HINT] Run app's module compilation not the processor's module compilation (app's compilation runs annotation processing!)
We DO NOT normally add any Java compiler settings in Android Studio (i.e. File -> other settings -> Default settings)
EXTENDED VERSION (use gradle.properties)
Add the following to your gradle.properties file:
org.gradle.daemon=false
org.gradle.debug=true
Run the compilation from terminal:
./gradlew :app:clean :app:compileDebugJavaWithJavac
ADVANCED VERSION (just press debug in IDE)
Add a bash script to your project main dir (e.g. compile.sh)
#!/bin/bash
./gradlew :app:clean :app:compileDebugJavaWithJavac &
Remember about the '&' sign for background processing.
Go to APT configuration settings we created in step 1 and add a Before launch configuration. Select Run external tool.
Add the path to the compile.sh script we created earlier.
Warning
Messing up gradle compilation, NullPointer exceptions during compilation etc. sometimes result in AndroidStudio being stuck (frozen on gradle refresh stage). If you cannot stop gradle from the IDE then use this command in the terminal:
ps -A | grep gradle | awk '{ print $1; }' | xargs kill -9
Turning off debug option during project refresh sometimes helps Android Studio to come back to the right track.

Follow these steps, These worked for me on android studio for gradle project:-
1).In gradle.properties add following lines
org.gradle.daemon=true
org.gradle.jvmargs=-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005
2).Edit Build COnfiguration and add Remote Configration
3).Run recently created run configuration APT.
4).Add break point in annotation processing code and build overall project

It is possible to run javac and debug it, as indicated higher. However in my case it was tedious to write the complete classpath, so I wanted to leave this to IDEA. So in the module where I wanted to apply my annotation processor, just create a class with main method.
public static void main(String[] args) {
com.sun.tools.javac.Main.main("-proc:only",
"-processor", "my.pkgs.MyAnnotationProcessor",
"my/pkgs/any/ClassIWantProcess.java");
}
For this to work you need to add $JAVA_HOME/lib/tools.jar to your SDK's JARs (by default it is not there). This is the same reason why appservers compiling JSPs need this JAR on their classpath - they need the compiler.
Then just set proper working directory for your run configuration (so the relative path to the java file is correct), set your break-point into the processor and debug at your will!
Benefit - classpath is set already by IDEA and used by the "inner" javac, because here it is not a separate process. I believe it's possible to translate it to other IDEs too.

For a Maven project, this post, which explains the following steps in a little more detail, worked for me:
Add "Remote" run configuration and set "port" to 8000.
Issue the command mvnDebug clean install from the project's directory (on the command line).
Run the run configuration. In order to start a new session after the processes quit, repeat from (2).
Remember to run mvn install on the project's dependencies when they change (e.g. if the annotation processor is in a different artifact than the project you are debugging it from).

I found the following resource that can help you: http://code.google.com/p/acris/wiki/AnnotationProcessing_DebuggingEclipse
The guy explains step-by-step how to debug annotation processors using Eclipse.

Annotation processing occurs during compilation, so normal debugging won't work. If you want to debug it in the context of you project, you can use IntelliJ remote debugging, while having Gradle or Maven in debug mode. Then you can put breakpoints in the Annotation Processor's files.
See Debugging an Annotation Processor in any project.
Disclaimer: I wrote the post.

Debugging an annotation processor with IntelliJ IDEA and Gradle
Set a custom VM option -Dcompiler.process.debug.port=5005: press Ctrl + Shift + A and select Edit Custom VM Options... in the list of actions to add a custom VM option then restart the IDE.
Create a remote debug configuration with default parameters: Run -> Edit Configurations... -> Add New Configuration (Alt + Insert) -> Remote.
Set breakpoints.
Build with Gradle from the terminal: $ ./gradlew --no-daemon -Dorg.gradle.debug=true clean build (it's okay if the execution of the command is frozen, don't terminate a process).
Debug the remote debug configuration within the IDE (see step 3): select a suitable remote debug configuration and press Shift + F9.
Hope it helps somebody :)

Headless Eclipse Build returns ERRORLEVEL 13

Everything was going well. Nightly builds ran for more than a month with no problems. However, suddenly when invoking the feature builder from Eclipse the execution ends right away with the message.
ERRORLEVEL 13
As far as I know I haven't changed anything, as this computer is normally not touched. (It is only used for the nightly builds).
I've googled around to see what this error means but to no avail. I found a link from IBM that shows a custom bat file that catches this error, but the explanation given is not very useful.
My guess is that this is related to the workspace, somehow, or that the whole eclipse installation is corrupted.
Do you have any idea what this error means and how can it be corrected?

After reading what the error code means thanks to the answer from VonC I understood where to look. The problem was a lot more obscure that it seems.
I looked into the configuration folder for Eclipse (logs are either written there or in the .metadata folder when something goes wrong), and I found a huge log file. Inside the file I found the following error:
application org.eclipse.sdk not found
and the following exception, followed by a plugin name, several times:
java.util.zip.ZipException: Too many open files
Several plugins could not be loaded, causing a cascade of missing dependencies that prevented Eclipse from launching. I searched the web for this exception and found the following bug description from SUN, which says that Java 1.5.0 can not open more than 2,100 zip files.
The problem started a while after I installed the BABEL project translations for Eclipse into the build computer. These are more than 900 fragments, containing translations for many plugins, one for each language. As I installed it on top of an existing eclipse installation, it seemed that it was not a problem to open them.... until I cleared the workspace for the builds. Then Eclipse wouldn't launch anymore. I went over the limit. It didn't help that the first thing I tried to fix the build was, again.... clearing everything.
Because I only use this computer for headless builds, I didn't realize that the problem was in Eclipse itself and I was looking inside the build process. I only realized when I looked into the log file.
After installing Java 1.6.0_11 I was able to launch Eclipse and go on with my build.

It should mean "ant build failed", meaning the headless ant script fails at some point.
You should check if you can catch the log/output generated by this script to analyze this ant session and see at what point the ant script fails.
If it fails right away, it usually is because of:
a change in rights (writing access), or
in environment variable modifications, or
in resource access (path non accessible).
You also have to check if the computer is still in its original windows domain, and if the rights (admin ?) associated with the account running the ant script are still the same.