providerlookup.java

一个非常好的ssh客户端实现

/******************************************************************************
 *
 * Copyright (c) 1999-2003 AppGate Network Security AB. All Rights Reserved.
 * 
 * This file contains Original Code and/or Modifications of Original Code as
 * defined in and that are subject to the MindTerm Public Source License,
 * Version 2.0, (the 'License'). You may not use this file except in compliance
 * with the License.
 * 
 * You should have received a copy of the MindTerm Public Source License
 * along with this software; see the file LICENSE.  If not, write to
 * AppGate Network Security AB, Otterhallegatan 2, SE-41118 Goteborg, SWEDEN
 *
 *****************************************************************************/

package com.mindbright.jca.security;

public final class ProviderLookup {

    Provider provider;
    Object   impl;

    private ProviderLookup(Object impl, Provider provider) {
	this.provider = provider;
	this.impl     = impl;
    }

    public Object getImpl() {
	return impl;
    }

    public Provider getProvider() {
	return provider;
    }

    private static String className(String type, String algorithmSpec,
				    Provider provider) {
	String aliasFor =
	    provider.getProperty("Alg.Alias." + type + "." + algorithmSpec);
	if(aliasFor != null) {
	    algorithmSpec = aliasFor;
	}
	return provider.getProperty(type + "." + algorithmSpec);
    }

    public static ProviderLookup getImplementation(String type,
						   String algorithmSpec,
						   String providerName)
	throws NoSuchAlgorithmException, NoSuchProviderException
    {
	Provider provider = Security.getProvider(providerName);

	if(provider == null) {
	    throw new NoSuchProviderException("Provider not found: " +
					      providerName);
	}

	String className = className(type, algorithmSpec, provider);
	if(className == null) {
	    throw new NoSuchAlgorithmException("Algorithm not found: " +
					       algorithmSpec);
	}

	Object impl = null;
	try {
	    impl = Class.forName(className).newInstance();
	} catch (ClassNotFoundException e) {
	    throw new NoSuchAlgorithmException("Class " + className +
					       " not found (" +
					       provider + " - " +
					       algorithmSpec + ")");
	} catch (InstantiationException e) {
	    throw new NoSuchAlgorithmException("Class " + className +
					       " can't be instantiated (" +
					       provider + " - " +
					       algorithmSpec + ") error: " +
					       e.getMessage());
	} catch (IllegalAccessException e) {
	    throw new NoSuchAlgorithmException("Class " + className +
					       " can't be accessed (" +
					       provider + " - " +
					       algorithmSpec + ") error: " +
					       e.getMessage());
	}

	return new ProviderLookup(impl, provider);
    }

    public static String findImplementingProvider(String type,
						  String algorithmSpec)
	throws NoSuchAlgorithmException
    {
	Provider[] providers = Security.getProviders();
	for(int i = 0; i < providers.length; i++) {
	    if(className(type, algorithmSpec, providers[i]) != null) {
		return providers[i].getName();
	    }
	}
	throw new NoSuchAlgorithmException("No implementing provider found: '" +
					   type + "' - '" + algorithmSpec + "'");
    }

}