Java实现自定义字符缓冲区，把给定文件中的内容复制到目标文件中

可以通过Java中的字符缓冲区类BufferedReader和BufferedWriter来实现自定义字符缓冲区，以下是一个示例代码：

import java.io.*;

public class CustomBufferedIO {

    public static void main(String[] args) {
        String sourceFilePath = "source.txt";
        String targetFilePath = "target.txt";
        int bufferSize = 1024; // 设置缓冲区大小为1024字节

        try (CustomBufferedReader reader = new CustomBufferedReader(new FileReader(sourceFilePath), bufferSize);
             CustomBufferedWriter writer = new CustomBufferedWriter(new FileWriter(targetFilePath), bufferSize)) {
            String line;
            while ((line = reader.readLine()) != null) {
                writer.write(line);
                writer.newLine(); // 写入换行符
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class CustomBufferedReader extends Reader {
    private Reader reader;
    private char[] buffer;

    public CustomBufferedReader(Reader reader, int bufferSize) {
        this.reader = reader;
        buffer = new char[bufferSize];
    }

    @Override
    public int read(char[] cbuf, int off, int len) throws IOException {
        int readCount = reader.read(buffer, 0, buffer.length);
        if (readCount == -1) {
            return -1;
        }

        int i = off;
        int j = 0;
        while (j < readCount && i < off + len) {
            cbuf[i++] = buffer[j++];
        }
        return i - off;
    }

    @Override
    public void close() throws IOException {
        reader.close();
    }

    public String readLine() throws IOException {
        StringBuilder sb = new StringBuilder();
        int c;
        while ((c = reader.read()) != -1) {
            if (c == '\n') {
                break;
            } else if (c == '\r') {
                continue;
            }
            sb.append((char) c);
        }
        if (sb.length() == 0) {
            return null;
        } else {
            return sb.toString();
        }
    }
}

class CustomBufferedWriter extends Writer {
    private Writer writer;
    private char[] buffer;

    public CustomBufferedWriter(Writer writer, int bufferSize) {
        this.writer = writer;
        buffer = new char[bufferSize];
    }

    @Override
    public void write(char[] cbuf, int off, int len) throws IOException {
        int i = off;
        int j = 0;
        while (j < len) {
            buffer[j++] = cbuf[i++];
            if (j == buffer.length) {
                writer.write(buffer);
                j = 0;
            }
        }
        if (j > 0) {
            writer.write(buffer, 0, j);
        }
    }

    @Override
    public void flush() throws IOException {
        writer.flush();
    }

    @Override
    public void close() throws IOException {
        writer.close();
    }

    public void newLine() throws IOException {
        writer.write(System.lineSeparator());
    }
}

在上述代码中，我们分别定义了CustomBufferedReader和CustomBufferedWriter两个类来实现自定义字符缓冲区的读写操作。在CustomBufferedReader类中，我们使用了一个char数组来作为缓冲区，实现了read和readLine方法；在CustomBufferedWriter类中，我们也使用了一个char数组来作为缓冲区，实现了write和newLine方法。在使用时，我们只需要创建CustomBufferedReader和CustomBufferedWriter的实例，然后调用其read、readLine、write和newLine等方法即可完成文件的复制。