Develop Reference

Eclipse add external jars doesn't work to add them as Referenced libraries

I'm currently doing this tutorial on Hibernate over here http://www.javatpoint.com/example-to-create-hibernate-application-in-eclipse-ide and I downloaded the hibernate.zip and oracle.jar files, tried to add them to the project through right clicking on the project -> build path -> configure build path -> add external jars and selecting the jars, but they are not getting imported in a "Referenced library", they just appear as stand alone .jar files that don't to anything and can't be referenced to.
How can I make them "go" into the Referenced Libraries? That folder isn't even created when I import the jar files.
Thanks!

You should use Maven for handling your dependencies and let Eclipse & Maven together take care of downloading and organizing your dependencies. You won't even need to download the jar files manually anymore.
This is the basic usage of Maven with Eclipse:
http://www.tech-recipes.com/rx/39279/create-a-new-maven-project-in-eclipse/
In case you're totally new to Maven, i'm happy to provide further help via comments.

I suppose your Eclipse perspective is selected "Resource", not "Java" or "Java EE".
After you change the perspective to "Java", you will see the Referenced Libraries.

Check this Option : Right click Project >> Show In >> Project Explorer

IntelliJ Idea generated source

Just new to IntelliJ Idea. I have maven project which has few generated source java files.
When I import that project Idea complaints about generated source files are missing but I can see those files under target/generated-sources. How can I add those files in the classpath.

You can go to Files > Project Structure and then choose your module and on the sources tab you can navigate to the generated-sources dir and click Mark as > Sources:
Additionally, folder could be assigned to the specific type from the Project panel via mark directory as context menu.
To have maven do it automatically, look here: How to create folder for generated sources in Maven?

If you are using Springboot Application.
just follow the step in IntelliJ.
Right-click on project folder.
Select maven.
Generate source and update the project folder

How to create a jar with external libraries included in Eclipse?

I am done with the project which connects to database (MySQL). Now I want to export the project as jar. But I don't know how to include its external dependencies? Is there any way of doing it in Eclipse or should I use any scripts for that?.

When you export your project as a 'Runnable jar' (Right mouse on project -> Export -> Runnable jar) you have the option to package all dependencies into the generated jar. It also has two other ways (see screenshot) to export your libraries, be aware of the licences when deciding which packaging method you will use.
The 'launch configuration' dropdown is populated with classes containing a main(String[]) method. The selected class is started when you 'run' the jar.
Exporting as a runnable jar uses the dependencies on your build path (Right mouse on project -> Build Path -> Configure Build Path...). When you export as a 'regular' (non-runnable) jar you can select any file in your project(s). If you have the libraries in your project folder you can include them but external dependencies, for example maven, cannot be included (for maven projects, search here).

You could use the Export->Java->Runnable Jar to create a jar that includes its dependencies
Alternatively, you could use the fatjar eclipse plugin as well to bundle jars together

You can right-click on the project, click on export, type 'jar', choose 'Runnable JAR File Export'. There you have the option 'Extract required libraries into generated JAR'.

Personally,
None of the answers above worked for me, I still kept getting NoClassDefFound errors (I am using Maven for dependencies). My solution was to build using "mvn clean install" and use the "[project]-jar-with-dependencies.jar" that that command creates. Similarly in Eclipse you can right click the project -> Run As -> Maven Install and it will place the jars in the target folder.

If you want to export all JAR-files of a Java web-project, open the latest generated WAR-file with a ZIP-tool (e.g. 7-Zip), navigate to the /WEB-INF/lib/ folder. Here you will find all JAR-files you need for this project (as listed in "Referenced Libraries").

While exporting your source into a jar, make sure you select runnable jar option from the options. Then select if you want to package all the dependency jars or just include them directly in the jar file. It depends on the project that you are working on.
You then run the jar directly by java -jar example.jar.

To generate jar file in eclipse right click on the project for which you want to generate, Select Export>Java>Runnable Jar File,
Its create jar which includes all the dependencies from Pom.xml, But please make sure license issue if you are using third-party dependency for your application.

If it is a standalone (Main method) java project then Not any specific path put all the jars inside the project not any specific path then right click on the project - > export - > Runnable jar --> Select the lunch configuration and Library handeling then choose the radio button option "Package required libraries into generated jar" -- > Finish.
Or
If you have a web project then put all the jars in web-inf/lib folder and do the same step.

Before exporting, click on Buildpath and configure java buildpath and add external jars inside the library. Then try to export as a runnable jar.

add other projects as library in netbeans

I have a project A (for example an Ant based Java Application project) and a second project B (a Java Class Library project or another Java Application project, both Ant build based.)
Project B has some additional Java library dependencies (.jar files in the Libraries folder).
A depends on B. A can use classes which are written by myself in B but it can not see classes in the additional libraries of B unless I add those libraries/jar files to A.
Is there a way to get NetBeans to automatically manage the library dependencies in A by including the dependencies of B in addition to B's own jar file? In eclipse when you add .jar files to project B, it is not necessary to add them to A again.
Thanks.

In your project folder you should see a folder called Dependencies, right click on that folder and choose Add Dependency.... Open the Open Projects tab; from there you can select your project from the list. Click Add.
This works for NetBeans IDE 7.2.1.

The simpler NetBeans Ant project Libraries folder is used for compile time and run time dependencies of each individual project. If your "Java Class Library" type Ant based project B has additional library dependencies, they are not automatically forwarded or updated in Project A when you include B as a library of A.
When project A is built, it's .jar file will only contain Project A code and the lib/ folder will only include .jar files from it's Libraries folder. This can cause confusion when you upgrade the dependent library versions and possibly forget to upgrade them everywhere you depend on project B.
You will need to manually manage the dependencies unless you switch to a project management and build system that handles this, like Maven.
A NetBeans Maven project will have a Dependencies folder instead of a Libraries folder and if project B is properly setup and registered as a Maven project and project A is also created as a Maven project, you could Add Dependency on B to A and B would forward it's dependency information to Maven project A.

If you want to add another project as a library in netbeans right click on the libraries directory and select "Add Project", select the project you want to add. When you do this the jar file(in the dist dir) that has been built for the project you are adding will be selected and then click the "Add Project jar files" and that should add the jar file to your project. Alternatively you could select "Add Jar" instead and add the jar file yourself the way that Ravi described.

In your project folder you see a folder called Libraries , right click on that folder from there you can select your .jar file. You need not to add .jar files repeatedly after adding once to your project. You just need to Clean and Build your project whenever new files are added to .jar file.

How Can I Add the Apache POI Library in and Eclipse Project?

I download the Apache POI from apache.org but don't know how use it with one of my existing project in Eclipse.

There are several ways, some good, some bad...
Add external Jar - as jjnguy says will work. However, not a good option...
The problem is that if you share your project with someone else and they have the jar in a different spot, they'll get build path errors
Add variable - similar to add external jar, but much more flexible. You can define a classpath variable (under Java prefs) that represents the dir containing jar. In your project, when you add variable, you choose the var you defined and press "extend" to specify the actual jar. As long as you and other developers of your project define the variable, you can have the jar in different spots if you like
Add the jar to your project - create a dir in your project (optional, maybe call it lib) and import the jar into it using File->Import or if your OS supports, drag it as an icon into the folder (On windows I open an explorer window and drag it from there into the folder in eclipse). Then, right-click the jar and select Build-Path->Add to build path.
Add the jar in a separate project and reference it. Add the jar as mentioned in the last bullet to a separate project for that jar. Choose Build-Path->Configure Build path from the project. Go to the "order and export" tab and make sure the jar is checked. Now you can configure your project to reference the new project. This makes things more modular.
Create a user library - under Java prefs you can define a "user library" that contains the jar. This is somewhat similar to a classpath variable, but can reference multiple jars and you only have to add it once to the project.
Create a classpath container plugin. This is more complex, but is a nice option if you are providing a set of plugins for folks. A classpath container can be added like a library to a project and it can manage the jars, even searching for them if you want it to.

You can find the option to add external jars to a project in: Project > Properties > Java Build Path > Libraries tab.
Click on 'Add External Jar' and find where you have the POI library.