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How import a file in a jar?

I have this project that it has this structure
Home
graphics
field.txt
example.java
I need to load field.txt in my example.java in jar and I use:
getClass().getClassLoader().getResource("field.txt").toUri();
but this code it give me "Null Pointer exception" .Anyone can help me?

example.class.getResource(“/graphics/field.txt“);
The class should belong to the same jar. For Class.getResource a relative “field.txt“ is possible (same package). With ClassLoader an absolute path for all classpaths is sought: “graphics/field.txt“.
To immediately read (never write) use getResourceAsStream or the URI of the getResource. One can use a Path on the URI. Files.copy(...).
One cannot at least should not) write a resource file (as it can reside in a jar jar:file://...; and jar might even be sealed; and resources might be cached by the jvm). Keep it as read-only template. Never File.
One technique is to create an application named directory in System.getProperty("user.home") and copy the template there.

To read the file it must be in classpath, you can put the file in the folder containing .class files or add it to the classpath with java -cp option.

The issue is not so much your code, but how you build and package your jar file. You will have to clarify how you are currently building your jar (using ant, maven, eclipse, etc ?).
Many articles will also advise you to separate out your resources from your source code (.java), and many IDE will support this separation direclty by allowing you to mark a folder as a resource folder. Even maven will allow you to customize this.
See following articles:
How to package resources in Jar properly
Using maven and netbeans, it is real simple: https://coderwall.com/p/d_cvrq/how-to-package-non-java-code-files-resources-in-a-jar-with-maven, or
use maven to pack javascript files in Jar?

How to package a jar file along with reference files?

Using eclipse, exporting a runnable jar file is pretty simple when I'm only using the application on my computer. Any files that the program is using (sprite sheets, audio tracks, etc.) only exist on my computer, so sending solely the jar to another machine won't work.
What is the easiest way to package a jar along with all the necessary files so that I could run the program on any machine?

I see from your tags that you are working in Eclipse. I am not sure if this method will work in other IDEs and I don't think it'll work at all if you're doing everything manually (it relies on the compiler automatically copying resources over to the bin folder.
The simplest way (at least what I use) is to define another sourcefolder (I like res).
Then you can just add packages to this source folder and dump the relevant images. Then rebuild your project.
Finally, you can use getClass().getResourceAsStream("package/path/file_name.whatever"); to get your files.
After an export as jar, it should work, even on other machines.

If you don't require the other files to be actual files on the file system (which means you can't use File, FileInputStream, etc) then you can use the resource system. If you put them inside the JAR, you can access them like this:
InputStream fileStream = SomeClassInYourJarFile.class
.getResourceAsStream("/path/to/file.png");
This example would give you an InputStream reading from the /path/to/file.png entry in your JAR file - that is, the "file.png" file inside a folder "to" inside a folder "path".
This does not require the files to be in a JAR file - it can load them from wherever your .class files are stored, JAR or not. If you put them in your source folder, Eclipse will automatically copy them to that place - so the above line would also work if you had a package path.to containing a file called file.png.

Accessing a file within Java project

I have a Java project which uses a third party application. I have the license file (.lic format) stored in the resources folder. Upon running the Ant script, it will copy this file into the /lib/jar directory as it rolls up the project into a Jar file to use on the server. This is where I will need to access the file when running the system live. Here is how the folder structure looks
MyProject
src
package
AccessingClass.java
resources
File.lic
lib
jar
File.lic (upon copy from Ant)
I am not sure the best way to do this so any suggestions other than how I have been trying will probably be helpful. The 3rd party project has a method in a class like License.setLicense(), which can either take a String to the location or an InputStream of the file.
I have been playing around with feeding it an InputStream, but always get a null value when calling getClass().getResourceAsStream(). Here is everything I have tried:
getClass().getResourceAsStream("../../../lib/jar/File.lic");
getClass().getResourceAsStream("/File.lic");
And as a backup I also tried (for local builds I figure I would try the resource folder):
getClass().getResourceAsStream("../../../resources/File.lic");
getClass().getResourceAsStream("/File.lic");
Is there a better method to perform this action? Or would someone be able to tell me why what I am trying is failing? Thanks ahead of time.

Are you running this code standalone or in IDE env looks like classpath issue. If you are running at command prompt you have to set classpath to lib dir if in ide make sure you resources dir is in classpath.

First, you need to ensure that the JAR is added in your class path.
Below should work.
InputStream inputStream =
getClass().getClassLoader().getResourceAsStream("/resources/File.lic");
Assuming File.lic is placed in root folder of the jar.

Accessing XMLBeans generated schemas.jar in Maven project

I have a schemas.jar supplied to me and am trying to access it from within a simple Maven project. I have put the schemas.jar file in my src/main/resources directory, which is in my classpath.
When I am trying to access the created documents with something like:
GetOrdersRequestDocument getOrdersRequestDocument = GetOrdersRequestDocument.Factory.newInstance();
It complains about the GetOrdersRequestDocument (can't find it).
How do I get the project to pick up these classes? Do I need to import anything specific?

I have put the schemas.jar file in my src/main/resources directory, which is in my classpath.
Yes, the files in src/main/resources directory are on your classpath. But this doesn't mean that the content of the jar itself is directly available. You could use a URLClassLoader to load the JAR though.
But... this is not how I would do things. If this is an option, I would just install the JAR in your corporate or local repository (using install:install-file) and declare it as a dependency. This would make the content of your JAR available to your code, like any other dependency.

Files not extracted from .jar file when run

I have updated my ant build.xml file to include a new file and a new folder. After creating the .jar I check if they exist in the jar by 'unzip\extract', and they are there.
But when executing the .jar neither the folder or the file gets extracted.
Am I missing a step?

Look into getResourceAsStream. It'll keep you from having to extract the files from the jar file. Unless that's your goal.

Your application should be able to use the file directly from within the jar, no need for extracting it. Or do you mean something else?

Are you doing something specific to extract the jar file? I ask because normally jar files are not extracted when executing them.
If you run "java -jar myJar.jar" or "java -cp myJar.jar com.example.MyMainClass" the jar files that is referenced will not be extracted. Java will load your classes and resources directly from the jar file without extracting it.

If you wrap your application up using One-JAR, you can specify an attribute in the Manifest file to extract files that you want (See the One-Jar-Expand manifest attribute).
As a bonus, you will also be able to wrap any dependent libraries along with your code, creating a single distributable jar.