Download 15Streams

Streams
input, output, FILE I/O, tokenization,
serialization and compression
What is a Stream?
• an unformatted sequence of bytes
• There are several stream oriented classed in
the java.io package.
– InputStream – interface
– OutputStream – interface
– FileInputStream implements InputStream
Why would I want a stream?
• To input and output data.
• To perform elementary data processing
• Streaming data is data that flows without
stopping.
• Higher performance
• Binary data processing
What kind of Streams are there?
• Two kinds:
– InputStream (FileInputStream)
– OutputStream (FileOutputStream)
– you need a File instance to
• make a new instance of a FileInputStream or
• a FileOutputStream
Byte Streams
Introducing java.io
Where are streams used?
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File IO
Socket IO
Web-based IO
Concurrent computing
Distributed computing
keyboard and terminal
printer and the scanner
Streams for input and output
• Abstract base classes for input and output functionality.
• Defines basic set of methods.
• Used to get data from files, other objects, etc.
Two base structures:
1.InputStream/OutputStream
Byte streams 8-bit
2.Reader/Writer
Character streams
16-bit UNICODE
Internationalization
Efficiency
Buffer (and not byte) operations
Better locking scheme
Streams and I/O
• basic classes for file IO
– FileInputStream, for reading from a file
– FileOutputStream, for writing to a file
• Example:
Open a file "myfile.txt" for reading
FileInputStream fis = new FileInputStream("myfile.txt");
Open a file "outfile.txt" for writing
FileOutputStream fos = new FileOutputStream ("myfile.txt");
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InputStream methods
• int read()
• int read(byte[] )
• int read(byte[], int,
int)
• void close
• int available()
• skip(long)
OutputStream methods
• void write(int)
• void write(byte[] )
• void write(byte[], int,
int)
• void close()
• void flush()
Basic Stream Classes
• FileInputStream
• FileOutputStream
• DataInputStream
– byte readByte(), long readLong(),
double readDouble()
• DataOutputStream
– writeByte(byte), writeLong(long),
writeDouble(double)
• PipedInputStream - PipedOutputStream
How do I use a FileInputStream?
public static FileInputStream
getFileInputStream(String prompt) {
try {
return new
FileInputStream(getReadFile(prompt));
} catch (IOException e) {
System.out.println("Er:
FileOutputStream in Futil.java");
}
return null;
}
Display File Contents
import java.io.*;
public class FileToOut1 {
public static void main(String args[]) {
try {
FileInputStream infile = new FileInputStream("testfile.txt");
byte buffer[] = new byte[50];
int nBytesRead;
do {
nBytesRead = infile.read(buffer);
System.out.write(buffer, 0, nBytesRead);
} while (nBytesRead == buffer.length);
}
catch (FileNotFoundException e) {
System.err.println("File not found");
}
catch (IOException e) { System.err.println("Read failed"); }
}
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}
copying a file...
public static void
binaryCopyFile(FileInputStream fis,
FileOutputStream fos)
throws IOException {
byte buffer[] = new byte[512];
int count;
while ((count = fis.read(buffer)) > 0)
fos.write(buffer, 0, count);
}
Byte Example (EOF)
import java.io.*;
public class CopyBytes {
public static void main(String[] args)
throws IOException {
File inputFile = new File("farrago.txt");
File outputFile = new File("outagain.txt");
FileInputStream in = new FileInputStream(inputFile);
FileOutputStream out = new FileOutputStream(outputFile);
int c;
while ((c = in.read()) != -1) //EOF condition test
out.write(c);
in.close();
out.close();
}
}
Working with Filter Streams
• Filters data being read from or written to a
stream
• Some streams buffer data, some count data,
others convert data to another form.
– DataInputStream & DataOutputStream
– BufferedInputStream &
BufferedOutputStream
– LineNumberInputStream
– PushbackInputStream (Character based)
– PrintStream (This is an output stream.)
DataInputStream &
DataOutputStream
Conceptually, data looks like this, although in binary form (non-text):
19.99 12
Java T-shirt
9.99
8
Java Mug
The data might have been created with the following:
DataOutputStream out =
new DataOutputStream(new FileOutputStream("invoice1.bin"));
for (int i = 0; i < prices.length; i ++) {
out.writeDouble(prices[i]);
//out.writeChar('\t');
out.writeInt(units[i]);
//out.writeChar('\t');
out.writeChars(descs[i]);
out.writeChar('\n');
}
out.close();
DataInputStream in = new DataInputStream(new
FileInputStream("invoice1.bin"));
// break on EOF
while (true) {
price = in.readDouble();
unit = in.readInt();
desc = new StringBuffer(20);
//end of line (carriage return linefeed)
char lineSep = System.getProperty("line.separator").charAt(0);
char chr;
while (((chr = in.readChar()) != lineSep) && chr != -1) {
desc.append(chr);
}
if (chr == -1) break;
System.out.println("You've ordered " + unit + " units of “ +
desc + " at $" + price);
total = total + unit * price;
}
System.out.println("For a TOTAL of: $" + total);
in.close();
write out the bytes
public static boolean writeBytes(File f, byte
b[]) {
FileOutputStream fos = null;
try {
fos = new FileOutputStream(f);
fos.write(b);
fos.close();
return true;
} catch (IOException e) {
System.out.println("Futil.writeBytes,Could
not open" + f);
return false;
}
How big is that file?
public static int available(File file) {
FileInputStream fis = null;
int sizeInBytes = -1;
try {
fis = new FileInputStream(file);
sizeInBytes = fis.available();
fis.close();
} catch (IOException e) {
System.out.println("Futil:Could not open
file");
}
return sizeInBytes;
}
Filters
•Once a stream (e.g., file) has been opened, we can
attach filters
•Filters make reading/writing more efficient
•Most popular filters:
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For basic types:
•DataInputStream, DataOutputStream
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For objects:
•ObjectInputStream, ObjectOutputStream
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Writing data to a file using Filters
import java.io.*;
public class GenerateData {
public static void main(String args[]) {
try {
FileOutputStream fos = new FileOutputStream("stuff.dat");
DataOutputStream dos = new DataOutputStream(fos);
dos.writeInt(2);
dos.writeDouble(2.7182818284590451);
dos.writeDouble(3.1415926535);
dos.close(); fos.close();
}
catch (FileNotFoundException e) {
System.err.println("File not found");
}
catch (IOException e) {
System.err.println("Read or write failed");
}
}
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}
Reading data from a file using filters
import java.io.*;
public class ReadData {
public static void main(String args[]) {
try {
FileInputStream fis = new FileInputStream("stuff.dat");
DataInputStream dis = new DataInputStream(fis);
int n = dis.readInt();
System.out.println(n);
for( int i = 0; i < n; i++ ) { System.out.println(dis.readDouble());
}
dis.close(); fis.close();
}
catch (FileNotFoundException e) {
System.err.println("File not found");
}
catch (IOException e) { System.err.println("Read or write failed");
}
}
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}
Random-Access Files
• A program can start reading or writing a
random-access file at any place and read or
write any number of bytes at a time.
• “Random-access file” is an abstraction: any
file can be treated as a random-access file.
• You can open a random-access file both for
reading and writing at the same time.
Random Access Files
new RandomAccessFile(“data.txt", "rw");
int skipBytes(int) --Moves the file pointer forward
the specified number of bytes
void seek(long) --Positions the file pointer just before
the specified byte
long getFilePointer() --Returns the current byte
location of the file pointer
The RandomAccessFile class implements both the DataInput and
DataOutput interfaces
Does not extend stream class
No support for Serialized Objects
Random-Access Files (cont’d)
• A binary file containing fixed-length data
records is suitable for random-access
treatment.
• A random-access file may be accompanied by
an “index” (either in the same or a different
file), which tells the address of each record.
• Tape : CD == Stream : Random-access
Serialization
• a way to write instance to a stream
• Anything that implements the interface
serializable can be serialized
• Most java core classes implement
serializable.
• All primitive data types can be serialized
Object serialization
Write objects to a file, instead of writing
primitive types.
Use the ObjectInputStream,
ObjectOutputStream classes, the same way
that filters are used.
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Why do I need serialization?
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Persistence (data storage)
Transmission via a stream
comparison
Distributed computing (CORBA, RMI, etc.)
serialization is an application of streams.
ObjectOutputStream
(Serialization)
FileOutputStream out =
new FileOutputStream("theTime");
ObjectOutputStream s =
new ObjectOutputStream(out);
s.writeObject("Today");
s.writeObject(new Date());
s.flush();
The writeObject method throws a NotSerializableException
if it's given an object that is not serializable. An object is
serializable only if its class implements the Serializable
interface.
ObjectInputStream
(Deserialization)
FileInputStream in =
new FileInputStream("theTime");
ObjectInputStream s =
new ObjectInputStream(in);
String today =
(String)s.readObject();
Date date = (Date)s.readObject();
ObjectInputStream stream implements the DataInput interface
that defines methods for reading primitive data types
How can I use serialization?
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Make an instance of an ObjectOutputStream
ObjectOutputStream resides in java.io.
To read back use ObjectInputStream.
Object o = ois.read();
oos.write(o);
Customer c = (Customer)o; //CNFE?
Write an object to a file
import java.io.*;
import java.util.*;
public class WriteDate {
public WriteDate () {
Date d = new Date();
try {
FileOutputStream f = new FileOutputStream("date.ser");
ObjectOutputStream s = new ObjectOutputStream (f);
s.writeObject (d);
s.close ();
}
catch (IOException e) { e.printStackTrace(); }
public static void main (String args[]) {
new WriteDate ();
}
}
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Read an object from a file
import java.util.*;
public class ReadDate {
public ReadDate () {
Date d = null;
ObjectInputStream s = null;
try { FileInputStream f = new FileInputStream ("date.ser");
s = new ObjectInputStream (f);
} catch (IOException e) { e.printStackTrace(); }
try { d = (Date)s.readObject (); }
catch (ClassNotFoundException e) { e.printStackTrace(); }
catch (InvalidClassException e) { e.printStackTrace(); }
catch (StreamCorruptedException e) { e.printStackTrace(); }
catch (OptionalDataException e) { e.printStackTrace(); }
catch (IOException e) { e.printStackTrace(); }
System.out.println ("Date serialized at: "+ d);
}
public static void main (String args[]) { new ReadDate (); }
}
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How do I control what is saved?
• I need a special java keyword for this!
• transient is a keyword...for example
class Customer implements Serializable {
transient String name = null;
}
java.util.zip Package
CheckedInputStream & CheckedOutputStream
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An input and output stream pair that maintains a checksum as the
data is being read or written.
DeflaterOutputStream & InflaterInputStream
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Compresses or uncompresses the data as it is being read or
written.
GZIPInputStream & GZIPOutputStream
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Reads and writes compressed data in the GZIP format.
ZipInputStream & ZipOutputStream
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Reads and writes compressed data in the ZIP format
Save a gzip file
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public void saveGzDb(final File writeFile) throws IOException {
if (writeFile == null) return;
FileOutputStream fos
= new FileOutputStream(writeFile);
GZIPOutputStream gos
= new GZIPOutputStream(fos);
ObjectOutputStream oos
= new ObjectOutputStream(gos);
oos.writeObject(addressVector);
oos.flush();
oos.close();
gos.finish();
fos.close();
System.out.println("saved to:"+writeFile);
}
Read in the gzip object
• FileInputStream fis
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= new FileInputStream(readFileName);
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GZIPInputStream gis
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= new GZIPInputStream(fis);
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ObjectInputStream ois
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= new ObjectInputStream(gis);
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final Object o = ois.readObject();
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addressVector = (Vector) o;
Playing Audio from a File
• audio is stored in a file format.
• One way to open and play the audio is via
the ULawCodec.
• The ULawCodec resides in the sound
package.
• Run the main and it will open and play an
au file.
Project ideas
• write a java program that will prompt the user for
a directory containing AU files.
• Play all au files contained in the directory or the
subdirectories from the root selected by the users.
• Use the sound.UlawCodec class to help you.
• You can use the web to get multiple au files.
Whats a codec?
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Coder + decoder = codec.
Why do I need a codec?
How many codec do I need?
Can I writing my own codec?
When should I write my own codec?
How does the Ulaw Codec work?
• public UlawCodec() {
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String fileName =
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Futil.getReadFileName(
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"select an au file");
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readAUFile(fileName);
• }
How do you get the bytes from a
file?
• private void
readUlawDataFromAFile(String fileName)
throws IOException {
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FileInputStream fis = new
FileInputStream(fileName);
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ulawData = readData(fis);
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fis.close();
• }
Reading from an input stream
• public static byte[] readData(InputStream is)
throws IOException {
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AudioStream as = new AudioStream(is);
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int length = as.getLength();
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byte b[] = new byte[length];
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as.read(b, 0, length);
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return b;
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}
How do you play the sound?
• public static void playFromFile() {
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UlawCodec ulc = new UlawCodec();
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ulc.play();
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//ulc.writeAUFile();
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How does play work?
• public void play() {
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stop();
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AudioData audioData =
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new AudioData(ulawData);
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audioDataStream = new
AudioDataStream(audioData);
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AudioPlayer.player.start(audioDataStream);
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}
What is audioData?
• a class in package sun.audio;
• public class AudioData {
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AudioFormat format;
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byte[] buffer;
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public AudioData(byte[] bytes) { /* compiled code */ }
AudioData(AudioFormat audioFormat, byte[] bytes) { /*
compiled code */ }
• }
What is an AudioDataStream?
• public class AudioDataStream extends
ByteArrayInputStream {
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AudioData ad;
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public AudioDataStream(AudioData audioData) { /*
compiled code */ }
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AudioData getAudioData() { /* compiled code */ }
• }
What is an AudioPlayer?
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public class AudioPlayer extends Thread {
private AudioDevice devAudio;
private static boolean DEBUG;
public static final AudioPlayer player;
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private static ThreadGroup getAudioThreadGroup() { /* compiled code */ }
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private static AudioPlayer getAudioPlayer() { /* compiled code */ }
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private AudioPlayer() { /* compiled code */ }
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public synchronized void start(InputStream inputStream) { /* compiled code */ }
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public synchronized void stop(InputStream inputStream) { /* compiled code */ }
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public void run() { /* compiled code */ }
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AudioPlayer(sun.audio.AudioPlayer$1 audioPlayer$1) { /* compiled code */ }