--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/langtools/src/share/classes/com/sun/tools/sjavac/comp/SmartFileObject.java	Fri Jan 18 00:16:21 2013 +0100
@@ -0,0 +1,126 @@
+/*
+ * Copyright (c) 2012, 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.sjavac.comp;
+
+import java.io.*;
+import java.net.URI;
+import javax.lang.model.element.Modifier;
+import javax.lang.model.element.NestingKind;
+import javax.tools.JavaFileObject;
+
+/**
+ * The SmartFileObject will return an outputstream that cache the written data
+ * and compare the new content with the old content on disk. Only if they differ,
+ * will the file be updated.
+ *
+ * <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></p>
+ */
+public class SmartFileObject implements JavaFileObject {
+
+    JavaFileObject file;
+    PrintWriter stdout;
+
+    public SmartFileObject(JavaFileObject r, PrintWriter pw) {
+        file = r;
+        stdout = pw;
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        return file.equals(other);
+    }
+
+    @Override
+    public int hashCode() {
+        return file.hashCode();
+    }
+
+    public Kind getKind() {
+        return file.getKind();
+    }
+
+    public boolean isNameCompatible(String simpleName, Kind kind) {
+        return file.isNameCompatible(simpleName, kind);
+    }
+
+    public URI toUri() {
+        return file.toUri();
+    }
+
+    public String getName() {
+        return file.getName();
+    }
+
+    public InputStream openInputStream() throws IOException {
+        return file.openInputStream();
+    }
+
+    public OutputStream openOutputStream() throws IOException {
+        return file.openOutputStream();
+    }
+
+    public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {
+        return file.getCharContent(ignoreEncodingErrors);
+    }
+
+    static String lineseparator = System.getProperty("line.separator");
+
+    public Writer openWriter() throws IOException {
+        StringBuilder s = new StringBuilder();
+        try (BufferedReader r = new BufferedReader(file.openReader(true))) {
+            while (r.ready()) {
+                s.append(r.readLine()+lineseparator);
+            }
+        } catch (FileNotFoundException e) {
+            // Perfectly ok.
+        }
+        return new SmartWriter(file, s.toString(), file.getName(), stdout);
+    }
+
+    public long getLastModified() {
+        return file.getLastModified();
+    }
+
+    public boolean delete() {
+        return file.delete();
+    }
+
+    public Modifier getAccessLevel() {
+        return file.getAccessLevel();
+    }
+
+    public NestingKind getNestingKind() {
+        return file.getNestingKind();
+    }
+
+    public Reader openReader(boolean ignoreEncodingErrors) throws IOException {
+        return file.openReader(ignoreEncodingErrors);
+    }
+
+}