LogServiceUtil.java

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package com.buglabs.util;

import java.io.PrintWriter;
import java.io.StringWriter;
import java.util.Dictionary;
import java.util.Hashtable;

import org.osgi.framework.BundleContext;
import org.osgi.framework.BundleException;
import org.osgi.framework.Constants;
import org.osgi.framework.ServiceReference;
import org.osgi.service.log.LogReaderService;
import org.osgi.service.log.LogService;

import com.buglabs.osgi.log.LogServiceImpl;

/**
 * Utility functions relating to OSGi log service.
 * 
 * @author kgilmer
 * 
 */
public class LogServiceUtil {

	/**
	 * @param context
	 *            if context is null, it will return a log service that uses
	 *            stdout.
	 * @return Either the first LogService available in the runtime if available
	 *         or a SysoutLogService.
	 */
	public static LogService getLogService(BundleContext context) {
		final LogService logService;
		// See if LogService is available.
		// also protect against context being null
		ServiceReference sr = null;
		if (context != null)
			sr = context.getServiceReference(LogService.class.getName());

		if (sr != null) {
			logService = (LogService) context.getService(sr);
		} else {
			LogServiceImpl logServiceImpl = new LogServiceImpl(context);
			logService = (LogService) logServiceImpl;

			//We will register a log service and just let it dangle out there for the lifetime of the OSGi framework instance.
			context.registerService(LogService.class.getName(), logServiceImpl, getLogServiceProperties(logServiceImpl));
			context.registerService(LogReaderService.class.getName(), logServiceImpl, getLogServiceProperties(logServiceImpl));
		}

		return logService;
	}

	
	/**
	 * @return Properties associated with this service implementation.
	 */
	private static Dictionary getLogServiceProperties(LogServiceImpl logServiceImpl) {
		Hashtable dict = new Hashtable();
		dict.put("Implementation", LogServiceImpl.class.getName());
		dict.put("Log Level", "" + logServiceImpl.logLevel);
		dict.put("Quiet", "" + logServiceImpl.quiet);
		dict.put("Output Stream", LogServiceImpl.out.getClass().getName());
		dict.put("Error Stream", LogServiceImpl.err.getClass().getName());
		dict.put("Buffer Size", "" + logServiceImpl.bufferSize);
		dict.put(Constants.SERVICE_RANKING, -4096);
		return dict;
	}

	/**
	 * Log a bundle exception and print nested exception if it exists.
	 * 
	 * @param logService
	 * @param message
	 * @param exception
	 */
	public static void logBundleException(LogService logService, String message, BundleException exception) {
		// Add error handling to be specific about what exactly happened.
		logService.log(LogService.LOG_ERROR, message + ": " + exception.getMessage() + "\n" + stackTraceToString(exception));
		stackTraceToString(exception);

		if (exception.getNestedException() != null) {
			logService.log(LogService.LOG_ERROR, "Nested Exception: " + exception.getNestedException().getMessage() + "\n" + stackTraceToString(exception.getNestedException()));
		}
	}

	/**
	 * Log an exception and print nested exception if it exists.
	 * 
	 * @param logService
	 * @param message
	 * @param exception
	 */
	public static void logBundleException(LogService logService, String message, Exception exception) {
		// Add error handling to be specific about what exactly happened.
		logService.log(LogService.LOG_ERROR, message + ": " + exception.getMessage() + "\n" + stackTraceToString(exception));
	}

	/**
	 * @param t
	 * @return A stack trace as a string.
	 */
	private static String stackTraceToString(Throwable t) {
		StringWriter sw = new StringWriter();
		t.printStackTrace(new PrintWriter(sw));
		return sw.getBuffer().toString();
	}
}