www.pudn.com > cryptix-asn1-0.1.11.zip > Factory.java

/* $Id: Factory.java,v 1.1.1.1 2001/02/24 04:58:58 raif Exp $ 
 * 
 * Copyright (C) 1997-2001 The Cryptix Foundation Limited. All rights reserved. 
 * 
 * Use, modification, copying and distribution of this software is subject to 
 * the terms and conditions of the Cryptix General Licence. You should have 
 * received a copy of the Cryptix General Licence along with this library; if 
 * not, you can download a copy from http://www.cryptix.org/ 
 */ 
package cryptix.asn1.encoding; 
 
import cryptix.asn1.io.ASNReader; 
import cryptix.asn1.io.ASNWriter; 
 
/** 
 * A Factory class to locate/return registered/designated ASN.1 decoders and 
 * encoders.
 
 * 
 * @version $Revision: 1.1.1.1 $ 
 * @author  Raif S. Naffah 
 */ 
public class Factory { 
 
	// Constructor(s) 
	// ....................................................................... 
 
	/** 
	 * Trivial private constructor to enforce Singleton pattern. 
	 */ 
	private Factory() { 
		super(); 
	} 
 
   // Class methods 
   // ....................................................................... 
 
	/** 
	 * Returns an implementation that decodes an ASN.1 input stream according to 
	 * a designated encoding rule set. 
	 * 
	 * @param encoding the designated name for the encoding. The concrete class 
	 * is assumed to be visible with a name that is constructed from the given 
	 * string by (a) converting it to lowercases, (b) changing the first 
	 * character to its titlecase equivalent, and (c) appending to it the string 
	 * "Decoder". For example the concrete class for the "DER" decoder would be 
	 * "DerDecoder." The package where this class is assumed to be found is 
	 * looked up in the properties file of this package under the key 
	 * "${class}.package" where ${class} is the cosntructed name of the decoder 
	 * as described before. 
	 * @exception InstantiationException the designated class is either an 
	 * interface or an abstract class. 
	 * @exception IllegalAccessException if the designated class does not have 
	 * a zero-argument public constructor. 
	 * @exception ClassNotFoundException if the current class loader cannot find 
	 * bytecode for the designated class. 
	 * @exception ClassCastException if the designated class does not extend the 
	 * ASNReader base class. 
	 */ 
	public static ASNReader getDecoder(String encoding) 
	throws InstantiationException, IllegalAccessException, ClassNotFoundException { 
		return ((ASNReader) getCodec(encoding, true)); 
	} 
 
	/** 
	 * Returns an implementation that encodes to an ASN.1 output stream according 
	 * to a designated encoding rule set. 
	 * 
	 * @param encoding the designated name for the encoding. The concrete class 
	 * is assumed to be visible with a name that is constructed from the given 
	 * string by (a) converting it to lowercases, (b) changing the first 
	 * character to its titlecase equivalent, and (c) appending to it the string 
	 * "Encoder". For example the concrete class for the "DER" encoder would be 
	 * "DerEncoder." The package where this class is assumed to be found is 
	 * looked up in the properties file of this package under the key 
	 * "${class}.package" where ${class} is the cosntructed name of the encoder 
	 * as described before. 
	 * @exception InstantiationException the designated class is either an 
	 * interface or an abstract class. 
	 * @exception IllegalAccessException if the designated class does not have 
	 * a zero-argument public constructor. 
	 * @exception ClassNotFoundException if the current class loader cannot find 
	 * bytecode for the designated class. 
	 * @exception ClassCastException if the designated class does not extend the 
	 * the ASNWriter base class. 
	 */ 
	public static ASNWriter getEncoder(String encoding) 
	throws InstantiationException, IllegalAccessException, ClassNotFoundException { 
		return ((ASNWriter) getCodec(encoding, false)); 
	} 
 
	/** 
	 * Utility class method to instantitate a coder/decoder object from its type. 
	 * 
	 * @param type the type of the encoding. 
	 * @param decoder true if the decoder object is required, false if the encoder 
	 * object is required. 
	 * @return an instance of designated Codec type. 
	 */ 
	private static Object getCodec(String type, boolean decoder) 
	throws InstantiationException, IllegalAccessException, ClassNotFoundException { 
		type = type.toLowerCase(); 
		type = Character.toTitleCase(type.charAt(0))+type.substring(1); 
		String clazz = type + (decoder ? "Decoder" : "Encoder"); 
		String pkg = PackageProperties.getProperty(clazz+".package"); 
		String name = pkg+"."+clazz; 
 
		return (Class.forName(name).newInstance()); 
	} 
}