8283335: Add exists and readAttributesIfExists methods to FileSystemProvider

Reviewed-by: alanb

Author: Lance Andersen

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

@@ -80,7 +80,6 @@
 import jdk.internal.util.ArraysSupport;
 import sun.nio.ch.FileChannelImpl;
 import sun.nio.cs.UTF_8;
-import sun.nio.fs.AbstractFileSystemProvider;
 
 /**
  * This class consists exclusively of static methods that operate on files,
@@ -1594,7 +1593,7 @@ public static long mismatch(Path path, Path path2) throws IOException {
         byte[] buffer1 = new byte[BUFFER_SIZE];
         byte[] buffer2 = new byte[BUFFER_SIZE];
         try (InputStream in1 = Files.newInputStream(path);
-             InputStream in2 = Files.newInputStream(path2);) {
+             InputStream in2 = Files.newInputStream(path2)) {
             long totalRead = 0;
             while (true) {
                 int nRead1 = in1.readNBytes(buffer1, 0, BUFFER_SIZE);
@@ -2310,14 +2309,10 @@ public static boolean isSymbolicLink(Path path) {
      *          method denies read access to the file.
      */
     public static boolean isDirectory(Path path, LinkOption... options) {
-        if (options.length == 0) {
-            FileSystemProvider provider = provider(path);
-            if (provider instanceof AbstractFileSystemProvider)
-                return ((AbstractFileSystemProvider)provider).isDirectory(path);
-        }
-
         try {
-            return readAttributes(path, BasicFileAttributes.class, options).isDirectory();
+            var attrs = provider(path)
+                    .readAttributesIfExists(path, BasicFileAttributes.class, options);
+            return (attrs != null) && attrs.isDirectory();
         } catch (IOException ioe) {
             return false;
         }
@@ -2353,14 +2348,10 @@ public static boolean isDirectory(Path path, LinkOption... options) {
      *          method denies read access to the file.
      */
     public static boolean isRegularFile(Path path, LinkOption... options) {
-        if (options.length == 0) {
-            FileSystemProvider provider = provider(path);
-            if (provider instanceof AbstractFileSystemProvider)
-                return ((AbstractFileSystemProvider)provider).isRegularFile(path);
-        }
-
         try {
-            return readAttributes(path, BasicFileAttributes.class, options).isRegularFile();
+            var attrs = provider(path)
+                    .readAttributesIfExists(path, BasicFileAttributes.class, options);
+            return (attrs != null) && attrs.isRegularFile();
         } catch (IOException ioe) {
             return false;
         }
@@ -2502,7 +2493,7 @@ private static boolean followLinks(LinkOption... options) {
      *          the path to the file to test
      * @param   options
      *          options indicating how symbolic links are handled
-     * .
+     *
      * @return  {@code true} if the file exists; {@code false} if the file does
      *          not exist or its existence cannot be determined.
      *
@@ -2515,27 +2506,7 @@ private static boolean followLinks(LinkOption... options) {
      * @see FileSystemProvider#checkAccess
      */
     public static boolean exists(Path path, LinkOption... options) {
-        if (options.length == 0) {
-            FileSystemProvider provider = provider(path);
-            if (provider instanceof AbstractFileSystemProvider)
-                return ((AbstractFileSystemProvider)provider).exists(path);
-        }
-
-        try {
-            if (followLinks(options)) {
-                provider(path).checkAccess(path);
-            } else {
-                // attempt to read attributes without following links
-                readAttributes(path, BasicFileAttributes.class,
-                               LinkOption.NOFOLLOW_LINKS);
-            }
-            // file exists
-            return true;
-        } catch (IOException x) {
-            // does not exist or unable to determine if file exists
-            return false;
-        }
-
+        return provider(path).exists(path, options);
     }
 
     /**

src/java.base/share/classes/java/nio/file/spi/FileSystemProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2007, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2007, 2022, 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
@@ -1170,4 +1170,122 @@ public abstract Map<String,Object> readAttributes(Path path, String attributes,
     public abstract void setAttribute(Path path, String attribute,
                                       Object value, LinkOption... options)
         throws IOException;
+
+    /**
+     * Tests whether a file exists. This method works in exactly the
+     * manner specified by the {@link Files#exists(Path, LinkOption...)} method.
+     *
+     * @implSpec
+     * The default implementation of this method invokes the
+     * {@link #checkAccess(Path, AccessMode...)} method when symbolic links
+     * are followed. If the option {@link LinkOption#NOFOLLOW_LINKS NOFOLLOW_LINKS}
+     * is present then symbolic links are not followed and the method
+     * {@link #readAttributes(Path, Class, LinkOption...)} is called
+     * to determine whether a file exists.
+     *
+     * @param   path
+     *          the path to the file to test
+     * @param   options
+     *          options indicating how symbolic links are handled
+     *
+     * @return  {@code true} if the file exists; {@code false} if the file does
+     *          not exist or its existence cannot be determined.
+     *
+     * @throws  SecurityException
+     *          In the case of the default provider, the {@link
+     *          SecurityManager#checkRead(String)} is invoked to check
+     *          read access to the file.
+     *
+     * @since 20
+     */
+    public boolean exists(Path path, LinkOption... options) {
+        try {
+            if (followLinks(options)) {
+                this.checkAccess(path);
+            } else {
+                // attempt to read attributes without following links
+                readAttributes(path, BasicFileAttributes.class,  LinkOption.NOFOLLOW_LINKS);
+            }
+            // file exists
+            return true;
+        } catch (IOException x) {
+            // does not exist or unable to determine if file exists
+            return false;
+        }
+    }
+
+    /**
+     * Reads a file's attributes as a bulk operation if it exists.
+     *
+     * <p> The {@code type} parameter is the type of the attributes required
+     * and this method returns an instance of that type if supported. All
+     * implementations support a basic set of file attributes and so invoking
+     * this method with a  {@code type} parameter of {@code
+     * BasicFileAttributes.class} will not throw {@code
+     * UnsupportedOperationException}.
+     *
+     * <p> The {@code options} array may be used to indicate how symbolic links
+     * are handled for the case that the file is a symbolic link. By default,
+     * symbolic links are followed and the file attribute of the final target
+     * of the link is read. If the option {@link LinkOption#NOFOLLOW_LINKS
+     * NOFOLLOW_LINKS} is present then symbolic links are not followed.
+     *
+     * <p> It is implementation specific if all file attributes are read as an
+     * atomic operation with respect to other file system operations.
+     *
+     * @implSpec
+     * The default implementation of this method invokes the
+     * {@link #readAttributes(Path, Class, LinkOption...)} method
+     * to read the file's attributes.
+     *
+     * @param   <A>
+     *          The {@code BasicFileAttributes} type
+     * @param   path
+     *          the path to the file
+     * @param   type
+     *          the {@code Class} of the file attributes required
+     *          to read
+     * @param   options
+     *          options indicating how symbolic links are handled
+     *
+     * @return  the file attributes or null if the file does not exist
+     *
+     * @throws  UnsupportedOperationException
+     *          if an attributes of the given type are not supported
+     * @throws  IOException
+     *          if an I/O error occurs
+     * @throws  SecurityException
+     *          In the case of the default provider, a security manager is
+     *          installed, its {@link SecurityManager#checkRead(String) checkRead}
+     *          method is invoked to check read access to the file. If this
+     *          method is invoked to read security sensitive attributes then the
+     *          security manager may be invoked to check for additional permissions.
+     *
+     * @since 20
+     */
+    public <A extends BasicFileAttributes> A readAttributesIfExists(Path path,
+                                                                    Class<A> type,
+                                                                    LinkOption... options)
+        throws IOException
+    {
+        try {
+            return readAttributes(path, type, options);
+        } catch (NoSuchFileException ignore) {
+            return null;
+        }
+    }
+
+    private static boolean followLinks(LinkOption... options) {
+        boolean followLinks = true;
+        for (LinkOption opt: options) {
+            if (opt == LinkOption.NOFOLLOW_LINKS) {
+                followLinks = false;
+                continue;
+            }
+            if (opt == null)
+                throw new NullPointerException();
+            throw new AssertionError("Should not get here");
+        }
+        return followLinks;
+    }
 }

src/java.base/share/classes/sun/nio/fs/AbstractFileSystemProvider.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2022, 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
@@ -27,7 +27,6 @@
 
 import java.nio.file.Path;
 import java.nio.file.LinkOption;
-import java.nio.file.attribute.BasicFileAttributes;
 import java.nio.file.spi.FileSystemProvider;
 import java.io.IOException;
 import java.util.Map;
@@ -110,51 +109,6 @@ public final boolean deleteIfExists(Path file) throws IOException {
         return implDelete(file, false);
     }
 
-    /**
-     * Tests whether a file is a directory.
-     *
-     * @return  {@code true} if the file is a directory; {@code false} if
-     *          the file does not exist, is not a directory, or it cannot
-     *          be determined if the file is a directory or not.
-     */
-    public boolean isDirectory(Path file) {
-        try {
-            return readAttributes(file, BasicFileAttributes.class).isDirectory();
-        } catch (IOException ioe) {
-            return false;
-        }
-    }
-
-    /**
-     * Tests whether a file is a regular file with opaque content.
-     *
-     * @return  {@code true} if the file is a regular file; {@code false} if
-     *          the file does not exist, is not a regular file, or it
-     *          cannot be determined if the file is a regular file or not.
-     */
-    public boolean isRegularFile(Path file) {
-        try {
-            return readAttributes(file, BasicFileAttributes.class).isRegularFile();
-        } catch (IOException ioe) {
-            return false;
-        }
-    }
-
-    /**
-     * Checks the existence of a file.
-     *
-     * @return  {@code true} if the file exists; {@code false} if the file does
-     *          not exist or its existence cannot be determined.
-     */
-    public boolean exists(Path file) {
-        try {
-            checkAccess(file);
-            return true;
-        } catch (IOException ioe) {
-            return false;
-        }
-    }
-
     /**
      * Returns a path name as bytes for a Unix domain socket.
      * Different encodings may be used for these names on some platforms.

src/java.base/unix/classes/sun/nio/fs/UnixFileAttributes.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2008, 2022, 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
@@ -74,6 +74,19 @@ static UnixFileAttributes get(UnixPath path, boolean followLinks)
         return attrs;
     }
 
+    // get the UnixFileAttributes for a given file. Returns null if the file does not exist.
+    static UnixFileAttributes getIfExists(UnixPath path) throws UnixException {
+        UnixFileAttributes attrs = new UnixFileAttributes();
+        int errno = UnixNativeDispatcher.stat2(path, attrs);
+        if (errno == 0) {
+            return attrs;
+        } else if (errno == UnixConstants.ENOENT) {
+            return null;
+        } else {
+            throw new UnixException(errno);
+        }
+    }
+
     // get the UnixFileAttributes for an open file
     static UnixFileAttributes get(int fd) throws UnixException {
         UnixFileAttributes attrs = new UnixFileAttributes();
@@ -251,16 +264,6 @@ BasicFileAttributes asBasicFileAttributes() {
         return UnixAsBasicFileAttributes.wrap(this);
     }
 
-    // unwrap BasicFileAttributes to get the underlying UnixFileAttributes
-    // object. Returns null is not wrapped.
-    static UnixFileAttributes toUnixFileAttributes(BasicFileAttributes attrs) {
-        if (attrs instanceof UnixFileAttributes)
-            return (UnixFileAttributes)attrs;
-        if (attrs instanceof UnixAsBasicFileAttributes) {
-            return ((UnixAsBasicFileAttributes)attrs).unwrap();
-        }
-        return null;
-    }
 
     // wrap a UnixFileAttributes object as a BasicFileAttributes
     private static class UnixAsBasicFileAttributes implements BasicFileAttributes {
@@ -274,9 +277,6 @@ static UnixAsBasicFileAttributes wrap(UnixFileAttributes attrs) {
             return new UnixAsBasicFileAttributes(attrs);
         }
 
-        UnixFileAttributes unwrap() {
-            return attrs;
-        }
 
         @Override
         public FileTime lastModifiedTime() {