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NGClasspath.java

/*   

  Copyright 2004, Martian Software, Inc.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.

*/

package com.martiansoftware.nailgun.builtins;

import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;

import com.martiansoftware.nailgun.NGContext;

/**
 * <p>Provides a means to display and add to the system classpath at runtime.
 * If called with no arguments, the classpath is displayed.  Otherwise, each
 * argument is turned into a java.io.File and added to the classpath.  Relative
 * paths will be resolved relative to the directory in which the nailgun server
 * is running.  This is very likely to change in the future.</p>
 * 
 * <p>This is aliased by default to the command "<code>ng-cp</code>".</p>
 * 
 * @author <a href="http://www.martiansoftware.com/contact.html">Marty Lamb</a>
 */
00038 public class NGClasspath {
      
      /**
       * Adds the specified URL (for a jar or a directory) to the System
       * ClassLoader.  This code was written by antony_miguel and posted on
       * http://forum.java.sun.com/thread.jsp?forum=32&thread=300557&message=1191210
       * I assume it has been placed in the public domain.
       * 
       * @param url the URL of the resource (directory or jar) to add to the
       * System classpath 
       * @throws Exception if anything goes wrong.  The most likely culprit, should
       * this ever arise, would be that your VM is not using a URLClassLoader as the
       * System ClassLoader.  This would result in a ClassClastException that you
       * probably can't do much about.
       */
00053       private static void addToSystemClassLoader(URL url) throws Exception {
            URLClassLoader sysloader = (URLClassLoader) ClassLoader.getSystemClassLoader();
            Class sysclass = URLClassLoader.class;

            java.lang.reflect.Method method = sysclass.getDeclaredMethod("addURL", new Class[] {URL.class});
            method.setAccessible(true);
            method.invoke(sysloader, new Object[]{url});
      }
      
      public static void nailMain(NGContext context) throws Exception {
            String[] args = context.getArgs();
            if (args.length == 0) {
                  URLClassLoader sysLoader = (URLClassLoader) ClassLoader.getSystemClassLoader();
                  URL[] urls = sysLoader.getURLs();
                  for (int i = 0; i < urls.length; ++i) {
                        context.out.println(urls[i]);
                  }
            } else {
                  for (int i = 0; i < args.length; ++i) {
                        File file = new File(args[i]);
                        addToSystemClassLoader(file.toURL());
                  }
            }
      }
}

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