How to download log file from build result through plain java client library

code in one of my tools

ITeamBuildClient buildClient = (ITeamBuildClient) RepoServer.getClientLibrary(ITeamBuildClient.class);
// get build result
...
// use build result to get log contribution content object and data
IBuildResultContribution[] ibrcl =buildClient.getBuildResultContributions(br, IBuildResultContribution.LOG_EXTENDED_CONTRIBUTION_ID, null);
for(IBuildResultContribution ibrc : ibrcl)
{
String s=getContent(ibrc.getExtendedContributionData(), RepoServer.contentManager());
}
// worker routine to get the string from the content object
    private static String getContent(IContent ic, IContentManager icm)
    {
        // make an output stream for the content manager
        OutputStream os = new ByteArrayOutputStream();
        // get the content of the content object.
        try
        {
            if (ic != null)
            {
                icm.retrieveContent(ic, os, null);
                return os.toString();
            }
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        return null;
    }