Java Programming
Mehdi Ebady Manaa
3rd class – Department of Network
College of IT- University of Babylon
Section Two
Reading data from InputStream using files
Table 1: Fundamental Stream Classes
1. Data Within Streams
Java technology supports two types of streams: character and byte.
Input and output of character data is handled (implemented) by
subclass readers and writers.
Input and output of byte data is handled (implemented) by subclass
inputStream and OutputStream
3.1. Byte Streams
The following sections describe the fundamental byte stream
3.1.1 The InputStream Methods
The following three methods provide access to the data from the
input stream:
The three basic read methods are:
int read()
// return an int from input stream, which contains either a byte read
from the stream or a -1
It means The java.io.InputStream.read() method reads the next
byte of the data from the the input stream and returns
int in the range of 0 to 255. If no byte is available
because the end of the stream has been reached, the
returned value is -1.
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Monday, May 30, 2016
Java Programming
Mehdi Ebady Manaa
3rd class – Department of Network
College of IT- University of Babylon
int read(byte[] buffer)
// read the stream into a byte array and return the number of bytes
read
int read(byte[] buffer, int offset, int length)
// read the stream into a byte array and return the number of bytes
read , the two int arguments in the third method
indicate a sub range in the target array that needs to be
filled
Other methods include:
void close()
//it closes the stream
long skip(long n)
//this method discards the specified number of bytes from the stream.
3.1.2 The OutputStream Methods
These methods write to the output of stream:
The three basic write methods are:
void write(int c)//
void write(byte[] buffer)
void write(byte[] buffer, int offset, int length)
• Other methods include:
void close()
void flush()// output stream uses it to force write when the write
accumulate before committing
Java InputStream Example
Java InputStream's are used for reading byte based data, one byte at a
time. Here is a Java InputStream example:
InputStream inputstream = new FileInputStream("c:/text.txt");
int data = inputstream.read();
while(data != -1) {
//do something with data...
// doSomethingWithData(data);
data = inputstream.read();
}
inputstream.close();
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Monday, May 30, 2016
Java Programming
Mehdi Ebady Manaa
3rd class – Department of Network
College of IT- University of Babylon
import java.io.FileInputStream;
import java.io.InputStream;
public class InputStreamDemo {
public static void main(String[] args) throws Exception {
InputStream x = null;
int i; char c;
try{
// new input stream created
x = new FileInputStream("C:\\test.txt");
System.out.println("Characters printed:");
// reads till the end of the stream
while((i=x.read())!=-1)
{
// converts integer to character
c=(char)i;
// prints character
System.out.print(c);
}
}catch(Exception e){
// if any I/O error occurs
e.printStackTrace();
}finally{
// releases system resources associated with this stream
if(x!=null)
x.close();
}
}}
Example 2: create buffer of byte to read from input file stream
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
public class BufferedReaderDemo {
public static void main(String[] args) throws Exception {
InputStream is = null;
InputStreamReader isr = null;
BufferedReader br = null;
try{
// open input stream test.txt for reading purpose.
is = new FileInputStream("c:/test.txt");
// create new input stream reader
isr = new InputStreamReader(is);
// create new buffered reader
br = new BufferedReader(isr);
// creates buffer
char[] cbuf = new char[is.available()];
//is.available to check the next invoking of byte
// reads characters to buffer.
br.read(cbuf);
// for each character in the buffer
for (char c:cbuf)
{
// if char is empty
if(c == (char)0)
{
c='&';
}
// prints characters
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Monday, May 30, 2016
Java Programming
Mehdi Ebady Manaa
3rd class – Department of Network
College of IT- University of Babylon
System.out.print(c);
}catch(Exception e){
e.printStackTrace();
}finally{// releases resources associated with the streams
if(is!=null)
is.close();
if(isr!=null)
isr.close();
if(br!=null)
br.close();
}
}
}
Example2
import
import
import
import
public
java.io.FileInputStream;
java.io.IOException;
java.io.InputStream;
java.util.Arrays;
class InputStreamExample {
private static final String FILE_PATH="c://cc.txt";
public static void main(String[] args){
InputStream fileInputStream = null;
byte[] bytes = new byte[20];
try {
FileInputStream = new FileInputStream(FILE_PATH);
System.out.println("Available bytes of
file:"+fileInputStream.available());
int bytesread = fileInputStream.read(bytes, 0, 15);
System.out.println("Bytes read :"+bytesread);
System.out.println(Arrays.toString(bytes));
} catch (IOException e) {
e.printStackTrace();
}finally{
try {
fileInputStream.close();
} catch (IOException e) {
e.printStackTrace();
}}}}
Of course you can use all the above methods to bridge the byte
stream to a character streams. So let’s see how you can read a text
file,line by line
package com.javacodegeeks.core.io.inputstream;
import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
public class InputStreamExample {
private static final String FILE_PATH="c:/cc.txt";
public static void main(String[] args){
InputStream fileInputStream = null;
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Monday, May 30, 2016
Java Programming
Mehdi Ebady Manaa
3rd class – Department of Network
College of IT- University of Babylon
BufferedReader bufferedReader = null;
try {
fileInputStream = new FileInputStream(FILE_PATH);
bufferedReader = new BufferedReader(new
InputStreamReader(fileInputStream));
String line="";
while( (line = bufferedReader.readLine()) != null ){
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}finally{
try {
bufferedReader.close();
} catch (IOException e) {
e.printStackTrace();
}}}}
Example: read and write in input and output stream
import java.io.*;
public class OutputStreamDemo {
public static void main(String[] args) {
byte[] b = {'h', 'e', 'l', 'l', 'o'};
try {
// create a new output stream
OutputStream os = new FileOutputStream("c:/test1.txt");
// craete a new input stream
InputStream is = new FileInputStream("c:/test1.txt");
// write something
os.write(b);
// read what we wrote
for (int i = 0; i < b.length; i++) {
System.out.print("" + (char) is.read());
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
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