--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/file/CacheFSInfo.java	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,123 @@
+/*
+ * Copyright (c) 2005, 2014, 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.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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 com.sun.tools.javac.file;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+import com.sun.tools.javac.util.Context;
+import com.sun.tools.javac.util.Context.Factory;
+
+/**
+ * Caching implementation of FSInfo.
+ *
+ * <p><b>This is NOT part of any supported API.
+ * If you write code that depends on this, you do so at your own risk.
+ * This code and its internal interfaces are subject to change or
+ * deletion without notice.</b>
+ */
+public class CacheFSInfo extends FSInfo {
+
+    /**
+     * Register a Context.Factory to create a CacheFSInfo.
+     */
+    public static void preRegister(Context context) {
+        context.put(FSInfo.class, (Factory<FSInfo>)c -> {
+                FSInfo instance = new CacheFSInfo();
+                c.put(FSInfo.class, instance);
+                return instance;
+            });
+    }
+
+    public void clearCache() {
+        cache.clear();
+    }
+
+    @Override
+    public Path getCanonicalFile(Path file) {
+        Entry e = getEntry(file);
+        return e.canonicalFile;
+    }
+
+    @Override
+    public boolean exists(Path file) {
+        Entry e = getEntry(file);
+        return e.exists;
+    }
+
+    @Override
+    public boolean isDirectory(Path file) {
+        Entry e = getEntry(file);
+        return e.isDirectory;
+    }
+
+    @Override
+    public boolean isFile(Path file) {
+        Entry e = getEntry(file);
+        return e.isFile;
+    }
+
+    @Override
+    public List<Path> getJarClassPath(Path file) throws IOException {
+        // don't bother to lock the cache, because it is thread-safe, and
+        // because the worst that can happen would be to create two identical
+        // jar class paths together and have one overwrite the other.
+        Entry e = getEntry(file);
+        if (e.jarClassPath == null)
+            e.jarClassPath = super.getJarClassPath(file);
+        return e.jarClassPath;
+    }
+
+    private Entry getEntry(Path file) {
+        // don't bother to lock the cache, because it is thread-safe, and
+        // because the worst that can happen would be to create two identical
+        // entries together and have one overwrite the other.
+        Entry e = cache.get(file);
+        if (e == null) {
+            e = new Entry();
+            e.canonicalFile = super.getCanonicalFile(file);
+            e.exists = super.exists(file);
+            e.isDirectory = super.isDirectory(file);
+            e.isFile = super.isFile(file);
+            cache.put(file, e);
+        }
+        return e;
+    }
+
+    // could also be a Map<File,SoftReference<Entry>> ?
+    private final Map<Path,Entry> cache = new ConcurrentHashMap<>();
+
+    private static class Entry {
+        Path canonicalFile;
+        boolean exists;
+        boolean isFile;
+        boolean isDirectory;
+        List<Path> jarClassPath;
+    }
+}