8006884: (fs) Add Files.list, lines and find

Reviewed-by: briangoetz, mduigou
Contributed-by: alan.bateman@oracle.com, henry.jen@oracle.com

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

+/*
+ * Copyright (c) 2013, 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 java.nio.file;
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.Objects;
+import java.nio.file.FileTreeWalker.Event;
+
+/**
+ * An {@code Iterator to iterate over the nodes of a file tree.
+ *
+ * <pre>{@code
+ *     try (FileTreeIterator iterator = new FileTreeIterator(start, maxDepth, options)) {
+ *         while (iterator.hasNext()) {
+ *             Event ev = iterator.next();
+ *             Path path = ev.file();
+ *             BasicFileAttributes attrs = ev.attributes();
+ *         }
+ *     }
+ * }</pre>
+ */
+
+class FileTreeIterator implements Iterator<Event>, Closeable {
+    private final FileTreeWalker walker;
+    private Event next;
+
+    /**
+     * Creates a new iterator to walk the file tree starting at the given file.
+     *
+     * @throws  IllegalArgumentException
+     *          if {@code maxDepth} is negative
+     * @throws  IOException
+     *          if an I/O errors occurs opening the starting file
+     * @throws  SecurityException
+     *          if the security manager denies access to the starting file
+     * @throws  NullPointerException
+     *          if {@code start} or {@code options} is {@ocde null} or
+     *          the options array contains a {@code null} element
+     */
+    FileTreeIterator(Path start, int maxDepth, FileVisitOption... options)
+        throws IOException
+    {
+        this.walker = new FileTreeWalker(Arrays.asList(options), maxDepth);
+        this.next = walker.walk(start);
+        assert next.type() == FileTreeWalker.EventType.ENTRY ||
+               next.type() == FileTreeWalker.EventType.START_DIRECTORY;
+
+        // IOException if there a problem accessing the starting file
+        IOException ioe = next.ioeException();
+        if (ioe != null)
+            throw ioe;
+    }
+
+    private void fetchNextIfNeeded() {
+        if (next == null) {
+            FileTreeWalker.Event ev = walker.next();
+            while (ev != null) {
+                IOException ioe = ev.ioeException();
+                if (ioe != null)
+                    throw new UncheckedIOException(ioe);
+
+                // END_DIRECTORY events are ignored
+                if (ev.type() != FileTreeWalker.EventType.END_DIRECTORY) {
+                    next = ev;
+                    return;
+                }
+                ev = walker.next();
+            }
+        }
+    }
+
+    @Override
+    public boolean hasNext() {
+        if (!walker.isOpen())
+            throw new IllegalStateException();
+        fetchNextIfNeeded();
+        return next != null;
+    }
+
+    @Override
+    public Event next() {
+        if (!walker.isOpen())
+            throw new IllegalStateException();
+        fetchNextIfNeeded();
+        if (next == null)
+            throw new NoSuchElementException();
+        Event result = next;
+        next = null;
+        return result;
+    }
+
+    @Override
+    public void close() {
+        walker.close();
+    }
+}

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

@@ -29,8 +29,8 @@ import java.nio.file.attribute.BasicFileAttributes;
 import java.io.Closeable;
 import java.io.IOException;
 import java.util.ArrayDeque;
+import java.util.Collection;
 import java.util.Iterator;
-import java.util.Set;
 import sun.nio.fs.BasicFileAttributesHolder;
 
 /**
@@ -164,8 +164,17 @@ class FileTreeWalker implements Closeable {
 
     /**
      * Creates a {@code FileTreeWalker}.
+     *
+     * @throws  IllegalArgumentException
+     *          if {@code maxDepth} is negative
+     * @throws  ClassCastException
+     *          if (@code options} contains an element that is not a
+     *          {@code FileVisitOption}
+     * @throws  NullPointerException
+     *          if {@code options} is {@ocde null} or the options
+     *          array contains a {@code null} element
      */
-    FileTreeWalker(Set<FileVisitOption> options, int maxDepth) {
+    FileTreeWalker(Collection<FileVisitOption> options, int maxDepth) {
         boolean fl = false;
         for (FileVisitOption option: options) {
             // will throw NPE if options contains null
@@ -175,6 +184,9 @@ class FileTreeWalker implements Closeable {
                     throw new AssertionError("Should not get here");
             }
         }
+        if (maxDepth < 0)
+            throw new IllegalArgumentException("'maxDepth' is negative");
+
         this.followLinks = fl;
         this.linkOptions = (fl) ? new LinkOption[0] :
             new LinkOption[] { LinkOption.NOFOLLOW_LINKS };

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

@@ -29,6 +29,7 @@ import java.nio.file.attribute.*;
 import java.nio.file.spi.FileSystemProvider;
 import java.nio.file.spi.FileTypeDetector;
 import java.nio.channels.SeekableByteChannel;
+import java.io.Closeable;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.io.Reader;
@@ -38,7 +39,13 @@ import java.io.BufferedWriter;
 import java.io.InputStreamReader;
 import java.io.OutputStreamWriter;
 import java.io.IOException;
+import java.io.UncheckedIOException;
 import java.util.*;
+import java.util.function.BiPredicate;
+import java.util.stream.CloseableStream;
+import java.util.stream.DelegatingStream;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
 import java.nio.charset.Charset;
@@ -2587,9 +2594,6 @@ public final class Files {
                                     FileVisitor<? super Path> visitor)
         throws IOException
     {
-        if (maxDepth < 0)
-            throw new IllegalArgumentException("'maxDepth' is negative");
-
         /**
          * Create a FileTreeWalker to walk the file tree, invoking the visitor
          * for each event.
@@ -3177,4 +3181,336 @@ public final class Files {
         }
         return path;
     }
+
+    // -- Stream APIs --
+
+    /**
+     * Implementation of CloseableStream
+     */
+    private static class DelegatingCloseableStream<T> extends DelegatingStream<T>
+        implements CloseableStream<T>
+    {
+        private final Closeable closeable;
+
+        DelegatingCloseableStream(Closeable c, Stream<T> delegate) {
+            super(delegate);
+            this.closeable = c;
+        }
+
+        public void close() {
+            try {
+                closeable.close();
+            } catch (IOException ex) {
+                throw new UncheckedIOException(ex);
+            }
+        }
+    }
+
+    /**
+     * Return a lazily populated {@code CloseableStream}, the elements of
+     * which are the entries in the directory.  The listing is not recursive.
+     *
+     * <p> The elements of the stream are {@link Path} objects that are
+     * obtained as if by {@link Path#resolve(Path) resolving} the name of the
+     * directory entry against {@code dir}. Some file systems maintain special
+     * links to the directory itself and the directory's parent directory.
+     * Entries representing these links are not included.
+     *
+     * <p> The stream is <i>weakly consistent</i>. It is thread safe but does
+     * not freeze the directory while iterating, so it may (or may not)
+     * reflect updates to the directory that occur after returning from this
+     * method.
+     *
+     * <p> When not using the try-with-resources construct, then the stream's
+     * {@link CloseableStream#close close} method should be invoked after the
+     * operation is completed so as to free any resources held for the open
+     * directory. Operating on a closed stream behaves as if the end of stream
+     * has been reached. Due to read-ahead, one or more elements may be
+     * returned after the stream has been closed.
+     *
+     * <p> If an {@link IOException} is thrown when accessing the directory
+     * after this method has returned, it is wrapped in an {@link
+     * UncheckedIOException} which will be thrown from the method that caused
+     * the access to take place.
+     *
+     * @param   dir  The path to the directory
+     *
+     * @return  The {@code CloseableStream} describing the content of the
+     *          directory
+     *
+     * @throws  NotDirectoryException
+     *          if the file could not otherwise be opened because it is not
+     *          a directory <i>(optional specific exception)</i>
+     * @throws  IOException
+     *          if an I/O error occurs when opening the directory
+     * @throws  SecurityException
+     *          In the case of the default provider, and a security manager is
+     *          installed, the {@link SecurityManager#checkRead(String) checkRead}
+     *          method is invoked to check read access to the directory.
+     *
+     * @see     #newDirectoryStream(Path)
+     * @since   1.8
+     */
+    public static CloseableStream<Path> list(Path dir) throws IOException {
+        DirectoryStream<Path> ds = Files.newDirectoryStream(dir);
+        final Iterator<Path> delegate = ds.iterator();
+
+        // Re-wrap DirectoryIteratorException to UncheckedIOException
+        Iterator<Path> it = new Iterator<Path>() {
+            public boolean hasNext() {
+                try {
+                    return delegate.hasNext();
+                } catch (DirectoryIteratorException e) {
+                    throw new UncheckedIOException(e.getCause());
+                }
+            }
+            public Path next() {
+                try {
+                    return delegate.next();
+                } catch (DirectoryIteratorException e) {
+                    throw new UncheckedIOException(e.getCause());
+                }
+            }
+        };
+
+        return new DelegatingCloseableStream<>(ds,
+            StreamSupport.stream(Spliterators.spliteratorUnknownSize(it,
+                                                                     Spliterator.DISTINCT)));
+    }
+
+    /**
+     * Return a {@code CloseableStream} that is lazily populated with {@code
+     * Path} by walking the file tree rooted at a given starting file.  The
+     * file tree is traversed <em>depth-first</em>, the elements in the stream
+     * are {@link Path} objects that are obtained as if by {@link
+     * Path#resolve(Path) resolving} the relative path against {@code start}.
+     *
+     * <p> The {@code stream} walks the file tree as elements are consumed.
+     * The {@code CloseableStream} returned is guaranteed to have at least one
+     * element, the starting file itself. For each file visited, the stream
+     * attempts to read its {@link BasicFileAttributes}. If the file is a
+     * directory and can be opened successfully, entries in the directory, and
+     * their <em>descendants</em> will follow the directory in the stream as
+     * they are encountered. When all entries have been visited, then the
+     * directory is closed. The file tree walk then continues at the next
+     * <em>sibling</em> of the directory.
+     *
+     * <p> The stream is <i>weakly consistent</i>. It does not freeze the
+     * file tree while iterating, so it may (or may not) reflect updates to
+     * the file tree that occur after returned from this method.
+     *
+     * <p> By default, symbolic links are not automatically followed by this
+     * method. If the {@code options} parameter contains the {@link
+     * FileVisitOption#FOLLOW_LINKS FOLLOW_LINKS} option then symbolic links are
+     * followed. When following links, and the attributes of the target cannot
+     * be read, then this method attempts to get the {@code BasicFileAttributes}
+     * of the link.
+     *
+     * <p> If the {@code options} parameter contains the {@link
+     * FileVisitOption#FOLLOW_LINKS FOLLOW_LINKS} option then the stream keeps
+     * track of directories visited so that cycles can be detected. A cycle
+     * arises when there is an entry in a directory that is an ancestor of the
+     * directory. Cycle detection is done by recording the {@link
+     * java.nio.file.attribute.BasicFileAttributes#fileKey file-key} of directories,
+     * or if file keys are not available, by invoking the {@link #isSameFile
+     * isSameFile} method to test if a directory is the same file as an
+     * ancestor. When a cycle is detected it is treated as an I/O error with
+     * an instance of {@link FileSystemLoopException}.
+     *
+     * <p> The {@code maxDepth} parameter is the maximum number of levels of
+     * directories to visit. A value of {@code 0} means that only the starting
+     * file is visited, unless denied by the security manager. A value of
+     * {@link Integer#MAX_VALUE MAX_VALUE} may be used to indicate that all
+     * levels should be visited.
+     *
+     * <p> When a security manager is installed and it denies access to a file
+     * (or directory), then it is ignored and not included in the stream.
+     *
+     * <p> When not using the try-with-resources construct, then the stream's
+     * {@link CloseableStream#close close} method should be invoked after the
+     * operation is completed so as to free any resources held for the open
+     * directory. Operate the stream after it is closed will throw an
+     * {@link java.lang.IllegalStateException}.
+     *
+     * <p> If an {@link IOException} is thrown when accessing the directory
+     * after this method has returned, it is wrapped in an {@link
+     * UncheckedIOException} which will be thrown from the method that caused
+     * the access to take place.
+     *
+     * @param   start
+     *          the starting file
+     * @param   maxDepth
+     *          the maximum number of directory levels to visit
+     * @param   options
+     *          options to configure the traversal
+     *
+     * @return  the {@link CloseableStream} of {@link Path}
+     *
+     * @throws  IllegalArgumentException
+     *          if the {@code maxDepth} parameter is negative
+     * @throws  SecurityException
+     *          If the security manager denies access to the starting file.
+     *          In the case of the default provider, the {@link
+     *          SecurityManager#checkRead(String) checkRead} method is invoked
+     *          to check read access to the directory.
+     * @throws  IOException
+     *          if an I/O error is thrown when accessing the starting file.
+     * @since   1.8
+     */
+    public static CloseableStream<Path> walk(Path start, int maxDepth,
+                                             FileVisitOption... options)
+        throws IOException
+    {
+        FileTreeIterator iterator = new FileTreeIterator(start, maxDepth, options);
+        return new DelegatingCloseableStream<>(iterator,
+            StreamSupport.stream(Spliterators.spliteratorUnknownSize(iterator, Spliterator.DISTINCT))
+                   .map(entry -> entry.file()));
+    }
+
+    /**
+     * Return a {@code CloseableStream} that is lazily populated with {@code
+     * Path} by walking the file tree rooted at a given starting file.  The
+     * file tree is traversed <em>depth-first</em>, the elements in the stream
+     * are {@link Path} objects that are obtained as if by {@link
+     * Path#resolve(Path) resolving} the relative path against {@code start}.
+     *
+     * <p> This method works as if invoking it were equivalent to evaluating the
+     * expression:
+     * <blockquote><pre>
+     * walk(start, Integer.MAX_VALUE, options)
+     * </pre></blockquote>
+     * In other words, it visits all levels of the file tree.
+     *
+     * @param   start
+     *          the starting file
+     * @param   options
+     *          options to configure the traversal
+     *
+     * @return  the {@link CloseableStream} of {@link Path}
+     *
+     * @throws  SecurityException
+     *          If the security manager denies access to the starting file.
+     *          In the case of the default provider, the {@link
+     *          SecurityManager#checkRead(String) checkRead} method is invoked
+     *          to check read access to the directory.
+     * @throws  IOException
+     *          if an I/O error is thrown when accessing the starting file.
+     *
+     * @see     #walk(Path, int, FileVisitOption...)
+     * @since   1.8
+     */
+    public static CloseableStream<Path> walk(Path start,
+                                             FileVisitOption... options)
+        throws IOException
+    {
+        return walk(start, Integer.MAX_VALUE, options);
+    }
+
+    /**
+     * Return a {@code CloseableStream} that is lazily populated with {@code
+     * Path} by searching for files in a file tree rooted at a given starting
+     * file.
+     *
+     * <p> This method walks the file tree in exactly the manner specified by
+     * the {@link #walk walk} method. For each file encountered, the given
+     * {@link BiPredicate} is invoked with its {@link Path} and {@link
+     * BasicFileAttributes}. The {@code Path} object is obtained as if by
+     * {@link Path#resolve(Path) resolving} the relative path against {@code
+     * start} and is only included in the returned {@link CloseableStream} if
+     * the {@code BiPredicate} returns true. Compare to calling {@link
+     * java.util.stream.Stream#filter filter} on the {@code Stream}
+     * returned by {@code walk} method, this method may be more efficient by
+     * avoiding redundant retrieval of the {@code BasicFileAttributes}.
+     *
+     * <p> If an {@link IOException} is thrown when accessing the directory
+     * after returned from this method, it is wrapped in an {@link
+     * UncheckedIOException} which will be thrown from the method that caused
+     * the access to take place.
+     *
+     * @param   start
+     *          the starting file
+     * @param   maxDepth
+     *          the maximum number of directory levels to search
+     * @param   matcher
+     *          the function used to decide whether a file should be included
+     *          in the returned stream
+     * @param   options
+     *          options to configure the traversal
+     *
+     * @return  the {@link CloseableStream} of {@link Path}
+     *
+     * @throws  IllegalArgumentException
+     *          if the {@code maxDepth} parameter is negative
+     * @throws  SecurityException
+     *          If the security manager denies access to the starting file.
+     *          In the case of the default provider, the {@link
+     *          SecurityManager#checkRead(String) checkRead} method is invoked
+     *          to check read access to the directory.
+     * @throws  IOException
+     *          if an I/O error is thrown when accessing the starting file.
+     *
+     * @see     #walk(Path, int, FileVisitOption...)
+     * @since   1.8
+     */
+    public static CloseableStream<Path> find(Path start,
+                                             int maxDepth,
+                                             BiPredicate<Path, BasicFileAttributes> matcher,
+                                             FileVisitOption... options)
+        throws IOException
+    {
+        FileTreeIterator iterator = new FileTreeIterator(start, maxDepth, options);
+        return new DelegatingCloseableStream<>(iterator,
+            StreamSupport.stream(Spliterators.spliteratorUnknownSize(iterator, Spliterator.DISTINCT))
+                   .filter(entry -> matcher.test(entry.file(), entry.attributes()))
+                   .map(entry -> entry.file()));
+    }
+
+    /**
+     * Read all lines from a file as a {@code CloseableStream}.  Unlike {@link
+     * #readAllLines(Path, Charset) readAllLines}, this method does not read
+     * all lines into a {@code List}, but instead populates lazily as the stream
+     * is consumed.
+     *
+     * <p> Bytes from the file are decoded into characters using the specified
+     * charset and the same line terminators as specified by {@code
+     * readAllLines} are supported.
+     *
+     * <p> After this method returns, then any subsequent I/O exception that
+     * occurs while reading from the file or when a malformed or unmappable byte
+     * sequence is read, is wrapped in an {@link UncheckedIOException} that will
+     * be thrown form the
+     * {@link java.util.stream.Stream} method that caused the read to take
+     * place. In case an {@code IOException} is thrown when closing the file,
+     * it is also wrapped as an {@code UncheckedIOException}.
+     *
+     * <p> When not using the try-with-resources construct, then stream's
+     * {@link CloseableStream#close close} method should be invoked after
+     * operation is completed so as to free any resources held for the open
+     * file.
+     *
+     * @param   path
+     *          the path to the file
+     * @param   cs
+     *          the charset to use for decoding
+     *
+     * @return  the lines from the file as a {@code CloseableStream}
+     *
+     * @throws  IOException
+     *          if an I/O error occurs opening the file
+     * @throws  SecurityException
+     *          In the case of the default provider, and a security manager is
+     *          installed, the {@link SecurityManager#checkRead(String) checkRead}
+     *          method is invoked to check read access to the file.
+     *
+     * @see     #readAllLines(Path, Charset)
+     * @see     #newBufferedReader(Path, Charset)
+     * @see     java.io.BufferedReader#lines()
+     * @since   1.8
+     */
+    public static CloseableStream<String> lines(Path path, Charset cs)
+        throws IOException
+    {
+        BufferedReader br = Files.newBufferedReader(path, cs);
+        return new DelegatingCloseableStream<>(br, br.lines());
+    }
 }

test/java/nio/file/Files/FaultyFileSystem.java

+/*
+ * Copyright (c) 2013, 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.
+ */
+
+import java.io.IOException;
+import java.net.URI;
+import java.nio.channels.SeekableByteChannel;
+import java.nio.file.AccessMode;
+import java.nio.file.CopyOption;
+import java.nio.file.DirectoryIteratorException;
+import java.nio.file.DirectoryStream;
+import java.nio.file.FileStore;
+import java.nio.file.FileSystem;
+import java.nio.file.FileSystemAlreadyExistsException;
+import java.nio.file.FileSystemNotFoundException;
+import java.nio.file.Files;
+import java.nio.file.LinkOption;
+import java.nio.file.NoSuchFileException;
+import java.nio.file.OpenOption;
+import java.nio.file.Path;
+import java.nio.file.PathMatcher;
+import java.nio.file.WatchService;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.nio.file.attribute.FileAttribute;
+import java.nio.file.attribute.FileAttributeView;
+import java.nio.file.attribute.UserPrincipalLookupService;
+import java.nio.file.spi.FileSystemProvider;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Set;
+import java.util.function.Supplier;
+
+/**
+ * A {@code FileSystem} that helps testing by trigger exception throwing based on filenames.
+ */
+class FaultyFileSystem extends FileSystem {
+    final Path root;
+    final boolean removeRootAfterClose;
+    final FileSystem delegate;
+    boolean isOpen;
+
+    FaultyFileSystem(Path root) throws IOException {
+        if (root == null) {
+            root = Files.createTempDirectory("faultyFS");
+            removeRootAfterClose = true;
+        } else {
+            if (! Files.isDirectory(root)) {
+                throw new IllegalArgumentException("must be a directory.");
+            }
+            removeRootAfterClose = false;
+        }
+        this.root = root;
+        delegate = root.getFileSystem();
+        isOpen = true;
+    }
+
+    private static Path unwrap(Path p) {
+        return PassThroughFileSystem.unwrap(p);
+    }
+
+    Path getRoot() {
+        return new PassThroughFileSystem.PassThroughPath(this, root);
+    }
+
+    @Override
+    public void close() throws IOException {
+        if (isOpen) {
+            if (removeRootAfterClose) {
+                TestUtil.removeAll(root);
+            }
+            isOpen = false;
+        }
+    }
+
+    @Override
+    public FileSystemProvider provider() {
+        return FaultyFSProvider.getInstance();
+    }
+
+    @Override
+    public boolean isOpen() {
+        return isOpen;
+    }
+
+    @Override
+    public boolean isReadOnly() {
+        return delegate.isReadOnly();
+    }
+
+    @Override
+    public String getSeparator() {
+        return delegate.getSeparator();
+    }
+
+    private <T> Iterable<T> SoleIterable(final T element) {
+        return new Iterable<T>() {
+            @Override
+            public Iterator<T> iterator() {
+                return new Iterator<T>() {
+                    private T soleElement = element;
+
+                    @Override
+                    public boolean hasNext() {
+                        return soleElement != null;
+                    }
+
+                    @Override
+                    public T next() {
+                        try {
+                            return soleElement;
+                        } finally {
+                            soleElement = null;
+                        }
+                    }
+                };
+            }
+        };
+    }
+
+    @Override
+    public Iterable<Path> getRootDirectories() {
+        return SoleIterable(getRoot());
+    }
+
+    @Override
+    public Iterable<FileStore> getFileStores() {
+        FileStore store;
+        try {
+            store = Files.getFileStore(root);
+        } catch (IOException ioe) {
+            store = null;
+        }
+        return SoleIterable(store);
+    }
+
+    @Override
+    public Set<String> supportedFileAttributeViews() {
+        // assume that unwrapped objects aren't exposed
+        return delegate.supportedFileAttributeViews();
+    }
+
+    @Override
+    public Path getPath(String first, String... more) {
+        return new PassThroughFileSystem.PassThroughPath(this, delegate.getPath(first, more));
+    }
+
+    @Override
+    public PathMatcher getPathMatcher(String syntaxAndPattern) {
+        final PathMatcher matcher = delegate.getPathMatcher(syntaxAndPattern);
+        return new PathMatcher() {
+            @Override
+            public boolean matches(Path path) {
+                return matcher.matches(unwrap(path));
+            }
+        };
+    }
+
+    @Override
+    public UserPrincipalLookupService getUserPrincipalLookupService() {
+        // assume that unwrapped objects aren't exposed
+        return delegate.getUserPrincipalLookupService();
+    }
+
+    @Override
+    public WatchService newWatchService() throws IOException {
+        // to keep it simple
+        throw new UnsupportedOperationException();
+    }
+
+    static class FaultyException extends IOException {
+        FaultyException() {
+            super("fault triggered.");
+        }
+    }
+
+    static class FaultyFSProvider extends FileSystemProvider {
+        private static final String SCHEME = "faulty";
+        private static volatile FaultyFileSystem delegate;
+        private static FaultyFSProvider INSTANCE = new FaultyFSProvider();
+        private boolean enabled;
+
+        private FaultyFSProvider() {}
+
+        public static FaultyFSProvider getInstance() {
+            return INSTANCE;
+        }
+
+        public void setFaultyMode(boolean enable) {
+            enabled = enable;
+        }
+
+        private void triggerEx(String filename, String... names) throws IOException {
+            if (! enabled) {
+                return;
+            }
+
+            if (filename.equals("SecurityException")) {
+                throw new SecurityException("FaultyFS", new FaultyException());
+            }
+
+            if (filename.equals("IOException")) {
+                throw new FaultyException();
+            }
+
+            for (String name: names) {
+                if (name.equals(filename)) {
+                    throw new FaultyException();
+                }
+            }
+        }
+
+        private void triggerEx(Path path, String... names) throws IOException {
+            triggerEx(path.getFileName().toString(), names);
+        }
+
+        @Override
+        public String getScheme() {
+            return SCHEME;
+        }
+
+        private void checkScheme(URI uri) {
+            if (!uri.getScheme().equalsIgnoreCase(SCHEME))
+                throw new IllegalArgumentException();
+        }
+
+        private void checkUri(URI uri) {
+            checkScheme(uri);
+            if (!uri.getSchemeSpecificPart().equals("///"))
+                throw new IllegalArgumentException();
+        }
+
+        @Override
+        public FileSystem newFileSystem(Path fakeRoot, Map<String,?> env)
+            throws IOException
+        {
+            if (env != null && env.keySet().contains("IOException")) {
+                triggerEx("IOException");
+            }
+
+            synchronized (FaultyFSProvider.class) {
+                if (delegate != null && delegate.isOpen())
+                    throw new FileSystemAlreadyExistsException();
+                FaultyFileSystem result = new FaultyFileSystem(fakeRoot);
+                delegate = result;
+                return result;
+            }
+        }
+
+        @Override
+        public FileSystem newFileSystem(URI uri, Map<String,?> env)
+            throws IOException
+        {
+            if (env != null && env.keySet().contains("IOException")) {
+                triggerEx("IOException");
+            }
+
+            checkUri(uri);
+            synchronized (FaultyFSProvider.class) {
+                if (delegate != null && delegate.isOpen())
+                    throw new FileSystemAlreadyExistsException();
+                FaultyFileSystem result = new FaultyFileSystem(null);
+                delegate = result;
+                return result;
+            }
+        }
+
+        @Override
+        public FileSystem getFileSystem(URI uri) {
+            checkUri(uri);
+            FileSystem result = delegate;
+            if (result == null)
+                throw new FileSystemNotFoundException();
+            return result;
+        }
+
+        @Override
+        public Path getPath(URI uri) {
+            checkScheme(uri);
+            if (delegate == null)
+                throw new FileSystemNotFoundException();
+
+            // only allow absolute path
+            String path = uri.getSchemeSpecificPart();
+            if (! path.startsWith("///")) {
+                throw new IllegalArgumentException();
+            }
+            return new PassThroughFileSystem.PassThroughPath(delegate, delegate.root.resolve(path.substring(3)));
+        }
+
+        @Override
+        public void setAttribute(Path file, String attribute, Object value, LinkOption... options)
+            throws IOException
+        {
+            triggerEx(file, "setAttribute");
+            Files.setAttribute(unwrap(file), attribute, value, options);
+        }
+
+        @Override
+        public Map<String,Object> readAttributes(Path file, String attributes, LinkOption... options)
+            throws IOException
+        {
+            triggerEx(file, "readAttributes");
+            return Files.readAttributes(unwrap(file), attributes, options);
+        }
+
+        @Override
+        public <V extends FileAttributeView> V getFileAttributeView(Path file,
+                                                                    Class<V> type,
+                                                                    LinkOption... options)
+        {
+            return Files.getFileAttributeView(unwrap(file), type, options);
+        }
+
+        @Override
+        public <A extends BasicFileAttributes> A readAttributes(Path file,
+                                                                Class<A> type,
+                                                                LinkOption... options)
+            throws IOException
+        {
+            triggerEx(file, "readAttributes");
+            return Files.readAttributes(unwrap(file), type, options);
+        }
+
+        @Override
+        public void delete(Path file) throws IOException {
+            triggerEx(file, "delete");
+            Files.delete(unwrap(file));
+        }
+
+        @Override
+        public void createSymbolicLink(Path link, Path target, FileAttribute<?>... attrs)
+            throws IOException
+        {
+            triggerEx(target, "createSymbolicLink");
+            Files.createSymbolicLink(unwrap(link), unwrap(target), attrs);
+        }
+
+        @Override
+        public void createLink(Path link, Path existing) throws IOException {
+            triggerEx(existing, "createLink");
+            Files.createLink(unwrap(link), unwrap(existing));
+        }
+
+        @Override
+        public Path readSymbolicLink(Path link) throws IOException {
+            Path target = Files.readSymbolicLink(unwrap(link));
+            triggerEx(target, "readSymbolicLink");
+            return new PassThroughFileSystem.PassThroughPath(delegate, target);
+        }
+
+
+        @Override
+        public void copy(Path source, Path target, CopyOption... options) throws IOException {
+            triggerEx(source, "copy");
+            Files.copy(unwrap(source), unwrap(target), options);
+        }
+
+        @Override
+        public void move(Path source, Path target, CopyOption... options) throws IOException {
+            triggerEx(source, "move");
+            Files.move(unwrap(source), unwrap(target), options);
+        }
+
+        private DirectoryStream<Path> wrap(final DirectoryStream<Path> stream) {
+            return new DirectoryStream<Path>() {
+                @Override
+                public Iterator<Path> iterator() {
+                    final Iterator<Path> itr = stream.iterator();
+                    return new Iterator<Path>() {
+                        private Path next = null;
+                        @Override
+                        public boolean hasNext() {
+                            if (next == null) {
+                                if (itr.hasNext()) {
+                                    next = itr.next();
+                                } else {
+                                    return false;
+                                }
+                            }
+                            if (next != null) {
+                                try {
+                                    triggerEx(next, "DirectoryIteratorException");
+                                } catch (IOException ioe) {
+                                    throw new DirectoryIteratorException(ioe);
+                                } catch (SecurityException se) {
+                                    // ??? Does DS throw SecurityException during iteration?
+                                    next = null;
+                                    return hasNext();
+                                }
+                            }
+                            return (next != null);
+                        }
+                        @Override
+                        public Path next() {
+                            try {
+                                if (next != null || hasNext()) {
+                                    return new PassThroughFileSystem.PassThroughPath(delegate, next);
+                                } else {
+                                    throw new NoSuchElementException();
+                                }
+                            } finally {
+                                next = null;
+                            }
+                        }
+
+                        @Override
+                        public void remove() {
+                            itr.remove();
+                        }
+                    };
+                }
+                @Override
+                public void close() throws IOException {
+                    stream.close();
+                }
+            };
+        }
+
+        @Override
+        public DirectoryStream<Path> newDirectoryStream(Path dir, DirectoryStream.Filter<? super Path> filter)
+            throws IOException
+        {
+            triggerEx(dir, "newDirectoryStream");
+            return wrap(Files.newDirectoryStream(unwrap(dir), filter));
+        }
+
+        @Override
+        public void createDirectory(Path dir, FileAttribute<?>... attrs)
+            throws IOException
+        {
+            triggerEx(dir, "createDirectory");
+            Files.createDirectory(unwrap(dir), attrs);
+        }
+
+        @Override
+        public SeekableByteChannel newByteChannel(Path file,
+                                                  Set<? extends OpenOption> options,
+                                                  FileAttribute<?>... attrs)
+            throws IOException
+        {
+            triggerEx(file, "newByteChannel");
+            return Files.newByteChannel(unwrap(file), options, attrs);
+        }
+
+
+        @Override
+        public boolean isHidden(Path file) throws IOException {
+            triggerEx(file, "isHidden");
+            return Files.isHidden(unwrap(file));
+        }
+
+        @Override
+        public FileStore getFileStore(Path file) throws IOException {
+            triggerEx(file, "getFileStore");
+            return Files.getFileStore(unwrap(file));
+        }
+
+        @Override
+        public boolean isSameFile(Path file, Path other) throws IOException {
+            triggerEx(file, "isSameFile");
+            return Files.isSameFile(unwrap(file), unwrap(other));
+        }
+
+        @Override
+        public void checkAccess(Path file, AccessMode... modes)
+            throws IOException
+        {
+            triggerEx(file, "checkAccess");
+            // hack
+            if (modes.length == 0) {
+                if (Files.exists(unwrap(file)))
+                    return;
+                else
+                    throw new NoSuchFileException(file.toString());
+            }
+            throw new RuntimeException("not implemented yet");
+        }
+    }
+}

test/java/nio/file/Files/PassThroughFileSystem.java

 /*
- * Copyright (c) 2010, 2011, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2010, 2013, 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
@@ -304,7 +304,7 @@ class PassThroughFileSystem extends FileSystem {
         public DirectoryStream<Path> newDirectoryStream(Path dir, DirectoryStream.Filter<? super Path> filter)
             throws IOException
         {
-            return wrap(Files.newDirectoryStream(dir, filter));
+            return wrap(Files.newDirectoryStream(unwrap(dir), filter));
         }
 
         @Override