According to [1] and [2] a custom provided socket factory has to be a subclass of javax.net.SocketFactory. Actually this requirement is not checked. Now any class will do provided it (or any of its ancestors) has a public static ? getDefault() method. i.e. it's effectively a case of duck typing here which must be fixed.

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[1] http://docs.oracle.com/javase/6/docs/technotes/guides/jndi/jndi-ldap.html#pooling
[2] http://docs.oracle.com/javase/jndi/tutorial/ldap/security/ssl.html