old-autovect-branch/libjava/classpath/vm/reference/gnu/classpath/VMStackWalker.java

   1 /* VMStackWalker.java -- Reference implementation of VM hooks for stack access
   2    Copyright (C) 2005 Free Software Foundation
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package gnu.classpath;
  39
  40 /**
  41  * This class provides access to the classes on the Java stack
  42  * for reflection and security purposes.
  43  *
  44  * <p>
  45  * This class is only available to privileged code (i.e., code loaded
  46  * by the bootstrap loader).
  47  *
  48  * @author John Keiser
  49  * @author Eric Blake <ebb9@email.byu.edu>
  50  * @author Archie Cobbs
  51  */
  52 public final class VMStackWalker
  53 {
  54   /**
  55    * Get a list of all the classes currently executing methods on the
  56    * Java stack. <code>getClassContext()[0]</code> is the class associated
  57    * with the currently executing method, i.e., the method that called
  58    * <code>VMStackWalker.getClassContext()</code> (possibly through
  59    * reflection). So you may need to pop off these stack frames from
  60    * the top of the stack:
  61    * <ul>
  62    * <li><code>VMStackWalker.getClassContext()</code>
  63    * <li><code>Method.invoke()</code>
  64    * </ul>
  65    *
  66    * @return an array of the declaring classes of each stack frame
  67    */
  68   public static native Class[] getClassContext();
  69
  70   /**
  71    * Get the class associated with the method invoking the method
  72    * invoking this method, or <code>null</code> if the stack is not
  73    * that deep (e.g., invoked via JNI invocation API). This method
  74    * is an optimization for the expression <code>getClassContext()[1]</code>
  75    * and should return the same result.
  76    *
  77    * <p>
  78    * VM implementers are encouraged to provide a more efficient
  79    * version of this method.
  80    */
  81   public static Class getCallingClass()
  82   {
  83     Class[] ctx = getClassContext();
  84     if (ctx.length < 3)
  85       return null;
  86     return ctx[2];
  87   }
  88
  89   /**
  90    * Get the class loader associated with the Class returned by
  91    * <code>getCallingClass()</code>, or <code>null</code> if no such class
  92    * exists or it is the boot loader. This method is an optimization for the
  93    * expression <code>VMStackWalker.getClassLoader(getClassContext()[1])</code>
  94    * and should return the same result.
  95    *
  96    * <p>
  97    * VM implementers are encouraged to provide a more efficient
  98    * version of this method.
  99    */
 100   public static ClassLoader getCallingClassLoader()
 101   {
 102     Class[] ctx = getClassContext();
 103     if (ctx.length < 3)
 104       return null;
 105     return getClassLoader(ctx[2]);
 106   }
 107
 108   /**
 109    * Retrieve the class's ClassLoader, or <code>null</code> if loaded
 110    * by the bootstrap loader. I.e., this should return the same thing
 111    * as {@link java.lang.VMClass#getClassLoader}. This duplicate version
 112    * is here to work around access permissions.
 113    */
 114   public static native ClassLoader getClassLoader(Class cl);
 115 }
 116