make ConfigException abstract

config/src/main/java/com/typesafe/config/ConfigException.java

@@ -7,7 +7,7 @@ package com.typesafe.config;
 /**
  * All exceptions thrown by the library are subclasses of ConfigException.
  */
-public class ConfigException extends RuntimeException {
+public abstract class ConfigException extends RuntimeException {
     private static final long serialVersionUID = 1L;
 
     final private ConfigOrigin origin;
@@ -343,4 +343,20 @@ public class ConfigException extends RuntimeException {
             return sb.toString();
         }
     }
+
+    /**
+     * Exception that doesn't fall into any other category.
+     */
+    public static class Generic extends ConfigException {
+        private static final long serialVersionUID = 1L;
+
+        public Generic(String message, Throwable cause) {
+            super(message, cause);
+        }
+
+        public Generic(String message) {
+            this(message, null);
+        }
+    }
+
 }

config/src/main/java/com/typesafe/config/ConfigFactory.java

@@ -123,8 +123,9 @@ public final class ConfigFactory {
             if (specified == 0) {
                 return load("application");
             } else if (specified > 1) {
-                throw new ConfigException(
+                throw new ConfigException.Generic("You set more than one of config.file='" + file
-                        "You set more than one system property from config.file, config.url, config.resource; don't know which one to use!");
+                        + "', config.url='" + url + "', config.resource='" + resource
+                        + "'; don't know which one to use!");
             } else {
                 if (resource != null) {
                     // this deliberately does not parseResourcesAnySyntax; if
@@ -136,8 +137,9 @@ public final class ConfigFactory {
                     try {
                         return load(parseURL(new URL(url)));
                     } catch (MalformedURLException e) {
-                        throw new ConfigException("Bad URL in config.url system property: '" + url
+                        throw new ConfigException.Generic(
-                                + "'", e);
+                                "Bad URL in config.url system property: '" + url + "': "
+                                        + e.getMessage(), e);
                     }
                 }
             }