Java: Checking while run time if class exists

Question

I am working on a software which depends on an 3rd party library. Due to license agreements this library cannot be shipped along with the software and the user has to have the library already locally when starting the program.

Is there any way to check if this particular library exist in the class path and can be loaded? If not I would like to offer a dialog to allow the user pointing to the location and add this location to the class path dynamically.

Thanks for your help!

score 4 · Answer 1 · edited Feb 28 '18 at 06:47

4

The fastest way in terms of computing time I know is:

public class ClazzUtil {

    public static boolean isClassnameAvailable(String clazzName) {
        try {
            Class.forName(clazzName, false, ClazzUtil.class.getClassLoader());
        } catch (LinkageError | ClassNotFoundException e) {
            return false;
        }
        return true;
    }

}

edited Feb 28 '18 at 06:47

Sakiboy

7,252
7
52
69

answered Jul 02 '16 at 11:25

user2131878

161
1
7

As a side effect, this also loads the class if it was not loaded yet. This is usually not what you want. – toolforger Jun 23 '22 at 14:27

score 3 · Answer 2 · answered Nov 21 '14 at 12:06

3

Try this:

try {
    Class<?> clazz = Class.forName("com.acme.SecretClass");
} catch (ClassNotFoundException e) {
    // Show dialog
}

answered Nov 21 '14 at 12:06

RockAndRoll · Answer 3 · 2018-06-12T12:26:07.300

1

If a class is not present at runtime,it will throw ClassNotFoundException. You can check for this in the following way.

try {
    Class cls = Class.forName("yourClassName");
} catch (ClassNotFoundException e) {
    e.printStackTrace();
}

edited Jun 12 '18 at 12:26

answered Nov 21 '14 at 12:10

RockAndRoll

2,247
2
16
35

score -1 · Answer 4 · answered Oct 07 '16 at 22:40

-1

Just solved the problem in my code, supper useful without raising an exception.

@SuppressWarnings("finally")
private boolean existClass(String className){
    Class<?> classname= null;
    try {
        classname = Class.forName(className);
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } finally{
        if(classname == null) 
            return false;
        else 
            return true;
    }
}

answered Oct 07 '16 at 22:40

Jing Tian

9

do not use e.printStackTrace() for production code. Do a proper exception handling/logging... – Lonzak Sep 16 '20 at 09:40

Java: Checking while run time if class exists

4 Answers4

Linked