So I'm still a noob in Java and I'm experimenting around with a few things.
I recently created a .jar file for my class using jar cvf <name>.jar <source files> and then used that jar to compile my driver class (javac -cp <name>.jar Driver.java) though how do I now run that class using the jar?
I've tried the following 2 commands:
java Driver and,
java -cp <name>.jar Driver.
The first gives me a NoClassDefFoundError for the class used, whereas the latter just gave me a single line error.
Error: Could not find or load man class Driver
What am I doing wrong? Is it possible I'm confusing this for something else?
I'm trying to do as much as I can without the use of any IDE.
You should put jar file and compiler output into classpath and specify main class:
java -classpath "<name.jar>;classes" Driver
EDIT (thanks to Kayaman):
If you are running command from linux/unix you have to use ":" as separator (in Windows works ";"). "classes" is a path to folder containing compiler output.
When creating an executable jar ( jar which contain a class with the main method) you should tell the jar which is the mainClass to be executed and for that you should create a file called 'Manifest.mf'.
The file should contain this:
Main-Class: MyPackage.MyClass
And when creating the jar you should use this to include your manifest:
jar cfm MyJar.jar Manifest.mf MyPackage/*.class
And for launching your jar :
java -jar MyJar.jar
Related
I need to compile and run simple code using the gson library, but I can't use Maven, Gradle or the IDE.
The directory contains Main.java and gson-2.9.0.jar
javac -cp gson-2.9.0.jar Main.java works correctly and creates Main.class
But when I run java -cp ./*: Main, I get
Error: Could not find or load main class Main.
Caused by: java.lang.ClassNotFoundException: Main
I also tried the following commands:
java -cp gson-2.9.0.jar Main
java -cp gson-2.9.0.jar: Main
java -cp ./gson-2.9.0.jar:./* Main
But all these commands give the same result. I've never had to run code from the command line without Maven or IDEA before, so I think it's the classpath specification that's the problem. What am i doing wrong here?
If your main class is in a package (has a package ... declaration), you need to include the package name in the java call, e.g. java -cp ... mypackage.Main.
Additionally, the java documentation says about -cp / --class-path:
As a special convenience, a class path element that contains a base name of an asterisk (*) is considered equivalent to specifying a list of all the files in the directory with the extension .jar or .JAR.
Therefore, using * for .class files does not work; instead you have to specify the directory name. Based on your question it looks like you are using Linux, and that the .class file and the JAR are in the same directory, so the following should work in your case:
java -cp gson-2.9.0.jar:. Main
(note the . after the :, indicating to include the current directory for the classpath)
After converting my java program to executable jar file using commands in command prompt in windows 10,while executing jar file I am getting error:
Could find or load main class Combine.class" caused
by:java.lang.ClassNotFoundException:Combine.class
My jdk-11.0.1 has javamail api and excelapi.While executing I have set my classpath as:
classpath=%classpath%;C:\Program Files\Java\jdk-11.0.1\javamail_api\javax.mail-1.6.2.jar;C:\Program Files\Java\jdk-11.0.1\javamail_api\activation.jar;C:\Program Files\Java\jdk-11.0.1\jexcelapi\jxl.jar;.;
It was compiling and executing properly but after converting to executable jar file it is not running and giving above error.
Any help would be appreciated.
Thank you
The clue is in the exception message. It is trying to load a class with the name Combine.class. But the classes real name is Combine.
You have created the JAR file incorrectly.
echo Main-Class: Combine.class > manifest.txt
jar cmf manifest.txt FinalExecutable.jar Combine.class
If Combine is in the default package (i.e. it doesn't have a package statement) then the above should be:
echo Main-Class: Combine > manifest.txt
jar cmf manifest.txt FinalExecutable.jar Combine.class
If Combine is declared in package foo.bar, then the above should be.
echo Main-Class: foo.bar.Combine > manifest.txt
jar cmf manifest.txt FinalExecutable.jar foo/bar/Combine.class
and you need to be in the directory above the foo directory.
NB: the "Main-Class" attribute in the manifest must be a Java fully qualified class name, NOT a filename or file pathname.
It also should be noted that the CLASSPATH environment variable and the -cp argument will be ignored when you run a JAR using java -jar .... If your executable JAR depends on other JAR files, you should either combine them (to create a shaded JAR) or you should add a "Class-Path" attribute to the manifest; see https://docs.oracle.com/javase/tutorial/deployment/jar/downman.html
Finally, my advice would be to use a build tool (e.g. Maven) to compile your code, create the executable JAR file, etc rather than doing it by hand.
I want to run a java project in windows. I first compiled the .class file in linux. Copy back to windows. Now under the path H:\deletefiles has delete.class, delete.java, a.jar, b.jar. The package for class delete is deleteFiles.
My java class path is C:\program Files\Java\jre7\bin, Where I have no access to write.
I run in command prompt C:\program Files\Java\jre7\bin>
java -cp H:\deleteFiles\deleteFiles.delete
always has the problem could not find or load main class, what's the problem? thanks
You are missing the actual class to be run. The -cp H:\deleteFiles\deleteFiles.delete only defines the classpath to be used, but not which class you want to run (and you limit the classpath to a single class as well).
What you want is:
java -cp H:\deleteFiles\deleteFiles delete
Note the blank (space) between H:\deleteFiles\deleteFiles which means you are passing two parameters to the java command:
-cp H:\deleteFiles\deleteFiles - the classpath to use
delete - the class to run
If you need the classes that are part of the jar files, you need to add them to the classpath as well:
java -cp H:\deleteFiles\deleteFiles;H:\deleteFiles\deleteFiles\a.jar;H:\deleteFiles\deleteFiles\b.jar delete
You need to set the classpath to the location which contains the package hierarchy. If your package is named deleteFiles the location needs to contain a directory named deleteFiles which contains the class file.
In your example you would run it with
java -cp H:\ deleteFiles.delete
you should call delete.class in your java command line, like this:
java -cp H:\deleteFiles\delete
To execute a Java program you have two options. Using a class file or using a jar file.
If your program only contains a single source file, executing the class file would be fine. But if you have multiple sources, you would have to copy all of them. Then a jar would be more practicable.
For class:
java -cp <class path> <class name>
For jar (if the main class is set):
java -jar <jar file>
I use a jar file called korat.jar. I executed with the command line:
java -cp $CLASSPATH korat.Korat --visualize --class test.Add --args 3
The classpath contains the path of the jar and also the Add.class file.
I want to execute this jar in my own program java in netbeans IDE. I think I would use:
String []s={test.Add.class.getName(),"--visualize","--class","test.Add","--args","3"};
Korat.main(s);
I get this exception: java.lang.NoClassDefFoundError
What do you mean "to execute the jar in my own program"? The jar contains some classes, if they are in your class path, you can instantiate the classes themselves and invoke some methods. In that case, you should use test.Add class. But it seems like the class is not in your classpath - java.lang.NoClassDefFoundError.
This is annoying.
I have a directory structure like this
-lib
--some jar files
-packageName
--Main.java
--SomeOtherPackage
--SomeOtherJavaClass.java
Main.java imports SomeOtherPackage. And both java files uses jars in the lib.
What I do is add the jar files independently in the CLASSPATH. And then run as:
javac packageName/Main.java
but it gives the error that Package not found SomeOtherPackage . Shouldn't it automatically realize the dependency and build SomeOtherPackage as well? What would be the javac command and the classpath for the above case?
Thanks
The normal practice is to add the package root to the classpath.
When you're already in the package root, use -cp .. E.g.
cd /path/to/all/packages
javac -cp . packageName/Main.java
If you want to include JAR files as well, use the ; (or in *nix, the :) as classpath path separator:
javac -cp .;lib/file.jar packageName/Main.java
To save the time in repeating all the typing of shell commands, use a .bat (or in *nix a .sh) file. Or just an IDE if you're already familiar with java/javac and so on.
You need to add packageName to the CLASSPATH so it can find SomeOtherPackage