Added Logging trait

src/scala/spark/Logging.scala

+package spark
+
+import org.slf4j.Logger
+import org.slf4j.LoggerFactory
+
+/**
+ * Utility trait for classes that want to log data. Creates a SLF4J logger
+ * for the class and allows logging messages at different levels using
+ * methods that only evaluate parameters lazily if the log level is enabled.
+ */
+trait Logging {
+  // Make the log field transient so that objects with Logging can
+  // be serialized and used on another machine
+  @transient private var log_ : Logger = null
+
+  // Method to get or create the logger
+  def log: Logger = {
+    if (log_ == null)
+      log_ = LoggerFactory.getLogger(this.getClass())
+    return log_
+  }
+
+  // Log methods that take only a String
+  def logInfo(msg: => String) = if (log.isInfoEnabled) log.info(msg)
+
+  def logDebug(msg: => String) = if (log.isDebugEnabled) log.debug(msg)
+
+  def logWarning(msg: => String) = if (log.isWarnEnabled) log.warn(msg)
+
+  def logError(msg: => String) = if (log.isErrorEnabled) log.error(msg)
+
+  // Log methods that take Throwables (Exceptions/Errors) too
+  def logInfo(msg: => String, throwable: Throwable) =
+    if (log.isInfoEnabled) log.info(msg)
+
+  def logDebug(msg: => String, throwable: Throwable) =
+    if (log.isDebugEnabled) log.debug(msg)
+
+  def logWarning(msg: => String, throwable: Throwable) =
+    if (log.isWarnEnabled) log.warn(msg, throwable)
+
+  def logError(msg: => String, throwable: Throwable) =
+    if (log.isErrorEnabled) log.error(msg, throwable)
+}