Client for handlersocket server
The type of the resultSet reference could be simply Map&lt;...&gt;:

private final Map&lt;HSQuery, List&lt;ChannelBuffer&gt;&gt; resultSet


Reference: Effective Java, 2nd edition, Item 52: Refer to objects by their interfaces
Instead of the Map&lt;HSQuery, List&lt;ChannelBuffer&gt;&gt; I'd use Guava's Multimap. It was 
designed for this case.
Constructors and methods should validate their input parameters.

public HSResult(Charset charset) {
    this.charset = charset;
}


Does it make sense to have a charset with null? If not, check it and throw an NullPointerException. (Effective Java, Second Edition, Item 38: Check parameters for validity)