从 JAR 文件导入 VSCode 无法解析 class

Question

We have a java app that needs to use a public class form a JAR file. After much frustration with the main application, we have created a simple repo here to try to figure out what is going on.
The overly simple file that ends up in the JAR file is as follows:

package com.mystuff.helpers;

public class printStuff {
    public void showMsg(String msg) {
        System.out.println(msg);
    }
}

We create the JAR file with this command:

jar cvf MyJavaHelpers.jar com

The folder structure is as follows (the printStuff.java file is in the helpers folder):

A listing of the JAR contents is as follows:

jar tf MyJavaHelpers.jar

META-INF/
META-INF/MANIFEST.MF
com/
com/mystuff/
com/mystuff/helpers/
com/mystuff/helpers/printStuff.java
com/mystuff/helpers/README.md 

Finally, the program that we have to use this simple class is as follows:

package com.mystuff.testapp;

import com.mystuff.helpers.*;

// To build the JAR file
// jar cvf MyJavaHelpers.jar com
// To display the contents of the JAR file
// jar tf MyJavaHelpers.jar



public class testDriver {
    public static void main(String[] args) {
        System.out.println("Starting testDriver");    
         com.mystuff.helpers.printStuff ps = new com.mystuff.helpers.printStuff();
        // testPrintStuff(ps);
        // testPrintStuffAgain(ps);
    }
   /*
    private static void testPrintStuffAgain(printStuff ps) {
        ps.showMsg("This is a fine kettle of clams");
    }

    private static void testPrintStuff(printStuff ps) {
        ps.showMsg("This is a fine kettle of fish");
    }
    */
}

In VS Code (v 1.55.0) We have a Java Project to contain our TestDriver that looks like this:

Finally , the issue is that when we try to run the test driver, we get the message:

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
        com.mystuff.helpers.printStuff cannot be resolved to a type
        com.mystuff.helpers.printStuff cannot be resolved to a type

        at com.mystuff.testapp.testDriver.main(testDriver.java:15)

We have tried the command Clean Java Language Server Workspace which seems to indicate that it works, but we cannot get past this error. Based on what we have looked at, the JAR file appears to be in the correct place (It is in the lib folder of the main app). The import com.mystuff,helpers.; line does not show as an error, so it seems to us that it is found, however, the actual import of the printStuff class fails. We have tried the fully qualified class name as well as relying on the import and only using the short name. They both fail.
We have seem some guidance about setting the classpath , but have not been able to find how to do that explicitly in VS Code. Of course, if we do not have this little helper in a JAR file, but just as a side-by-side in the same project, it works just fine. The issue that started us down this journey is trying to use a public class from a pre-packaged JAR file.

Any and all help is greatly appreciated. Thanks in advance.

Answer 1

Before adding the jar to library, you may run the command java -jar printStuff.jar to test if it could be executed successfully.

The error occurs because the class must be called with its fully qualified name. To be clear, the name of this class is not printStuff , It's com.mystuff.helpers.printStuff , so the right command should be:

1. Turn to the folder;

2. Compile.java file: javac com\mystuff\helpers\printStuff.java

3. Generate.jar: jar cvfe printStuff.jar com.mystuff.helpers.printStuff.\

Then readd it to referenced libraries and see if the error goes away.