Java™ I/O, NIO, and NIO.2

Java I/O support is included in the java.io and java.nio packages. Together these packages include the following features:

Input and output through data streams, serialization and the file system.
Charsets, decoders, and encoders, for translating between bytes and Unicode characters.
Access to file, file attributes and file systems.
APIs for building scalable servers using asynchronous or multiplexed, non-blocking I/O.

Tutorials and Programmer's Guides

The Basic I/O section of The Java Tutorial and, in particular, File I/O (featuring NIO.2)
Developing a Custom File System Provider
Zip File System Provider
Troubleshooting Tips

java.io (description) - Supports system input and output, and object serialization. to the file system
java.nio (description) - Defines buffers for bulk memory operations. Buffers may be allocated in direct memory for high performance.
java.nio.channels (description) - Defines channels, an abstraction for devices capable of performing I/O operations; defines selectors for multiplexed, non-blocking I/O
java.nio.channels.spi (description) - Provides implementations for channels
java.nio.file - Defines interfaces and classes to access files and file systems.
java.nio.file.attribute - Defines interfaces and classes for accessing file system attributes.
java.nio.file.spi - Defines classes for creating a file system implementation.
java.nio.charset (description) - Defines charsets, decoders, and encoders, for translating between bytes and Unicode characters
java.nio.charset.spi (description) - Provides implementations for charsets