IO In Java

I/O In Java Parag Shah Adaptive Software Solutions http://www.adaptivesoftware.biz http://www.adaptivelearningonline.net

Agenda
Files
Streams
Serialization
Tokenization

Overview
What should an IO system encompass?
Abstractions for the following
Communicating with various sources and sinks of I/O
Console
Files
Network sockets...
Doing the I/O in multiple ways
Character
Binary
Buffered...
Approach taken by Java for the IO system

Vocabulary
Streams
Buffers
Readers
Writers

Standard IO
Reading from StandardInput (see Echo.java)
System.in (Raw IOStream)
Writing to Standard Output
System.out (PrintStream)
Standard Error
System.err (PrintStream)
Redirecting standard IO [see: Redirecting.java]

A Simple Example
System.out.println();
System is a class
out is a static attribute of system
out is of type PrintStream

A Simple Example contd.
System.in.read();
BufferedReader br = new BufferedInputStream(new InputStreamReader(System.in));
System is a class
in is a static attribute of system
in is of type InputStream
InputStreamReader converts an InputStream to the Reader hierarchy
BufferedReader adds buffering and line reading capabilities to the Reader

Files & Directories
The File class is an abstract represention of file and directory pathnames
It does NOT represent a file
see FileExample.java
RandomAccessFile does represent a file
Can read or write at arbitrary locations

Streams
What are Streams?
Arbitrary data source/destination
Details of the device is abstracted
InputStream
Data input source
Abstract class java.io.InputStream
OutputStream
Data output destination
Abstract class java.io.OutputStream

InputStream
Various sources of data
Array of bytes
String object
File
Pipe

InputStream
See [StreamExample.java]

OutputStream
Data Sinks
ByteArray
File
Pipe

OutputStream
See [StreamExample.java]

FilterInputStream
Used to format/filter data being read from an InputStream
Types of FilterInputStream
DataInputStream
BufferedInputStream
LineNumberInputStream
PushbackInputStream

FilterOutputStream
Used to write formatted/filtered data to an OutputStream
Types of FilterOutputStream
DataOutputStream
PrintStream
BufferedOutputStream

Readers & Writers
Purpose of Readers & Writers
Input/Output Stream are for byte based I/O
Readers for unicode based char I/O
Modifying stream behaviour
FilterReader
FilterWriter (abstract class with no subclasses)

The Reader Hierarchy
The Reader Hierarchy

The Writer Hierarchy
The Writer Hierarchy

IO Best Practices
Best Practice
Use Readers / Writers for character IO
Use Input/OutputStream for byte based IO
For reading/writing data in a portable manner use DataInput(Output)Stream
Use buffering
Always close the streams

Object Serialization - 1
What is serialization
When do we need serialization

Serializing objects
ObjectOutputStream
Deserializing objects
ObjectInputStream
Remember no constructors are called
see [SerializationExample.java]

Controlling serialization
The Serializable interface
The transient keyword
The Externalizable interface

Tokenizing
What are tokens?
StringTokenizer
StreamTokenizer

String Tokenizer
Tokenizes a String
We must define delimiting characters
Throws an Exception if we go beyond the String size.
See [StringTokenizingExample.java]
It is recommended to use the split() method in String
See [StringSplitExample.java]

Stream Tokenizer
Tokenizes an input stream
Parsing process is controlled by a table and flags
Each byte read from the input stream is regarded as a character in the range 'u0000' through 'u00FF'

Stream Tokenizer
The character value is used to look up five possible attributes of the character
White space
Alphabetic
Numeric
String quote
Comment character
Each character can have zero or more of these attributes

Stream Tokenizer
Each tokenizer has four flags :-
Whether line terminators are to be returned as tokens or treated as white space that merely separates tokens.
Whether C-style comments are to be recognized and skipped.
Whether C++-style comments are to be recognized and skipped.
Whether the characters of identifiers are converted to lowercase.

Using Stream Tokenizer
Create an instance of StreamTokenizer
Set up tables and flags
Loop through the stream calling nextToken until a TT_EOF is returned.
See [StreamTokenizingExample.java]

Summary
Streams
Types of Input & Output streams
The decorator design pattern
The need for so many stream classes
Serialization
Tokenizing

Where to Get More Information
Thinking In Java By Bruce Eckel
Sun Java Trail
http://java.sun.com/docs/books/tutorial/essential/io/index.html

IO In Java

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IO In Java

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