Allow the application to customize the conversion of arbitrary error messages

to friendly error text.


git-svn-id: https://samskivert.googlecode.com/svn/trunk@1758 6335cc39-0255-0410-8fd6-9bcaacd3b74c

projects/samskivert/src/java/com/samskivert/velocity/Application.java

@@ -24,6 +24,7 @@ import java.util.Properties;
 
 import javax.servlet.ServletConfig;
 import javax.servlet.ServletContext;
+import javax.servlet.http.HttpServletRequest;
 
 import org.apache.velocity.app.Velocity;
 
@@ -34,6 +35,7 @@ import com.samskivert.servlet.MessageManager;
 import com.samskivert.servlet.RedirectException;
 import com.samskivert.servlet.SiteIdentifier;
 import com.samskivert.servlet.SiteResourceLoader;
+import com.samskivert.servlet.util.ExceptionMap;
 import com.samskivert.util.StringUtil;
 
 /**
@@ -43,6 +45,16 @@ import com.samskivert.util.StringUtil;
  * represents the web application. The application class is responsible
  * for initializing services that will be used by the application's logic
  * objects as well as cleaning them up when the application is shut down.
+ *
+ * <p><b>Error handling</b><br>
+ * The application provides a common error handling mechanism. The design is to
+ * catch any exceptions thrown by the logic and to convert them into friendly
+ * error messages that are inserted into the invocation context with the key
+ * <code>"error"</code> for easy display in the resulting web page.
+ *
+ * <p> The default process of mapping exceptions to friendly error messages is
+ * done using the {@link ExceptionMap} class. This can be replaced by
+ * overriding {@link #handleException}.
  */
 public class Application
 {
@@ -198,6 +210,22 @@ public class Application
         return error;
     }
 
+    /**
+     * If a generic exception propagates up from {@link Logic#invoke} and is
+     * not otherwise converted into a friendly or redirect exception, the
+     * application will be required to provide a generic error message to be
+     * inserted into the context and should take this opportunity to log the
+     * exception.
+     */
+    protected String handleException (
+        HttpServletRequest req, Logic logic, Exception error)
+    {
+        Log.warning("Choked on request [logic=" + logic +
+                    ", req=" + req.getRequestURI() + "].");
+        Log.logStackTrace(error);
+        return ExceptionMap.getMessage(error);
+    }
+
     /**
      * This should be overridden by the application implementation to
      * perform any necessary cleanup.

projects/samskivert/src/java/com/samskivert/velocity/DispatcherServlet.java

@@ -46,7 +46,6 @@ import com.samskivert.servlet.MessageManager;
 import com.samskivert.servlet.RedirectException;
 import com.samskivert.servlet.SiteIdentifier;
 import com.samskivert.servlet.SiteResourceLoader;
-import com.samskivert.servlet.util.ExceptionMap;
 import com.samskivert.servlet.util.FriendlyException;
 
 import com.samskivert.util.ConfigUtil;
@@ -136,19 +135,7 @@ import com.samskivert.util.StringUtil;
  * inserted in the future (ie. if I ever want to use this to develop a
  * cobranded web site).
  *
- * <p><b>Error handling</b><br>
- * The dispatcher servlet provides a common error handling mechanism. The
- * design is to catch any exceptions thrown by the logic and to convert
- * them into friendly error messages that are inserted into the invocation
- * context with the key <code>"error"</code> for easy display in the
- * resulting web page.
- *
- * <p> The process of mapping exceptions to friendly error messages is
- * done using the {@link ExceptionMap} class. Consult its documentation
- * for an explanation of how it works.
- *
  * @see Logic
- * @see ExceptionMap
  */
 public class DispatcherServlet extends VelocityServlet
     implements MethodExceptionEventHandler
@@ -382,10 +369,7 @@ public class DispatcherServlet extends VelocityServlet
             errmsg = fe.getMessage();
 
 	} catch (Exception e) {
-            errmsg = ExceptionMap.getMessage(e);
+            errmsg = _app.handleException(req, logic, e);
-            Log.warning("Choked on request [logic=" + logic +
-                        ", req=" + req.getRequestURI() + "].");
-	    Log.logStackTrace(e);
 	}
 
         // if we have an error message, insert it into the template