作者：未知 来源：月光软件站 加入时间：2005-2-28　月光软件站

java.security.CodeSource;
java.security.ProtectionDomain;

CodeSource 可以给出类的原始URL的位置，但并不是每个类都有CodeSource。如果类通过引导类装载器装载，CodeSource为空。

import java.lang.reflect.Method;
import java.net.URL;
import java.security.CodeSource;
import java.security.ProtectionDomain;

public class Debug
{

   public static void displayClassInfo(Class clazz, StringBuffer results)
   {
      displayClassInfo(clazz, results, true);
   }
   public static void displayClassInfo(Class clazz, StringBuffer results,
         boolean showParentClassLoaders)
   {

      ClassLoader cl = clazz.getClassLoader();
      results.append("\n"+clazz.getName()+"("+Integer.toHexString(clazz.hashCode())+").ClassLoader="+cl);
      ClassLoader parent = cl;
      while( parent != null )
      {
         results.append("\n.."+parent);
         URL[] urls = getClassLoaderURLs(parent);
         int length = urls != null ? urls.length : 0;
         for(int u = 0; u < length; u ++)
         {
            results.append("\n...."+urls[u]);
         }
         if( showParentClassLoaders == false )
            break;
         if( parent != null )
            parent = parent.getParent();
      }
      CodeSource clazzCS = clazz.getProtectionDomain().getCodeSource();
      if( clazzCS != null )
         results.append("\n++++CodeSource: "+clazzCS);
      else
         results.append("\n++++Null CodeSource");

      results.append("\nImplemented Interfaces:");
      Class[] ifaces = clazz.getInterfaces();
      for(int i = 0; i < ifaces.length; i ++)
      {
         Class iface = ifaces[i];
         results.append("\n++"+iface+"("+Integer.toHexString(iface.hashCode())+")");
         ClassLoader loader = ifaces[i].getClassLoader();
         results.append("\n++++ClassLoader: "+loader);
         ProtectionDomain pd = ifaces[i].getProtectionDomain();
         CodeSource cs = pd.getCodeSource();
         if( cs != null )
            results.append("\n++++CodeSource: "+cs);
         else
            results.append("\n++++Null CodeSource");
      }
   }

   /** Use reflection to access a URL[] getURLs or ULR[] getAllURLs method so
    that non-URLClassLoader class loaders, or class loaders that override
    getURLs to return null or empty, can provide the true classpath info.
    */
   public static URL[] getClassLoaderURLs(ClassLoader cl)
   {
      URL[] urls = {};
      try
      {
         Class returnType = urls.getClass();
         Class[] parameterTypes = {};
         Method getURLs = cl.getClass().getMethod("getURLs", parameterTypes);
         if( returnType.isAssignableFrom(getURLs.getReturnType()) )
         {
            Object[] args = {};
            urls = (URL[]) getURLs.invoke(cl, args);
         }
      }
      catch(Exception ignore)
      {
      }
      return urls;
   }

}

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