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How to debug the '-cp' option in Java seemingly not working? [duplicate]

I've compiled a JAR file and specified the Main-Class in the manifest (I used the Eclipse Export function). My dependencies are all in a directory labeled lib. I can't seem to get a straight answer on how to execute my JAR file while specifying it should use the lib/* as the classpath.
I've tried:
]$ java -jar -cp .:lib/* MyJar.jar
]$ java -cp .:lib/* -jar MyJar.jar
]$ java -cp .:lib/* com.somepackage.subpackage.Main
etc...
Each gives an error saying:
Error: Could not find or load main class ....
or gives the NoClassDefFoundError indicating the libraries are not being found.
I even tried remaking the JAR file and included the lib directory and contents, but still no dice...
How can I execute a JAR file from the command line and specify the classpath to use?

When you specify -jar then the -cp parameter will be ignored.
From the documentation:
When you use this option, the JAR file is the source of all user classes, and other user class path settings are ignored.
You also cannot "include" needed jar files into another jar file (you would need to extract their contents and put the .class files into your jar file)
You have two options:
include all jar files from the lib directory into the manifest (you can use relative paths there)
Specify everything (including your jar) on the commandline using -cp:
java -cp MyJar.jar:lib/* com.somepackage.subpackage.Main

Run a jar file and specify a class path like this:
java -cp <jar_name.jar:libs/*> com.test.App
jar_name.jar is the full name of the JAR you want to execute
libs/* is a path to your dependency JARs
com.test.App is the fully qualified name of the class from the JAR that has the main(String[]) method
The jar and dependent jar should have execute permissions.

You can do these in unix shell:
java -cp MyJar.jar:lib/* com.somepackage.subpackage.Main
You can do these in windows powershell:
java -cp "MyJar.jar;lib\*" com.somepackage.subpackage.Main

Alternatively, use the manifest to specify the class-path and main-class if you like, so then you don't need to use -cp or specify the main class. In your case it would contain lines like this:
Main-Class: com.test.App
Class-Path: lib/one.jar lib/two.jar
Unfortunately you need to spell out each jar in the manifest (not a biggie as you only do once, and you can use a script to build the file or use a build tool like ANT or Maven or Gradle). And the reference has to be a relative or absolute directory to where you run the java -jar MyJar.jar.
Then execute it with
java -jar MyJar.jar

You can do a Runtime.getRuntime.exec(command) to relaunch the jar including classpath with args.

Create .class file from a jar file -java

I am using Java8. I have one .jar file containing .class files.
I downloaded the source code of the same .jar file. And I edited one of the file in it. It is .java file.
Now I want to compile all these .java files in the source code and create a new .jar file with .class files
Any clues?

There are many options
1. if you want to do it from command prompt then you would need to set the classpath and then either create a list of java files with package name and use it for compiling, something like this
# Linux
$ find -name "*.java" > source.txt
$ javac -classpath "${CLASSPATH}" #source.txt
:: Windows
> dir /s /B *.java > source.txt
> javac -classpath %{CLASSPATH}% #source.txt
or use build tool like Ant.
Once you have the .class files, you can use "jar" command to create a jar of the .class files
2. Use IDE - you can use any of these IDEs - eclipe, intellij, netbeans.
You need to setup a project with the java files and compile project and export as jar using class files.
I think it would work out better for you to use an IDE.

1) Compile the classes (javac command)
If you don't have any jar dependencies required at compile time, you should not need to set the classpath.
Otherwise you should specify the cp argument with.
Example (Unix way) :
javac -cp "myLib.jar:myOtherLib.jar" *.java
2) Then create a jar from these compiled class (jar command)
Example :
jar cf myjar myFolderWithCompiledClass

extract your jar to a folder and run this:
javac [folder]/*.java
read that for more info:
https://docs.oracle.com/javase/7/docs/technotes/tools/windows/javac.html

java manifest classpath vs. -classpath

I'm trying to figure out an odd problem I have with an executable jar file:
xyz.jar has a classpath in the manifest file / and depends on abc.jar library.
Unfortunately, the manifest classpath in xyz.jar is incorrect. To save from disaster, I'm updating the execution commands to use: java -classpath path/abc.jar:etc instead of java -jar
The problem is that xyz.jar malfuntions unless abc.jar is NOT on the classpath. When abc.jar is removed the program executes correctly, and no exceptions are thrown.
Why? xyz.jar must be picking up abc.jar from somewhere else. xyz.jar calls methods in abc.jar.
-classpath should override any $CLASSPATH setting. Is it possible that java still looks at the manifest classpath even when using -classpath?

If you specify -jar, only the class-path in the manifest is used. All others are ignored. If you need to respecify the classpath, don't use -jar.

It is my belief that the Class-Path attribute of a jar manifest file is used to declare the dependencies of classes within that jar, and so is independent of the main classpath.
While it is true that using -cp with the java command replaces the ClassPath environment variable, it should have no affect on the individual Class-Path of each jar.

compiling a packaged project dependent on a jar

This seems to me to be a trivial question, but I've had a lot of trouble getting an answer.
I've developed a project in eclipse that is dependent on a jar file, which resides in the project's root directory. All my files are in a package "a.b.c" in a src folder. It runs just fine in eclipse. I now want to run this project from the command line. I do this command to compile the project:
javac -classpath dependency.jar -d ./bin/ ./src/a/b/c/*.java
Everything is compiled into class files and put into the bin/a/b/c folder. Then I do these commands to run the project:
cd bin
java -cp ../dependency.jar a.b.c.Main
Now I get "java.lang.NoClassDefFoundError: a/b/c/Main".
So, how do I run a project that is in a package and depends on a jar file?

Just include the current dir in the classpath as well - i.e. java -cp ../dependency.jar:. a.b.c.Main

You also need to specify your compiled files on the classpath, these will contain your a.b.c.Main. On *nix flavor machines the path separator for cp is the colon (:), and on windows it's a semicolon (;), so on *nix, your run command should be (because you're running from the bin directory):
java -cp ../dependency.jar:. a.b.c.Main

Java Classpath problem

I have a Java Program that references a Jar File.
The Jar File is present in the same directory as the .class File but when I try to run the program from console, I get NoClassDefFound error :-(
Alternatively it runs Ok from Eclipse.
Why ?

The java program will not automatically include JAR files in its class path. You add a JAR file to its class path via the -classpath option. For example:
java -classpath .;yourJarFile.jar your.MainClass
Eclipse is automatically adding the JAR file whenever you run the program.
Note: The -classpath option expects a semicolon (;) when running on Windows and a colon (:) otherwise.

JAR files are not automatically included in the classpath. You can add a Class-Path entry and a Main-Class entry to the to JAR file containing the main method that you wish to execute. Then you can execute your code like so:
java -jar yourJarFile.jar
See the JAR File Specification for more details.
or specify the classpath on the command line:
java -classpath lib1.jar:lib2.jar:yourJarFile.jar your.MainClass