package test;

import java.util.Hashtable;

/**
 * A simple test class loader capable of loading from
 * multiple sources, such as local files or a URL. Must be
 * subclassed and the abstract method loadClassBytes()
 * implemented to provide the preferred source.
 *
 * This class is derived from an article by Chuck McManis
 * http://www.javaworld.com/javaworld/jw-10-1996/indepth.src.html
 * with large modifications.
 *
 * @author Jack Harich - 8/18/97
 */
public abstract class MultiClassLoader extends ClassLoader {

//---------- Fields --------------------------------------
private Hashtable classes = new Hashtable();
private char      classNameReplacementChar;

protected boolean   monitorOn = false;
protected boolean   sourceMonitorOn = true;

//---------- Initialization ------------------------------
public MultiClassLoader() {
}
//---------- Superclass Overrides ------------------------
/**
 * This is a simple version for external clients since they
 * will always want the class resolved before it is returned
 * to them.
 */
public Class loadClass(String className) throws ClassNotFoundException {
    return (loadClass(className, true));
}
//---------- Abstract Implementation ---------------------
public synchronized Class loadClass(String className,
        boolean resolveIt) throws ClassNotFoundException {

    Class   result;
    byte[]  classBytes;
    monitor(">> MultiClassLoader.loadClass(" + className + ", " + resolveIt + ")");

    //----- Check our local cache of classes
    result = (Class)classes.get(className);
    if (result != null) {
        monitor(">> returning cached result.");
        return result;
    }

    //----- Check with the primordial class loader
    try {
        result = super.findSystemClass(className);
        monitor(">> returning system class (in CLASSPATH).");
        return result;
    } catch (ClassNotFoundException e) {
        monitor(">> Not a system class.");
    }

    //----- Try to load it from preferred source
    // Note loadClassBytes() is an abstract method
    classBytes = loadClassBytes(className);
    if (classBytes == null) {
        throw new ClassNotFoundException();
    }

    //----- Define it (parse the class file)
    result = defineClass(classBytes, 0, classBytes.length);
    if (result == null) {
        throw new ClassFormatError();
    }

    //----- Resolve if necessary
    if (resolveIt) resolveClass(result);

    // Done
    classes.put(className, result);
    monitor(">> Returning newly loaded class.");
    return result;
}
//---------- Public Methods ------------------------------
/**
 * This optional call allows a class name such as
 * "COM.test.Hello" to be changed to "COM_test_Hello",
 * which is useful for storing classes from different
 * packages in the same retrival directory.
 * In the above example the char would be '_'.
 */
public void setClassNameReplacementChar(char replacement) {
    classNameReplacementChar = replacement;
}
//---------- Protected Methods ---------------------------
protected abstract byte[] loadClassBytes(String className);

protected String formatClassName(String className) {
    if (classNameReplacementChar == '\u0000') {
        // '/' is used to map the package to the path
        return className.replace('.', '/') + ".class";
    } else {
        // Replace '.' with custom char, such as '_'
        return className.replace('.',
            classNameReplacementChar) + ".class";
    }
}
protected void monitor(String text) {
    if (monitorOn) print(text);
}
//--- Std
protected static void print(String text) {
    System.out.println(text);
}

} // End class