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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?

class.getResource() is null though it is in classpath

I have a jar containing the main class of a project. This depends on several other jars that reside in a lib directory. One class of such a dependend jar loads a ressource "/Data/foo/bar/file.txt". But loading this file as ressource leads to null.
Here is the directory structure:
./main.jar
./lib/lib1.jar
./lib/lib2.jar
./lib/lib3.jar
./lib/runtimedata/Data/foo/bar/file.txt
This is the classpath of the manifest.mf of the main.jar:
lib/lib1.jar lib/lib2.jar lib/lib3.jar lib/runtimedata
I start the application via
java -jar main.jar
The lib2.jar contains a class that tries to load the file with
ThatClass.class.getResource("/Data/foo/bar/file.txt");
But that happens to be null. Why? lib/runtimedata is in the classpath.
I even tried to put the Data directory into lib/lib/runtimedata, in case the path is relative to the jar file containing the loading class. But that doesn't help.
What am I doing wrong here?
EDIT:
Running the application with
java -cp main.jar:lib/*.jar:lib/runtimedata my.package.Main
works correctly.
EDIT 2:
I cannot change that lib that does the resource loading. I am only using that lib. The only things I can change is the main.jar the classpath and the command line.

When you start the path with a "/", it's considered as absolute. Try ThatClass.class.getResource("/runtime/Data/foo/bar/file.txt");
Otherwise, if you cant't change the code, put the file on /Data/foo/bar/file.txt

In a development environment, this can sometimes happen when resources have not been processed during the build. Using Gradle and building your main JAR or main test JAR will depend on the compileJava tasks in your libs, but will not trigger their resources to be processed. You can see if this is happening by looking in your build dir to see if resources for your libs have been copied over. If they haven't been copied the resource loader won't find them at runtime.
If this is the problem, a full build will fix the issue and published JARs should always have their resources. But, it's nice to be able to trigger e.g. the test task for an individual module and know that it will always pull in everything it needs. If you have a library with essential resources that must always be present, you can force them to be processed in partial builds by adding this to the build.gradle of the library:
compileJava.dependsOn(processResources)

Load files from the source folder of a project using a loader from a different project

I have a utility project file that I've put code in for loading resource files. However, when I reference this project from a different one to use this loading code, the loader still uses its own src folder, instead of the src folder of the project referencing it.
I'm loading all my resources like this:
ClassLoader.class.getResourceAsStream(filepath)
...where filepath might be something like "/res/index.txt"
My first guess as to how to make this work would be to use a different class in the project I want to load from instead of the ClassLoader to get resources? What would the most elegant solution to this be?
I am using Netbeans, if that makes a difference.

If you use "/" in the beginning of filepath, it's gonna be resolved from the package root (it is clearly stated in the JavaDocs).
Try to make your build script copy the resources to the bin directory (IIRC NetBeans was compiling with Ant scripts, haven't used it for a while).

Jar cannot find the path to the file inside

In my Maven project I have a properties file that has a property for a location of keystore file file=filename.p12 (I think the file type doesn't really matter now).
The problem I have that when i built it with maven, I see that the file is inside the root of jar and when i run java -jar the-jar-file.jar I get the IO exception that the filename.p12 is not found.
Everything runs fine in Eclipse, it finds the file and the application runs. Not to confuse somebody, I keep a copy of that filename.p12 as well in src/main/resources folder so that the paths are resolved running in Eclipse and standalone. But this is going to be my other question.
What I can't do is to get the filename.p12 as a resource, because I have external jar that gets as argument my properties file and then handles that properties file itself where the row file=filename.p12 is. Why is the file not found inside the jar, even though I see it's there? My other property files that I have open with Spring's ClassPathResource run just fine.

In order to access internal/embedded resources you need to use Class#getResource or Class#getResourceAsStream depending on your needs

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.