Added requireProperty() and associated MissingPropertyException.

git-svn-id: https://samskivert.googlecode.com/svn/trunk@2972 6335cc39-0255-0410-8fd6-9bcaacd3b74c

src/main/java/com/samskivert/util/MissingPropertyException.java

@@ -0,0 +1,34 @@
+//
+// $Id$
+//
+// samskivert library - useful routines for java programs
+// Copyright (C) 2001-2010 Michael Bayne, et al.
+// 
+// This library is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License as published
+// by the Free Software Foundation; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.samskivert.util;
+
+/**
+ * An exception thrown when a required property was not found.
+ *
+ * @see PropertiesUtil#requireProperty
+ */
+public class MissingPropertyException extends RuntimeException
+{
+    public MissingPropertyException (String message)
+    {
+        super(message);
+    }
+}

src/main/java/com/samskivert/util/PropertiesUtil.java

@@ -218,4 +218,28 @@ public class PropertiesUtil
             return null;
         }
     }
+
+    /**
+     * Returns the specified property from the supplied properties object.
+     * @throws MissingPropertyException with the text "Missing required property
+     * '<code>key</code>'." if the property does not exist or is the empty string.
+     */
+    public static String requireProperty (Properties props, String key)
+    {
+        return requireProperty(props, key, "Missing required property '" + key + "'.");
+    }
+
+    /**
+     * Returns the specified property from the supplied properties object.
+     * @throws MissingPropertyException with the supplied message if the property does not exist or
+     * is the empty string.
+     */
+    public static String requireProperty (Properties props, String key, String missingMessage)
+    {
+        String value = props.getProperty(key);
+        if (StringUtil.isBlank(value)) {
+            throw new MissingPropertyException(missingMessage);
+        }
+        return value;
+    }
 }