Java IO

Java IO简介

字节流与字符流

字节流可以处理所有类型的数据，如MP3、图片、文字、视频等。在读取时，读到一个字节就返回一个字节

在Java中对应的类都以“Stream”结尾

字符流仅能处理纯文本数据，如txt文本等。在读取时，读到一个或者多个字节，先查找指定的编码表，然后将查到的字符返回。

在Java中对应的类都以“Reader”或“Writer”结尾

使用字节流读数据：

			FileInputStream fis = new FileInputStream("text.txt");
			byte[] input = new byte[20];
			fis.read(input);
			
//			String inputString = new String(input);
			String inputString = new String(input, "UTF-8");
			System.out.println(inputString);
			
			fis.close();

使用字节流写数据：

			FileOutputStream fos = new FileOutputStream("textw.txt");
			
			String outString = "write 123456写出数据";
			
			byte[] output = outString.getBytes("UTF-8");
			
			fos.write(output);
			fos.close();

使用字节流读写数据：

			FileInputStream fis = new FileInputStream("mao.mp3");
			FileOutputStream fos = new FileOutputStream("mao_new.mp3");
			
			byte[] input = new byte[50];
			while (fis.read(input) != -1) {
				fos.write(input);
			}
			fis.close();
			fos.close();
			System.out.println("done");

使用带有缓冲的字符流读写数据：

			FileInputStream fis = new FileInputStream("mao.mp3");
			BufferedInputStream bis = new BufferedInputStream(fis, 100000);
			FileOutputStream fos = new FileOutputStream("mao_new1.mp3");
			BufferedOutputStream bos = new BufferedOutputStream(fos, 100000);
			
			byte[] input = new byte[1000];
			int count = 0;
			long before = System.currentTimeMillis();
//			System.out.println(System.currentTimeMillis());
			while (bis.read(input) != -1) {
				bos.write(input);
				count++;
			}
			bis.close();
			fis.close();
			bos.close();
			fos.close();
			System.out.println(System.currentTimeMillis() - before + "ms");
			System.out.println(count + "times");

使用字符流读写数据：

//			File file = new File("java.txt");
//			FileInputStream fis = new FileInputStream(file);
			FileInputStream fis = new FileInputStream("java.txt");
			FileOutputStream fos = new FileOutputStream("java_new.txt");
			InputStreamReader isr = new InputStreamReader(fis, "GBK");
			OutputStreamWriter osw = new OutputStreamWriter(fos, "GBK");
			char[] input = new char[100];
			int l = 0;
			while ((l = isr.read(input)) != -1) {
//				System.out.println(input);
//				System.out.println(new String(input, 0, l));
//				String inputString = new String(input, 0, l);
				osw.write(input, 0, l);
			}
			isr.close();
			fis.close();
			osw.close();
			fos.close();
			System.out.println("done");

Ctrl + i 

代码格式化

使用带有缓冲的字符流读写数据：

//			File file = new File("java.txt");
			FileInputStream fis = new FileInputStream("java.txt");
			FileOutputStream fos = new FileOutputStream("java_new_buff.txt");
			InputStreamReader isr = new InputStreamReader(fis, "GBK");
			OutputStreamWriter osw = new OutputStreamWriter(fos, "GBK");
			
			BufferedReader br = new BufferedReader(isr);
			// 使用BufferedWriter会导致换行符丢失
//			BufferedWriter bw = new BufferedWriter(osw);
			PrintWriter pw = new PrintWriter(osw, true); // auto flush
			
			String input; 
			while ((input = br.readLine()) != null) {
//				bw.write(input);
				pw.println(input);
			}
			
//			pw.flush();
			br.close();
//			bw.flush();
//			bw.close();
			pw.close();
			isr.close();
			fis.close();
			osw.close();
			fos.close();
			System.out.println("done");

FileReader与FileWriter：

			FileReader fr = new FileReader("java.txt");
			BufferedReader br = new BufferedReader(fr);
			
			FileWriter fw = new FileWriter("java_new.txt");
			BufferedWriter bw = new BufferedWriter(fw);
			
			String line;
			while ((line = br.readLine()) != null) {
				bw.write(line + "\n");
			}
			
			bw.flush();
			bw.close();
			fw.close();
			br.close();
			fr.close();
			System.out.println("done");