Finding Installed JDBC Drivers

Question

I\'m writing a database validation tool in Java and have preference screens so the user can define their database connections. The tool should be able to cope with DB2, Orac

Answer 1

To the point, you need to scan the entire classpath (and subfolders) for classes implementing java.sql.Driver. This way you will also cover drivers which are not loaded manually by Class#forName() or automagically by META-INF/services.

Here's a basic example:

public static void main(String[] args) throws Exception {
    List> drivers = findClassesImplementing(Driver.class);
    System.out.println(drivers);
}        

public static  List> findClassesImplementing(Class cls) throws IOException {
    List> classes = new ArrayList>();

    for (URL root : Collections.list(Thread.currentThread().getContextClassLoader().getResources(""))) {
        for (File file : findFiles(new File(root.getFile()), ".+\\.jar$")) {
            JarFile jarFile = new JarFile(file);
            for (JarEntry jarEntry : Collections.list(jarFile.entries())) {
                String name = jarEntry.getName();
                if (name.endsWith(".class")) try {
                    Class found = Class.forName(name.replace("/", ".").replaceAll("\\.class$", ""));
                    if (cls.isAssignableFrom(found)) {
                        classes.add((Class) found);
                    }
                } catch (Throwable ignore) {
                    // No real class file, or JAR not in classpath, or missing links.
                }
            }
        }
    }

    return classes;
}

public static List findFiles(File directory, final String pattern) throws IOException {
    File[] files = directory.listFiles(new FileFilter() {
        public boolean accept(File file) {
            return file.isDirectory() || file.getName().matches(pattern);
        }
    });

    List found = new ArrayList(files.length);

    for (File file : files) {
        if (file.isDirectory()) {
            found.addAll(findFiles(file, pattern));
        } else {
            found.add(file);
        }
    }

    return found;
}

Instead you can also consider to use the Google Reflections API which does this all in a single line:

Set> drivers = reflections.getSubTypesOf(Driver.class);