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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 wrote a program that works on my laptop perfectly, but I really want it to work on a server that I have. Using NetBeans, I've clean and built the project. I copied the contents of the folder dist on my server but I cannot seem to get to work by using command
java -jar nameOfFile.jar
I get the error
java.lang.NoClassDefFoundError: org/....
I have been doing some reading and from what I gather is that I need to pretty much specify where the libraries that I've used are located. Well they are located in a subfolder called lib.
Question:
So what would I need to do in order to be able to run my jar?
CLASSPATH is an environment variable that helps us to educate the Java Virtual Machine from where it will start searching for .class files.
We should store the root of the package hierarchies in the CLASSPATH environment variables.
In case of adding or using jar libraries in our project, we should put the location of the jar file in the CLASSPATH environment variable.
Example: If we are using jdbc mysql jar file in our java project, We have to update the location of the mysql jar file in the CLASSPATH environment variable. if our mysql.jar is in c:\driver\mysql.jar then
We can set the classpath through DOS in Windows
set CLASSPATH=%CLASSPATH%;c:\driver\mysql.jar
In Linux we can do
export CLASSPATH=$CLASSPATH:[path of the jar]
Hope it helps!
Try that:
java -classpath "$CLASSPATH:nameOfFile.jar:lib/*" path.to.your.MainClass
What this does is setting the classpath to the value of $CLASSPATH, plus nameOfFile.jar, plus all the .jar files in lib/.
Classpath
A compiler(e.g. javac) creates from .java - .class files and JVM uses these .class files.
classpath - local codebase[About] - points on the root of source. classpath + import_path = full path
For example for MacOS
//full path
/Users/Application.jar/my/package/MainClass
//classpath
/Users/Application.jar
//import_path
my.package.MainClass
Android classpath
ANDROID_HOME/platforms/android-<version>/android.jar
//e.g
/Users/alex/Library/Android/sdk/platforms/android-23/android.jar
When you use a META-INF/MANIFEST.MF file to specify the Main-Class dependencies must be specified in the manifest too.
The -jar switch ignores all other classpath information - see the tools docs for more.
You need to set class path using
The below works in bash .
This is temporary
set CLASSPATH=$CLASSPATH=[put the path here for lib]
If you want it permanent then you can add above lines in ~/.bashrc file
export CLASSPATH=$CLASSPATH:[put the path here for lib]:.
You have 2 questions, one is the "title question" and another is the "foot note question" after elaborating your problem.
Read this documentation bellow to get a better understanding of CLASSPATH.
https://docs.oracle.com/javase/tutorial/essential/environment/index.html
https://docs.oracle.com/javase/8/docs/technotes/tools/windows/classpath.html
This is fast and straight forward for what you need.
For your first question, this will do:
The documentation recommends us to set a classpath for every application we are running at the moment using (use in the command-line):
java -classpath C:\yourDirectoryPath myApp
For your second question, look this exercise in the java documentation. It seems to be the same problem:
https://docs.oracle.com/javase/tutorial/essential/environment/QandE/answers.html
Answers to Questions and Exercises: The Platform Environment
Question 1.A programmer installs a new library contained in a .jar file. In order to access the library from his code, he sets the CLASSPATH environment variable to point to the new .jar file. Now he finds that he gets an error message when he tries to launch simple applications:
java Hello
Exception in thread "main" java.lang.NoClassDefFoundError: Hello
In this case, the Hello class is compiled into a .class file in the current directory — yet the java command can't seem to find it. What's going wrong?
Answer 1. A class is only found if it appears in the class path. By default, the class path consists of the current directory. If the CLASSPATH environment variable is set, and doesn't include the current directory, the launcher can no longer find classes in the current directory. The solution is to change the CLASSPATH variable to include the current directory. For example, if the CLASSPATH value is c:\java\newLibrary.jar (Windows) or /home/me/newLibrary.jar (UNIX or Linux) it needs to be changed to .;c:\java\newLibrary.jar or .:/home/me/newLibrary.jar."
I am getting an exception:
Cannot find symbol: FileUploadException;
I have a piece of code which uses
FileUploadException
The library that needs importing is:
org.apache.commons.fileupload.FileUploadException
The path to my project is :
D:\Projects\website
In the project folder I have each in its folder:
Tomcat, Derby, Website
I have copied:
commons-fileupload.jar and commons-io.jar
into both:
Tomcat/lib and Website/Web-INF/lib
---------------I tried this--------------
just importing the library on its own
import org.apache.commons.fileupload.FileUploadException;
adding the jars to the class path upon build:
javac -cp .;D:Projects\website\Tomcat\lib\commons-fileupload.jar;D:\Projects\website\Tomcat\lib\commons-io.jar com/otrocol/app/*.java
adding them to the Environment variables CLASSPATH
D:Projects\website\Tomcat\lib\commons-fileupload.jar;D:\Projects\website\Tomcat\lib\commons-io.jar
I also tried adding the jars where my .java files are as #Scot Ship suggested
----mentions---
I am not using any IDE
The code contains more unrecognized symbols, but I'm trying to solve one at a time
First time using apache, tomcat, jsp.. please be gentle
Vlad, the web container will automatically look for JARs inside
/WEB-INF/lib
even without any developer intervention. Take note that it's all caps WEB-INF. As long as your JAR is there, it will be in your web application's classpath.
Try to display this in one of your servlets or JSP:
System.getProperty("java.class.path")
and you'll get a better view of what classes and JARs were actually loaded.
Update: After reviewing your question, it appears you're facing issues in compiling the files to begin with and you're doing it outside an IDE.
Take note that when you use -cp in javac like this:
javac -cp .;D:Projects\website\Tomcat\lib\commons-fileupload.jar;D:\Projects\website\Tomcat\lib\commons-io.jar com/otrocol/app/*.java
Whatever value you have set in the CLASSPATH environment variable becomes ignored.
Be absolutely sure that the class FileUploadException is indeed inside one of the JARs you're trying to import: you can view the JAR directly using an unarchiving tool.
Also, change the com/otrocol/app/*.java to com\otrocol\app*.java - you should be using your system delimiter (not that this may affect your problem).
Create a simple HelloWorld in the same location as the file you're compiling, add the SystemOut mentioned above, and compile it the same way you're doing for the concerned file.
Read this http://commons.apache.org/proper/commons-fileupload/faq.html#class-not-found. Probably you have the fileupload jar but you also need commons-io.jar in your classpath as well.
I know this has come up a number of times, but previous responses just don't seem to help.
My environment variables are :
CLASSPATH C:\Program Files\Java\jre7\lib;C:\Program
Files\Java\jdk1.7.0_15\bin;
PATH C:\Program Files\Java\jdk1.7.0_15\bin;
When moving to the directory as follows C:\Users\Oli\My Documents\java I can compile using javac, but cannot runt he program using java. I know its most likely got something to do with environment variables but I cannot get it to work. P.S the error is "could not find or load main class"
Any help would be appreciated.
CLASSPATH is the place where JRE looks for classes. You've set your CLASSPATH to a value and expect to run the class from current Directory, which won't work.. for instant solution you may use
java -cp C:\Users\Oli\My Documents\java ClassName
Or undo setting CLASSPATH. Default CLASSPATH is current directory
Lets assume that your ".java" file default package ( no package defined) survivies in "C:\Src"
You dont need to set the CLASSPATH in this case.
cd C:\Src
javac MyJava.java
java MyJava
If with package say com.test
cd C:\Src
javac com\test\MyJava.java
java com.test.MyJava
However if you are not in the same folder as Source files and want to run from anywhere
set CLASSPATH=%CLASSPATH%;C:\src
javac MyJava.java or javac com\test\MyJava.java
and
java com.test.MyJava or java com.test.MyJava
Unset CLASSPATH and just use the default one provided by the JVM. Here is a link to the Java Tutorial that covers the environment variables.
Seems like the problem is not in the path...
Does your code use the 'package' statement? (i.e. package my_package;)
If so, go to 'java' directory and execute:
java my_package.MyClass
where 'my_package' is the name of... the package, and MyClass is your compiled .java file (without the .class extension).
Good luck.
I have Windows 7, installed jdk1.7.0 and its supporting jre7.
My problem is compilation part works perfectly, but while running the Java program I get this error saying:
"Could not find or load main class"
I am storing all my programs in javalab folder. I have set the path to it. Procedure looks like this:
C:\Users\user>cd\
C:\>cd javalab
C:\javalab>autoexec.bat
C:\javalab>set path=C:\Program Files\Java\jdk1.7.0\bin
C:\javalab>javac p1.java
C:\javalab>java p1
Error: Could not find or load main class p1
C:\javalab>
I was having a similar issue with my very first java program.
I was issuing this command
java HelloWorld.class
Which resulted in the same error.
Turns out you need to exclude the .class
java HelloWorld
Try:
java -cp . p1
This worked for me when I had the same problem, using Fedora (linux)
Simple way to compile and execute java file.(HelloWorld.java doesn't includes any package)
set path="C:\Program Files (x86)\Java\jdk1.7.0_45\bin"
javac "HelloWorld.java"
java -cp . HelloWorld
pause
javac should know where to search for classes. Try this:
javac -cp . p1.java
You shouldn't need to specify classpath. Are you sure the file p1.java exists?
I had almost the same problem, but with the following variation:
I've imported a ready-to-use maven project into Eclipse IDE from PC1 (project was working there perfectly) to another PC2
when was trying to run the project on PC 2 got the same error "Could not find or load main class"
I've checked PATH variable (it had many values in my case) and added JAVA_HOME variable (in my case it was JAVA_HOME = C:\Program Files\Java\jdk1.7.0_03)
After restarting Ecplise it still didn't work
I've tried to run simple HelloWorld.java on PC2 (in another project) - it worked
So I've added HelloWorld class to the imported recently project, executed it there and - huh - my main class in that project started to run normally also.
That's quite odd behavour, I cannot completely understand it.
Hope It'll help somebody. too.
i guess that you have a different class name in p1.java
Check you class name first. It should be p1 as per your batch file instruction. And then check you package of that class, if it is inside any package, specify when you run.
If package is x.y
java x.y.p1
Here is my working env path variables after much troubleshooting
CLASSPATH
.;C:\Program Files (x86)\Java\jre7\lib\ext\QTJava.zip;C:\Program Files (x86)\Java\jdk1.6.0_27\bin
PATH <---sometimes this PATH fills up with too many paths and you can't add a path(which was my case!)
bunchofpaths;C:\Program Files (x86)\Java\jdk1.6.0_27\bin
Additionally, when you try to use the cmd to execute the file...make sure your in the local directory as the file your trying to execute (which you did.)
Just a little checklist for people that have this problem still.
I've had similar problems. If you work with Eclipse, you need to go to the folder where you have your src/ folder... If you used a package - then you use
javac -cp . packageName/className
which means if you've had a package named def and main class with name TextFrame.java you'd write
javac -cp . def/TextFrame
omitting the trailing .java extension, and then you run it with the
java def/TextFrame
and if you have have arguments, then you need to supply it with arguments corresponding to your program.
I hope this helps a bit.
First, put your file *.class (e.g Hello.class) into 1 folder (e.g C:\java). Then you try command and type cd /d C:\java. Now you can type "java Hello" !
You might have the CLASSPATH environment variable already added!!
Use following to avoid further usage of -cp . in java -cp . CLASSFILE
Add . to CLASSPATH in system properties->environment variables or by cmd
set CLASSPATH=%CLASSPATH%;.;
I faced a similar problem in Eclipse. Whenever I clicked on the Run button it gave me the message, "Error: Could not find or load main class". But when I right click on the java file in the project explorer and Run As Java configuration, it works perfectly.
I think this is because it tries by default to run it in some other configuration which causes problems.
Hope this answer helps some.
If you have a single .java file to compile using command-line , then remove
topmost package parts from the code, the compile again, it will work.
This worked for me.
Sometimes what might be causing the issue has nothing to do with the main class. I had to find this out the hard way, it was a referenced library that I moved and it gave me the:
Could not find or load main class xxx Linux
I just delete that reference and added again and it worked fine again.
i had
':'
in my project name e.g 'HKUSTx:part-2'
renaming it 'HKUSTx-part-2' worked for me
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