Develop Reference

Netbeans project file generation extremely slow (unusable)

I've been having issues with a Java project that I've been working on for a while.
Starting about 1 or 2 weeks ago, whenever I use Netbeans (8.0.2) to generate a new file in the project (right click on package > new file), the wizard will hang for up to 10 minutes before releasing control back to me. The file is created after about 5 minutes. This doesn't happen with any other project, only this one; but I can't find anything different in my project's configuration compared to projects that work.
I created a bug report about this on the Netbeans bug tracker, but it hasn't been looked at in over a week. It has a copy of the Netbeans output log, and a profiling snapshot of the class generation.
I've tried reinstalling Netbeans (remaining at 8.0.2), which didn't help, and I don't really know what else I can do to locate the problem. If anyone has experienced anything like this, or has any advice on how I can track down the issue, it would be greatly appreciated.
Here is a link to my project on Dropbox. Feel free to download a copy, compile it, run it, etc.
I am using Windows 7 64-bit, and I am using the official Netbeans 8.0.2 from netbeans.org, launched straight from the desktop (I am not using any particular command line arguments or enviroment variables, as far as I know)

It turned out that the issue was that my Mercurial client was hanging when it made status calls, and Netbeans, due to a bug, was stuck waiting for it forever.
The issue with Mercurial can be worked around by deleting the Mercurial log file, and the bug with Netbeans was eventually fixed.

IntelliJ IDEA doesn't redeploy changes

I have a Spring Web application and when I debug with IDEA's debbuger in Tomcat and redeploy the project after some changes, the changes are not deployed and debugger "sees" the old code (stepping through wrong or empty lines). Only thing that helps is to run maven clean install and then start the Tomcat again.
I tried clearing IDEA caches but it didn't help.
Hotswap also doesn't work, although I have correct options selected in settings, but I can live with that.
Note that I use redeploy not hotswap, so the whole application is started again, it should reload all classes but it doesn't. Only after maven build it works.
Note 2: I think it work ok one month ago, but no changes I can think of could do this (project- or IDEA-wise)
EDIT: So hotswap is now working OK (magically, I didn't do anything). But when I make larger modifications (eg. method signature change, etc), they are not picked up during REDEPLOY to the server. So I neeed to run maven clean install and start the server again to see the changes and for hotswap to work properly after method body modifications on this new code. Any idea why?

You need to check your run configurations of tomcat, in "Before launch" there should be Make and Build artifact steps, also be sure that all you changed classes are really compiling during redeploy - this is the place I would start from.
Also I don't get why you use redeploy instead of hot-swap? Redeploy is usually same time-consuming as restart server, but hot-swap is nearly instant. Though it allows only to change method bodies and constants, usually it's much prefferable then redeploy in development. Personally I'm using JRebel which is free for non-commercial projects now and restart server very rare.
EDIT:
I don't know why your classes are old even after redeploy, but the reason is 99% that they do not compile after changes into exploded folder. Doing maven clean install after each code change is too much (IDE compilation should be enough).
What I can suggest you is not to redeploy but to restart server after big changes. So that IDE perform Make, Build artifact and Deploy artifact tasks.

In addition to david.lucky hints, make sure that on your Tomcat configuration in the deployment section you're using an exploded artifact

I had exactly the same problem! I've spent hours in solving this issue.
I don't know why, but the solution for me was that (I'm working on MacOS High Sierra):
First, I had some of my tutorial projects, I was working on, on my Desktop in a folder /Desktop/tutorial/... These project were working fine. I could redeploy and Tomcat was recognizing the changes in my java files.
Then I started some new, own projects, and I placed them in my home directory, something like /Users/myHomeDirectory/WebApps/.
I could build and run these objects, but when I made changes, I had the same exact problem, that Tomcat was not recognizing the result. Only thing that helped out, when I clicked Maven-Button "Reimport all Maven Projects".
I tried really lots of different things. Nothing worked.
Then I thought, maybe, theres something wrong with my project. So I took one of my projects from Desktop and copied them into my home directory. But suddenly, I had again the same problem.
So here's my solution: I created a new project on Desktop again. And I don't know why, but now it's working fine. I really have no clue why. And believe me, I did not change any settings. I did exactly the same!
And regarding the life reload without redeploying. This works really fine for me (without any plugins like JREbel):
Go Run –> Edit Configurations –> “Deployment” tab, clicks + icon –> select an “exploded artifact”
Select “Server” tab, update the following options :
On ‘Update’ action -> Update classes and resources
On frame deactivation -> Update classes and resources
Run web application in Debug mode. Try to modify some codes or resources (Java files, ...), the modified classes and resources will be reloaded automatically.

This has been happening me for some time now Ultimate Edition after switching from eclipse to Intellij a few months ago.
Standard tomcat config and debug settings mentioned above used.
Intellij will show green popup after nothing to reload or reloaded one class.
Yet the debuggers bytecode is not the same reloaded/updated code.
You can force a recompile which will work for small changes ctr shift F9.
Other than that a clean install seems to work for annotation, method definition changes etc. If you try a recompile the debugger will fail the server.
So the answer is ctrl shift F9 on the file you change

Sudden weird errors on a project

Today I came to work, happy. But when I opened my Eclipse, I saw that one of my projects has errors.It's weird because it shows that it has errors only in the window bar, and not in the Navigator. I don't have any Java errors, this is a valid project that was fine all the time:
Some of the errors on the error log of Eclipse:
JavaBuilder handling ImageBuilderInternalException while building: SP_Procedure
Cannot connect to VM
File <SomeFile> has been skipped, problem while reading ('Resource is out of sync with the file system')
Unhandled event loop exception
Internal error
When I run an application from this project, I get a warning message but when I proceed, it works fine, but still. It's very disturbing and I'm not sure if it's harmless.
I tried to:
Restart Eclipse
Restart my machine
Clean projects and recompiling them.
Refresh projects
Pray
Nothing helped. What could be the problem? (I'm using Indigo Service Release 2)

The following nuclear option has desperation written all over it. But I have been where the OP has been with the Juno version of Eclipse.
Run a "Synchronize with Repository" and save all of your local updates to a different directory.
Delete the project. (Check the box to delete the contents on disk. Scary step, but that's OK, because you saved it in a different directory in the previous step, right?)
Read in a fresh project from the repository. It builds happily at this point.
Integrate your local updates.
Keep on praying.

Looks that one unused JAR was deleted, but for some reason, I didn't get errors in any file, even in the files that imports this JAR! So what I did was restoring this JAR, delete unused imports and deleted the JAR again.
I've found this error after two days of navigating on this project on each file.. This is weird that Eclipse didn't recognize that1 this is an error, and throw many unrelated errors such as:
Cannot connect to VM
File has been skipped, problem while reading ('Resource is out of sync with the file system')
Unhandled event loop exception
Is this a bug in Eclipse? (All errors and warnings are enabled!)
1 As seen in the image in the question..

A class from the list of imports for the file seems to have moved out or the jar file containing the class is missing.
Expand the imports section and check if you find some classes that are missing but have been imported.

Though it is a pain, sometimes the easiest solution is to back up all your projects (either in a repository or somewhere else on your computer) then uninstall and reinstall eclipse. No it's not fun, but it should reset eclipse so everything works again. The downfall though is that you have to reconfigure eclipse to any special settings you had/reinatall any extra functionality currently installed (eg. android add-on) and reconnect to any repositories you have. While punting isn't fun, it can be effective... I hope you don't have to resort to this though.

I have went through that problem a lot of times, and tried everything you tried. Rebuild, recompile, refresh, remove and add JDK, remove and reinstall Eclipse... nothing worked
The only thing I concluded is that the workspace metadata was corrupted.
What I did (every time it happened) was
Create an empty workspace
Import -> existing projects into worskpace
Mark the "copy projects" (else it will only link them)
Wait for the copy, and start working with the new workspace
If you work with SCM systems (Git, SVN, etc), making a full checkout will do the trick too, but the worskpace import will let you retrieve those changes you didn't get to commit (if any).
It's a little painful if you have somethings already set (like JDK names, servers, etc), but then I realized it was faster than keep searching how to fix the workspace
Regards!
PS : I've been working with Kepler lately, and everything works fine till now

Click Window -> Show View -> Other -> General -> Problems
This view will show you what is wrong.

Did you, by any chance, update your virtual machine outside of Eclipse? I can't help but feel that we're both missing a finer detail here. I just keep seeing "cannot connect to VM" and thinking that it's a major clue.
Have you tried running anything from the terminal? Does it work there?
If so, do you know where your current edition of Java is located? Is Eclipse looking somewhere else?
Is this exclusive to one project? Do you use any additional libraries to the JDK?

Maybe try this for Resource is out of sync with the file system error:
Right click project in Eclipse Package Explorer
Close Project.
Right click project in Eclipse Package Explorer
Open Project.

Other things not mentioned:
project properties > java build path, see if any of those tabs got changed, local file got moved? read/write permissions on some file you are linking to?
project properties > java compiler, see if workplace settings have changed? maybe under errors/warnings, you can systematically set them to 'ignore' until the error goes away to determine what type of error it is?
maybe update some of the eclipse plugins?

I saw something like this happening for a number of reasons. Mainly because of validation in files other Java source code. See if you are validating XML for instance.
Right click your project and chose Properties (Alt+Enter) and Validation to see the related configuration.
As for the danger, I lived with those marks for ages and nothing wrong ever happened.

Eclipse doesn't import java libraries on cold start, plus other compiling errors

Eclipse is giving me a few problems.
After a cold start and the loading of android libs, Eclipse underline the import statements or says that java.lang.Object couldn't be found.
Closing it and reopening often fix the problem. If it doesn't, another close-open fix it definitely. But it shows at each cold-start.
It also gives
"The type java.lang.Enum cannot be resolved. It is indirectly referenced from required .class files"
"The project cannot be build until build path errors are resolved"
But if i restart the build path errors and the enum problem are not show any more(sometimes the enum proble got fixed some time after eclipse's loading finished)
"Project 'xxx' is missing required source folder: 'gen' "
that should be generated automatically generated while building, and still restarting will fix them
In addition, in many projects, while building or cleaning, eclipse says that it couldn't delete the bin/. directory. I noticed that that directory is read-only, and if i try to remove the attribute(even from dos), it immediately return to read-only.
This problems aren't show-stoppers, i still can code and i still can get my apps exported, but it is quite annoying to have to restart eclipse a few times before being able to use it(and eclipse isn't that fast at opening), and i would really know how to fix it.
I searched in the net a bit, but i dind't found nothing useful or that worked.
Is there a way to fix them?
I didn't "unistalled"(it is just stored in a directory) Eclipse, since i should then reinstall android sdk, mercurial plugin, and re download and set up a few libraries i use in quite all my project, and i really hope there is another way.
final notes:
everything works when this problems doesn't show: the app works, logcat too, the right device is used to install the app, so i think java and android sdks are installed just right

I had that problem before so I just saved my projects to a different file and uninstalled everything ( java, android sdk, eclipse ). When I reinstalled it all I put the android sdk on the root of my c drive as I have a windows machine and then instead of picking where java was installed I let it do its own thing. I dont use a mercurial plug in but your "read only" problem could be related to that. Its possible your downloading files that are "read only" and there for you have no way to alter them. Im guessing since you said youve been programing you already know how to set the build paths and stuff. It might just be where everything is installed or something silly like privilege settings on your machine.
What were you using the mercurial plug in for anyway? just curious :)

Have you included the java lib in your project or? For a couple of weeks ago I sat with an project where i absolutly needed some of the methods, so because android just have some of the java lib I imported the need libs and used that.

eclipse/tomcat: deploy doesn't work any more (ClassNotFoundException)

I'm running Eclipse Helios Service Release 1, with Tomcat 7.0.12 in Linux Ubuntu Natty Narwhal.
I've been happily hot re-deploying my webapp until it stopped working for apparently no reason. The following exception is displayed:
SEVERE: Allocate exception for servlet Index
java.lang.ClassNotFoundException: obliquid.servlet.Index
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1676)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1521)
In Servers tab I've "Tomcat v7.0 Server at localhost [Started,Synchronized]
My project appears as a child of Tomcat v7.0 Server
In Properties, Java Build Path, Source I've Project/src Source folder
In Properties, Web Deployment Assembly, I've the following mappings: /WebContent -> /, /src -> /WEB-INF/classes, /test -> /build/classes
My src directory contains a Servlet in obliquid/servlet/Index.java
I tried already to click on Clean Module Work Directory... and Publish
I tried to stop and start the Server from within Eclipse Servers tab
What else should I check? Thank you.
UPDATE Despite now I'm working with the new project, I came back to check the old one, and mysteriously now it's working. I think I won't be able to find what has happened.
However today with the new project, I had 404 errors with no apparent reason and I found out that right clicking on the Tomcat server and selecting "Clean..." can be useful. Maybe it could have helped.
Selecting "Clean..." says: "Clean will discard all publish state and republish from scratch. Are you sure you want to clean all published resources?". Selecting yes, I solved the problem
UPDATE 2 It happened again on the new project. 404 errors, this time they don't go away.
Stop -> Clean... -> Start (404)
Stop -> Clean Tomcat Work Directory... -> Start (404)
Stop -> Clean Tomcat Work Directory... -> Clean... -> Start (404)
Stop -> Remove on the application -> Clean... -> Run As -> Run on Server -> (404)
Exit Eclipse, Start Eclipse
Start the server -> (404)
UPDATE 3 It turned out that this time I just didn't notice an exception caused by a listener-class during startup. After solving the problem, it worked. Guess I should stop working at 3 AM.

While on Tomcat 6 and Eclipse Ganymede I found out the following chain to work like charm:
1 stop server
2 project -> clean
3 project build (I had automatic build disabled)
4 delete server
5 delete Servers folder
6 restart Eclipse
7 create new server, add project and start :)
takes some time but worked like charm. My problem was a irritating Listener start problem, but this seems to be something similar: a property at tomcat. Btw: nowadays I am also a big Glassfish fan.

I found that this procedure is useful:
Click on Servers tab and Stop the server in use if it's running
Right click on the server again and select Clean...
Right click again and select Clean Tomcat Work Directory...
Hopefully the ClassNotFoundException should be gone now.
Another time I had a problem with a class launched at server startup, an exception in a listener class (ServletContextListener). When a ServletContextListener raises an exception during startup the application deployment is aborted, hence the 404 errors. In that case fixing the problem that caused the exception, made the application working again.
EDIT: This shorter procedure worked for me most of the times, but today didn't work and I had to follow Mico's extended procedure. My suggestion is, if you have a similar problem, first try this shorter procedure. If the problem persists, try with Mico's.

I'd recommend that you stop and start the Tomcat server again. Hot deploy does not work forever; there are some issues that will cause you to have to restart after a few redeploys.

I wonder when I see the accepted answer with +25 is it really accurate?
First if you are going to delete the server then whats the point in cleaning it? It will take your time unnecessarily and nothing useful will you gain.
So i will say just 5, 6, 7 steps should do the magic
5 delete Servers folder
6 restart Eclipse
7 create new server, add project and start

This could be something I learned on con-fess 2011. For me this sounds like a classloader problem.
The theory behind:
Java does not only use the type of the class but also the classloader which loaded it to identify the type of an instance. This means a simle operation could fail, e.g.
ClassA a1 = new a1;
ClassA a2 = SomeOtherClass.giveMeInstanceOfA();
a1 = a2;
This example would fail if SomeOtherClass uses a different classloader because Java would say that they are not the same.
The speaker also mentioned that some servers use per default about 45 different classloaders.
What does this mean in practice:
You deploy your webapp to the server, everything runs fine. The server caches the classes and everything he needs to load them somewhere. Now you make a hot deploymen and the server may loads new classes with a new (or different) classloader. This is the point where it starts to become dangerous because from now on you have two different classes in the memory which should be the same. Simple operations like casts (ClassA a = (ClassA) new ClassA()) fail, new Methods within the class are not found (because the server takes a cached version without this method),....
This is the point where I restart the server, clean the working directory (to get rid of the cached versions) and start thinking about hot deployment as critical thing.
If it is possible to try Mikkos procedere and this solves the problem this explanation could help you understand why.
I know this does not solve your problem but could give you some hints what maybe could have happened.

Speaking of hot deployment of Tomcat, you would indeed experience various problems, the least of which is memory leak, which is why you would have to restart the application. I would recommend to try JRebel for fast turnaround of "make and save any changes and then refresh the browser and see the changes immediately". You can find the JRebel hands-on lab, which shows how to use it with Tomcat and Eclipse. http://www.javapassion.com/rebels/jrebel_basics/

I have gained some new experience on programming and I am not anymore starving on Eclipse + Tomcat combination. Several ways here can help you out of the need of the usage of that combination:
First of all, don't use them together!
You can use other available IDEs, e.g. IntellijIdea (that is not free, but is worth of investing) has an property that when you debug a Java code, you can change code on fly and compile the Java files one by one and then it suggests if you'll want to have it updated on server. No restart needed almost never (of course it sometimes gets lost, but mainly it works).
Use standalone tomcat server, not the one inside Eclipse / your IDE. That first trick works only when you debug external server, nothing inside IDE. There comes the second tip: if you happen to change only jsp or html content, those files can be copied to the right place inside tomcat's webapp folder manually with unix cp or windows copy command and if you happen to develop files in same foulder long time, you can copy the folder content (e.g. myFolder/*.jsp) as many times as you wish and no restart is needed at all. The changes come visible when you touch or edit&save the web.xml file inside the webapps folder and then after that with refreshing the visible page on browser. Probably hard refresh with CTRL+F5 is the best way.
Thanks to #Verdan about his comment, otherwise I wouldn't have came back to answer again.

I was able to solve this by disabling the maven nature (right click on project >> maven >> disable maven nature). Then re-enabling it (right click on project >> configure >> convert to maven project). I had tried all of the other tips and tricks above, but this is the one that finally worked.

I was running into the same problem - tried all of the above, Eclipse always freezed when i tried to start the server, even after i deleted all the server configs and created a new one with a freshly downloaded tomcat instance. Anyways, problem wasnt solved until i moved to a new workspace, reimported the projects and created a new server. Seems like an Eclipse bug to me...So in case nothing else works, this is the way to go...

I'm currently struggling with the same problem, but nothing mentioned here does not help me. Anyway, I found out that if I:
stop server in eclipse
run tomcat elsewhere (in my case the xamp distribution)
stop currently running tomcat
start tomcat in eclipse
everything works just fine, of course until I change something in code and try to test it again.