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FileClassLoader.java

package gov.nasa.arc.ase.util;

// By: Roby Joehanes
// Adapted from magelang.com tutorial.

import java.io.*;
import java.net.*;
import java.util.*;

public class FileClassLoader extends ClassLoader {

  private String root;
  public static FileClassLoader v = new FileClassLoader();


  private FileClassLoader() {
// root == null means that we're looking it through the java.class.path system
// property
    root = null;
  }  
  public FileClassLoader (String rootDir) {
    if (rootDir == null) 
      throw new IllegalArgumentException ("Null root directory");
    root = rootDir;
  }  
  public static Class load(String name) throws ClassNotFoundException {
    return v.loadClass(name);
  }  
  protected Class loadClass (String name, boolean resolve) 
       throws ClassNotFoundException {

    // Since all support classes of loaded class use same class loader
    // must check subclass cache of classes for things like Object

    // Class loaded yet?
    Class c = findLoadedClass (name);
    if (c == null) {
      try {
    c = findSystemClass (name);
      } catch (Exception e) {
    // Ignore these
      }
    }

    if (c == null) {
    // Convert class name argument to filename
    // Convert package names into subdirectories
      String filename = name.replace ('.', File.separatorChar) + ".class";
      try {
      // Load class data from file and save in byte array
    byte data[] = loadClassData(filename);

      // Convert byte array to Class
    c = defineClass (name, data, 0, data.length);

      // If failed, throw exception
    if (c == null) throw new ClassNotFoundException (name);
      } catch (IOException e) {
       throw new ClassNotFoundException ("Error reading file: " + filename);
      }
    }

    // Resolve class definition if approrpriate
    if (resolve) resolveClass (c);

    // Return class just created
    return c ;
  }  
  private byte[] loadClassData (String filename) throws IOException {
  // Create a file object relative to directory provided
    File f = null;

    if (root == null) {
    // Fetch from the classpath
      String classPath = System.getProperty("java.class.path");
      StringTokenizer tok = new StringTokenizer(classPath, File.pathSeparator);
      boolean found = false;

      while (tok.hasMoreTokens()) {
    f = new File(tok.nextToken(), filename);
    if (f.exists()) { found = true; break; }
      }
      if (!found) 
        throw new IOException(filename+
                              " cannot be found in class path: "+classPath);
    } else 
      f = new File (root, filename);

      // Get size of class file
      int size = (int)f.length();

      // Reserve space to read
      byte buff[] = new byte[size];

      // Get stream to read from
      FileInputStream fis = new FileInputStream(f);
      DataInputStream dis = new DataInputStream (fis);

      // Read in data
      dis.readFully (buff);

      // close stream
      dis.close();

      // return data
      return buff;
   }   
   public void setRootDirectory(String r) {
     if (r != null) root = r;
   }   
}

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