Working with files and directories in NIO.2

In previous articles I discussed creation (Creating files and directories) and selection (Listing and filtering directory contents) of files and directories. The last logical step to take is to explore what can we do with them and how. This is a part of the library that was redesigned in a big way. Updates in this area include guarantee of atomicity of certain operations, API improvements, performance optimization as well as introduction of proper exception hierarchy that replaced boolean returning methods from prior versions of IO library.

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Listing and filtering directory contents in NIO.2

There hasn’t been much happening in the area of listing directory contents until the release of Java 7. But since NIO.2 introduced a new way to do this it might be worth it to cover this area. One of big pluses of NIO.2 is the ability to use listing and filtering at once in one method call. This provides an elegant solution to most of listing/filtering needs related to work with a file system.

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Creating files and directories in NIO.2

Great number of applications nowadays create files or directories for very wide range of purposes. Whether it is to generate a report, export piece of configuration or simply to store some data it is important to be able to handle these tasks. Creating files and directories is one of the most heavily used functionality while working with a file system. This part of library underwent quite a modernization. Updates in this area include guarantee of atomicity of certain operations, creation of files and directories with preset file attributes, performance optimization as well as introduction of exception hierarchy that replaced boolean returning methods from prior versions of IO library.

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Links in NIO.2

One of the most important features in the NIO.2 library is the introduction of mechanism to work with links directly from your Java code (this was not possible to do without the use of native code in previous IO libraries). Most of the advanced users are already familiar with concept of hard links and symbolic links. Before we start to talk about links lets review some basic characteristics of both types:

Hard link or simply link is a directory entry that links file with name in given file system. Single file can be linked using multiple hard links. Hard link must always have an existing target and this target can only be a file. User does not lose access to a target file by removing a hard link. Hard link provides linked file even after the target file was removed. Hard links are always bound to a single file system.
Symbolic link or soft link is a specific file containing relative or absolute path to a target file. Single file can be linked using multiple symbolic links. Symbolic links do not require an existing target and their target might be file or directory. User does not lose access to a target file by removing a symbolic link. Symbolic link is not influenced by removing of the target file, since its target is not required to exist. These kind of links are called dead links or broken links. Symbolic links are not bound to a single file system.

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File Attributes in NIO.2

One of the biggest problems with pre-NIO.2 libraries was inefficient work with metadata of files and directories. Authors of NIO.2 library introduce concept of file attribute views to address this problem and also to solve couple of other issues that are dependent on this one. These problems included inability to create files with file attributes initialized at the creation time, inability to copy files with file attributes as well as problematic and inefficient way of handling file attributes. This concept was also adapted on file stores so the work with file system with regard to attributes and metadata feels seamless and consistent.

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