无法使用 Jar 文件找到或加载主 class

Question

I'm trying to load a jar using

@echo off
java -jar Test.jar
pause

With the manifest of

Manifest-Version: 1.0
Main-Class: classes.TestClass

In the Jar directory, I can clearly see a classes\TestClass file when I extract it.

Edit: classes.TestClass does have a public static void main(String[] args) .

Package Deceleration in classes.TestClass is package classes;

But I still keep getting the error message

Could not find or load main class classes.TestClass

I've been through everything I've been able to find with this problem, and none of it seems to help.

I've tried editing the classpath, redoing the manifest, installing the new JRE.

What else should I be doing?

Answer 1

I got it working like this:

TestClass.Java

package classes;

public class TestClass {

    public static void main(String[] args) {
        System.out.println("Test");
    }

}

Use javac on the command line to produce TestClass.class . Put TestClass.class in a folder classes/ .

MANIFEST.MF

Manifest-Version: 1.0
Main-Class: classes.TestClass

Then run

jar cfm test.jar MANIFEST.MF classes/

Then run it as

java -jar test.jar

Answer 2

java -cp "full-path-of-your-jar" Main

to run any other class having "public static void main" in some package,

java -cp "full-path-of-your-jar" package1.package2.packages-hierarchy.ClassHavingMain

Answer 3

This error comes even if you miss "-" by mistake before the word jar

Wrong command java jar test.jar

Correct command java -jar test.jar

Answer 4

1.Create a text file calles Manifest.txt and provide the value as

Main-Class: classes.TestClass

2.Create the jar as

jar cfm test.jar Manifest.txt classes/*.class

3.Run the jar as

java -jar test.jar

Answer 5

I know this is an old question, but I had this problem recently and none of the answers helped me. However, Corral's comment on Ryan Atkinson's answer did tip me off to the problem.

I had all my compiled class files in target/classes , which are not packages in my case. I was trying to package it with jar cvfe App.jar target/classes App , from the root directory of my project, as my App class was in the default unnamed package.

This doesn't work, as the newly created App.jar will have the class App.class in the directory target/classes . If you try to run this jar with java -jar App.jar , it will complain that it cannot find the App class. This is because the packages inside App.jar don't match the actual packages in the project.

This could be solved by creating the jar directly from the target/classes directory, using jar cvfe App.jar . App jar cvfe App.jar . App . This is rather cumbersome in my opinion.

The simple solution is to list the folders you want to add with the -C option instead of using the default way of listing folders. So, in my case, the correct command is java cvfe App.jar App -C target/classes . . This will directly add all files in the target/classes directory to the root of App.jar , thus solving the problem.

Answer 6

I had the same problem due to copying and pasting code from a Microsoft Word Document. Seems there was a slightly different type of dash - character used, when I replaced the longer dash character with the correct - the program executed properly

Answer 7

This is very difficult to debug without complete information.

The two most likely-looking things at this point are that either the file in the jar is not stored in a directory WITHIN THE JAR, or that it is not the correct file.

You need to be storing TestClass.class - some people new at this store the source file, TestClass.java.

And you need to create the jar file so that TestClass.class appears with a path of classes. Make sure it is not "/classes". Use zip to look at the file and make sure it has a path of "classes".

Answer 8

I had a similar problem which I could solve by granting execute-privilege for all parent folders in which the jar-file is located (on a linux system).

Example:

/folder1/folder2/folder3/executable.jar

all 3 folders (folder1, folder2 and folder3) as well as the executable.jar need execute-privilege for the current user, otherwise the error "Could not find or load main class ..." is returned.

Answer 9

I had a weird issue when an incorrect entry in MANIFEST.MF was causing loading failure. This was when I was trying to launch a very simply scala program:

Incorrect:

Main-Class: jarek.ResourceCache
Class-Path: D:/lang/scala/lib/scala-library.jar

Correct:

Main-Class: jarek.ResourceCache
Class-Path: file:///D:/lang/scala/lib/scala-library.jar

With an incorrect version, I was getting a cryptic message, the same the OP did. Probably it should say something like malformed url exception while parsing manifest file .

Using an absolute path in the manifest file is what IntelliJ uses to provide a long classpath for a program.

Answer 10

At least the way I've done this is as follows:

If you have a nested src tree (say com.test.myclass.MyClass) and you are compiling from a root directory you need to do the following:

1) when you create the jar (usually put this in a script): jar -cvfm my.jar com/test/myclass/manifest.txt com/test/myclass/MyClass.class

2) The manifest should look like:

Mainfest-version: 1.0 Main-Class: com.test.myclass.MyClass Class-Path: . my.jar

3) Now you can run the jar from anywhere like this:

java -jar my.jar

Hope this helps someone

Answer 11

I follow the following instruction to create a executable .jar in Eclipse. Then Run command "java -jar .jar " to launch the program.

It takes care of creating mainfest and includeing main class and library files parts for you.

http://java67.blogspot.com/2014/04/how-to-make-executable-jar-file-in-Java-Eclipse.html

Answer 12

我有这个错误，因为我在我的MANIFEST.MF写了一个错误的类路径

Answer 13

If you use package names, it won't work with folders containing dots ( Error: Could not find or load main class ). Even though it compiles and creates the jar file successfully.

Instead it requires a complete folder hierarchy.

Fails:

com.example.mypackage/
    Main.java

Works:

com/
    example/
        mypackage/
            Main.java

To compile in Linux:

javac `find com/ -name '*.java'` \\ && jar cfe app.jar com.example.mypackage.Main `find com/ -name '*.class'`

Answer 14

in IntelliJ, I get this error when trying to add the lib folder from the main project folder to an artifact.

Placing and using the lib folder in the src folder works.

Answer 15

A possible reason for this error message:

Could not find or load main class

is when the main class extends (or implements) another class (or interface), which is not on the classpath.

Answer 16

我通过FTP传输jar文件并忘记设置二进制模式后收到相同的错误消息。

Answer 17

I had this error because I extracted JAR files from libraries to the target JAR by IntellijIDEA. When I choose another option "copy to the output directory...", it solved the problem. Hope this helps you

Answer 18

I was getting this error because my main class is in test package, and I am creating artifact using IntelliJ. After I checked the box Include Tests when creating artifact, it got resolved.

Screenshot from IntelliJ showing Include Tests checkbox

Answer 19

Sometimes could missing the below line under <build> tag in pom.xml when packaging through maven. since src folder contains your java files

<sourceDirectory>src</sourceDirectory>

Answer 20

If you have your setup with Maven project -- make sure that the following match your JDK in the pom.xml file.

<maven.compiler.source>17</maven.compiler.source> <maven.compiler.target>17</maven.compiler.target>

in my case I had it set to 14 whereas my application was set to 14 -- and the conflict was causing my jar file to give the class not found error.

Answer 21

For IntelliJ users - this can also happen when class that cannot be found was placed in a directory marked as Tests (indicated by green color on directory icon).

To solve this:

a. move the class to sources directory (prefered)

or

b. make sure "include tests" checkbox is selected when creating an artifact

Answer 22

I faced the same issue while using artifact in IntelliJ. After using copy all dependency jar, it works for me.

Answer 23

You need to use -jar argument to set the path to your jar:

java -jar your_jar.jar

You don't need to set main class manualy if your manifest is correct.

Answer 24

我有一个incorret class-path librarie并解决相同的错误