In this example we are going to talk about InputStreamReader Java Class. InputStreamReader is a subclass of Reader. A Reader‘s job is to connect your program to a data source, and fetch data from that source and make them available to your program for manipulation. But its purpose is to bridge the byte stream from that source to a character stream. It automatically encodes the bytes that it reads to a specified character set, like UTF-8.
So, as you can imagine, an InputStreamReader wraps around an InputStream, and “converts” the reading input stream form a byte stream to a character stream. Naturally, InputStreamReader is particularly useful when you want to read a text source, e.g a text file.
1. Obtain an InputStreamReader from a file
Let’s see how you can use an InputStreamReader to read sequences of characters form a text file.
InputStreamReaderExample.java:
package com.javacodegeeks.core.io.bufferedreader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
public class InputStreamReaderExample {
private static final String OUTPUT_FILE = "C:\\Users\\nikos\\Desktop\\TestFiles\\testFile.txt";
public static void main(String[] args) {
char[] chars = new char[100];
try (InputStreamReader inputStreamReader = new InputStreamReader(new FileInputStream(OUTPUT_FILE),"UTF-8")) {
// read 100 characters from the file
inputStreamReader.read(chars);
System.out.println(Arrays.toString(chars));
Arrays.fill(chars,' ') ;
/// read 50 character from the file
// and place them after chars[4] position in the array
inputStreamReader.read(chars,4,50);
System.out.println(Arrays.toString(chars));
} catch (IOException e) {
e.printStackTrace();
}
}
}
Output:
[a, o, s, b, c, o, i, a, c, o, i, a, n, i, s, c, n, a, o, n, c, o, a, n, s, c, n, a, o, s, n, c, o, i, a, n, c, i, o, a, n, s, c, i, a, n, c, i, a, n, s, i, c, n, a, s, i, c, n, a, s, i, o, c, n, s, a, o, i, c, n, o, a, i, s, n, c, i, o, a, n, s, c, i, o, n, a, s, o, i, c, n, i, a, s, n, c, i, a, n]
[ , , , , s, o, i, c, n, a, s, c, a, o, s, c, n, a, o, i, s, n, c, i, o, a, n, c, o, a, n, s, i, c, n, a, s, o, i, c, n, a, o, i, s, n, c, o, i, a, s, n, c, i, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ]
It’s fairly easy to read the whole file by packs of N characters and print them out as Strings.
InputStreamReaderExample.java:
package com.javacodegeeks.core.io.bufferedreader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
public class InputStreamReaderExample {
private static final String OUTPUT_FILE = "C:\\Users\\nikos\\Desktop\\TestFiles\\testFile.txt";
public static void main(String[] args) {
char[] chars = new char[100];
try (InputStreamReader inputStreamReader = new InputStreamReader(new FileInputStream(OUTPUT_FILE),"UTF-8")) {
// read 100 characters from the file
while (inputStreamReader.read(chars) != -1)
System.out.println(new String(chars));
} catch (IOException e) {
e.printStackTrace();
}
}
}
Output:
aosbcoiacoianiscnaoncoanscnaosncoiancioanscianciansicnasicnasiocnsaoicnoaisncioanscionasoicniasncian
soicnascaoscnaoisncioancoansicnasoicnaoisncoiasncioancioasncioasc
aopscmnapsmcamcoampcmasomcaspcasc
aspcmpaosmcpas
apocsmoamcpoamscopasmcpomasopcmasopcmaosmcascpaosmcopamsc
aopscmnapsmcamcoampcmasom
caspcascaspcmpaosmcpas
apocsmoamcpoamscopasmcpomasopcmasopcmaosmcascpaosmcopamsc
aopscmnapsmcamcoa
mpcmasomcaspcascaspcmpaosmcpas
apocsmoamcpoamscopasmcpomasopcmasopcmaosmcascpaosmcopamsc
aopscmnap
smcamcoampcmasomcaspcascaspcmpaosmcpas
apocsmoamcpoamscopasmcpomasopcmasopcmaosmcascpaosmcopamsc
a
opscmnapsmcamcoampcmasomcaspcascaspcmpaosmcpas
apocsmoamcpoamscopasmcpomasopcmasopcmaosmcascpaosmco
pamsc
aopscmnapsmcamcoampcmasomcaspcascaspcmpaosmcpas
apocsmoamcpoamscopasmcpomasopcmasopcmaosmcas
cpaosmcopamsc
...
As you can see in the above example I’ve wrapped an InputStreamReader around a FileInputStream, which of course is an InputStream. This shows that you can use InputStreamReader along with any InputStream class or sub class obtained from a great variety of sources e.g a socket, a pipe , a database or even an in-memory location.
2. Obtain an InputStreamReader from the Standard Input
Let’s see how you can use InputStreamReader to read characters form the console.
InputStreamReaderExample.java:
package com.javacodegeeks.core.io.bufferedreader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
public class InputStreamReaderExample {
private static final String OUTPUT_FILE = "C:\\Users\\nikos\\Desktop\\TestFiles\\testFile.txt";
public static void main(String[] args) {
char[] chars = new char[100];
try (InputStreamReader inputStreamReader = new InputStreamReader(System.in,"UTF-8")) {
System.out.print("Type in some characters :");
inputStreamReader.read(chars);
System.out.println(Arrays.toString(chars));
System.out.println(new String(chars).trim());
} catch (IOException e) {
e.printStackTrace();
}
}
}
Output:
Type in some characters :Java Code Geeks Rock Big Time!
[J, a, v, a, , C, o, d, e, , G, e, e, k, s, , R, o, c, k, , B, i, g, , T, i, m, e, !, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ]
Java Code Geeks Rock Big Time!
3. Obtain an InputStreamReader from in-memory buffer
Let’s see how you can use InputStreamReader to read characters form an in-memory buffer.
InputStreamReaderExample.java:
package com.javacodegeeks.core.io.bufferedreader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
public class InputStreamReaderExample {
private static final String OUTPUT_FILE = "C:\\Users\\nikos\\Desktop\\TestFiles\\testFile.txt";
public static void main(String[] args) {
char[] chars = new char[100];
String content = "Java Code Geeks Rock Big Time!";
try (ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream()) {
byteArrayOutputStream.write(content.getBytes());
try (InputStreamReader inputStreamReader = new InputStreamReader(new ByteArrayInputStream(byteArrayOutputStream.toByteArray()), "UTF-8")) {
inputStreamReader.read(chars);
System.out.println(Arrays.toString(chars));
System.out.println(new String(chars).trim());
} catch (IOException e) {
e.printStackTrace();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
Output:
Type in some characters :[J, a, v, a, , C, o, d, e, , G, e, e, k, s, , R, o, c, k, , B, i, g, , T, i, m, e, !, , , , , , , , , , , , , , , , , , , , , , , , , ]
Java Code Geeks Rock Big Time!
