8379557: Further optimize URL.toExternalForm

Reviewed-by: vyazici

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1995, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1995, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -481,14 +481,33 @@ public abstract class URLStreamHandler {
      * @return  a string representation of the {@code URL} argument.
      */
     protected String toExternalForm(URL u) {
-        String s;
+        // The fast paths and branch-free concatenations in this method are here for
+        // a reason and should not be updated without checking performance figures.
+
+        // Optionality, subtly different for authority
+        boolean emptyAuth = u.getAuthority() == null || u.getAuthority().isEmpty();
+        boolean emptyPath = u.getPath() == null;
+        boolean emptyQuery = u.getQuery() == null;
+        boolean emptyRef = u.getRef() == null;
+        var path = emptyPath ? "" : u.getPath();
+        // Fast paths for empty components
+        if (emptyQuery && emptyRef) {
+            return emptyAuth
+                    ? (u.getProtocol() + ":" + path)
+                    : (u.getProtocol() + "://" + u.getAuthority() + path);
+        }
+        // Prefer locals for efficient concatenation
+        var authSep = emptyAuth ? ":" : "://";
+        var auth = emptyAuth ? "" : u.getAuthority();
+        var querySep = emptyQuery ? "" : "?";
+        var query = emptyQuery ? "" : u.getQuery();
+        var refSep = emptyRef ? "" : "#";
+        var ref = emptyRef ? "" : u.getRef();
         return u.getProtocol()
-            + ':'
-            + ((s = u.getAuthority()) != null && !s.isEmpty()
-               ? "//" + s : "")
-            + ((s = u.getPath()) != null ? s : "")
-            + ((s = u.getQuery()) != null ? '?' + s : "")
-            + ((s = u.getRef()) != null ? '#' + s : "");
+                + authSep + auth
+                + path
+                + querySep + query
+                + refSep + ref;
     }
 
     /**

test/jdk/java/net/URL/Constructor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2026, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -48,6 +48,7 @@ public class Constructor {
         entries.addAll(Arrays.asList(jarURLs));
         entries.addAll(Arrays.asList(normalHttpURLs));
         entries.addAll(Arrays.asList(abnormalHttpURLs));
+        entries.addAll(Arrays.asList(blankComponents));
         if (hasFtp())
             entries.addAll(Arrays.asList(ftpURLs));
         URL url;
@@ -252,4 +253,20 @@ public class Constructor {
                   "/dir1/entry.txt",
                   "ftp://br:pwd@ftp.foo.com/dir1/entry.txt")
     };
+
+    static Entry[] blankComponents = new Entry[] {
+        new Entry(null, "http://host/path#", "http://host/path#"),
+        new Entry(null, "http://host/path?", "http://host/path?"),
+        new Entry(null, "http://host/path?#", "http://host/path?#"),
+        new Entry(null, "http://host/path#?", "http://host/path#?"),
+        new Entry(null, "file:/path#", "file:/path#"),
+        new Entry(null, "file:/path?", "file:/path?"),
+        new Entry(null, "file:/path?#", "file:/path?#"),
+        new Entry(null, "file:///path#", "file:/path#"),
+        new Entry(null, "file:///path?", "file:/path?"),
+        new Entry(null, "file:/path#?", "file:/path#?"),
+        new Entry("file:/path", "path?#", "file:/path?#"),
+        new Entry(null, "file:", "file:"),
+        new Entry(null, "file:#", "file:#")
+    };
 }

test/micro/org/openjdk/bench/java/net/URLToString.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2026, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code 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 General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package org.openjdk.bench.java.net;
+
+import org.openjdk.jmh.annotations.*;
+
+import java.net.MalformedURLException;
+import java.net.URI;
+import java.net.URL;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Tests java.net.URL.toString performance
+ */
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Thread)
+@Warmup(iterations = 5, time = 1)
+@Measurement(iterations = 5, time = 1)
+@Fork(value = 3)
+public class URLToString {
+
+    @Param({"false", "true"})
+    boolean auth;
+
+    @Param({"false", "true"})
+    boolean query;
+
+    @Param({"false", "true"})
+    boolean ref;
+
+    private URL url;
+
+    @Setup()
+    public void setup() throws MalformedURLException {
+        StringBuilder sb = new StringBuilder();
+        if (auth) {
+            sb.append("http://hostname");
+        } else {
+            sb.append("file:");
+        }
+        sb.append("/some/long/path/to/jar/app-1.0.jar!/org/summerframework/samples/horseclinic/HorseClinicApplication.class");
+        if (query) {
+            sb.append("?param=value");
+        }
+        if (ref) {
+            sb.append("#fragment");
+        }
+
+        url = URI.create(sb.toString()).toURL();
+    }
+
+    @Benchmark
+    public String urlToString() {
+        return url.toString();
+    }
+}