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Where are external libraries in a jar file?

I recently wanted to decompile a jar and edit the contents, so I used jd-gui to decompile it, I saved the project, and I unzipped it. I opened the project in IntelliJ and I was getting a lot of errors for missing types. All the imports that were not built into Java said unknown. Where are these libraries in the jar, and how do I get them out and add them to intellij?

An application may have dependencies that are not included in the jar at all. In that case, the user would be expected to install the dependencies themselves.

Compiling JAVA project with external libraries, is this possible?

I'm currently trying to compile my project which would include two external libraries.
json-simple.jar and mysql-connector-java-5.1.42-bin.jar
At the moment I compiling my program and the problem is that i need to include these libraries in the classpath of created compiled project, but i do need only that these libraries would inside .jar project compiled file and i can simply run .jar file and make it work withuot including classpaths or something like that.
Is that possible, don't have idea how.

Yes, it is possible.
I'll help you a bit:
How to make an executable jar file?
Basically unpack the files from the libraries into the folder with your compiled classes (you know how to compile them, right?) then prepare a MANIFEST.MF, put it the folder with all these classes, then create a jar as explained in the answers under the link (jar cfm jarexample.jar jexample.mf *.class). If you have any problems then read the documentation of the commands like jar and javac.
Have fun!

Runtime Directory in Android Project

I have a android project with a runtime directory, and there is a jar file in this directory. This project can be built in eclipse. However, if I put the jar file in some other place, say, libs directory. This project would fail to build. In addition, even if I place the jar file in the runtime directory, this project cannot be built in Intellij. When the project fails to build, the error logs looks like the following.
Android Dex: [GameDemo] EXCEPTION FROM SIMULATION:
..... bad range 5..6; actual size 5
at bytecode offset 0000005
while processing ()V
So here are my questions:
Given a project in Eclipse, why project can be built when the jar file is in runtime library, but not when it's in libs directory.
Even though the jar is in runtime directory, why this project cannot be built in Itellij. What's the difference in build process of the two ide in term of android project.
Thanks!

I believe you are having this issue because you are trying to integrate CMCC's mobile SDK. It's a piece of garbage but that's another topic. For your purpose, just setting the library as "Provided" instead of "Compile" in the module settings of your IntelliJ project will get you past the compile stage. the SDK's probably loading it on the fly but not sure why that's necessary. Also be careful how you add the dynamic lib they provided. Make sure you do a plain copy instead of through the android NDK module dependency crap.

Seems they wanna avoid their sdk to be easily decompiled and byte hacked.
So they provided a dev time lib written in java that has interface feature only and implemented the real logic/type/class in a native lib.

Can't compile .java code, no changes were made

I have downloaded example session bean servlet from here http://www.roseindia.net/jboss/sessionbeanservlet.shtml , download is under "Download the code of this lesson." label. Files are compiled using ant and just after downloading it works. I compile ant script and build is successfull but when I delete one letter from one of the files with .java code and write it back and save it I receive few errors.
Output:
http://pastebin.com/H0JYUckX
Any ideas?
//I took src files and I've made netbeans project and it works. So I don't more have to worry about this issue. Greets.

The servlet API is not part of the standard Java API. You have to add the JAR file that contains the servlet API to the classpath to be able to compile code that uses this API.
If you're using for example Apache Tomcat, you can find the JAR file servlet-api.jar in the lib directory of your Tomcat installation.

Include servlet.jar in your classpath.

I assume you have downloaded both the source and the compiled version of the code.
This can mean that the code is not re-compiled as you have a compiled version already. However it is when you modify the file that you discover that your program would never have built, most likely because your environment is not setup to build this file. i.e. There are libraries this source needs which you don't have in your build.

I went back to this issue and solution is adding servlet-api.jar and jboss-j2ee.jar to ant/lib folder. In console I could see information that build is successful, but really this files weren't compiled. It just assumed that .class files are in package so it doesn't need to compile it again. Message was "BUILD SUCCESSFUL" but it hasn't been compiled at all. So when I deleted them real compilation started and I needed to provide this .jar files.
Greets.

NoClassDefFoundError on external library project for Android

I use eclipse for Google Android development.
I've created a library project ([x] Is Library in the Android-settings), which includes an external jar-file (Referenced Libraries). This library project are referenced in another Project (the actual project which will use the library project). This is done by add the project under the Android-settings.
the source compiles but if I want to execute it on the device, I get the NoClassDefFoundError for a class which is inside the jar-file which is included in the library project.
Edit: The jar-file ist added to the exported entries ([x] my.jar on the Order and Export-Tab from the library project)
Is there a clean way to get this working?

It has been clearly stated in offcial API here:
A library project can include a JAR library
You can develop a library project that itself includes a JAR library, however you need to manually edit the dependent application project's build path and add a path to the JAR file
The jar lib must be manually added to the dependent application project's build path, not only the library project build path itself.
Update from SDK r17:
This is automatically handled by ADT now, check out new feature for ADT 17.0.0 release here:
Added feature to automatically setup JAR dependencies. Any .jar files in the /libs folder are added to the build configuration (similar to how the Ant build system works). Also, .jar files needed by library projects are also automatically added to projects that depend on those library projects. (more info)

For those who followed the steps(even check the projects in "Order and Export") and still have the java.lang.ClassNotFoundException in the API 17, the final step is to check that your compiler does not run with Java 1.7. If is 1.7 then you should change it to 1.6 for all your projects. After that it will ask to rebuild all the projects and successfully ran on my phone :)
To change the java compile version in eclipse, this is located in: Project properties > Java Compiler > Compiler Compliance level: 1.6

Go to project properties -> build path-> libraies
If you see your jar files like this
snmp4j.jar - e:\software\jars
Its may your problem
Add libs folder in your project and copy jar file in that folder. Right click jar file and go build path -> add to build path. Then you can see your jar as
snmp4j.jar - project_name/libs
Its worked for me.

I had two projects using the same library: one working, the other one crashing with java.lang.NoClassDefFoundError.
After nothing else helped me, I looked into the file project.properties in the root directory of my project.
The working project had the android.library.reference line (the last line below), the crashing one did not:
# Project target.
target=android-17
android.library.reference.1=../my-library-project
I manually added the line and it started working!
(Yes, I did try both (project) properties -- java build path -- projects and (project) properties -- java build path -- order and exports -- nothing helped.)
PS By the way, "project properties" has also the "project references" tab. No idea if it would work.

I had a minor issue when I upgraded to ADT17 where my libs weren't being imported properly. Turns out this is because my librarys were being linked as dependancies from my lib folder not libs!
Seems librarys have to be in the libs folder from now

I had a similar problem and non of the solutions out here fixed it.
Short version: the JAR was compiled in Java 1.7 and could not be found by Dalvik.
We build an internal JAR that we share across backend and mobile clients with Maven. The problem ended up being that the JAR was compiled with Java 1.7. Androids dalvik only supports Java 1.5 and 1.6. This is why everything works fine in Eclipse as it's not compiled to dalvik at this point.
We even specified the target and source version in the Maven compiler plugin to compile with Java 1.6. This did not work because only JDK 1.7 was installed on the build machine. A small note at the bottom of the Maven page gave us the hint: Note: Merely setting the target option does not guarantee that your code actually runs on a JRE with the specified version.
To see if you have this problem as well, rename your *.jar file to *.zip unpack it, and look in the MANIFEST.MF file for the Build-Jdk: parameter to see what Java version actually compiled your JAR.

Another thing to pay attention to is library package names.
If you are using ADT21 and you happen to have libraries that have the same package name, there will be error during compile but it will still compile and run in Eclipse, giving you an APK that is missing some of the resource classes. Hence the crash when you run the app.
If you compile it with ANT then you can see the compile error that says two or more libraries use the same package name.
To fix this, rename your library project by using Android Tools -> Rename Application Package. Then everything will go back to normal.
It took me almost entire day to figure this out...