New I/O (JSR 51)

Robert “Rock” Howard

Chief Technology Officer Tower Technology

New Features

• Scalable Network I/O • High Performance File I/O • Pluggable Characters Sets – Character conversion • Regular Expressions • Features considered but not included: – Formatting and scanning – Improved filesystem interface

New Abstractions

• Channels – Connections for I/O • Buffers – Containers for primitive data • Charsets (decoders, encoders) • Pattern Matchers • Selectors – Selectable channels

Channels

• Defined by interface classes – Reading, writing – Inherit both for bi-directional I/O • Asynchronous Closing and Interruption Defined methods are a grab bag of utilities for buffer manipulation.

Buffers

• Based on primitive types – For int, long, float, double, char, etc.

• On Heap or else managed directly (not GC’d) – Memory mapped files are allowed • Indexes are managed wrt. # of primitives – Big or little endian hidden in implementation – Nice set of operators for manipulating buffers (reading, writing, managing indices, etc.)

Random Notes: New I/O

• Buffer operations return the buffer so that they can be “chained”: – MyIntbuffer.clear().write(17); • Selector allows monitoring of many channels via a single thread • Old I/O unchanged and retained in entirety

Random Notes: JDK 1.4

• The thread stack size can be set via a new Thread constructor • JVMPI and JVMDI (profiling and debugging interfaces) are being replaced – See JSRs for debugging, profiling, monitoring • New “Assert” capability can be enabled – Usage: assert expression ; – Optional Usage: assert expression : error_message ; – Generates AssertionError if triggered – Make sure there are no side effects in assert expression!

Conclusion

The new I/O mechanism is sufficiently powerful and scalable that I expect all major commercial Java frameworks to be rewritten for them within 6 to 12 months.

The APIs are simple enough that you can pick them up in about one day of concentrated effort.