How does Java I/O stream perform stream conversion?

Java I/O stream conversion converts one stream to another stream to change the data format. Predefined stream conversion: BufferedReader, BufferedWriter and other classes are provided to convert byte streams and character streams. Custom stream conversion: written using Reader/Writer interface and FilterInputStream/FilterOutputStream class to meet specific needs.

Stream conversion of Java I/O streams

Introduction

Java I /O stream conversion refers to converting one type of stream into another type of stream. This is often necessary to convert data from one format to another. Java provides a variety of predefined stream transformations, and you can also write custom stream transformations using specific converters.

Predefined stream conversion

Java provides several predefined stream conversion classes, including:

• BufferedReader : Convert byte stream to character stream.
• BufferedWriter: Convert character stream to byte stream.
• DataInputStream: Convert a byte stream to a data input stream.
• DataOutputStream: Convert the data output stream to a byte stream.
• ObjectInputStream: Convert the byte stream to an object input stream.
• ObjectOutputStream: Convert the object output stream to a byte stream.

Using predefined stream transformations

Using predefined stream transformations is very simple. Just create the transformation stream using the appropriate constructor and pass the input stream as a parameter. For example:

// 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));

Custom stream transformation

Sometimes, the predefined stream transformations cannot meet specific needs. In this case, you can write a custom stream transformation. To do this, you need to use the Reader or Writer interface and the FilterInputStream or FilterOutputStream class. For example:

// 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));
    }
}

Practical case

The following is an example of reading a text file and converting its contents to uppercase characters:

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();
        }
    }
}

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