demo1.java

package Advances.IOFlow2;

// https://www.youtube.com/watch?v=ITikQNDAYEc&list=PLmOn9nNkQxJH0qBIrtV6otI0Ep4o2q67A&index=599
// https://www.youtube.com/watch?v=JE-Vpvvdzr0&list=PLmOn9nNkQxJH0qBIrtV6otI0Ep4o2q67A&index=600

import java.io.*;
import java.nio.charset.StandardCharsets;

import org.junit.jupiter.api.Test;

/**
 * IOFlow2 demo1 : Transformation flow : -> transform between 字節流 (byte, 8 bits) & 字符流 (char, 16
 * bits)
 *
 * <p>1) Types: (belongs to 字符流 (char, 16 bits)) InputStreamReader : byte input to char input
 * OutputStreamWriter : char output to byte output
 *
 * <p>2) use cases : byte <-> char
 *
 * <p>3) decode : byte, byte array -> char, char array encode : char, char array -> byte, byte array
 */
public class demo1 {

  /**
   * demo 1:
   *
   * <p>1) Exception handling : we should still use try-catch-finally as standard style 2) demo how
   * to use InputStreamReader : byte input -> char input transformation
   */
  @Test
  public void test1() throws IOException {

    FileInputStream fis = new FileInputStream("src/main/java/Advances/IOFlow2/hello.txt");
    InputStreamReader isr = new InputStreamReader(fis); // use system default char setting
    // InputStreamReader isr = new InputStreamReader(fis, "UTF-8"); // use UTF-8 char type
    // explicitly

    char[] cbuf = new char[20];
    int len;
    while ((len = isr.read(cbuf)) != -1) {
      String str = new String(cbuf, 0, len);
      System.out.println(str);
    }
    // close resources
    isr.close();
    fis.close();
  }

  /**
   * demo 2 : InputStreamReader and OutputStreamWriter
   *
   * <p>1) Exception handling : we should still use try-catch-finally as standard style
   */
  @Test
  public void test2() throws IOException {

    // step 1) make doc, flow
    File file1 = new File("src/main/java/Advances/IOFlow2/hello.txt");
    File file2 = new File("src/main/java/Advances/IOFlow2/hello2.txt");

    FileInputStream fis = new FileInputStream(file1);
    FileOutputStream fos = new FileOutputStream(file2);

    InputStreamReader isr = new InputStreamReader(fis, StandardCharsets.UTF_8);
    OutputStreamWriter osw = new OutputStreamWriter(fos, "gbk");

    // step 2) read, write data
    char[] cbuf = new char[20];
    int len;
    while ((len = isr.read(cbuf)) != -1) {
      osw.write(cbuf, 0, len);
    }

    // step 3) close resources
    isr.close();
    osw.close();
    fis.close();
    fos.close();
  }
}