Jedi Slides Intro2 Chapter12 Advanced Io Streams

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

Topics Writer Classes Writer Methods Node Writer Classes Filter Writer Classes InputStream Classes InputStream Methods Node InputStream Classes Filter InputStream Classes

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

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

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

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

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

The File Class Not a stream class Important since stream classes manipulate File objects Abstract representation of actual files and directory pathnames

The File Class: Constructors Has four constructors

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...

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...

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...

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...

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."); } } }

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...

Basic Reader / Writer Example while ((data = reader.read() ) != -1) { writer.write(data); } reader.close(); writer.close(); } catch (IOException ie) { ie.printStackTrace(); } } //continued...

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); } }

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...

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...

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); } }

The InputStream Class: Methods

The OutputStream Class: Methods

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...

Basic InputStream / OutputStream Example while ((data = inputStr.read() ) != -1) { outputStr.write(data); } inputStr.close(); outputStr.close(); } catch (IOException ie) { ie.printStackTrace(); } } //continued...

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); } }

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...

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...

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); } }

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

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

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

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

Serialization: Writing an Object Stream Use the ObjectOutputStream class Use its writeObject method public final void writeObject(Object obj) throws IOException where, obj is the object to be written to the stream

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...

Serialization: Writing an Object Stream } catch (IOException ie) { ie.printStackTrace(); } } public static void main(String args[]) { SerializeBoolean sb = new SerializeBoolean(); } }

Deserialization: Reading an Object Stream Use the ObjectInputStream class Use its readObject method public 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

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...

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...

Deserialization: Reading an Object Stream public static void main(String args[]) { UnserializeBoolean usb = new UnserializeBoolean(); } }

Summary General Stream Types Character and Byte Streams Input and Output Streams Node and Filter Streams The File Class Constructor File(String pathname) Methods

Summary Reader Classes Methods read , close , mark , markSupported , reset Node Reader Classes FileReader , CharArrayReader , StringReader , PipedReader Filter Reader Classes BufferedReader , FilterReader , InputStreamReader , LineNumberReader , PushbackReader

Summary Writer Classes Methods write , close , flush Node Writer Classes FileWriter , CharArrayWriter , StringWriter , PipedWriter Filter Writer Classes BufferedWriter , FilterWriter , OutputStreamWriter , PrintWriter

Summary InputStream Classes Methods read , close , mark , markSupported , reset Node InputStream Classes FileInputStream , BufferedArrayInputStream , PipedInputStream Filter InputStream Classes BufferedInputStream , FilterInputStream , ObjectInputStream , DataInputStream , LineNumberInputStream , PushbackInputStream

Summary OutputStream Classes Methods write , close , flush Node OutputStream Classes FileOutputStream , BufferedArrayOutputStream , PipedOutputStream Filter OutputStream Classes BufferedOutputStream , FilterOutputStream , ObjectOutputStream , DataOutputStream , PrintStream

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

Jedi Slides Intro2 Chapter12 Advanced Io Streams

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Jedi Slides Intro2 Chapter12 Advanced Io Streams