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Five ways to maximize Java NIO and NIO.2

Build more responsive Java applications with the New Input/Output APIs

By Cameron Laird, JavaWorld.com, 10/16/12

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Java NIO -- the New Input/Output API package-- was introduced with J2SE 1.4 in 2002. Java NIO's purpose was to improve the programming of I/O-intensive chores on the Java platform. A decade later, many Java programmers still don't know how to make the best use of NIO, and even fewer are aware that Java SE 7 introduced More New Input/Output APIs (NIO.2). In this tutorial you'll find five easy examples that demonstrate the advantages of the NIO and NIO.2 packages in common Java programming scenarios.

The primary contribution of NIO and NIO.2 to the Java platform is to improve performance in one of the core areas of Java application development: input/output processing. Neither package is particularly easy to work with, nor are the New Input/Output APIs required for every Java I/O scenario. Used correctly, though, Java NIO and NIO.2 can slash the time required for some common I/O operations. That's the superpower of NIO and NIO.2, and this article presents five relatively simple ways to leverage it:

  1. Change notifiers (because everybody needs a listener)
  2. Selectors help multiplex
  3. Channels -- promise and reality
  4. Memory mapping -- where it counts
  5. Character encoding and searching

The NIO context

How is it that a 10-year-old enhancement is still the New Input/Output package for Java? The reason is that for many working Java programmers the basic Java I/O operations are more than adequate. Most Java developers don't have to learn NIO for our daily work. Moreover, NIO isn't just a performance package. Instead, it's a heterogeneous collection of facilities related to Java I/O. NIO boosts Java application performance by getting "closer to the metal" of a Java program, meaning that the NIO and NIO.2 APIs expose lower-level-system operating-system (OS) entry points. The tradeoff of NIO is that it simultaneously gives us greater control over I/O and demands that we exercise more care than we would with basic I/O programming. Another aspect of NIO is its attention to application expressivity, which we'll play with in some of the exercises that follow.

Starting out with NIO and NIO.2

Plenty of good references are available for NIO -- see Resources for some selected links. For starting out with NIO and NIO.2, the Java 2 SDK Standard Edition (SE) documentation and Java SE 7 documentation are indispensable. In order to run the examples in this article you will need to be working with JDK 7 or greater.

For many developers the first encounter with NIO might happen during maintenance work: an application has correct functionality but is slow to respond, so someone suggests using NIO to accelerate it. NIO shines when it's used to boost processing performance, but its results will be closely tied to the underlying platform. (Note that NIO is platform dependent.) If you're using NIO for the first time, it will pay you to measure carefully. You might discover that NIO's ability to accelerate application performance depends not only on the OS, but on the specific JVM, host virtualization context, mass storage characteristics, and even data. Measurement can be tricky to generalize, however. Keep this in mind particularly if a mobile deployment is among your targets.

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