如何用Java中的其他ClassLoader重新加载已加载的类？

Question

public class ClassScanner
{
  // scan extraClasspath for specific classes
  public List<Class<?>> scanClasspathForClass(String scanCriteria)
  {
    ...
  }

  public static Class<?> reloadClass(Class<?> clazz, ClassLoader clazzLoader)
  {
    // Question: how to reload a loaded class (ClassScanner in this example) with a different arbitrary ClassLoader?
  }

  // an example of how reloadClass() would be used
  // in real case, this function would be in different class
  public List<Class<?>> scan(URL[] extraClasspath)
  {
    URLClassLoader urlClazzLoader = new URLClassLoader(extraClasspath, null);
    Class<?> newClass = reloadClass(ClassScanner.class, urlClazzLoader);
    return ((ClassScanner) newClass.newInstance()).scanClasspathForClass();
  }
}

Above code demonstrates the question and why it is a question. I need to implement reloadClass() . I wonder if there is a reliable solution in Java 1.6. One useful reference would be Find where java class is loaded from .

Thanks for help!

Answer 1

Found myself the answer from http://www2.sys-con.com/itsg/virtualcd/java/archives/0808/chaudhri/index.html .

Basically what I need is to make one ClassLoader A to share its namespace with another ClassLoader B. The way I found to achieve this is to use the ClassLoader parent-delegation model. Here, ClassLoader A is the parent ClassLoader.

public List<Class<?>> scan(URL[] extraClasspath) throws Exception
{
  URLClassLoader urlClazzLoader = new URLClassLoader(extraClasspath, ClassScanner.class.getClassLoader());
  return urlClazzLoader.loadClass(ClassScanner.getName()).newInstance();
}