nio : Java Glossary

nio

Introduced in Java 1.4, the java.nio (new i/ o) package allows I/O more like that available in other lower level languages like C. You can memory map files. You can read and write blocks of data direct from disk, rather than byte by byte. It deals with the endian problem when you fish the data out of the buffer, not during the read. You can do non-blocking asynchronous I/O. You can lock files or parts of files. Regular I/O is based on stacking the methods you need in a rather verbose and highly assymetric way, in InputStream, Reader, BufferedReader. The nio design is cleaner, simpler and more efficient. You could do all your I/O with nio if you chose. Unfortunately, at this point the File I/O Amanuensis will not generate nio examples, however there some examples in the ByteBuffer entry.

Memory mapped files chew up huge amounts of virtual RAM and real RAM as well for the lookup tables and cached data, so they are not for routine use. They will mainly help random access especially when you have several threads accessing the same file. Don’t just assume they will improve performance. Further, they are limited by the address space. In a 32-bit JVM, you will be lucky if you can even handle a 1GB file window. Test both ways.

Direct buffers help primarily for bulk file operations, slewing through files doing little processing of the data or bulk copying. They are only for when you can allocate a mighty buffer at the start of the program and keep it till completion. Normal GC does not recover the unused direct buffers. Again, test both ways. Also be aware performance ratios will differ on different platforms.

Read and writing individual bytes goes through a lot of indirection, even though what you are trying to achieve is very simple. For Sun’s HotSpot you need to make sure that the method with your inner loop is very small. If it isn’t then the access code won’t be inlined and it will run very slowly.

Books

recommend book⇒Java NIO

paperback

ISBN13:

978-0-596-00288-6

publisher:

O’Reilly

published:

2002-08-15

by:

Ron Hitchens

Covers NIO (new I/O) that arrived with JDK 1.4.

	abe books.co.uk	abe books.ca
	amazon.co.uk	amazon.ca
	abe books.de	chapters.indigo.ca
	amazon.de	abe books.com
	abe books.fr	amazon.com
	amazon.fr	barnes and noble.com
	abe books.it	powells.com
	iberlibro.com	sony e-books
	abe books anz	o’reilly safari

Learning More

Sun’s Javadoc on nio overview : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s JDK Technote Guide on nio examples : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 on your local Windows J: drive.

Sun’s Javadoc on CharSet class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s Javadoc on CharSetDecoder class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s Javadoc on ByteBuffer class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s Javadoc on MappedByteBuffer class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s Javadoc on CharBuffer class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s Javadoc on FileChannel class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s Javadoc on SocketChannel class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

Sun’s Javadoc on Pipe class : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 or in the old JDK 1.5.0_22 on your local Windows J: drive.

argument against using NIO
ByteBuffer
Camperon Purdy’s nio benchmarks
channel
encoding
Files and directories
nio tutorial in PDF
Servlets and NIO
standard File I/O
UnifiedIO

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