JAVA中的IO流

一、流的分类

• 数据类型
  • 字节流：传输类型为字节
  • 字符流：传输类型为字符
• 流向
  • 输入流：读数据
  • 输出流：写数据

    为什么buffer比直接输入输出流快？ 因为直接写每次调用都会触发系统调用，就会导致内核态切换，而缓冲它默认为8k，也就是每8k才会调用一次，速度就会快很多。

二、IO流类图

三、文件读取

public class FileBIO {
    /**
     * 字节流读取文件,需要关闭IO流
     */
    @Test
    public void readByte() {
        File file = new File("e:\\test.log");
        FileInputStream inputStream = null;
        try {
            inputStream = new FileInputStream(file);
            int len;
            List<Byte> list = new ArrayList<>();
            while ((len = inputStream.read()) != -1) {
                list.add((byte) len);
            }
            byte[] bytes = new byte[list.size()];
            for (int i = 0; i < list.size(); i++) {
                bytes[i] = list.get(i);
            }
            System.out.println(new String(bytes, StandardCharsets.UTF_8));
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    /**
     * 字节流读取文件,优雅方式,不用手动关闭流
     */
    @Test
    public void readByteElegance() {
        File file = new File("e:\\610.log");
        try (FileInputStream inputStream = new FileInputStream(file)) {
            long begin = System.currentTimeMillis();
            int len;
            List<Byte> list = new ArrayList<>();
            while ((len = inputStream.read()) != -1) {
                list.add((byte) len);
            }
            byte[] bytes = new byte[list.size()];
            for (int i = 0; i < list.size(); i++) {
                bytes[i] = list.get(i);
            }
            System.out.println(new String(bytes, StandardCharsets.UTF_8));
            System.out.println(System.currentTimeMillis() - begin);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    /**
     * 字节流读取文件,缓冲区读取字节流
     */
    @Test
    public void readByteBuffer() {
        File file = new File("e:\\610.log");
        try (FileInputStream inputStream = new FileInputStream(file)) {
            long begin = System.currentTimeMillis();
            BufferedInputStream bis = new BufferedInputStream(inputStream);
            int len;
            List<Byte> list = new ArrayList<>();
            while ((len = bis.read()) != -1) {
                list.add((byte) len);
            }
            byte[] bytes = new byte[list.size()];
            for (int i = 0; i < list.size(); i++) {
                bytes[i] = list.get(i);
            }
            System.out.println(new String(bytes, StandardCharsets.UTF_8));
            System.out.println(System.currentTimeMillis() - begin);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    /**
     * 字节流读取文件,缓冲区读取字节流,以数组的方式读取
     */
    @Test
    public void readByteBufferArray() {
        File file = new File("e:\\610.log");
        try (FileInputStream inputStream = new FileInputStream(file)) {
            long begin = System.currentTimeMillis();
            BufferedInputStream bis = new BufferedInputStream(inputStream);
            int len;
            byte[] byt = new byte[1024];
            List<Byte> list = new ArrayList<>();
            while ((len = bis.read(byt)) != -1) {
                for (int i = 0; i < len; i++) {
                    list.add(byt[i]);
                }
            }
            byte[] bytes = new byte[list.size()];
            for (int i = 0; i < list.size(); i++) {
                bytes[i] = list.get(i);
            }
            System.out.println(new String(bytes, StandardCharsets.UTF_8));
            System.out.println(System.currentTimeMillis() - begin);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    /**
     * 字符读取文件
     */
    @Test
    public void readChar() {
        File file = new File("e:\\610.log");
        try (FileInputStream inputStream = new FileInputStream(file)) {
            long begin = System.currentTimeMillis();
            InputStreamReader isr = new InputStreamReader(inputStream, 
                                                          StandardCharsets.UTF_8);
            int len = 0;
            StringBuilder builder = new StringBuilder();
            while ((len = isr.read()) != -1) {
                builder.append((char) len);
            }
            System.out.println(builder.toString());
            System.out.println(System.currentTimeMillis() - begin);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    /**
     * 字符读取文件,通过缓冲流读取
     */
    @Test
    public void readCharBuffer() {
        File file = new File("e:\\test.log");
        try (FileInputStream inputStream = new FileInputStream(file)) {
            long begin = System.currentTimeMillis();
            BufferedReader br = new BufferedReader(
                new InputStreamReader(inputStream,
                                      StandardCharsets.UTF_8));
            String len;
            StringBuilder builder = new StringBuilder();
            while ((len = br.readLine()) != null) {
                //一行行读取的时候换行符就没有了，需要自己添加
                builder.append(len).append("\n");
            }
            builder.deleteCharAt(builder.length() - 1);
            System.out.println(builder.toString());
            System.out.println(System.currentTimeMillis() - begin);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}