added simple semaphore file mechanism for session directory.

git-svn-id: https://svn.lifesci.dundee.ac.uk/svn/repository/trunk@183 be28352e-c001-0410-b1a7-c7978e42abec

diff --git a/src/org/vamsas/client/simpleclient/SessionFlagFile.java b/src/org/vamsas/client/simpleclient/SessionFlagFile.java
new file mode 100644 (file)
index 0000000..7826fbc
--- /dev/null
+++ b/src/org/vamsas/client/simpleclient/SessionFlagFile.java
@@ -0,0 +1,85 @@
+package org.vamsas.client.simpleclient;
+
+import java.io.File;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+/**
+ * methods for setting and checking 
+ * binary flags in a vamsas session directory.
+ * all methods apart from the constructor will 
+ * throw a fatal error if the flagFile is not
+ * a valid java.io.File object.
+ * LATER: extract SessionFlag interface for generalizing the vamsas session code 
+ * @author jimp
+ *
+ */
+public class SessionFlagFile {
+  private static Log log = LogFactory.getLog(SessionFlagFile.class);
+  protected File flagFile=null;
+  private void checkFlagFile() {
+    if (flagFile==null) {
+      log.fatal("Implementation error - uninitialized SessionFlagFile", 
+          new Error("Implementation error - uninitialized SessionFlagFile"));
+    }
+  }
+  /**
+   * will log a warning if exceptions occur during flag creation.
+   * @return true if flag was set successfully
+   */
+  public boolean setFlag() {
+    checkFlagFile();
+    try {
+      if (flagFile.createNewFile()) {
+        log.debug("Set session flag "+flagFile);
+      } else {
+        log.debug("Session flag already set "+flagFile);
+      }
+      return true;
+    }
+    catch (Exception e) {
+      log.warn("Couldn't set session flag "+flagFile, e);
+    }
+    return false;
+  }
+  /**
+   * 
+   * @return true if flag was cleared successfully
+   */
+  public boolean clearFlag() {
+    checkFlagFile();
+    if (flagFile.exists()) {
+      log.debug("clearing session flag "+flagFile);
+      if (!flagFile.delete()) {
+        log.warn("failed to clear session flag "+flagFile);
+        return false;
+      }
+    } else {
+      log.debug("clearFlag called for already cleared flag "+flagFile);
+    }
+    return true;
+  }
+    /**
+     * 
+     * @return state of session flag
+     */
+  public boolean checkFlag() {
+    checkFlagFile();
+    if (flagFile.exists()) {
+      if (log.isDebugEnabled())
+        log.debug("Flag '"+flagFile+"' is set.");
+      return true;
+    }
+    if (log.isDebugEnabled())
+      log.debug("Flag '"+flagFile+"' is not set.");    
+    return false;
+  }
+    /**
+     * @param flagFile
+     */
+    public SessionFlagFile(File flagFile) {
+      super();
+      this.flagFile = flagFile;
+    };
+}