http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5. 
package org.bouncycastle.asn1;

import java.io.IOException;

public class DERExternalParser
    implements DEREncodable, InMemoryRepresentable
{
    private ASN1StreamParser _parser;

    /**
     * 
     */
    public DERExternalParser(ASN1StreamParser parser)
    {
        this._parser = parser;
    }

    public DEREncodable readObject()
        throws IOException
    {
        return _parser.readObject();
    }

    public DERObject getLoadedObject()
        throws IOException
    {
        try
        {
            return new DERExternal(_parser.readVector());
        }
        catch (IllegalArgumentException e)
        {
            throw new ASN1Exception(e.getMessage(), e);
        }
    }
    
    public DERObject getDERObject()
    {
        try 
        {
            return getLoadedObject();
        }
        catch (IOException ioe) 
        {
            throw new ASN1ParsingException("unable to get DER object", ioe);
        }
        catch (IllegalArgumentException ioe) 
        {
            throw new ASN1ParsingException("unable to get DER object", ioe);
        }
    }
}