8294626: Improve URL protocol lower casing

Reviewed-by: dfuchs

Author: cl4es

src/java.base/share/classes/java/net/URL.java

@@ -440,7 +440,7 @@ public URL(String protocol, String host, int port, String file,
             }
         }
 
-        protocol = toLowerCase(protocol);
+        protocol = lowerCaseProtocol(protocol);
         this.protocol = protocol;
         if (host != null) {
 
@@ -633,7 +633,7 @@ public URL(URL context, String spec, URLStreamHandler handler)
             for (i = start ; !aRef && (i < limit) &&
                      ((c = spec.charAt(i)) != '/') ; i++) {
                 if (c == ':') {
-                    String s = toLowerCase(spec.substring(start, i));
+                    String s = lowerCaseProtocol(spec.substring(start, i));
                     if (isValidProtocol(s)) {
                         newProtocol = s;
                         start = i + 1;
@@ -1384,9 +1384,13 @@ public URLStreamHandler run() {
      * Returns the protocol in lower case. Special cases known protocols
      * to avoid loading locale classes during startup.
      */
-    static String toLowerCase(String protocol) {
-        if (protocol.equals("jrt") || protocol.equals("file") || protocol.equals("jar")) {
-            return protocol;
+    static String lowerCaseProtocol(String protocol) {
+        if (protocol.equals("jrt")) {
+            return "jrt";
+        } else if (protocol.equals("file")) {
+            return "file";
+        } else if (protocol.equals("jar")) {
+            return "jar";
         } else {
             return protocol.toLowerCase(Locale.ROOT);
         }

src/java.base/share/classes/java/net/URLConnection.java

@@ -1092,7 +1092,7 @@ public void setDefaultUseCaches(boolean defaultusecaches) {
      * @since 9
      */
     public static void setDefaultUseCaches(String protocol, boolean defaultVal) {
-        protocol = protocol.toLowerCase(Locale.US);
+        protocol = URL.lowerCaseProtocol(protocol);
         defaultCaching.put(protocol, defaultVal);
     }
 
@@ -1108,7 +1108,7 @@ public static void setDefaultUseCaches(String protocol, boolean defaultVal) {
      * @since 9
      */
     public static boolean getDefaultUseCaches(String protocol) {
-        Boolean protoDefault = defaultCaching.get(protocol.toLowerCase(Locale.US));
+        Boolean protoDefault = defaultCaching.get(URL.lowerCaseProtocol(protocol));
         if (protoDefault != null) {
             return protoDefault.booleanValue();
         } else {

src/java.base/share/classes/sun/net/util/URLUtil.java

@@ -49,17 +49,24 @@ public static String urlNoFragString(URL url) {
 
         String protocol = url.getProtocol();
         if (protocol != null) {
-            /* protocol is compared case-insensitive, so convert to lowercase */
-            protocol = protocol.toLowerCase();
+            /* protocol is compared case-insensitive, so convert to lowercase
+             * if needed. URL will store from lower-cased String literals for
+             * built-in protocols, so avoid calling toLowerCase for these and
+             * use identity tests for speed
+             */
+            if (protocol != "file" && protocol != "jrt" && protocol != "jar") {
+                protocol = protocol.toLowerCase();
+            }
             strForm.append(protocol);
             strForm.append("://");
         }
 
         String host = url.getHost();
         if (host != null) {
             /* host is compared case-insensitive, so convert to lowercase */
-            host = host.toLowerCase();
-            strForm.append(host);
+            if (!host.isEmpty()) {
+                strForm.append(host.toLowerCase());
+            }
 
             int port = url.getPort();
             if (port == -1) {