I have a program written in java using Eclipse. For some reason that I won't write here, I decided to move to VS Code. If I run my code in debug mode, all works, but, when I want to export as jar file some errors comes out.
Some information:
- The program is composed by several classes.
- I use 3 external jars included via Eclipse.
- If I run the code with the extension 'Java extension pack - microsoft' all works. Compiling via terminal with
javac MyApp.java
it doesn't compile. (It doesn't find some classes belonging to external jars)
- If I use
jar -cvfm MyApp.jar manifest.txt *.class
where *.class are created by compiling via 'Java extension pack' the error is 'Unable to find or load the main class'
- I'm using a MacBook Pro and the last version of VS Code
What do I do wrong? Which more information you need to help me?
Let's say your project has app package. Under that a App.java class resides which has the main method. Now after building the class files let's assume the class file folder structure is
bin
|app
|App.class
Now go to the bin folder and copy the manifest.txt file in bin folder. manifest.txt file must contain Main-Class . here app.App is the name of the Main-Class.
Main-Class: app.App
Note manifest.txt file must be ended with a new line or carriage return . After Main-Class: app.App put a new line at least.Now run this command from the bin folder
jar cfmv App.jar manifest.txt app/
then test the Jar with
java -jar App.jar
Related
To put it simply, I have a different error where Eclipse won't allow me to export the recent version of a JAR. So, I'm trying in command prompt instead.
I'm using JDK 1.8.0.
1) First, I extracted all class files from their individual folders.
2) I created a manifest.txt which contains the following (including a carriage return at the end as described in the oracle tutorial)
Main-Class: Start
3) I'm creating the runnable jar with the following command, being verbose as possible to ensure correct versioning:
C:\correctDirectory\"C:\Program Files\Java\jdk1.8.0\bin\jar.exe" cvfm ERSR.jar manifest.txt *.class
4) That runs fine. I then inspect the JAR to ensure it containts the Start.class file which contains the main method:
C:\correctDirectory\"C:\Program Files\Java\jdk1.8.0\bin\jar.exe" tf ERSR.jar
The output of that is (reduced to useful info):
META-INF/
META-INF/MANIFEST.MF
Start.class
5) Then I run the JAR with the following command:
C:\correctDirectory\"C:\Program Files\Java\jdk1.8.0\bin\java" -jar ERSR.jar
To which I get the error:
Error: Could not find or load main class Start.
Thanks in advance kind folks.
Does your Start class contain any static field that is initialized with a contents of a resource (a .properties file, or alike)?
If that is the case, then it's likely the problem. The command you use in step 3) only packages the .class files into the JAR, but ignores the rest:
...\jar.exe cvfm ERSR.jar manifest.txt *.class
Modify it to include everything:
...\jar.exe cvfm ERSR.jar manifest.txt *
I'm learning Java and I have a problem. I created 6 different classes, each has it's own main() method. I want to create executable .jar for each class, that is 6 executable .jar files.
So far I tried
java -jar cf myJar.jar myClass.class
and I get 'Unable to access jarfile cf'. I'm doing something wrong but I don't know what. I'm also using Eclipse IDE if that means something.
In order to create a .jar file, you need to use jar instead of java:
jar cf myJar.jar myClass.class
Additionally, if you want to make it executable, you need to indicate an entry point (i.e., a class with public static void main(String[] args)) for your application. This is usually accomplished by creating a manifest file that contains the Main-Class header (e.g., Main-Class: myClass).
However, as Mark Peters pointed out, with JDK 6, you can use the e option to define the entry point:
jar cfe myJar.jar myClass myClass.class
Finally, you can execute it:
java -jar myJar.jar
See also
Creating a JAR File
Setting an Application's Entry Point with the JAR Tool
Sine you've mentioned you're using Eclipse... Eclipse can create the JARs for you, so long as you've run each class that has a main once. Right-click the project and click Export, then select "Runnable JAR file" under the Java folder. Select the class name in the launch configuration, choose a place to save the jar, and make a decision how to handle libraries if necessary. Click finish, wipe hands on pants.
Often you need to put more into the manifest than what you get with the -e switch, and in that case, the syntax is:
jar -cvfm myJar.jar myManifest.txt myApp.class
Which reads: "create verbose jarFilename manifestFilename", followed by the files you want to include.
Note that the name of the manifest file you supply can be anything, as jar will automatically rename it and put it into the right place within the jar file.
way 1 :
Let we have java file test.java which contains main class testa
now first we compile our java file simply as javac test.java
we create file manifest.txt in same directory and we write Main-Class: mainclassname . e.g :
Main-Class: testa
then we create jar file by this command :
jar cvfm anyname.jar manifest.txt testa.class
then we run jar file by this command : java -jar anyname.jar
way 2 :
Let we have one package named one and every class are inside it.
then we create jar file by this command :
jar cf anyname.jar one
then we open manifest.txt inside directory META-INF in anyname.jar file and write
Main-Class: one.mainclassname
in third line., then we run jar file by this command :
java -jar anyname.jar
to make jar file having more than one class file : jar cf anyname.jar one.class two.class three.class......
Put all the 6 classes to 6 different projects. Then create jar files of all the 6 projects. In this manner you will get 6 executable jar files.
I have created my JAR on Windows 2000 having java version 1.5 which contains following directories/files:
manifest.txt
com
lib
lib contains all JARS which I want to make part of my JAR. com contains my class files and below is manfiest.txt file
Main-Class: com.as.qst.result.ResultTriggerSchedular
Class-Path: lib/axis.jar lib/c3p0-0.9.1.1.jar lib/commons-discovery-0.2.jar lib/commons-logging-1.0.4.jar lib/jaxrpc.jar lib/log4j-1.2.16.jar lib/medplus-hub-8.2-wsclients.jar lib/medplus-hub-13.1-jaxws-clients.jar lib/quartz-2.2.1.jar lib/quartz-jobs-2.2.1.jar lib/saaj.jar lib/slf4j-api-1.6.6.jar lib/slf4j-log4j12-1.6.6.jar lib/ wsdl4j-1.5.1.jar lib/xercesImpl.jar com\as\qst\result
I used following command to generate my JAR
jar cvfm test.jar manifest.txt com lib
It has successfully created a JAR file but when I try to run it with
java -jar test.jar
it does not execute and throws above exception. I used the same process for Windows 7 which has version 1.7 and it did work out even without class files path in manifest.txt com\as\qst\result. Is something more to do with class-path besides defining in manifest? and why is it working in Windows 7?
You do not need the class file path in your class path entry. So instead of adding com\as\qst\result to your class-path.
More over you must not package other jar files in your runnable jar.
Other required jars must be provided in the same folder as your jar file (may be in separate folder) and Add current directory "." (without quotes) to your class-path.
Hope this helps.
EDIT
Just found this Stackoverflow Link. This might give you more insight. Please read through it.
I've been learning about JAR files and wanted to try and create and run one myself. I carried out the following steps:
Created a project folder with a 'source' subfolder and a 'classes' subfolder
I wrote 2 source files, one with a main method which creates an instance of the other class and runs a simple method in it.
Compiled these to the 'classes' subfolder. I checked to see if they would run. They did
I created a manifest.txt file and filled in the Main-Class: xxxx and hit the return key. I saved this in the sources subfolder
Created a jar file in the classes subfolder by writing
jar -cvmf manifest.txt zzz.jar *.class
Tried to execute the jar file by typing
java -jar zzz.jar
This gives a ClassNotFound exception. If I try to execute the jar by double clicking on it in windows I get an errorbox saying "Could not find the main class xxxx"
I've double checked the spelling of the class inside the manifest file and it's correct.
Possibly important: I have to compile my programs using java -cp . xyz as there is an issue with my classpath. Does this mean that I need to execute jars in a different way as well? I tried
java -cp . -jar zzz.jar
but ended up with the same exception.
Edit: I ended up starting from scratch and now it runs (with the basic -jar zzz.jar command). Frustrating that I don't know what I was doing wrong but glad that it is working!
Shouldn't number 5. be run in the classes subfolder, where all your class files are? And if your classes are in packages, which they should be, you'll likely want to use * instead of *.class..?
To check what your jar file contains you can run:
jar tf zzz.jar
You will probably have to supply the entire path of the .class file you wish to execute after the classpath. ie java -cp xxx.jar classes.mainProgram.class. Where classes is the name of the folder which contains your class files.
I am trying to run a jar file using my command prompt (Windows XP) but get NoClassDefFoundError.
I have my DateAndTime.class file in a folder called dateandtime and also indicated a package called dateandtime in the source file.
Outside the folder I have a manifest.mf file with specification
Main-Class: dateandtime.DateAndTime
I put this in the command file
jar cmf manifest.mf myJarFile.jar dateandtime
and this creates the myJarFile.jar in the same folder as manifest.mf.
When I try to run this jar file however I get the NoClassDefFoundError
java -jar myJarFile.jar
If I jave all the classes in the same directory with no package specified then the .jar file runs fine but as soon as I try to specify a package, even though myJarFile.jar was created I get the error.
Why is that?
Regards
If you are getting a NoClassDefFoundError it means a class that was present during compilation of your classes is absent during their execution. Which implies that you JAR file does not contain all the dependencies requires by your classes in order to run. Since your question is lacking detail on your project structure I can only recommend you revisit your application's dependency tree and determine all the classes that need to be included in the JAR.
Syntax:
java -jar fileName.jar
Example:
java -jar myfile.jar