Develop Reference

How to import JAR file as a project into an IDE?

I have a Maven project. After I make changes to the project, I package the project up into an Uber Jar file and upload that to my backups. I am wondering, if my computer were to break or I lose all the code to the project, can I get the project back using only the Uber Jar file or would the project be gone forever?
How can I open this Jar file as a project and view all the Java code inside of it?

It would be entirely gone; that jar file contains only class files, not your source files, and you can't 'recover' source files from class files (you can decompile them which is mostly useless for this purpose; all comments, most names, most structure - all gone. You can't feasibly continue your project with this).
As it isn't in there, it's not possible to 'open a jar file and see all java code inside it'.
You'll need to set up backups.
The proper way forward is to first set up version control; this ensures that you don't just have a backup of the latest state of your source files, but every state of it - you can travel back to any time. Protects against code you deleted by accident, and means you can freely remove code you think you no longer need without that nagging feeling of: Yeah but what if.... maybe later? - so stop commenting out stuff you don't need, just get rid of it. It also means if there's a bug, you can time travel to the exact point in time when you added the line, and you can review the changes made by others in a project (presumably you're writing this on your own for now, but at some point you'll work with more people than just yourself!)
Read up on git which is the version control system that 80%+ or so of the community uses, probably best not to spring for exotic options if you aren't familiar. There are a billion tutorials out there to find if you search the web.
Host your git on a site like github or bitbucket which therefore also takes care of backups. Alternatively, host it on your own server (it's not complicated; git is open source). If you can't do that either, just let git write to a local directory and then use e.g. backblaze or something similar to ensure that file is backed up.

Yes, you can view your code by using a decompiler. I have experience mostly with IntelliJ, and this IDE includes a decompiler of its own. In case you lose everything and have only the jar file. You can use this included decompiler to get your source back from your .class files. But instructions on doing that are a story for another question...
If you want to secure your code use GIT. A version control tool that is a must when it comes to programming. Google about it and after a few days of playing around with it, you will never worry about such things.

Right-click on your project.
Select Build Path.
Click on Configure Build Path.
Click on Libraries, select Modulepath and select Add External JARs.
Select the jar file from the required folder.
Click and Apply and Ok.

How can I stop eclipse to modify .classpath automatically

I check out a java project from svn repository include .classpath and .project files. And I import these codes into eclipse. But the eclipse will modify the content of .classpath file. How can I stop eclipse to do this? just write off build automatically option?

You can't. But instead of putting a JAR on the Java build path you could
choose an execution environment which should stay stable when you change
the JRE and hence the .classpath file will not change either.

.Project and .classpath files should not be checked in under svn repos.Blindly copying such files from one machine to another may be risky. These are the files that eclipse automatically constructs for you as per your project structure. If you want to edit, you can do that.
Here is the nice explanation What's in an Eclipse .classpath/.project file?

Adding information to a 2-year old question just in case of any one else is stumbling across this.
Due to insufficient detail in the original question, I am guessing that the problem experienced is due to the project's classpath pointing to a different location on the questioner's machine as on the original project author's machine. When a project uses 3rd party libraries (JARs) and is shared between different team members (as hinted at by the use of a version control tool), this is a common occurrence.
A solution to this would be to have all team members set up the location of the directory containing all 3rd party JARs to have an identical structure on all individual machines. So instead of changing the classpath, change the directory structure to that required by the classpath.
Unfortunately this is not always the best solution:
Team members may have different operating systems (Windows vs Linux) and you will not be able to have a (absolute) class path that works on all platforms (e.g. C:\libraries\3rdparty.jar vs /opt/libs/3rdparty.jar)
Team members may differ in how they prefer to organize their directory structure. Especially, if a team member places libraries into his home directory (e.g. C:\User\abcd\libraries\3rdparty.jar or /usr/abcd/libs/3rdparty.jar), another team member will struggle to replicate that directory structure.
Eclipse provides various methods to set up a project so that it can easily be shared between team members. These however require team members to all agree on the convention, and will be slightly easier if set up by the original project author right from the start. Two methods most commonly used:
Add all third-party libraries to the project itself (the usual convention is to have a /lib directory inside the project for this - on the same level as /src and /bin etc.). The classpath can now be set up to be relative to the project's root and thus usable across different setups. A variation for large multi-project-file projects would be to have a separate eclipse project containing the libraries, then add it to other projects as a dependency ("Required projects on the build path" in the "Java Build Path" dialog).
This has the benefit of being able to version control your JARs too. However, it may use up a lot of extra storage/bandwith, so may not always be desirable. For instance, I would not do this with Java Enterprise Edition JARs contained in my preferred Application Server distribution, as I may want to migrate my project in future to a new version or another product, without such dependencies - I also do not want to have my project saddled with duplicate JARs that are in any case already available in the AS distribution. So you need to think through your requirements.
Eclipse also provides the concept of a classpath variable. This may be set up to point to the root of a team member's JAR-containing directory, and be extended with subdirectories and filenames inside the classpath. This needs to be done only once, and is also accessed via the "Java Build Path" dialog.
Whenever a new team member uses the project for the first time, he needs to configure eclipse (once) to point that variable to the relevant path on his own machine.
The above mechanisms are explained in more detail on various web pages, here is one reference: http://www.informit.com/articles/article.aspx?p=367962

Eclipse (java) web services, what files to version and how to properly pull the project to a new computer?

Alright, so I have a web service that was created using an eclipse dynamic web project. It is currently shared on a CVS repository, but the versioning system used is irrelevant. At the moment, I have literally NEVER been able to pull this project out as is and get it working. It leads to countless errors that cannot be fixed. Every time I need to work on this webservice in a new machine I have to create an entirely new dynamic project, copy over the source files, add all the necessary libraries and make the deployment assembly work correctly again. After finally making it run I share the project as the same one, stop after a second, and then synchronize again (in a way tricking eclipse into thinking this was the shared project all along).
I feel like others must have run into this problem and found a way around it. So if you have a web service or any dynamic web project, what files do you share, and how do you successfully pull it from the repository and get it to run on another machine besides what I currently do now?
Your help is much appreciated,
-Asaf
Edit: After reading some of the responses I feel that this question is actually more specific to those who use WTP to create/test their web services. Just wanted to add the clarification.
Edit2: Let me also clarify that the other 20 or so projects not using WTP are shared just fine. I am able to pull and run them with no problem. Only web service projects are an issue.

In general, you want to check in everything that's not "derived" (generated or compiled - that's usually the contents of the bin directory or other place where your code is compiled/built into). For Eclipse Java projects, you want to include the .project, .classpath, .settings, and any other similar files that Web Tools might create for Dynamic Web projects. The Eclipse CVS client will ignore files marked as Derived so you shouldn't have to worry to much about it.
Without more detail about what kind of problems you've run into, it's not possible to guess what was causing them. My only guess is that perhaps you had different versions of Eclipse and/or the WTP (Web Tools Platform) plugins installed on the different machine. That's just a wild guess, but could explain some incompatibility when you check out the project from CVS.
Bottom line, checking in those .* files is the long recommended approach from Eclipse gurus. Maven can kind of change things, but you didn't mention it so I'm assuming you aren't using it.

I am primarily sharing my experience, may be you can find some help.
Conceptually speaking, the files which the IDE can generate itself while creating new project should not be pushed. I.e the IDE specific files should not be pushed. And everything which the IDE cannot generate on its own must be pushed.
Forexample in case of eclipse, following files should not be pushed:
.settings
build
.classpath
.project
For setting the project on new machine, first pull the files from server, and then create a project from IDE using pulled files.
EDIT: If your project has external jars/libraries, then you will have to add to the classpath manually. You could also push .classpath but that might give errors while creating a new project.

I think it's easiest to use a build system and let the IDE generate the project from your build system.
Eclipse, Netbeans, and Intellij are all pretty good at building projects from maven or ant build files. With this solution you have a simple build that is easy to setup in CI (Hudson, Bamboo, whatever) and you don't have any IDE specific files checked in. If my workspace is totally different than yours, with different versions, plugins, whatever, I'm not stuck with your project file and you're not stuck with mine. My IDE creates the project appropriate for my environment and your IDE does the same for yours.

Since you mentioned having to manually add libraries, I assume you are not using any build manager (like, maven or ant) besides ecplise.
For ecplise to handle the project properly you need the source files (*.java) in their respective directories, any resources bundled with the web service (e.g. services.xml), the ".project", ".classpath", ".settings", etc. files for eclipse. This should be enough for eclipse to generate anything else necessary to build the project.
Any files/directories that are generated by eclipse during the build process (e.g. target & bin directory, *.class, *.war) should not be checked in -- they will be generated when needed during the build.
I am thinking that, since you are adding the necessary 3rd-party jars manually, these libraries might reside in a different path between computers (e.g. if the path contains the username, it will not be transferable to another computer for a different user). To fix that you can set up the classpath using an eclipse classpath variable. In Preferences->Java->Build Path->Classpath Variables set up a varable linked to the "root" folder where the 3rd party jars a stored. Then add the libraries to the project using this new variable, not their full path. To make it work on someone else's computer, you would only need to set this classpath variable to have the build path point to the correct libraries.
It might be beneficial if you migrated your project from eclipse only to a build manager (e.g. maven) that takes care of many of these issues for you. Eclipse can build a project from the configuration of the build manager, making it easier to manage the project.

How to set up a subvresion repository from my netbeans project

I was recently given some code that was worked on by someone other than myself, and after lots of work involving hunting down external dependencies, and editing the build.xml file to get ANT to build things in a sane way, I'd like to now get the code into a subversion repository.
The team I'm working on is rather small, but the members on the team change often. So I want people to be able to start working on this code as quickly as possible. A simple checkout from the repository, and opening the project in Netbeans to have everything building and executing properly would be ideal.
How do I achieve this when there are external dependencies that are not going to be on other team members machines?
Should I place the libraries my project uses in the VCS?
How do I instruct subversion to not track generated files such as class files and jar files?
Should binary resources that are unlikely to change such as images and sounds be placed in the VCS? If not what would be the best way to distribute them?
Thank you.

1) yes. Anything needed to build and deploy the application and isn't generated by the build process goes into version control (yah, I know the maven fanz don't like that).
2) make sure everything that's generated goes into distinct directories that you exclude from version control.
3) see 1). Same thing. Same with project documentation, release notes, etc. etc.
The biggest problem of course are directory names which will be set in your IDEs configuration files and differ between development machines.
Not just the location of the project directories, but the IDE itself, JDKs and other tools, appservers, can all be different between machines. It's a constant problem.

I usually use maven cause you can have a repository for jars and dependencies this makes life easier, but since you have already refactor your code to use ANT maybe this is not what you want, to use subversion with netbeans then you might want to add another folder for jars like libs or something and then another for the binaries like audio etc. Also check for the svn plugin for netbeans it will add the ignore to the dir and just update java files.
To add files to ignore you can use
svn propset svn:ignore -F .
or you can look for the config file in your subversion home and add something like this
global-ignores=*.classs
Hope this helps

What files should be added to SVN in an eclipse Java project?

I have a Java project I'd like to commit to my SVN repository, created with eclipse.
Now, what files (aside from the source code, obviously) are necessary? In the workspace root, there is a .settings folder with many files and subfolders, and inside the project folder there are two files - .classpath and .project, and another .settings folder with a single file - org.eclipse.jdt.core.prefs.
Which of these files should be committed to SVN and which can be safely excluded?

They're all useful if you want to have consistent settings across your team.
.classpath and .project mean everyone can get up and running with a project just by importing it. Any changes to the libraries and source files included in the project will be picked up by everyone when they're checked in.
The .settings directory has things like code formatting options and what the compiler considers as warnings, errors, or OK. For consistency, I've started checking these in as well (as long as everyone on your team can agree to a standard for formatting, I guess).
I've found that the biggest limitation in sharing things across version control in Eclipse is in the library definitions. Library definitions seem to be only stored on a per-user basis, so if you reference a "library" in the .classpath file, every other user has to manually define the contents of that library (or manually import your exported library definitions file).
Edit: (Addressing #mliebelt's comment below)
You'd only commit .settings files if you're trying to keep consistency/standardisation between developers. If that isn't an issue for the project, then not committing .settings files is one less thing to worry about maintaining. Files that are specific to an individual's favourite plugin(s) probably don't need to be committed either (although I don't think it would hurt if they were, would probably be ignored?).
The two most common ones I've found worth committing are org.eclipse.jdt.core.prefs and org.eclipse.jdt.ui.prefs, which are core to any (Java) Eclipse project.

You can exclude the .settings folder, but the .project file will be useful to other developers who want to reconstruct the same exact Eclipse project. If you examine the file it should only have relative references (if it doesn't, you should modify it as such.)

In contrast to the other answers I've made better experiences with not checking in the .project file in large open source projects that I work with.
You may disagree with me, but there is one problem with shared .project files: They contain references to the project natures used in the project. The project natures again depend on the plugins installed on the local developers machine.
Example: If you use Findbugs on a Java project, a new nature gets added to your Java project. Checking that file in, modifying it on another system (with no Findbugs installed) and afterwards using it on my system again has led to the Findbugs reference being lost for me (and therefore all Findbugs checks being removed silently).
But if you can have all of your developers agree on using the same tools, then you may be able to work around this problem easily.