This is a memo of Java (jdk1.8 or later) file input / output sample program.

1. Read the binary file

1.1. Bulk loading

This is a sample program that reads C: /dk/input.xlsx all at once and outputs it to standard output in hexadecimal. When reading in bulk, you need to be careful about the size so that it does not become Out of memory.

`BinaryFileInputNio.java`


package test.nio;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/**
 *Read a binary file
 */
public class BinaryFileInputNio {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		//The name of the read file
		Path path = Paths.get("C:/dk", "input.xlsx");

		try {
			
			//Bulk reading of binary files
			byte[] data = Files.readAllBytes(path);
			
			//Output the read binary data to standard output in hexadecimal
			for (int i = 0; i < data.length; i++) {
				System.out.printf("%02x ", data[i]);
			}
			System.out.println();

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

1.2. Split reading

This is a sample program that reads C: /dk/input.xlsx in 1024-byte units and outputs it to standard output in hexadecimal.

`BinaryFileInputNioPart.java`


package test.nio;

import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/**
 *Read a binary file
 */
public class BinaryFileInputNioPart {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		//The name of the read file
		Path path = Paths.get("C:/dk", "input.xlsx");

		//Input stream generation
		try (InputStream inst = Files.newInputStream(path)) {

			//Byte array for reading
			byte[] buf = new byte[1024];

			int len = 0;
			//Reading from the input stream (reading a file)
			while ((len = inst.read(buf)) != -1) {

				//Output the read binary data to standard output in hexadecimal
				for (int i = 0; i < len; i++) {
					System.out.printf("%02x ", buf[i]);
				}
				System.out.println();
			}

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

2. Writing a binary file

2.1. Bulk writing

This is a sample program that writes binary data to C: /dk/output.dat at once.

`BinaryFileOutputNio.java`


package test.nio;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/**
 *Write a binary file
 */
public class BinaryFileOutputNio {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		//The name of the write file
		Path path = Paths.get("C:/dk", "output.dat");

		//Binary data
		byte[] data = { (byte)0xe3, (byte)0x83, (byte)0x86, (byte)0xe3, (byte)0x82, (byte)0xad, (byte)0xe3, (byte)0x82, (byte)0xb9, (byte)0xe3, (byte)0x83, (byte)0x88, (byte)0xe3, (byte)0x83, (byte)0x95, (byte)0xe3, (byte)0x82, (byte)0xa1, (byte)0xe3, (byte)0x82, (byte)0xa4, (byte)0xe3, (byte)0x83, (byte)0xab, (byte)0xe5, (byte)0x87, (byte)0xba, (byte)0xe5, (byte)0x8a, (byte)0x9b, (byte)0x30, (byte)0x31, (byte)0x0d, (byte)0x0a, (byte)0xe3, (byte)0x83, (byte)0x86, (byte)0xe3, (byte)0x82, (byte)0xad, (byte)0xe3, (byte)0x82, (byte)0xb9, (byte)0xe3, (byte)0x83, (byte)0x88, (byte)0xe3, (byte)0x83, (byte)0x95, (byte)0xe3, (byte)0x82, (byte)0xa1, (byte)0xe3, (byte)0x82, (byte)0xa4, (byte)0xe3, (byte)0x83, (byte)0xab, (byte)0xe5, (byte)0x87, (byte)0xba, (byte)0xe5, (byte)0x8a, (byte)0x9b, (byte)0x30, (byte)0x32, (byte)0x0d, (byte)0x0a};

		try {
			//Binary data batch write
			Files.write(path, data);

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

2.2. Split writing

This is a sample program that writes binary data to C: /dk/output.dat in parts.

`BinaryFileOutputNioPart.java`


package test.nio;

import java.io.IOException;
import java.io.OutputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/**
 *Write a binary file
 */
public class BinaryFileOutputNioPart {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		//The name of the write file
		Path path = Paths.get("C:/dk", "output.dat");

		//Binary data
		byte[] data1 = { (byte)0xe3, (byte)0x83, (byte)0x86, (byte)0xe3, (byte)0x82, (byte)0xad, (byte)0xe3, (byte)0x82, (byte)0xb9, (byte)0xe3, (byte)0x83, (byte)0x88, (byte)0xe3, (byte)0x83, (byte)0x95, (byte)0xe3, (byte)0x82, (byte)0xa1, (byte)0xe3, (byte)0x82, (byte)0xa4, (byte)0xe3, (byte)0x83, (byte)0xab, (byte)0xe5, (byte)0x87, (byte)0xba, (byte)0xe5, (byte)0x8a, (byte)0x9b, (byte)0x30, (byte)0x31, (byte)0x0d, (byte)0x0a};
		byte[] data2 = { (byte)0xe3, (byte)0x83, (byte)0x86, (byte)0xe3, (byte)0x82, (byte)0xad, (byte)0xe3, (byte)0x82, (byte)0xb9, (byte)0xe3, (byte)0x83, (byte)0x88, (byte)0xe3, (byte)0x83, (byte)0x95, (byte)0xe3, (byte)0x82, (byte)0xa1, (byte)0xe3, (byte)0x82, (byte)0xa4, (byte)0xe3, (byte)0x83, (byte)0xab, (byte)0xe5, (byte)0x87, (byte)0xba, (byte)0xe5, (byte)0x8a, (byte)0x9b, (byte)0x30, (byte)0x32, (byte)0x0d, (byte)0x0a};

		//Binary data writing
		try (OutputStream os = Files.newOutputStream(path)) {
			os.write(data1);
			os.write(data2);

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

3. Read text file

3.1. Bulk reading

This is a sample program that reads C: /dk/input.txt in a batch and outputs it to standard output. When reading in bulk, you need to be careful about the size so that it does not become Out of memory.

`TextFileInputNio.java`


package test.nio;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;

/**
 *Reading a text file
 */
public class TextFileInputNio {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		//The name of the read file
		Path path = Paths.get("C:/dk", "input.txt");

		try {

			//Bulk read text files
			List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);

			//Output the read text file to standard output
			lines.forEach(line -> System.out.println(line));

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

3.2. Split reading (using BufferedReader)

This is a sample program that reads C: /dk/input.txt with BufferedReader and outputs it to standard output.

`TextFileInputNioPart1.java`


package test.nio;

import java.io.BufferedReader;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/**
 *Reading a text file
 */
public class TextFileInputNioPart1 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		//The name of the read file
		Path path = Paths.get("C:/dk", "input.txt");

		//Generate BufferedReader
		try (BufferedReader br = Files.newBufferedReader(path, StandardCharsets.UTF_8)) {

			String msg;

			//Reading from a text file
			while ((msg = br.readLine()) != null) {

				//Output to standard output
				System.out.println(msg);

			}

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

3.3. Split read (using Stream)

This is a sample program that reads C: /dk/input.txt as Stream and outputs it to standard output.

`TextFileInputNioPart2.java`


package test.nio;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.stream.Stream;

/**
 *Reading a text file
 */
public class TextFileInputNioPart2 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		//The name of the read file
		Path path = Paths.get("C:/dk", "input.txt");

		//Stream generation
		try (Stream<String> lines = Files.lines(path, StandardCharsets.UTF_8)) {

			//Output to standard output
			lines.forEach(line -> System.out.println(line));

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

4. Writing a text file

4.1. Writing (using BufferedWriter)

This is a sample program that writes text data to C: /dk/output.txt using BufferedWriter.

`TextFileOutputNio1.java`


package test.nio;

import java.io.BufferedWriter;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/**
 *Writing to a text file
 */
public class TextFileOutputNio1 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		//The name of the write file
		Path path = Paths.get("C:/dk", "output.txt");

		//Generate BufferedWriter
		try (BufferedWriter bw = Files.newBufferedWriter(path, StandardCharsets.UTF_8)) {

			//Write to file
			for (int i= 1; i <= 2; i++) {
				bw.write("Text file output" + String.format("%02d", i));
				bw.newLine();
			}

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

4.2. Writing (using PrintWriter)

This is a sample program that writes text data to C: /dk/output.txt using PrintWriter.

`TextFileOutputNio2.java`


package test.nio;

import java.io.BufferedWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/**
 *Writing to a text file
 */
public class TextFileOutputNio2 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		//The name of the write file
		Path path = Paths.get("C:/dk", "output.txt");

		try (
			//Generate PrintWriter
			BufferedWriter bw = Files.newBufferedWriter(path, StandardCharsets.UTF_8);
			PrintWriter pw = new PrintWriter(bw);
		) {
			//Write to file
			for (int i= 1; i <= 2; i++) {
				pw.println("Text file output" + String.format("%02d", i));
			}

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}

that's all