Find where java class is loaded from

Question

Does anyone know how to programmaticly find out where the java classloader actually loads the class from?

I often work on large projects where the classpath gets v

Answer 1

This is what we use:

public static String getClassResource(Class<?> klass) {
  return klass.getClassLoader().getResource(
     klass.getName().replace('.', '/') + ".class").toString();
}

This will work depending on the ClassLoader implementation: getClass().getProtectionDomain().getCodeSource().getLocation()

Answer 2

Typically, we don't what to use hardcoding. We can get className first, and then use ClassLoader to get the class URL.

        String className = MyClass.class.getName().replace(".", "/")+".class";
        URL classUrl  = MyClass.class.getClassLoader().getResource(className);
        String fullPath = classUrl==null ? null : classUrl.getPath();

Answer 3

Edit just 1st line: Main.class

Class<?> c = Main.class;
String path = c.getResource(c.getSimpleName() + ".class").getPath().replace(c.getSimpleName() + ".class", "");

System.out.println(path);

Output:

/C:/Users/Test/bin/

Maybe bad style but works fine!

Answer 4

Take a look at this similar question. Tool to discover same class..

I think the most relevant obstacle is if you have a custom classloader ( loading from a db or ldap )

Answer 5

Jon's version fails when the object's ClassLoader is registered as null which seems to imply that it was loaded by the Boot ClassLoader.

This method deals with that issue:

public static String whereFrom(Object o) {
  if ( o == null ) {
    return null;
  }
  Class<?> c = o.getClass();
  ClassLoader loader = c.getClassLoader();
  if ( loader == null ) {
    // Try the bootstrap classloader - obtained from the ultimate parent of the System Class Loader.
    loader = ClassLoader.getSystemClassLoader();
    while ( loader != null && loader.getParent() != null ) {
      loader = loader.getParent();
    }
  }
  if (loader != null) {
    String name = c.getCanonicalName();
    URL resource = loader.getResource(name.replace(".", "/") + ".class");
    if ( resource != null ) {
      return resource.toString();
    }
  }
  return "Unknown";
}

Answer 6

Simple way:

System.out.println(java.lang.String.class.getResource(String.class.getSimpleName()+".class"));

Out Example:

jar:file:/D:/Java/jdk1.8/jre/lib/rt.jar!/java/lang/String.class

Or

String obj = "simple test"; System.out.println(obj.getClass().getResource(obj.getClass().getSimpleName()+".class"));

Out Example:

jar:file:/D:/Java/jdk1.8/jre/lib/rt.jar!/java/lang/String.class