File

File file = new File("E:\\java\\io","aaa.txt");

FileOutputStream fileOutputStream = new FileOutputStream(file);

DataOutputStream dataOutputStream = new DataOutputStream(fileOutputStream);
dataOutputStream.writeUTF("联通2311151515");
fileOutputStream.close();
dataOutputStream.close();

DataInputStream dataInputStream = new DataInputStream(new FileInputStream(file));
String s = dataInputStream.readUTF();
System.out.println(s);

PrintWriter

按行读

        BufferedReader br = new BufferedReader(
                new InputStreamReader(
                        new FileInputStream("e:\\javaio\\imooc.txt")));
		/*BufferedWriter bw = new BufferedWriter(
				new OutputStreamWriter(
						new FileOutputStream("e:\\javaio\\imooc3.txt")));*/
        PrintWriter pw = new PrintWriter("e:\\javaio\\imooc4.txt");
        //PrintWriter pw1 = new PrintWriter(outputStream,boolean autoFlush);
        String line;
        while ((line = br.readLine()) != null) {
            System.out.println(line);

            pw.println(line);
            pw.flush();
        }
        br.close();
        //bw.close();
        pw.close();

#BufferedInputStream和BufferedOutputStream 使用缓冲

if(!srcFile.exists()){
			throw new IllegalArgumentException("�ļ�:"+srcFile+"������");
		}
		if(!srcFile.isFile()){
			throw new IllegalArgumentException(srcFile+"�����ļ�");
		}
		BufferedInputStream bis = new BufferedInputStream(
				new FileInputStream(srcFile));
		BufferedOutputStream bos = new BufferedOutputStream(
				new FileOutputStream(destFile));
		int c ;
		while((c = bis.read())!=-1){
			bos.write(c);
			bos.flush();//ˢ�»�����
		}
		bis.close();
		bos.close();

#InputStreamReader和OutputStreamWriter 读取字节流

FileInputStream in = new FileInputStream("e:\\javaio\\imoocutf8.txt");
		InputStreamReader isr = new InputStreamReader(in,"utf-8");
		FileOutputStream out = new FileOutputStream("e:\\javaio\\imoocutf81.txt");
		OutputStreamWriter osw = new OutputStreamWriter(out,"utf-8");
		/*int c ;
		while((c = isr.read())!=-1){
			System.out.print((char)c);
		}*/
		char[] buffer = new char[8*1024];
		int c;
	
		while(( c = isr.read(buffer,0,buffer.length))!=-1){
			String s = new String(buffer,0,c);
			System.out.print(s);
			osw.write(buffer,0,c);
			osw.flush();
		}
		isr.close();
		osw.close();

FileReader FileWriter处理字符串写入文件的类

FileReader fr = new FileReader("e:\\javaio\\imooc.txt");
FileWriter fw = new FileWriter("e:\\javaio\\imooc2.txt");
//FileWriter fw = new FileWriter("e:\\javaio\\imooc2.txt",true);
char[] buffer = new char[2056];
int c ;
while((c = fr.read(buffer,0,buffer.length))!=-1){
	fw.write(buffer,0,c);
	fw.flush();
}
fr.close();
fw.close();

IOUtils

Java程序员的日常—— IOUtils总结

www.cnblogs.com/xing901022/…

文件上传

@RestController
@RequestMapping("/file")
public class FileController {

	private String folder = "/Users/zhailiang/Documents/my/muke/inaction/java/workspace/github/imooc-security-demo/src/main/java/com/imooc/web/controller";

	@PostMapping
	public FileInfo upload(MultipartFile file) throws Exception {

		System.out.println(file.getName());
		System.out.println(file.getOriginalFilename());
		System.out.println(file.getSize());

		File localFile = new File(folder, new Date().getTime() + ".txt");

		file.transferTo(localFile);

		return new FileInfo(localFile.getAbsolutePath());
	}

	@GetMapping("/{id}")
	public void download(@PathVariable String id, HttpServletRequest request, HttpServletResponse response) throws Exception {

		try (InputStream inputStream = new FileInputStream(new File(folder, id + ".txt"));
				OutputStream outputStream = response.getOutputStream();) {
			
			response.setContentType("application/x-download");
			response.addHeader("Content-Disposition", "attachment;filename=test.txt");
			
			IOUtils.copy(inputStream, outputStream);
			outputStream.flush();
		} 

	}

}