7103889: (fs) Reduce String concatenation when iterating over directory

Reviewed-by: alanb
Contributed-by: mike.skells@talk21.com

src/share/classes/java/nio/file/Files.java

@@ -363,6 +363,17 @@ public final class Files {
 
     // -- Directories --
 
+    private static class AcceptAllFilter
+        implements DirectoryStream.Filter<Path>
+    {
+        private AcceptAllFilter() { }
+
+        @Override
+        public boolean accept(Path entry) { return true; }
+
+        static final AcceptAllFilter FILTER = new AcceptAllFilter();
+    }
+
     /**
      * Opens a directory, returning a {@link DirectoryStream} to iterate over
      * all entries in the directory. The elements returned by the directory
@@ -397,12 +408,7 @@ public final class Files {
     public static DirectoryStream<Path> newDirectoryStream(Path dir)
         throws IOException
     {
-        return provider(dir).newDirectoryStream(dir, new DirectoryStream.Filter<Path>() {
-            @Override
-            public boolean accept(Path entry) {
-                return true;
-            }
-        });
+        return provider(dir).newDirectoryStream(dir, AcceptAllFilter.FILTER);
     }
 
     /**

src/windows/classes/sun/nio/fs/WindowsDirectoryStream.java

@@ -124,26 +124,27 @@ class WindowsDirectoryStream
         private boolean atEof;
         private String first;
         private Path nextEntry;
+        private String prefix;
 
         WindowsDirectoryIterator(String first) {
             atEof = false;
             this.first = first;
+            if (dir.needsSlashWhenResolving()) {
+                prefix = dir.toString() + "\\";
+            } else {
+                prefix = dir.toString();
+            }
+        }
+
+        // links to self and parent directories are ignored
+        private boolean isSelfOrParent(String name) {
+            return name.equals(".") || name.equals("..");
         }
 
         // applies filter and also ignores "." and ".."
         private Path acceptEntry(String s, BasicFileAttributes attrs) {
-            if (s.equals(".") || s.equals(".."))
-                return null;
-            if (dir.needsSlashWhenResolving()) {
-                StringBuilder sb = new StringBuilder(dir.toString());
-                sb.append('\\');
-                sb.append(s);
-                s = sb.toString();
-            } else {
-                s = dir + s;
-            }
             Path entry = WindowsPath
-                .createFromNormalizedPath(dir.getFileSystem(), s, attrs);
+                .createFromNormalizedPath(dir.getFileSystem(), prefix + s, attrs);
             try {
                 if (filter.accept(entry))
                     return entry;
@@ -157,7 +158,7 @@ class WindowsDirectoryStream
         private Path readNextEntry() {
             // handle first element returned by search
             if (first != null) {
-                nextEntry = acceptEntry(first, null);
+                nextEntry = isSelfOrParent(first) ? null : acceptEntry(first, null);
                 first = null;
                 if (nextEntry != null)
                     return nextEntry;
@@ -184,6 +185,10 @@ class WindowsDirectoryStream
                         return null;
                     }
 
+                    // ignore link to self and parent directories
+                    if (isSelfOrParent(name))
+                        continue;
+
                     // grab the attributes from the WIN32_FIND_DATA structure
                     // (needs to be done while holding closeLock because close
                     // will release the buffer)

src/windows/classes/sun/nio/fs/WindowsPathParser.java

@@ -120,12 +120,18 @@ class WindowsPathParser {
                 off = next;
             } else {
                 if (isLetter(c0) && c1 == ':') {
-                    root = input.substring(0, 2);
-                    if (len > 2 && isSlash(input.charAt(2))) {
+                    char c2;
+                    if (len > 2 && isSlash(c2 = input.charAt(2))) {
+                        // avoid concatenation when root is "D:\"
+                        if (c2 == '\\') {
+                            root = input.substring(0, 3);
+                        } else {
+                            root = input.substring(0, 2) + '\\';
+                        }
                         off = 3;
-                        root += "\\";
                         type = WindowsPathType.ABSOLUTE;
                     } else {
+                        root = input.substring(0, 2);
                         off = 2;
                         type = WindowsPathType.DRIVE_RELATIVE;
                     }