@Override
    public void onPreAdd(final IoFilterChain chain, final String name,
            final NextFilter nextFilter) {
        if (chain.contains(ProxyFilter.class)) {
            throw new IllegalStateException(
                    "A filter chain cannot contain more than one ProxyFilter.");
        }
    }
@ Override public void onPreAdd ( final IoFilterChain chain , final String name , final NextFilter nextFilter ) { if ( chain . contains ( ProxyFilter . class ) ) { throw new IllegalStateException ( "A filter chain cannot contain more than one ProxyFilter." ) ; } }
Called before the filter is added into the filter chain.
Checks if chain already holds an {@link ProxyFilter} instance.

@param chain the filter chain
@param name the name assigned to this filter
@param nextFilter the next filter
@throws IllegalStateException if chain already contains an instance of
{@link ProxyFilter}