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 GCd) –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.