How can I enable logging in NVelocity?

Question

Any idea how to do what the title says? Only thing I found was on the original Velocity site, and I don't think

ve.setProperty( RuntimeConstants.RUNTIME_LOG_LOGSYSTEM_CLASS,
    "org.apache.velocity.runtime.log.Log4JLogChute" );

ve.setProperty("runtime.log.logsystem.log4j.logger",
   LOGGER_NAME);

will work wonderfully well on .NET. I am using log4net, which should make it quite easy, but the documentation on NVelocity is really a mess.

Answer 1

Update:

Currently, NVelocity does not support logging. The initializeLogger() and Log() methods in RuntimeInstance Class are commented out.

If you need to log, uncomment the two methods, add a private ILogSystem logSystem; property

Here's our on-the-fly implementation:

public class RuntimeInstance : IRuntimeServices
{
    private ILogSystem logSystem;
    ...
    ...
    private void initializeLogger()
    {
    logSystem = LogManager.CreateLogSystem(this);

    }
    ...
    ...
    private void Log(LogLevel level, Object message)
    {
    String output = message.ToString();

    logSystem.LogVelocityMessage(level, output);
    }
    ...
}

Then, we implemented ILogSystem for log4net

using log4net;
using NVelocity.Runtime;
using NVelocity.Runtime.Log;

namespace Services.Templates
{
    public class Log4NetILogSystem : ILogSystem
    {
        private readonly ILog _log;

        public Log4NetILogSystem(ILog log )
        {
            _log = log;
        }

        public void Init(IRuntimeServices rs)
        {

        }

        public void LogVelocityMessage(LogLevel level, string message)
        {
            switch (level)
            {
                case LogLevel.Debug:
                    _log.Debug(message);
                    break;
                case LogLevel.Info:
                    _log.Info(message);
                    break;
                case LogLevel.Warn:
                    _log.Warn(message);
                    break;
                case LogLevel.Error:
                    _log.Error(message);
                    break;
            }
        }
    }
}

Then, when creating the engine:

var engine = new VelocityEngine();
var props = new ExtendedProperties();    
props.SetProperty(RuntimeConstants.RUNTIME_LOG_LOGSYSTEM,
new Log4NetILogSystem(LogManager.GetLogger(typeof(NVelocityEngine))));
engine.Init(props);

Answer 2

Implement NVelocity.Runtime.Log.ILogSystem (you could write a simple implementation that bridges to log4net) and set this impl type in the property RuntimeConstants.RUNTIME_LOG_LOGSYSTEM_CLASS

How I got this information:

1. Get the code.
2. Search for "log" in the codebase
3. Discover the classes in NVelocity.Runtime.Log.
4. Read those classes' source, they're very simple and thoroughly documented.