A URLStreamHandlerFactory that lets you add arbitrary URLStreamHandlers.

git-svn-id: https://samskivert.googlecode.com/svn/trunk@1165 6335cc39-0255-0410-8fd6-9bcaacd3b74c

projects/samskivert/src/java/com/samskivert/net/AttachableURLFactory.java

@@ -0,0 +1,69 @@
+//
+// $Id: AttachableURLFactory.java,v 1.1 2003/07/09 18:44:11 ray Exp $
+
+package com.samskivert.net;
+
+import java.net.URL;
+import java.net.URLStreamHandler;
+import java.net.URLStreamHandlerFactory;
+
+import java.util.HashMap;
+
+import com.samskivert.Log;
+
+/**
+ * Allows other entities in an application to register URLStreamHandler
+ * classes for protocols of their own making.
+ */
+public class AttachableURLFactory implements URLStreamHandlerFactory
+{
+    /**
+     * Register a URL handler.
+     *
+     * @param protocol the protocol to register.
+     * @param handlerClass a Class of type java.net.URLStreamHandler
+     */
+    public static void attachHandler (String protocol, Class handlerClass)
+    {
+        if (!URLStreamHandler.class.isAssignableFrom(handlerClass)) {
+            throw new IllegalArgumentException(
+                "Specified class is not a java.net.URLStreamHandler.");
+        }
+
+        // set up the factory.
+        if (_handlers == null) {
+            _handlers = new HashMap();
+
+            // this could throw an Error if another factory is already
+            // registered. We let that error bubble on back.
+            URL.setURLStreamHandlerFactory(new AttachableURLFactory());
+        }
+
+        _handlers.put(protocol.toLowerCase(), handlerClass);
+    }
+
+    /**
+     * Do not let others instantiate us.
+     */
+    private AttachableURLFactory ()
+    {
+    }
+
+    // documentation inherited from interface URLStreamHandlerFactory
+    public URLStreamHandler createURLStreamHandler (String protocol)
+    {
+        Class handler = (Class) _handlers.get(protocol.toLowerCase());
+        if (handler != null) {
+            try {
+                return (URLStreamHandler) handler.newInstance();
+            } catch (Exception e) {
+                Log.warning("Unable to instantiate URLStreamHandler" +
+                    " [protocol=" + protocol + ", cause=" + e + "].");
+            }
+        }
+        return null;
+    }
+
+    /** A mapping of protocol name to handler classes. */
+    protected static HashMap _handlers;
+}