I am trying to run a Java application, but getting this error:
java.lang.ClassNotFoundException:
After the colon comes the location of the class that is missing. However, I know that that location does not exist since the class is located elsewhere. How can I update the path of that class? Does it have something to do with the class path?
A classpath is a list of locations to load classes from.
These 'locations' can either be directories, or jar files.
For directories, the JVM will follow an expected pattern for loading a class. If I have the directory C:/myproject/classes in my classpath, and I attempt to load a class com.mycompany.Foo, it will look under the classes directory for a directory called com, then under that a directory called mycompany, and finally it will look for a file called Foo.class in that directory.
In the second instance, for jar files, it will search the jar file for that class. A jar file is in reality just a zipped collection of directories like the above. If you unzip a jar file, you'll get a bunch of directories and class files following the pattern above.
So the JVM traverses a classpath from start to finish looking for the definition of the class when it attempts to load the class definition. For example, in the classpath :
C:/myproject/classes;C:/myproject/lib/stuff.jar;C:/myproject/lib/otherstuff.jar
The JVM will attempt to look in the directory classes first, then in stuff.jar and finally in otherstuff.jar.
When you get a ClassNotFoundException, it means the JVM has traversed the entire classpath and not found the class you've attempted to reference. The solution, as so often in the Java world, is to check your classpath.
You define a classpath on the command line by saying java -cp and then your classpath. In an IDE such as Eclipse, you'll have a menu option to specify your classpath.
Your classpath is broken (which is a very common problem in the Java world).
Depending on how you start your application, you need to revise the argument to -cp, your Class-Path entry in MANIFEST.MF or your disk layout.
This is the best solution I found so far.
Suppose we have a package called org.mypackage containing the classes:
HelloWorld (main class)
SupportClass
UtilClass
and the files defining this package are stored physically under the directory D:\myprogram (on Windows) or /home/user/myprogram (on Linux).
The file structure will look like this:
When we invoke Java, we specify the name of the application to run: org.mypackage.HelloWorld. However we must also tell Java where to look for the files and directories defining our package. So to launch the program, we have to use the following command:
NOTE: You have to execute the above java command no matter what your current location is. But this is not the case for javac. For
compiling you can even directly go into the directory where you have
your .java files and directly execute javac ClassName.java.
If you know the path of the class or the jar containing the class then add it to your classpath while running it. You can use the classpath as mentioned here:
on Windows
java -classpath .;yourjar.jar YourMainClass
on UNIX/Linux
java -classpath .:yourjar.jar YourMainClass
I had the same error and it took me a whole day to realize it's a dependency conflict issue:
I imported two libraries, A and B;
Both A and B depends on another library C, but different versions of C. Let's say A depends on C 1.0 and B depends on C 2.0;
B makes use of a class that only exists in C 2.0;
However, A is "closer" in the dependency tree, so Maven uses C 1.0 for both A and B and doesn't even warn you about this (it's quite astounding to me);
As a result, when B tries to use the class that only exists in C 2.0, a ClassNotFoundException is thrown;
Now the weird thing is: if you navigate the code of B in your IDE and try to jump to the class that only exists in C 2.0, it works correctly. C 2.0 is indeed installed and your IDE knows about it, but it's just ignored when running the application.
This really drove me mad...
I ended up having to add C 2.0 to my pom.xml so that it can be chosen over C 1.0.
Please refer to this post for how Maven chooses the closest dependency: https://stackoverflow.com/a/63815140/7438905
You can use mvn dependency:tree to visualize the dependency tree.
Try these if you use maven. I use maven for my project and when I do mvn clean install and try to run a program it throws the exception. So, I clean the project and run it again and it works for me.
I use eclipse IDE.
For Class Not Found Exception when running Junit test, try running mvn clean test once. It will compile all the test classes.
Basic Generic Question - Simplest Generic Answer ;)
Given the information I will make the assumption that you might be trying a basic approach to coding, building/compiling and running a simple console app like "Hello World", using some simple text editor and some Command Shell.
This error occurs in the fallowing scenario:
..\SomePath>javac HelloWorld.java
..\SomePath>java HelloWorld.class
In other words, use:
..\SomePath>java HelloWorld
P.S. The adding the file extension .class produces the same mistake.
Also be sure to have the Java's (JDK/JRE) bin folder in the operating system's Environment Variables's PATH.(Lookup for more details other posts on this)
P.P.S Was I correct in my assumption/s?
If you use maven, check that you have this plugin in your pom.xml:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>3.2.0</version>
<executions>
<!-- Attach the shade goal into the package phase -->
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
It will put your dependency (the exception reason) to your jar.
FYI:
this will include all dependencies inflated in the final jar
To add the location of a class to your classpath via command line simply add -cp or -classpath and the location of the class while running it. I.E.
java -cp "c:/location/of/file" YourProgram
Or if you're running an IDE such as eclipse you can right click on the project -> build path -> configure build path
and add the external JAR containing your class to the build path then it should work fine.
Use ';' as the separator. If your environment variables are set correctly, you should see your settings. If your PATH and CLASSPATH is correct, windows should recognize those commands. You do NOT need to restart your computer when installing Java.
Add the full path of jar file to the CLASSPATH.
In linux use: export CLASSPATH=".:/full/path/to/file.jar:$CLASSPATH". Other way worked (without editing the CLASSPATH) was unzipping the jar in the current project folder.
Ways didn't work for me:
1) Using -cp option with full path of jar file.
2) Using -cpwith only the name of jar when located in the current folder
3) Copying the jar to the current project folder
4) Copying the jar to standard location of java jars (/usr/share/java)
This solution is reported for class com.mysql.jdbc.Driver in mysql-connector-java.5-*.jar, working on linux with OpenJDK version 1.7
This can happen on Windows after a java update where the old version of the java SDK is missing and a new one is present. I would check if your IDE is using the installed java SDK version (IntelliJ: CTRL + SHIFT + ALT + S)
Go up to the top and remove the import statement if there is one, and re import the class. But if that isn't the case do a clean then build. Are you using Netbeans or Eclipse?
I ran into this as well and tried all of the other solutions. I did not have the .class file in my HTML folder, I only had the .java file. Once I added the .class file the program worked fine.
It could happen if your classpath is not correct
Let us posit a serializable class and deserializable class under same projectname. You run the serializable class, creating a serializable object in specific folder. Now you need the desearialized data. In the meantime, if you change the name of the project it will not work. You have to run the serializable class first and then deserialize the file.
If you are using maven
try to maven update all projects and force for snapshots.
It will clean as well and rebuilt all classpath..
It solved my problem..
I just did
1.Invalidate caches and restart
2.Rebuilt my project which solved the problem
It's worth noting that sometimes Java lies about the Class that is causing the problem.
You can get this error if java tries to load class A which depends on class B and class B can't be loaded.
In some circumstances java reports that class A can't be loaded when the problem is B.
From recollection the last time this occurred was when class A includes a static field or a static initializer that loaded class B.
So after checking your class path is correct (I actually dump the full classpath on startup) I then do a binary chop on class A.
By this I mean, I remove half of the code in A.
If it still fails I remove another half and so on until the problem (hopefully goes away).
I was trying to run .jar from C# code using Process class. The java code ran successfully from eclipse but it doesn't from C# visual studio and even clicking directly on the jar file, it always stopped with ClassNotFoundException: exception. Solution for my, was export the java program as "Runnable JAR file" instead of "JAR File". Hope it can help someone.
If you have added multiple (Third-Party)**libraries and Extends **Application class
Then it might occur.
For that, you have to set multiDexEnabled true and replace your extended Application class with MultiDexApplication.
It will be solved.
In my case the class thrown as class not found exception has properties related to ssl certificates. Close the eclipse and open with as “Run as Administrator” then issue got resolved. As eclipse have issue related permission it will throw such kind of exception.
I started having this issue after upgrading the "Java Language Support" plugin from Visual Studio Code from version 0.66.0 to 0.67.0.
Downgrading back allowed me to run the same code without any issue.
If you have moved your project to new machine or importing it from git, then try this.
Right Click on class > Run as > Run Configuration
remove main class reference
Apply > Close
Now again right click on class > run as java application.
It worked for me.
I ran the Java code at the Terminal and adding Class Path was solution like this:
> java -cp <JAR file> <JAVA Class file>
for example,
c:\code\prototype-app\target\classes>java -cp ..\prototype-app-1.0-SNAPSHOT.jar com_stree.app.DetectLabels
My runtime environment:
OS: Windows 10
JAVA: 15.0.1
Maven: 3.8.1
Check the .jar or .class file permissions. I had the jar on a project library with permission of -rw-r--r-- and I changed it to -rw-rw-r-- using on Linux:
chmod 664 <.jar>
One library was calling ClassLoader.loadClass which started the error when loading the class in the jar with wrong permission.
I deleted some unused imports and it fixed the problem for me. You can't not find a Class if you never look for it in the first place.
sorry i am late to the question, but i will explain it to you in the simplest layman language.
When you type 'javac <programname.java>
The compiler checks the program and finds errors, first of all make sure your program is in the same directory as you have executed in the command prompt. Then it creates a. Class file of your program. For ex. If the name of my program was Test.java then the class file created should be Test.class which will be executed in the next line.
Sometimes java takes some other name for your .class, use that name and voila you'll get the output.
Put all the code in try block then catch exception in a catch block
try
{
// code
}
catch(ClassNotFoundException e1)
{
e1.getmessage();
}
I'm trying to export a java project in eclipse as a runnable jar, but for some reason the runnable jar doesn't work. If I double click the executable jar, it doesn't do anything. I tried both extract and package required libraries into generated jar.
So I also tried to export some simpler projects, those worked fine. The biggest difference is my real project has files: images and xml files.
In code reference them like this:
File file = new File("Recources/test.xml");
ImageIcon imageIcon = new ImageIcon("Recources/" + num + ".gif");
The structure of the project looks like this:
But in the executable jar they look like this:
Thank you for your help.
Edit:
I have tried the 'java -jar filename.jar', but now it says it can't find my resources folder, while in eclipse it can still find it.
Files in a JAR-File aren't just like files stored in your hard-disc. If you include files in a JAR, they'll be seen as a Stream of Bytes. So you have to use different methods to access these resources.
//To read/access your XML-File
BufferedReader read = new BufferedReader(new InputStreamReader(getClass().getResourceAsStream("/test.xml")));
//To read/access your gif-Files
ImageIcon icon = new ImageIcon(this.getClass().getResource("/"+num+".gif"));
"/" is not the root-Folder of your file-system, but the root folder of the resources inside your JAR.
The issue may be that Java is not the default program to run the jar.
Try right click -> Open with, and select the Java Runtime, and it should run successfully.
Make it the default program to enable double-click running.
Right click -> Properties -> Change -> C:\Program Files\Java\jre7\bin\javaw.exe
Inspired by stratwine's answer at https://stackoverflow.com/a/8511277
So thank you all, but it seems like the problem wasn't the export only. There was an error I saw when I opened my program with cmd, I was using file name to open xml and images while I should have used inputStreams: https://docs.oracle.com/javase/tutorial/networking/urls/readingURL.html.
Hi Guys I have included the Webcam-Capture API in my project.
When I run it in Netbeans everything works fine. But when i compile everything to a runnable jar i get this message trying to run it by cmd line.
can anyone of you help me?
i already tried to unbound and rebound all jars and changing jdks but its not working
add -classpath flag in the command line ,pointing to the path where Webcam-Capture API exists in your file system, unless you want to create a single package executable.In your case It should be something like below
java -classpath YOURJAR.jar;folder_of_dependant_jar/*;. com.awesome.pagackage.Starter
Where YOURJAR.jar contains the com.awesome.pagackage.Starter.main(String args[])
You also mentioned that your jar is a runnable jar it also means that while exporting/building you can do one of the following way.( NOTE , this feature is in eclipse , but you would get the idea ).Each of the following options you see in the library handling does specific things.
The first option: Extracts the dependent jar into your target jar as java packaging.This means if your package is com.awesome.package and the dependent jar has package logic.package; , after the runnable jar is build you could find both these package exists in your jar file.
The second option: I think it is more on eclipse specific since eclipse adds few classes of its own , of runnable generation, so I am not explaining it here.
The third option : is the most interesting one. it creates folder stucture like below
ndon_lib\external.jar ( external jar file )
ndon.jar ( your jar file )
This time the manifest.mf file contains something like below.
Class-Path: . ndon_lib/external.jar
Main-Class: com.awesome.pagackage.Starter
You should set the classpath
java -cp "your.jar" "yourclass"
Yesterday, I had a problem because I couldn't manage to open a xml file (it owuld give me a FileNotFoundException) located in the ressources folder of my .jar file, which I managed to open on eclipse using the following lines of code. You can see my old problem here. This was my code with the problem :
File xmlFile = new File("ressources/emitter.xml");
ConfigurableEmitter emitter = ParticleIO.loadEmitter(xmlFile);
Someone told me it that one way was to use getClassLoader().getRessourceAsStream method to open a xml file in a .jar file that was exported
InputStream i= this.getClass().getClassLoader().getResourceAsStream("ressources/emitter.xml");
ConfigurableEmitter emitter = ParticleIO.loadEmitter(i);
Unfortunately, that solution only works when I export my project into a .jar file, so if I want to go back debugging my program, I have to take the old code that would only works on eclipse.
My question is: is there any better way to do this without having to change my code if I want to export it or if I want to debug it?
Thank you
edit :
Thank you all, it works perfectly fine now
my problem was that I put my ressources folder like that :
+project
+src
+ressources
+emitter.xml
InputStream i= this.getClass().getClassLoader().getResourceAsStream("/ressources/emitter.xml");
The above should work in both cases (Note is is /resources/.... This is assuming say your directory structure is below:
MyProject
+src
+ressources
emitter.xml
Place the file alongside your source files, then you can use the getResourceAsStream() method in both cases. Don't forget to update the path (which should be the package name of your class, but with slashes instead of dots).
My question is: is there any better way to do this without having to
change my code if I want to export it or if I want to debug it?
Yes, use Maven. Maven will handle that and it hooks into Eclipse beautifully (NetBeans too!) What you do is place the resource in src/main/resources and then you can have Eclipse run the test goal of the Maven project or you can just run mvn test from the command line. Another advantage of using Maven here is that you can also have src/test/resources/emitter.xml which overrides the one in src/main with environment-specific test instructions and it won't affect your deployment.
InputStream i= getClass().getClassLoader().getResourceAsStream("ressources/emitter.xml");
or
InputStream i= getClass().getResourceAsStream("/ressources/emitter.xml");
(note the absolute positioning)
both work when the class is in the same jar, on the same class path.
In the jar the names must be case sensitive, but as the jar already works. Ensure that the ressources directory is on the class path too, or copied to the target directory.
As "ressources" is probably configured yourself (not named "resources" as in English), you probably need to add it to the build somehow.
I am trying to run my program from my jar, called PViz.jar. The jar is sitting in a directory with all of its dependent jars and the .so files that they depend on. I am using Mac OS X. When I run this:
java -cp PViz.jar pviz.PVizStart
Then I get an UnsatisfiedLinkError saying "no jogl in java.library.path". This is reasonable, i'm using jogl.jar which makes use of the native library libjogl.so.
So I run this:
java -Djava.library.path=. -cp PViz.jar pviz.PVizStart
and I get the same error. But libjogl.so is in the current directory! I figured maybe I needed to give the whole path, so I tried this:
java -Djava.library.path=/bla/bla/bla/libjogl.so -cp PViz.jar pviz.PVizStart
and it still gives me the same UnsatisifedLinkError. Argh!
Here is a step by step explanation on how to setup jogl on different operating systems, OS X included.
Try loading the lib in a static initializer in one of the main classes of your app.
Example (Copied + renamed from one of my projects):
public class MainClass {
static {
System.loadLibrary( "Your_native_lib_file_name" ); // Note: do not include the file extension!
}
}
The native lib should be in the same directory as your jar.