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8283335: Add exists and readAttributesIfExists methods to FileSystemProvider

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Reviewed-by: alanb
This commit is contained in:
Lance Andersen 2022-07-05 19:45:08 +00:00
parent c45d613faa
commit d48694d0f3
13 changed files with 577 additions and 175 deletions
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47
src/java.base/share/classes/java/nio/file/Files.java
View file

@ -80,7 +80,6 @@ import java.util.stream.StreamSupport;
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 final class Files {
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 final class Files {
* 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 final class Files {
* 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 @@ public final class Files {
* 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 @@ public final class Files {
* @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);
}
/**

120
src/java.base/share/classes/java/nio/file/spi/FileSystemProvider.java
View file

@ -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 class FileSystemProvider {
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;
}
}