Java基础——IO概述
IO概述
- io:输入和输出
- 输入设备：
- 键盘，鼠标，麦克风
- 输出设备
- 显示器，打印机，音响
- 输入设备：
- 为什么程序需要io
- 做数据存储持久化。
- io流的分类(java.io 包下面的)
- 按流向（输入和输出流）
- 按数据单位（字节流字符流）
- 四大基本流
- 字节输入流
- 字节输出流
- 字符输入流
- 字符输出流
- 不管你是什么流，都需要关闭资源如果不关闭资源，磁盘文件会被占用，不能删除也不能修改
注意：操作IO流
- 输入输出的目标搞明白，程序写出去，输出，程序读进来，输入
- 输入
- read()
- 输出
- write()
- 输入
文件流
字节流
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字节流：
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FileInputStream 文件输入流
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需求：读 my.txt 的文件内容出来
常用方法 public FileInputStream(String name) throws FileNotFoundException { this(name != null ? new File(name) : null); } //通过文件获取输入流对象 public FileInputStream(File file) //通过 byte[] 数组读 public int read(byte b[]) throws IOException { return readBytes(b, 0, b.length); } //关闭资源的方式 public void close() ；//获取文件对象 File file = new File("D:\\javase\\homework\\practice\\day20\\my.txt"); //获取文件输入流对象 FileInputStream in = null; try { in = new FileInputStream(file); int length = -1; // while ((length = in.read()) != -1){ // System.out.println(length); // } byte[] bytes = new byte[1024]; while ((length = in.read(bytes)) != -1){ String s = new String(bytes); System.out.println(s); } } catch (Exception e) { e.printStackTrace(); }finally { try { in.close(); } catch (IOException e) { e.printStackTrace(); } }
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FileOutputStream 文件输出流
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需求：把 sy666 写进刚才读的文件里面
//append 表示是否追加 public FileOutputStream(String name, boolean append) //关闭资源 public void close() //写 public void write(byte b[])//获取文件对象 File file = new File("D:\\javase\\homework\\practice\\day20\\my.txt"); FileOutputStream out = null; try { out = new FileOutputStream(file,true); String sy = "sy666"; byte[] bytes = sy.getBytes(); out.write(bytes); } catch (Exception e) { e.printStackTrace(); }finally { if(out != null){ try { out.close(); } catch (IOException e) { e.printStackTrace(); } } }
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需求：将 sy.txt 文件中的内容，拷贝成一个新文件 new.txt
FileInputStream in = null; FileOutputStream out = null; try { in = new FileInputStream("D:\\javase\\homework\\practice\\day20\\my.txt"); out = new FileOutputStream("D:\\javase\\homework\\practice\\day20\\new.txt"); byte[] buffer = new byte[10]; int length = -1; // in.read 读数据到 buffer while ((length = in.read(buffer)) != -1){ out.write(buffer);//把 buffer 中的数据写出去 } } catch (Exception e) { e.printStackTrace(); } finally { try { if (in != null) { in.close(); } if (out != null) { out.close(); } } catch (IOException e) { e.printStackTrace(); } }
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字符流
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FileReader 输入
FileReader reader = null; try { reader = new FileReader("D:\\javase\\homework\\practice\\day20\\my.txt"); char[] buffer = new char[1024]; int length = -1; while ((length = reader.read(buffer) ) != -1){ String s = String.valueOf(buffer); System.out.println(s); } } catch (Exception e) { e.printStackTrace(); }finally { reader.close(); } -
FileWriter 输出
FileWriter fileWriter = new FileWriter("D:\\javase\\homework\\practice\\day20\\my.txt", true); fileWriter.write("你好"); fileWriter.write("上云"); //关闭资源 fileWriter.close();
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字节流与字符流的选择
- 二进制文件，图片，音频，视频必须使用字节流
- 文本文件（txt）使用字符流
- 不清楚类型，用字节流
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flush(刷新操作)
- 计算机直接访问磁盘文件的时候，比操作内存慢，设置一个缓冲区，写的时候直接先写到内存，达到特定值再写到磁盘
- 使用缓冲区意义：
- 提高cpu的使用率
- 回滚写入的数据
- 操作系统使用 -1 代表磁盘文件结尾的标志
- IO 是最影响程序性能的，缓冲区设置容量的整数倍，可以去有效的提高 io 性能 1024.
try catch 资源自动释放
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语法
try(需要关闭资源的文件写到这里){ }catch(){ } public static void copyFile1(String srcFilePath, String destFilePath) { try (FileInputStream in = new FileInputStream(srcFilePath); FileOutputStream out = new FileOutputStream(destFilePath); ) { byte[] buffer = new byte[10]; int length = -1; // in.read 读数据到 buffer while ((length = in.read(buffer)) != -1) { out.write(buffer);//把 buffer 中的数据写出去 } } catch (Exception e) { e.printStackTrace(); } }
缓冲流
- 缓冲流：其实就是个包装流，目的是起缓冲的作用，提升io 性能
- 字节缓冲流
- BufferedInputStream 字节缓冲输入流
- BufferedOutputStream 字节缓冲输出流
- 字符缓冲流
- BufferedReader 字符缓冲输入流
- BufferedWriter 字符缓冲输出流
使用缓冲流与不使用缓冲流性能的对比
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使用单字节拷贝方式
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使用传统字节流
public static void copy(String srcPath, String destPath) throws IOException { long begin = System.currentTimeMillis(); FileInputStream in = new FileInputStream(srcPath); FileOutputStream out = new FileOutputStream(destPath); int length = -1; while ((length = in.read()) != -1) { out.write(length); } in.close(); out.close(); long end = System.currentTimeMillis(); System.out.println("拷贝耗时：" + (end - begin)); } -
使用 Buffered 缓冲流
public static void copyBuffer(String srcPath, String destPath) throws IOException { long begin = System.currentTimeMillis(); FileInputStream in = new FileInputStream(srcPath); FileOutputStream out = new FileOutputStream(destPath); BufferedInputStream bufferedIn = new BufferedInputStream(in); BufferedOutputStream bufferedOut = new BufferedOutputStream(out); int length = -1; while ((length = bufferedIn.read()) != -1){ bufferedOut.write(length); } bufferedIn.close(); bufferedOut.close(); in.close(); out.close(); long end = System.currentTimeMillis(); System.out.println("buffered 拷贝耗时：" + (end - begin)); }
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读和写外面再加buffer
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使用传统字节流
long begin = System.currentTimeMillis(); FileInputStream in = new FileInputStream(srcPath); FileOutputStream out = new FileOutputStream(destPath); int length = -1; byte[] buffered = new byte[10]; while ((length = in.read(buffered)) != -1) { out.write(buffered,0,length); } in.close(); out.close(); long end = System.currentTimeMillis(); System.out.println("copyBufferedBuffered拷贝耗时：" + (end - begin)); -
使用缓冲流
public static void copyBufferBuffered(String srcPath, String destPath) throws IOException { long begin = System.currentTimeMillis(); FileInputStream in = new FileInputStream(srcPath); FileOutputStream out = new FileOutputStream(destPath); BufferedInputStream bufferedIn = new BufferedInputStream(in); BufferedOutputStream bufferedOut = new BufferedOutputStream(out); byte[] buffer = new byte[10]; int length = -1; while ((length = bufferedIn.read(buffer)) != -1){ bufferedOut.write(buffer,0,length); } bufferedIn.close(); bufferedOut.close(); in.close(); out.close(); long end = System.currentTimeMillis(); System.out.println("buffered buffer 拷贝耗时：" + (end - begin)); } -
总结：使用缓冲流真的快
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.write(buffer,0,length);
}
bufferedIn.close();
bufferedOut.close();
in.close();
out.close();
long end = System.currentTimeMillis();
System.out.println(“buffered buffer 拷贝耗时：” + (end - begin));
}
```
- 总结：使用缓冲流真的快