InputStream readNBytes(byte[], int, int) in Java

readNBytes(byte[], int, int): This method is available in the java.io.InputStream class of Java.

Syntax:

int java.io.InputStream.readNBytes(byte[] b, int off, int len) throws IOException

This method takes three arguments. This method reads the requested number of bytes from the input stream into the given byte array.

This method blocks until len bytes of input data have been read, the end of the stream is detected, or an exception is thrown. The number of bytes actually read, possibly zero, is returned. This method does not close the input stream.

Note:

1. In the case where the end of the stream is reached before len bytes have been read, then the actual number of bytes read will be returned. When this stream reaches the end of the stream, further invocations of this method will return zero.

2. If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read up to len bytes.

Parameters: Three parameters are required for this method.

b: the byte array into which the data is read.

off: the start offset in b at which the data is written.

len: the maximum number of bytes to read.

Returns: the actual number of bytes read into the buffer.

Throws:

1. IOException - if an I/O error occurs.

2. NullPointerException - if b is null.

3. IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than b.length - off.

Approach 1: When no exception

Java

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

public class InputStreamreadNBytes2 {
    public static void main(String[] args) throws IOException {
        File file = new File("D:\\hello.txt");
        InputStream inputStream = new FileInputStream(file);

        byte b[] = { 'a', 'b', 'c', 'd', 'e', 'f', 'g' };
        int off = 0, len = 5;

        try {
            System.out.println(inputStream.readNBytes(b, off, len));
        } catch (IOException e) {
            System.out.println("IOException occurs");
        } catch (NullPointerException e) {
            System.out.println("NullPointerException occurs");
        }

        catch (IndexOutOfBoundsException e) {
            System.out.println("IndexOutOfBoundsException occurs");
        }

        inputStream.close();
    }
}

Output:

0

Approach 2: IOException

Java

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

public class InputStreamreadNBytes2 {
    public static void main(String[] args) throws IOException {
        File file = new File("D:\\hello.txt");
        InputStream inputStream = new FileInputStream(file);

        byte b[] = { 'a', 'b', 'c', 'd', 'e', 'f', 'g' };
        int off = 0, len = 5;

        inputStream.close();
        try {
            System.out.println(inputStream.readNBytes(b, off, len));
        } catch (IOException e) {
            System.out.println("IOException occurs");
        } catch (NullPointerException e) {
            System.out.println("NullPointerException occurs");
        } catch (IndexOutOfBoundsException e) {
            System.out.println("IndexOutOfBoundsException occurs");
        }

    }
}

Output:

IOException occurs

Approach 3: NullPointerException 

Java

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

public class InputStreamreadNBytes2 {
    public static void main(String[] args) throws IOException {
        File file = new File("D:\\hello.txt");
        InputStream inputStream = new FileInputStream(file);

        byte b[] = null;
        int off = 0, len = 5;

        try {
            System.out.println(inputStream.readNBytes(b, off, len));
        } catch (IOException e) {
            System.out.println("IOException occurs");
        } catch (NullPointerException e) {
            System.out.println("NullPointerException occurs");
        } catch (IndexOutOfBoundsException e) {
            System.out.println("IndexOutOfBoundsException occurs");
        }

        inputStream.close();
    }
}

Output:

NullPointerException occurs

Approach 4: IndexOutOfBoundsException 

Java

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

public class InputStreamreadNBytes2 {
    public static void main(String[] args) throws IOException {
        File file = new File("D:\\hello.txt");
        InputStream inputStream = new FileInputStream(file);

        byte b[] = { 'a', 'b', 'c', 'd', 'e', 'f', 'g' };
        int off = 0, len = 15;

        try {
            System.out.println(inputStream.readNBytes(b, off, len));
        } catch (IOException e) {
            System.out.println("IOException occurs");
        } catch (NullPointerException e) {
            System.out.println("NullPointerException occurs");
        } catch (IndexOutOfBoundsException e) {
            System.out.println("IndexOutOfBoundsException occurs");
        }

        inputStream.close();
    }
}

Output:

IndexOutOfBoundsException occurs

Some other methods of InputStream

available(): This method returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking, which may be 0, or 0 when the end of the stream is detected.

close(): This method closes this input stream and releases any system resources associated with the stream.

mark(int):  This method marks the current position in this input stream.

markSupported(): This method tests if this input stream supports the mark and reset methods.

InputStream.nullInputStream(): This method returns a new InputStream that reads no bytes. The returned stream is initially open.

read(): This method reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255.

read(byte[]): This method reads some number of bytes from the input stream and stores them into the buffer array b.

read(byte[], int, int): his method reads up to len bytes of data from the input stream into an array of bytes.

readAllBytes(): This method reads all remaining bytes from the input stream.

readNBytes(int): This method reads up to a specified number of bytes from the input stream.

reset(): This method repositions this stream to the position at the time the mark method was last called on this input stream.

skip(long):  This method skips over and discards n bytes of data from this input stream.

skipNBytes(long): This method skips over and discards exactly n bytes of data from this input stream.

transferTo(OutputStream): This method reads all bytes from this input stream and writes the bytes to the given output stream in the order that they are read.