I'm learning Java and was trying to test my code on another machine but am running to the above error. I've looked at youtube videos, read forums(and SO) but still can't get this to work.
I basically wrote some code on my mac using eclipse that referenced an external jar file. I have that jar in my lib folder and have added it to my build path in Eclipse via right-click "Build Path -> Add to Build Path". The code works fine on my laptop.
But when I try to run it from a linux command line, I get the above error. I am taking the code from eclipse and copying it to a file(first_try.java) and then run this commands:
CLASSPATH=./jedis-2.0.0.jar;export CLASSPATH
javac first_try.java
java -classpath . first_try
but then I get the error: Exception in thread "main" java.lang.NoClassDefFoundError: redis/clients/jedis/Jedis I downloaded the program via wget and checked permissions and tried different variations. There was a similar question I found(out of the many related ones) that had a similar context as mine but it worked for the user to just type java filename (which is not working for me)
I am learning a bit of java code but have never been successful at running external jars. I'm wondering what I'm doing wrong and what I can do to permanently fix it(ideally I want to write code locally and then copy it and test it on another machine like this)?
Or is there a better way to deploy code that depends on third party jars to other systems?
You are building your class path env var but then you don't use the value in your java command. You need $CLASSPATH instead of the dot after -classpath
Good luck learning java, I have enjoyed using it for over 10 years now ;)
Related
I have written Java code that connects to a database, all works great in IntelliJ, as the connector is configured via the IDE. However, when I try to run the same code from the commandline, I run into some problems.
Firstly, I used the command:
javac -encoding UTF8 -cp mysql/mysql-connector-java-8.0.19.jar Main.java Logic.java
for compiling my Java files, (I've tried the same things with just javac -encoding UTF8 *.java as well) and then I have tried to run my Java program.
If I use "java Main.java" on the commandline, I get an error:
java.sql.SQLException: No suitable driver found for jdbc:mysql:***.
However, when I try to run java -cp mysql/mysql-connector-java-8.0.19.jar Main.java, I get the error:
Main.java:10: error: package Logic does not exist
I have tried to get it to work by moving the entire jar to the same folder as my files and also tried extracting the Driver.class file from the jar, yet I still can not get it to work.
I realise this was not probably the most efficient way to connect a database anyways, but this is where I am at. Sorry if it is a stupid question, but I have been at it for hours. Thanks!
IDEs are very helpful to provide a simple "sandbox" where you can work visually on the code, build it, run it, and debug it fast.
However, when you want to publish or deploy your application so it can be run outside your sandbox, you probably need to perform a "standard build". This standard build will produce an application that can be run anywhere.
Solution? Use any build tool, such as Maven, Ant, or Gradle. You'll need to learn the basics of the one you choose. There are plenty of examples online. Also, pretty much all IDEs provide integration with those three I mention.
You'll need to decide if you want to include the JDBC driver inside the application itself or as an external dependency, as well. Options, options, options.
I have been doing a coding exercise inside the IntelliJ IDEA Community Edition 14 IDE, using OpenJDK.
The project is split over 4 .java files all in the same package.
My end goal is to run this in the terminal/bash (I use System.console().readLine() which doesnt play nicely in the IDE's console).
I've tried navigating to the directory where these 4 files reside (they all reside in the same dir) and tried:
javac -classpath . BibliotecaApp.java Book.java BookManager.java LibraryDB.java
This creates 4 corresponding .class files fine.
The Main is in bibliotecaApp.java/class, so I try run it by:
java BibliotecaApp
But I get the error
Exception in thread "main" java.lang.NoClassDefFoundError: BibliotecaApp (wrong name: com/twu/biblioteca/BibliotecaApp)
Plus about 13 lines of specifics.
Now googling this error seems to be a class path problem, and this is where I get stuck.
From places I've read, usingecho $PATH gives me:
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
This is still from the directory of the .java files above.
That path means nothing to me. I have no idea what it is or what it does, or what even a classpath is! Theres alot of resources out there on setting a classpath, but they aren’t helping me because I don't know what it's meant for.
That was a dead end for me. I tried to create a .jar instead using IDEA's Build Artifacts as seen HERE. It created a .jar file but when I navigate to that directory and try run it via:
java -jar biblioteca_jar
I get
Error: Invalid or corrupt jarfile biblioteca_jar
Another issue is that in the file explorer, the file actually comes out as biblioteca.jar, but ls on that dir shows biblioteca_jar. Is that normal?
The code is on my GitHub if that helps anything
https://github.com/botagar/twu-biblioteca-JohnGeddes
Based on your compiler step, change this
java BibliotecaApp
to
java -cp . BibliotecaApp
Which will add the current directory to the classpath for the java runtime environment. See also the Oracle Technote Setting the Class Path.
A jar file is a kind of zip, and should have a .jar extension. So this
java -jar biblioteca_jar
should probably be
java -jar biblioteca.jar
And you can check if the file is valid with any zip archive reader. Including jar itself,
jar tvvf biblioteca.jar
Edit
Based on your comments below,
cd ~/Documents/ThoughtWorks Uni/TWU_Biblioteca-master/src/
and then
java -cp . com.twu.biblioteca.BibliotecaApp
I am trying to run a java program that uses protobuf.jar, but I keep getting this error.
I have set my classpath variable in linux so that:
CLASSPATH=/home/.../src/PlaceServer.class:/home/.../src/protobuf.jar:/home/.../src
export CLASSPATH
But then when I run my program in the command line after reading in the jar.
java PServer
I get this:
java.lang.NoClassDefFoundError: com/google/protobuf/MessageOrBuilder
However when I run another program that also reads the same jar, this one called BServer
java BServer
It works fine, and correctly as I want it. I even tried running under these commands instead
java -cp .protobuf.jar PServer
And it still did not work for PServer.
However, if I run the same programs on my Macbook from the command line (also in Eclipse in either OS) I do not get this Exception and it all works fine.
Thanks for your help!
There are a couple of things to check to get rid of this error:
Verify that all required Java classes are included in the application’s classpath. The most common mistake is not to include all the necessary classes, before starting to execute a Java application that has dependencies on some external libraries.
The classpath of the application is correct, but the Classpath environment variable is overridden before the application’s execution
When you run the application in Eclipse, the IDE resolves this by using the .classpath file inside the project folder. When you build an application (create the jar), you could accidentally omit this class, or change its location.
What you need to do is to first open the jar, and make sure that the class in question is in fact inside the jar, in the same path. Then, go through the list above.
I'm running snow leopard and I just wrote a Java class on eclipse. The eclipse project references a user library which itself points to a bunch of jar files I've got somewhere in the system. When I run the app through eclipse, everything goes smoothly.
Then I export the class as a jar file and try to run it form the terminal by typing:
java - jar myApp.jar
It throws a java.lang.NoClassDefFoundError exception, meaning that it can't find the libraries I try to reference.
Knowing that my user library jar files are in /Users/myname/tempJars, I also tried to either mention the classpath using the -cp option
(java -cp /Users/myname/tempJars -jar myApp.jar) or to directly reference it in the manifest file. Both attempts failed and the error is the same.
These libraries are Java 1.5 libraries, so I thought I should try and reference another java version by mean of the JAVA_HOME environment variable. I built the following script:
export JAVA_HOME=/System/Library/Frameworks/JavaVM.framework/Versions/1.5/Home
export PATH=$JAVA_HOME/bin:$PATH
export CLASSPATH=$CLASSPATH:/Users/myname/tempJars
java -jar myApp.jar
Again, no good. I googled how to execute jars in snow leopard, found the 32/64 bit big deal in some places and even tried executing with the -d32 option, but still to no avail.
Since the same code executes just fine in eclipse, I'm pretty convinced it's just a matter of setting up the JVM so that it includes the user libraries correctly.
Could anyone help me with this?
Thanks in advance.
You need to list the JARs themselves out on the classpath, not just the directory containing them. (Listing the directory is for when you have unarchived .class files in the package hierarchy lying around)
You will probably need to do -cp /Users/myname/tempJars/libA.jar:/.../libB.jar
I believe some (but potentially not all) JVMs support wildcards so -cp /Users/myname/tempJars/* or some variant thereof may work.
I'm a beginner in Java so this question might seem a little stupid, my JDK and JRE are installed in C:\program files. I write my program and save it in in my folder, G:\start.
Now my program compiles without any error (the .class file is also generated), but when I run my program it says "unable to locate G:\lib\amd64\jvm.cfg", so I copy the 'lib' folder from my JDK folder and paste it in G:. Again program compiles without any error, but when I run it, it gives me a new error saying "unable to locate G:\bin\server\jvm.dll", so I copy the 'bin' folder to g:, but now when I run, it gives me the same error again "unable to locate G:\bin\server\jvm.dll". Where am I going wrong?
Create an environment variable called JAVA_HOME and point it to the bin directory of your Java installation. Also add the same directory to your PATH variable. This should solve your problem.
PS: JAVA_HOME may not be required, but it will help if you have tomcat and stuff installed.
try to save it as a .jar, go to your cmd and use:
java -jar G:\bin\server\jvm.jar
this should work.
The best advise I can give you is to download an IDE to get started. BlueJ is an IDE aimed at getting people started using java and is used in many universities world wide.
take a look at www.bluej.org and you should be up and running in seconds.
Karl