Java I/O 스트림은 어떻게 스트림 변환을 수행합니까?

// 将字节流转换为字符流
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

// 将字符流转换为字节流
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));

// 创建一个自定义流转换，将大写字符转换为小写字符
class LowerCaseOutputStream extends FilterOutputStream {

    public LowerCaseOutputStream(OutputStream out) {
        super(out);
    }

    @Override
    public void write(int b) {
        super.write(Character.toLowerCase((char) b));
    }
}

import java.io.*;

public class ConvertToUpperCase {

    public static void main(String[] args) {
        try {
            // 创建一个文件输入流
            FileInputStream inputStream = new FileInputStream("input.txt");
            
            // 将文件输入流转换为字符流
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
            
            // 将字符流转换为大小写转换流
            BufferedReader reader = new BufferedReader(inputStreamReader);
            
            // 创建一个文件输出流
            FileOutputStream outputStream = new FileOutputStream("output.txt");
            
            // 将文件输出流转换为大小写转换流
            OutputStreamWriter outputStreamWriter = new OutputStreamWriter(outputStream);
            
            // 将输入流中的字符读入缓冲区，并将其转换为大写
            String line;
            while ((line = reader.readLine()) != null) {
                outputStreamWriter.write(line.toUpperCase());
            }
            
            // 关闭流
            reader.close();
            outputStreamWriter.close();
            
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}