Post on 19-May-2015
Introduction to Programming 2 1
12 Advanced I/O Streams
Introduction to Programming 2 2
Topics General Stream Types
Character and Byte Streams
Input and Output Streams
Node and Filter Streams
The File Class
Reader Classes Reader Methods
Node Reader Classes
Filter Reader Classes
Introduction to Programming 2 3
Topics Writer Classes
Writer Methods
Node Writer Classes
Filter Writer Classes
InputStream Classes InputStream Methods
Node InputStream Classes
Filter InputStream Classes
Introduction to Programming 2 4
Topics OutputStream Classes
OutputStream Methods
Node OutputStream Classes
Filter OutputStream Classes
Serialization The transient Keyword
Serialization: Writing an Object Stream
Deserialization: Reading an Object Stream
Introduction to Programming 2 5
General Stream Types Streams
Abstraction of a file or a device that allows a series of items to be read or written
General Stream Categories Character and Byte Streams
Input and Output Streams
Node and Filter Streams
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Character and Byte Streams Character streams
File or device abstractions for Unicode characters
Superclass of all classes for character streams: The Reader class The Writer class Both classes are abstract
Byte streams For binary data
Root classes for byte streams: The InputStream Class The OutputStream Class Both classes are abstract
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Input and Output Streams Input or source streams
Can read from these streams
Superclasses of all input streams: The InputStream Class The Reader Class
Output or sink streams Can write to these streams
Root classes of all output streams: The OutputStream Class The Writer Class
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Node and Filter Streams Node streams
Contain the basic functionality of reading or writing from a specific location
Types of node streams include files, memory and pipes
Filter streams Layered onto node streams between threads or processes
For additional functionalities
Adding layers to a node stream is called stream chaining
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The File Class Not a stream class
Important since stream classes manipulate File objects
Abstract representation of actual files and directory pathnames
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The File Class: Constructors Has four constructors
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The File Class: Methods
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The File Class: Methods
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The File Class: Example• import java.io.*;
• public class FileInfoClass {
• public static void main(String args[]) {
• String fileName = args[0];
• File fn = new File(fileName);
• System.out.println("Name: " + fn.getName());
• if (!fn.exists()) {
• System.out.println(fileName
• + " does not exists.");
• //continued...
Introduction to Programming 2 14
The File Class: Example• /* Create a temporary directory instead. */
• System.out.println("Creating temp
• directory...");
• fileName = "temp";
• fn = new File(fileName);
• fn.mkdir();
• System.out.println(fileName +
• (fn.exists()? "exists": "does not exist"));
• System.out.println("Deleting temp
• directory...");
• fn.delete();
• //continued...
Introduction to Programming 2 15
The File Class: Example• System.out.println(fileName +
• (fn.exists()? "exists": "does not exist"));
• return;
• } //end of: if (!fn.exists())
• System.out.println(fileName + " is a " +
• (fn.isFile()? "file." :"directory."));
• if (fn.isDirectory()) {
• String content[] = fn.list();
• System.out.println("The content of this
• directory:");
• //continued...
Introduction to Programming 2 16
The File Class: Example• for (int i = 0; i < content.length; i++) {
• System.out.println(content[i]);
• }
• } //end of: if (fn.isDirectory())
• if (!fn.canRead()) {
• System.out.println(fileName
• + " is not readable.");
• return;
• }
• //continued...
Introduction to Programming 2 17
The File Class: Example• System.out.println(fileName + " is " + fn.length()
• + " bytes long.");
• System.out.println(fileName + " is " +
• fn.lastModified() + " bytes long.");
• if (!fn.canWrite()) {
• System.out.println(fileName
• + " is not writable.");
• }
• }
• }
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The Reader Class: Methods
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The Reader Class: Methods
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Node Reader Classes
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Filter Reader Classes
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The Writer Class: Methods
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Node Writer Classes
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Filter Writer Classes
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Basic Reader/Writer Example• import java.io.*;
• class CopyFile {
• void copy(String input, String output) {
• FileReader reader;
• FileWriter writer;
• int data;
• try {
• reader = new FileReader(input);
• writer = new FileWriter(output);
• //continued...
Introduction to Programming 2 26
Basic Reader/Writer Example• while ((data = reader.read()) != -1) {
• writer.write(data);
• }
• reader.close();
• writer.close();
• } catch (IOException ie) {
• ie.printStackTrace();
• }
• }
• //continued...
Introduction to Programming 2 27
Basic Reader/Writer Example• public static void main(String args[]) {
• String inputFile = args[0];
• String outputFile = args[1];
• CopyFile cf = new CopyFile();
• cf.copy(inputFile, outputFile);
• }
• }
Introduction to Programming 2 28
Modified Reader/Writer Example
• import java.io.*;
• class CopyFile {
• void copy(String input, String output) {
• BufferedReader reader;
• BufferedWriter writer;
• String data;
• try {
• reader = new
• BufferedReader(new FileReader(input));
• writer = new
• BufferedWriter(new FileWriter(output));
• //continued...
Introduction to Programming 2 29
Modified Reader/Writer Example
• while ((data = reader.readLine()) != null) {
• writer.write(data, 0, data.length);
• }
• reader.close();
• writer.close();
• } catch (IOException ie) {
• ie.printStackTrace();
• }
• }
• //continued...
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Modified Reader/Writer Example
• public static void main(String args[]) {
• String inputFile = args[0];
• String outputFile = args[1];
• CopyFile cf = new CopyFile();
• cf.copy(inputFile, outputFile);
• }
• }
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The InputStream Class: Methods
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The InputStream Class: Methods
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Node InputStream Classes
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Filter InputStream Classes
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The OutputStream Class: Methods
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Node OutputStream Classes
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Filter OutputStream Classes
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Basic InputStream/ OutputStream Example
• import java.io.*;
• class CopyFile {
• void copy(String input, String output) {
• FileInputStream inputStr;
• FileOutputStream outputStr;
• int data;
• try {
• inputStr = new FileInputStream(input);
• outputStr = new FileOutputStream(output);
• //continued...
Introduction to Programming 2 39
Basic InputStream/ OutputStream Example
• while ((data = inputStr.read()) != -1) {
• outputStr.write(data);
• }
• inputStr.close();
• outputStr.close();
• } catch (IOException ie) {
• ie.printStackTrace();
• }
• }
• //continued...
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Basic InputStream/ OutputStream Example
• public static void main(String args[]) {
• String inputFile = args[0];
• String outputFile = args[1];
• CopyFile cf = new CopyFile();
• cf.copy(inputFile, outputFile);
• }
• }
Introduction to Programming 2 41
Modified InputStream/ OutputStream Example
• import java.io.*;
• class CopyFile {
• void copy(String input) {
• PushbackInputStream inputStr;
• PrintStream outputStr;
• int data;
• try {
• inputStr = new PushbackInputStream(new
• FileInputStream(input));
• outputStr = new PrintStream(System.out);
• //continued...
Introduction to Programming 2 42
Modified InputStream/ OutputStream Example
• while ((data = inputStr.read()) != -1) {
• outputStr.println("read data: " +
• (char) data);
• inputStr.unread(data);
• data = inputStr.read();
• outputStr.println("unread data: " +
• (char) data);
• }
• inputStr.close();
• outputStr.close();
• //continued...
Introduction to Programming 2 43
Modified InputStream/ OutputStream Example
• } catch (IOException ie) {
• ie.printStackTrace();
• }
• }
• public static void main(String args[]) {
• String inputFile = args[0];
• CopyFile cf = new CopyFile();
• cf.copy(inputFile);
• }
• }
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Serialization Definition:
Supported by the Java Virtual Machine (JVM)
Ability to read or write an object to a stream
Process of "flattening" an object
Goal: To save object to some permanent storage or to pass on to another object via the OutputStream class
Writing an object: Its state should be written in a serialized form such that the object
can be reconstructed as it is being read
Persistence Saving an object to some type of permanent storage
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Serialization Streams for serialization
ObjectInputStream For deserializing
ObjectOutputStream For serializing
To allow an object to be serializable: Its class should implement the Serializable interface
Its class should also provide a default constructor or a constructor with no arguments
Serializability is inherited Don't have to implement Serializable on every class Can just implement Serializable once along the class heirarchy
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Non-Serializable Objects When an object is serialized:
Only the object's data are preserved
Methods and constructors are not part of the serialized stream
Some objects are not serializable Because the data they represent constantly changes
Examples: FileInputStream objects Thread objects
A NotSerializableException is thrown if the serialization fails
Introduction to Programming 2 47
The transient Keyword A class containing a non-serializable object can still be
serialized Reference to non-serializable object is marked with the transient
keyword
Example:
• class MyClass implements Serializable {• transient Thread thread;• //try removing transient• int data;• /* some other data */• }
The transient keyword prevents the data from being serialized
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Serialization: Writing an Object Stream
Use the ObjectOutputStream class
Use its writeObject methodpublic final void writeObject(Object obj)
throws IOException
where, obj is the object to be written to the stream
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Serialization: Writing an Object Stream
• import java.io.*;
• public class SerializeBoolean {
• SerializeBoolean() {
• Boolean booleanData = new Boolean("true");
• try {
• FileOutputStream fos = new
• FileOutputStream("boolean.ser");
• ObjectOutputStream oos = new
• ObjectOutputStream(fos);
• oos.writeObject(booleanData);
• oos.close();
• //continued...
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Serialization: Writing an Object Stream
• } catch (IOException ie) {
• ie.printStackTrace();
• }
• }
• public static void main(String args[]) {
• SerializeBoolean sb = new SerializeBoolean();
• }
• }
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Deserialization: Reading an Object Stream
Use the ObjectInputStream class
Use its readObject methodpublic final Object readObject()
throws IOException, ClassNotFoundException
where, obj is the object to be read from the stream
The Object type returned should be typecasted to the appropriate class name before methods on that class can be executed
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Deserialization: Reading an Object Stream
• import java.io.*;
• public class UnserializeBoolean {
• UnserializeBoolean() {
• Boolean booleanData = null;
• try {
• FileInputStream fis = new
• FileInputStream("boolean.ser");
• ObjectInputStream ois = new
• ObjectInputStream(fis);
• booleanData = (Boolean) ois.readObject();
• ois.close();
• //continued...
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Deserialization: Reading an Object Stream
• } catch (Exception e) {
• e.printStackTrace();
• }
• System.out.println("Unserialized Boolean from "
• + "boolean.ser");
• System.out.println("Boolean data: " +
• booleanData);
• System.out.println("Compare data with true: " +
• booleanData.equals(new Boolean("true")));
• }
• //continued...
Introduction to Programming 2 54
Deserialization: Reading an Object Stream
• public static void main(String args[]) {
• UnserializeBoolean usb =
• new UnserializeBoolean();
• }
• }
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Summary General Stream Types
Character and Byte Streams
Input and Output Streams
Node and Filter Streams
The File Class Constructor
File(String pathname) Methods
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Summary Reader Classes
Methods read, close, mark, markSupported, reset
Node Reader Classes FileReader, CharArrayReader, StringReader, PipedReader
Filter Reader Classes BufferedReader, FilterReader, InputStreamReader,
LineNumberReader, PushbackReader
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Summary Writer Classes
Methods write, close, flush
Node Writer Classes FileWriter, CharArrayWriter, StringWriter, PipedWriter
Filter Writer Classes BufferedWriter, FilterWriter, OutputStreamWriter, PrintWriter
Introduction to Programming 2 58
Summary InputStream Classes
Methods read, close, mark, markSupported, reset
Node InputStream Classes FileInputStream, BufferedArrayInputStream, PipedInputStream
Filter InputStream Classes BufferedInputStream, FilterInputStream, ObjectInputStream, DataInputStream, LineNumberInputStream, PushbackInputStream
Introduction to Programming 2 59
Summary OutputStream Classes
Methods write, close, flush
Node OutputStream Classes FileOutputStream, BufferedArrayOutputStream, PipedOutputStream
Filter OutputStream Classes BufferedOutputStream, FilterOutputStream, ObjectOutputStream, DataOutputStream, PrintStream
Introduction to Programming 2 60
Summary Serialization
Definition
The transient Keyword
Serialization: Writing an Object Stream Use the ObjectOutputStream class Use its writeObject method
Deserialization: Reading an Object Stream Use the ObjectInputStream class Use its readObject method