I'm using a .jar file which I imported to Eclipse, and when I used Eclipse to run the application is works just fine.
But when I try running it from the command line with just the command java ClassName I get a NoClassDefFoundError message.
The .jar file is in the same directory as the main class I need to run.
I tried using the classpath command in the terminal
java -classpath pack.jar ClassName
but I got the same error but this time it was in the main thread
Exception in thread "main" java.lang.NoClassDefFoundError
Why does my program work in Eclipse but not on its own?
I guess you'll need to use: java -classpath .:pack.jar ClassName.
NoClassDefFoundError will come if a class was present during compile time but not available in java classpath during runtime.
Its Not Even Close To Being equal to ClassNotFoundException n u mustn't confuse them together, so u need to include the whoe path of the .jar file,
use the previously explained technique to do so, or if it was a jar file that want use frequently without using the call to java -classpath .. thing try importing the file into the OS class path directory.
Related
I'm on Ubuntu 22.04 trying to run my code in the terminal.
The program works without problems in VScode, also when running multiple instances.
The program is consisted of six class files.
The trouble occurs when I try and run it with terminal. When compiling the java file
with javac it shows errors at places where I use the external libraries.
If I compile it with VScode and run the class file in terminal, I get the following error java.lang.ClassNotFoundException
This is causing me problems since I'm also supposed to dockerize the program.
You can add the following code in your setting.json file "java.project.outputPath": "bin",
This will be the .class file generated by VS Code in the bin folder of the same directory when running the Java code.
You can use the java command after entering the file directory with the cd command.
This generally indicates that the class path with which you're compiling your program does not include the correct paths to your libraries. Assuming your libraries are jar files, your javac command should look something like this:
javac -cp libs/lib1.jar:libs/lib2.jar srcs/*.java
where libs/ is the relative path to your libraries and srcs/ is the relative path to your own java files.
And when you run the program, make sure your class path includes both the locations of your libraries and the location of your class files (which in this case would be the current directory):
java -cp .:libs/lib1.jar:libs/lib2.jar <MainClass>
Normally I can use javac to compile and java to run perfectly fine, they are set correctly into my computer's classpath. In this instance however, one of my files Graph.java is trying to import a jar file in the same directory Heap.jar.
When I try to use javac *.java, it tells me package mycs1 does not exist.
Normally in my lab on Linux machines, we can use export CLASSPATH=mycs1.jar:. and then javac will work normally again, and just add more files if there are more jars.
My problem is that this command does not work on my home computer running Windows 10. I am trying to set the classpath of multiple jars. This is similar to this question:
Unable to execute jar file despite having PATH and CLASSPATH set
But despite reading that, I still cannot find a way to set the path of multiple jar files in such a way that javac will work.
Is this possible? If not, what alternative command can I use?
Yesterday I solved a problem with an answer here on stackoverflow. But I ended up with another problem, I will try to be clear:
I have a project folder in the /home/demo/Desktop/xlsToCsv/ directory where inside of it is the java file "xlsToCsv.java" and another directory with the external jars that I need in /home/demo/Desktop/xlsToCsv/jars.
Now I need to compile and run my program. Yesterday I ran a command that assumed that I was already inside of /home/demo/Desktop/xlsToCsv/, and the commands were:
javac -cp ".:./jars/*" xlsToCsv.java
java -cp ".:./jars/*" xlsToCsv
The problem was solved and I was able to run my program without any problems. But, my program was supposed to run from the root directory, ie, the directory where it is when I open the linux terminal without the need to make a "cd" command.
So, when I open the terminal the path to the .java file is:
/home/demo/Desktop/xlsToCsv/
And the path to jars folder is:
/home/demo/Desktop/xlsToCsv/jars/*
Can someone explain to me what I have to do, and the reason so? Because more that run the program, I want to know the reasons and understand the classpath mechanism in java.
Avoid using relative classpath. and instread of "./jars/" use the absolute path "/home/demo/Desktop/xlsToCsv/jars/"
EDIT:
javac -cp "/home/demo/Desktop/xlsToCsv/jars/*" /home/demo/Desktop/xlsToCsv/xlsToCsv.java
java -cp "/home/demo/Desktop/xlsToCsv/:/home/demo/Desktop/xlsToCsv/jars/*" xlsToCsv
I am trying to call a java program in a batch file. My java program calls a dll with JNA. When running batch file, it says it cannot find jna library class. I have already put jna jar files to my batch file folder. What can be the missing point?
My batch file:
#ECHO OFF
java -cp .;jna-4.1.0.jar com/sun/jna/Library
java MyBenchmark
I am getting below error:
java.lang.NoClassDefFoundError: com/sun/jna/Library
My jna jar file also same folder with my benchmark batch file too.
When use java -cp .;jna-4.1.0.jar com/sun/jna/Library, cmd gives that error also:
Main method not found in class com.sun.jna.Library
Library is an interface and my called java program uses that interface. But cmd says it cannot load it without main. I have to use it for reaching jna.
You must specify the ClassPath "-cp": java -cp [path to your jar] [class file to run]
Check this
If you use JNA and want to call a java program which use its library from batch file, you must avoid using java file. Because it can not load classes at runtime when you call jna.jar from batch too.
My code was like:
#ECHO OFF
java -jar jna-4.1.0.jar
java MyBenchmark
I tried many other solution too but nothing works(I also used code at question part too).
Lastly I tried export my project as jar and used it. First of all I want to state that my IDE was Intellij IDEA. It cannot put project dependency to my manifest file(jna path) although I put jar dependency already. So if you use IDEA, you must enter that from artifact screen manually, otherwise your jar cannot work right. Then you can put your jar under same folder with your bacth and call it like below:
java -jar MyJarFile.jar
I have been following this tutorial accordingly.
Up to running the FirstExample class in the command prompt is when it starts to freak out for some reason. After attempting to run the following command:
java FirstExample
I get the following exception:
Exception in thread "main" java.lang.NoClassDefFoundError: FirstExample
I understand that it can't find the FirstExample class due to the classpath (for some reason) so I executed the following command:
java -cp . FirstExample
And now it returns a new exception:
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
Now it can't find the JDBC Driver. This confuses me because for starters, I ran the exact same coding through Eclipse and it works as expected, and secondly, I went as far as to ensure that I execute the same class file that Eclipse is executing, and the command prompt still returns exceptions. I also went as far as to put the FirstExample file in a separate folder, just for the purpose of copying and pasting the MySQL Connector into the same folder, and I still get exceptions.
I just don't understand whats going on, can someone help me please?
Many thanks.
The file path to the connector is as followed:
C:\Program Files\MySQL\mysql-connector-java-3.1.14\mysql-connector-java-3.1.14-bin.jar
Hope this helps.
For testing purposes, I have placed the FirstExample class under the following path:
C:\java
This confuses me because for starters, I ran the exact same coding through Eclipse and it works as expected
This is because in Eclipse you add the libraries to the Build Path, and it will use all the libraries specified there in the classpath automatically when running your project. This can be noted here:
In order for you to execute your project using third party libraries from command line tools, you should specify the libraries manually in your classpath explicitly:
java -cp <path/to/mysql_jar/goes/here>:. FirstExample
By your comment:
the path to the MySQL file is: C:\Program Files\MySQL\mysql-connector-java-3.1.14\mysql-connector-java-3.1.14-bin.jar (...) I have placed the FirstExample class under C:\java
This should be the command line to use:
java -cp "C:\Program Files\MySQL\mysql-connector-java-3.1.14\mysql-connector-java-3.1.14-bin.jar; ." FirstExample
Note that it is better to store all the third party libraries in a single folder within your project, usually called lib, and put a reference to there. Assuming your current folder has a lib folder and all the third party libraries are copied there, the command line would be:
java -cp "lib\*; ." FirstExample
Use the next example to add your jars to the classpath:
java -cp "jdbc.jar;lib/*" my.package.FirstExample
You need to have the class com.mysql.jdbc.Driver (and all the imported classes) in the classpath too.
You should download the jar (http://dev.mysql.com/downloads/connector/j/5.0.html) and add it to the classpath.
The ClassNotFound Exception rises when there is an issue with the class name that you have written in Class.forName() or if the package is not set to the classpath variable. Make sure that you have added the jar file to the classpath ( C:............\jarfilename.jar;).
This is applicable for any JDBC Driver and jar files. The .jar files that are added to the classpath will not be visible to IDEs, in this case, you need to add the jar files to buildpath (in eclipse) or you can also copy the jar files to ext folder available in the Java installation folder.
Also note that the jar files of the DB Softwares may vary based on the DB software version that you are using for example if you are using the Oracle 11g, you need ojdbc6.jar file, in other versions of Oracle the number changes like ojdbc14.jar etc.