Java LDAP 优雅断开连接

Currently from java I am connecting to LDAP with the following code, very typical example:

    Hashtable<String, String> env = new Hashtable<String, String>();

    env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.ldap.LdapCtxFactory");
    env.put(Context.PROVIDER_URL, url);
    env.put(Context.SECURITY_AUTHENTICATION, "simple");
    env.put(Context.SECURITY_PRINCIPAL, user);
    env.put(Context.SECURITY_CREDENTIALS, password);

    LdapContext ctx = null;

    try
    {
        ctx = new InitialLdapContext(env, null);
        return true;
    }
    catch (NamingException ex)
    {
        return false;
    }
    finally
    {
        if (ctx != null)
        {
            try {
                ctx.close();
            } catch (NamingException e) {
                log.warn(e.getMessage());
            }
        }
    }

这适用于对用户进行身份验证.但是，LDAP 管理员告诉我，当绑定不成功时，我没有正常断开连接.LDAP 端的错误是(例如):