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
Related
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.
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.
This question already has answers here:
Specifying classpath for a jar
(5 answers)
Closed 8 years ago.
I am not familiar with Java and I am trying to run a piece of Java code packaged as jar file.
On Windows command line, I specify the CLASSPATH to my jar folder like this:
set CLASSPATH="D:\jarFolder"
And there's a test.jar file in that folder. But when I run this
java -jar test.jar
it still failed with this error:
Unable to access jarfile test.jar
I can run the test.jar by specify the full path. But I want to know why the CLASSPATH doesn't work. My understanding is, it tells the java runtime where to locate the jar file.
Jarfiles have to be on the classpath explicitly. Specifying a classpath dir for a jarfile is not sufficient.
See the related Oracle docs on the Java command line:
When you use this option, the JAR file is the source of all user
classes, and other user class path settings are ignored.
Try to use
java -jar D:\jarFolder\test.jar
If you know main class name of your entry point of jar. You can use
set CLASSPATH="D:\jarFolder"
java yourpackage.yourEntryPoint
You can learn your entry point of your jar file using a zip program to extract jar file and reading file entry point section of manifest.mf file.
When you use -jar option, you need to specify which jar. Think of it this way. If you do not give jar name, which jar java should execute? You may have 10,20 may be 100 jars in your class path.
But if you give class name, then java searches among jars and execute correct one.
I have program in Java in path: C:\...\MyProgram.
This program have some dependencies to others *.jar files. I would run it using cmd. So what I do:
in cmd I write cd C:\...\MyProgram\bin and then java -cp C:\...\MyProgram\*;. main.Main. It is working. But now I exported MyProgram to jar file. Could you tell me how can I run this now? So I have file MyProgram.jar with these same dependencies. How run it by using cmd?
Folders and archive files
When classes are stored in a directory (folder), like /java/MyClasses/utility/myapp, then the class path entry points to the directory that contains the first element of the package name. (in this case, /java/MyClasses, since the package name is utility.myapp.)
But when classes are stored in an archive file (a .zip or .jar file) the class path entry is the path to and including the .zip or .jar file. For example, to use a class library that is in a .jar file, the command would look something like this:
% java -classpath /java/MyClasses/myclasses.jar utility.myapp.Cool
Found in http://docs.oracle.com/javase/7/docs/technotes/tools/solaris/classpath.html
You need to add a Class-Path entry to the manifest file (META-INF/manifest.mf) inside the jar:
Class-Path: /C:/.../MyProgram/ .
This assumes that there are dependent classes under C:/.../MyProgram/, not jar files.
You should also add an entry for the Main-class:
Main-Class: main.Main
Then just execute your jar as
java -jar MyProgram.jar
Set the path of JAR file in your classpath and then execute the other JAR file.
To add JAR using eclipse.
Right click on project -> properties
Java Build Path -> Click add external JARs.
This will add JAR to your classpath.
I have exported a jar file that I want to run the console. The code compiles and runs correctly in eclipse but I am having an issue running it from the console.
To me it looks like the referenced jar's I added via built path in the Eclipse project file and not being added to the export. If that is the case, how do I ensure that they do? If not, what am I doing wrong?
When you export your source code's class files to a jar using eclipse, only the .class files of your source are exported! Hence your exported jar file doesn't contain the referenced jars you mentioned in eclipse! Due to this, the error occurs while executing from command prompt.
Solution:
Take all the jar files required to execute the program, store it in the same directory as you store the exported jar file. Now while executing the java command, provide all the jar file's names in classpath field as following:
java -classpath .;JAR1.jar;JAR2.jar MainClass
Once you do this, your problem should be resolved!
The dependencies need to be on the classpath, i.e. run like this:
java -cp <path_to_jar1>;<path_to_jar2> -jar ScrumTimeCaptureMaintenence.jar
When running from the command line make sure any dependencies are set on the class path by listing them in the -classpath parameter