Legacy File I/O Code

Interoperability With Legacy Code

Prior to the Java SE 7 release, the java.io.File class was the mechanism used for file I/O, but it had several drawbacks.

• Many methods didn't throw exceptions when they failed, so it was impossible to obtain a useful error message. For example, if a file deletion failed, the program would receive a "delete fail" but wouldn't know if it was because the file didn't exist, the user didn't have permissions, or there was some other problem.
• The rename method didn't work consistently across platforms.
• There was no real support for symbolic links.
• More support for metadata was desired, such as file permissions, file owner, and other security attributes.
• Accessing file metadata was inefficient.
• Many of the File methods didn't scale. Requesting a large directory listing over a server could result in a hang. Large directories could also cause memory resource problems, resulting in a denial of service.
• It was not possible to write reliable code that could recursively walk a file tree and respond appropriately if there were circular symbolic links.

Perhaps you have legacy code that uses java.io.File and would like to take advantage of the java.nio.file.Path functionality with minimal impact to your code.

The java.io.File class provides the toPath method, which converts an old style File instance to a java.nio.file.Path instance, as follows:

Path input = file.toPath();

You can then take advantage of the rich feature set available to the Path class.

For example, assume you had some code that deleted a file:

file.delete();

You could modify this code to use the Files.delete method, as follows:

Path fp = file.toPath();
Files.delete(fp);

Conversely, the Path.toFile method constructs a java.io.File object for a Path object.

Mapping java.io.File Functionality to java.nio.file

Because the Java implementation of file I/O has been completely re-architected in the Java SE 7 release, you cannot swap one method for another method. If you want to use the rich functionality offered by the java.nio.file package, your easiest solution is to use the File.toPath method as suggested in the previous section. However, if you don't want to use that approach or it is not sufficient for your needs, you must rewrite your file I/O code.

There is no one-to-one correspondence between the two APIs, but the following table gives you a general idea of what functionality in the java.io.File API maps to in the java.nio.file API and tells you where you can obtain more information.

java.io.File Functionality	java.nio.file Functionality	Tutorial Coverage
java.io.File	java.nio.file.Path	The Path Class
java.io.RandomAccessFile	The SeekableByteChannel functionality.	Random Access Files
File.canRead, canWrite, canExecute	Files.isReadable, Files.isWritable, and Files.isExecutable. On UNIX file systems, the File Attributes package is used to check the nine file permissions.	Checking a File or Directory Managing Metadata
File.isDirectory(), File.isFile(), and File.length()	Files.isDirectory(Path, LinkOption...), Files.isRegularFile(Path, LinkOption...), and Files.size(Path)	Managing Metadata
File.lastModified() and File.setLastModified(long)	Files.getLastModifiedTime(Path, LinkOption...) and Files.setLastMOdifiedTime(Path, FileTime)	Managing Metadata
The File methods that set various attributes: setExecutable, setReadable, setReadOnly, setWritable	These methods are replaced by the Files method setAttribute(Path, String, Object, LinkOption...).	Managing Metadata
new File(parent, "newfile")	parent.resolve("newfile")	Path Operations
File.renameTo	Files.move	Moving a File or Directory
File.delete	Files.delete	Deleting a File or Directory
File.createNewFile	Files.createFile	Creating Files
File.deleteOnExit	Replaced by the DELETE_ON_CLOSE option specified in the createFile method.	Creating Files
File.createTempFile	Files.createTempFile(Path, String, FileAttributes<?>), Files.createTempFile(Path, String, String, FileAttributes<?>)	Creating Files Creating and Writing a File by Using Stream I/O Reading and Writing Files by Using Channel I/O
File.exists	Files.exists and Files.notExists	Verifying the Existence of a File or Directory
File.compareTo and equals	Path.compareTo and equals	Comparing Two Paths
File.getAbsolutePath and getAbsoluteFile	Path.toAbsolutePath	Converting a Path
File.getCanonicalPath and getCanonicalFile	Path.toRealPath or normalize	Converting a Path (toRealPath) Removing Redundancies From a Path (normalize)
File.toURI	Path.toURI	Converting a Path
File.isHidden	Files.isHidden	Retrieving Information About the Path
File.list and listFiles	Path.newDirectoryStream	Listing a Directory's Contents
File.mkdir and mkdirs	Path.createDirectory	Creating a Directory
File.listRoots	FileSystem.getRootDirectories	Listing a File System's Root Directories
File.getTotalSpace, File.getFreeSpace, File.getUsableSpace	FileStore.getTotalSpace, FileStore.getUnallocatedSpace, FileStore.getUsableSpace, FileStore.getTotalSpace	File Store Attributes