HI,
I have created a runnable .jar file using eclipse and compiled it with jdk1.4.2, i am able to run it perfectly on windows but whenever i run it on unix it says "failed to load main-class manifest attribute from abc.jar" Why is it so
Please help
Saurabh
I usually avoid executable jars. Assuming, we have a class com.example.MyClass that has has main method, then the "executable jar"'s manifest (myapp.jar) needs the line
Main-Class: com.example.MyClass
Then you can start the application like this
java -jar myapp.jar
Apart from some classpath annoyances, this is pretty similiar to
java -cp myapp.jar com.example.MyClass
The "annoyance": if run the application with the -jar option, the classpath has to be defined in the manifest - it will ignore any CLASSPATH entry or -cp attribute. So if you have dependencies, you'll have to copy and paste them from the manifests classpath attribute to the -cp attribute:
java -cp myapp.jar;<other libs> com.example.MyClass
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 plan to run a java class like
java -cp myjar.jar MyClass
myjar.jar will have a manifest file with classpath entry in it.
Is it a valid use case? I have a doubt since I have only seen usage of manifest when using java -jar myjar.jar
You cannot use -cp (or the CLASSPATH enviromment variable) together with -jar. If you need to specify a classpath to make an executable JAR file work, you can specify a Class-Path attribute in the JAR file's manifest.
On the other hand, the Class-Path attribute in a JAR file manifest is only used for classes loaded from the JAR file itself. (But it is not restricted to use with -jar option.)
For more details, refer to the JAR file specification and How classes are found.
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.
In Linux, how to execute Java jar file with external jar files?
Either use the -cp flag:
java -cp /path/to/somefolder/*.jar:/path/to/otherfolder/*.jar com.YourMainClass
Or add a Class-Path: header to your jar's manifest (see Jigar's answer)
Note to others who answered with java -jar <etc>: The -jar flag deactivates the standard -cp flag and CLASSPATH environment variable, because it retrieves the classpath from the JAR manifest. Any answer that combines -jar and either -cp or $CLASSPATH will not work.
This information is well-hidden, but I finally found a reference:
-jar
Execute a program encapsulated in a JAR file. The first argument is the
name of a JAR file instead of a
startup class name. In order for this
option to work, the manifest of the
JAR file must contain a line of the
form Main-Class: classname. Here,
classname identifies the class having
the public static void main(String[]
args) method that serves as your
application's starting point. See the
Jar tool reference page and the Jar
trail of the Java Tutorial for
information about working with Jar
files and Jar-file manifests. When you
use this option, the JAR file is the
source of all user classes, and other
user class path settings are ignored.
Source: java - the Java application launcher
java -jar /path/to/externalJarFile.jar
Update
You can add the required library in manifest with Class-Path: header
For example :
Class-Path: MyUtils.jar
See
Adding Classes to the JAR File's Classpath
I have created a JAR file in this way jar cf jar-file input-files. Now, I'm trying to run it. Running it does not work (jre command is not found):
jre -cp app.jar MainClass
This does not work either:
java -jar main.jar
(Failed to load Main-Class manifest attribute from main.jar).
I also found out that
To run an application packaged as a
JAR file (version 1.2 -- requires
Main-Class manifest header)
What is the "Main-Class manifest header"? How do I create it and where do I put it?
I'm not sure I believe your symptoms:
If the jre command isn't found, then running jre -cp app.jar should give the same error
Just adding a JAR file to the classpath shouldn't give the error you're seeing
I'd expect you to see this error if you run:
java -jar app.jar
The Main-Class header needs to be in the manifest for the JAR file - this is metadata about things like other required libraries. See the Sun documentation for how to create an appropriate manifest. Basically you need to create a text file which includes a line like this:
Main-Class: MainClass
Then run
jar cfm app.jar manifest.txt *.class
set the classpath and compile
javac -classpath "C:\Program Files\Java\jdk1.6.0_updateVersion\tools.jar" yourApp.java
create manifest.txt
Main-Class: yourApp newline
create yourApp.jar
jar cvf0m yourApp.jar manifest.txt yourApp.class
run yourApp.jar
java -jar yourApp.jar
You can run with:
java -cp .;app.jar package.MainClass
It works for me if there is no manifest in the JAR file.
I got this error, and it was because I had the arguments in the wrong order:
CORRECT
java maui.main.Examples tagging -jar maui-1.0.jar
WRONG
java -jar maui-1.0.jar maui.main.Examples tagging
The easiest way to be sure that you have created the runnable JAR file correctly, with the appropriate manifest file, is to use Eclipse to build it for you. In your Eclipse project, you basically just select File/Export from the menu, and follow the prompts.
That way, you can be sure that your JAR file is correct and will know to look elsewhere if there is still an issue. The process is described in full in FAQ How do I create an executable JAR file for a stand-alone SWT program?.
I was getting the same error when i ran:
jar cvfm test.jar Test.class Manifest.txt
What resolved it was this:
jar cvfm test.jar Manifest.txt Test.class
My manifest has the entry point as given in oracle docs (make sure there is a new line character at the end of the file):
Main-Class: Test
Try
java -cp .:mail-1.4.1.jar JavaxMailHTML
no need to have manifest file.
I discovered that I was also having this error in NetBeans.
I hope the following is helpful.
Make sure that when you go to Project Configuration you set the main class you intend for running.
Do a Build or Clean Build
Place the jar file where you wish and try: java -jar "YourProject.jar" again at the command line.
This was the problem I was getting because I had other "test" programs I was using in NetBeans and I had to make sure the Main Class under the Run portion of the Project configuration was set correctly.
many blessings,
John P
I faced the same problem. This unix command is not able to find the main class. This is because the runtime and compile time JDK versions are different. Make the jar through eclipse after changing the java compiler version. The following link helped me.
http://crunchify.com/exception-in-thread-main-java-lang-unsupportedclassversionerror-comcrunchifymain-unsupported-major-minor-version-51-0/
Try running the jar created after this step and then execute it
If your class path is fully specified in manifest,
maybe you need the last version of java runtime environment.
My problem fixed when i reinstalled the jre 8.
If you using eclipse, try below:
1. Right click on the project -> select Export
2. Select Runnable Jar file in the select an export destination
3. Enter jar's name and Select "Package required ... " (second radio button) -> Finish
Hope this helps...!