目 录
一、FileReader
二、FileWriter
三、文件复制2
四、缓冲流
五、字节缓冲流
1.BufferedInputStream
2.BufferedOutputStream
3.文件复制3
六、字符缓冲流
1.BufferedReader
2.BufferedReader 常见方法
（1）mark()
（2）reset()
3.BufferedWriter
一、FileReader
- 文件字符输入流；
- 是包装流；
- 以字符形式读取文件，一次至少读取一个完整字符；
- 创建 FileReader 对象时，若未指定字符集，则默认采取 UTF-8 解码。
public class FileReaderTest {public static void main(String[] args) {try (FileReader fileReader = new FileReader("D:\\Test.txt")) {char[] chars = new char[6];int readcount = 0;while ((readcount = fileReader.read(chars)) != -1) {System.out.print(new String(chars, 0, readcount) + "->"); // I love-> you!->}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}}
}二、FileWriter
文件字符输出流；
是包装流；
创建 FileWriter 对象时，若未指定字符集，则默认采取 UTF-8 编码。
public class FileWriterTest {public static void main(String[] args) {try (FileWriter fileWriter = new FileWriter("D:\\Test02.txt")) {fileWriter.write("宁溘死以流亡兮，");fileWriter.write("余不忍为此态也。".toCharArray());fileWriter.write("\n");fileWriter.write("噫吁嚱鸷鸟之不群兮,", 3, 7);fileWriter.write("自前世而固然。呜呼".toCharArray(), 0, 7);} catch (IOException e) {throw new RuntimeException(e);}}
}
三、文件复制2
使用文件字符输入输出流进行文件复制，但是只能复制普通文本文件。
public class FileCopyTest {public static void main(String[] args) {try (FileReader fileReader = new FileReader("D:\\VueWorkspace\\cm-web\\vue.config.js");FileWriter fileWriter = new FileWriter("D:\\vue.config.js")) {char[] chars = new char[1024];int readCount = 0;while ((readCount = fileReader.read(chars)) != -1) {fileWriter.write(chars, 0, readCount);}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}}
}
四、缓冲流
- 为提高效率，所以需要减少 IO 开销，因此产生了缓冲流；
- 字节缓冲流：BufferedInputStream、BufferedInputStream；
- 字符缓冲流：BufferedReader、BufferedWriter；
- FileInputStream 和 FileOutputStream 是节点流，而 BufferedInputStream 和 BufferedInputStream 是缓冲流 / 包装流 / 处理流；
- 缓冲流效率高，自带缓冲区，且自我维护。读写大文件时推荐使用。
五、字节缓冲流
1.BufferedInputStream
public class BufferedInputStreamTest {public static void main(String[] args) {BufferedInputStream bufferedInputStream = null;try {bufferedInputStream = new BufferedInputStream(new FileInputStream("D:\\Test.txt"));byte[] bytes = new byte[1024];int readCount = 0;while ((readCount = bufferedInputStream.read(bytes)) != -1) {System.out.println(new String(bytes, 0, readCount)); // I love you!}} catch (IOException e) {throw new RuntimeException(e);} finally {try {if (bufferedInputStream != null) {bufferedInputStream.close(); // 只需要关闭最外层包装流，不需要手动关闭节点流，因为底层会自动关闭}} catch (IOException e) {throw new RuntimeException(e);}}}
}2.BufferedOutputStream
public class BufferedOutputStreamTest {public static void main(String[] args) {BufferedOutputStream bufferedOutputStream = null;try {bufferedOutputStream = new BufferedOutputStream(new FileOutputStream("D:\\Test02.txt"));bufferedOutputStream.write("实迷途其未远，".getBytes());bufferedOutputStream.write("\n".getBytes());bufferedOutputStream.write("觉今是而昨非。".getBytes());} catch (IOException e) {throw new RuntimeException(e);} finally {if (bufferedOutputStream != null) {try {bufferedOutputStream.close();} catch (IOException e) {throw new RuntimeException(e);}}}}
}
3.文件复制3
使用字节缓冲流的方式复制文件，并计算总耗时。
public class FileCopyTest {public static void main(String[] args) {long begin = System.currentTimeMillis();try (BufferedInputStream in = new BufferedInputStream(new FileInputStream("D:\\Xmind\\Xmind.exe"));BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream("D:\\Xmind.exe"))) {byte[] bytes = new byte[1024];int readCount = 0;while ((readCount = in.read(bytes)) != -1) {out.write(bytes, 0, readCount);}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}long end = System.currentTimeMillis();System.out.println("使用缓冲区文件复制完成，耗时：" + (end - begin) + "毫秒"); // 使用缓冲区文件复制完成，耗时：345毫秒}
}
对比不使用缓冲区的文件复制效率。
public class FileCopyTest {public static void main(String[] args) {long begin = System.currentTimeMillis();try (FileInputStream in = new FileInputStream("D:\\Xmind\\Xmind.exe");FileOutputStream out = new FileOutputStream("D:\\Xmind.exe")) {byte[] bytes = new byte[1024];int readCount = 0;while ((readCount = in.read(bytes)) != -1) {out.write(bytes, 0, readCount);}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}long end = System.currentTimeMillis();System.out.println("不使用缓冲区文件复制完成，耗时：" + (end - begin) + "毫秒"); // 不使用缓冲区文件复制完成，耗时：1100毫秒}
}由此可见，效率差距还是比较大的。因此，建议大文件复制使用带有缓冲区的方式。
六、字符缓冲流
1.BufferedReader
public class BufferedReaderTest {public static void main(String[] args) {try (BufferedReader bufferedReader = new BufferedReader(new FileReader("D:\\Test.txt"))) {String line;while ((line = bufferedReader.readLine()) != null) {System.out.println(line); // I love you!}} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}}
}
2.BufferedReader 常见方法
（1）mark()
在当前位置做标记。
（2）reset()
回到上一个标记位置。
两个方法共同使用，作用是实现某段内容重复读取。
public class BufferedReaderTest {public static void main(String[] args) {try (BufferedReader bufferedReader = new BufferedReader(new FileReader("D:\\Test.txt"))) {System.out.println(bufferedReader.read()); // 97System.out.println(bufferedReader.read()); // 98System.out.println(bufferedReader.read()); // 99bufferedReader.mark(2); // 设置标记位置bufferedReader.reset(); // 重置标记位置System.out.println(bufferedReader.read()); // 100System.out.println(bufferedReader.read()); // 101System.out.println(bufferedReader.read()); // 102bufferedReader.reset();System.out.println(bufferedReader.read()); // 100System.out.println(bufferedReader.read()); // 101} catch (FileNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}}
}3.BufferedWriter
public class BufferedWriterTest {public static void main(String[] args) {try (BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("D://Test02.txt"))) {bufferedWriter.write("人生自古谁无死，");bufferedWriter.write("\n");bufferedWriter.write("留取丹心照汗青。".toCharArray());} catch (IOException e) {throw new RuntimeException(e);}}
}
