1. 经过测试可以复制 txt excel csv exe pdf文件其他格式的没测，估计也没问题

public class Hello {    private static final  String LINE_SEPARATOR = System.getProperty("line.separator");//换行    public static void main(String[] args) throws Exception {        FileInputStream reader = new FileInputStream("d:/毕向东Java基础课堂笔记.pdf");        FileOutputStream writer = new FileOutputStream("e:\\毕向东Java基础课堂笔记.pdf");        int len = 0;        byte[] buffer = new byte[1024*1024];//1MB缓存        while((len = reader.read(buffer))!=-1){ //len = reader.read(buffer) buffer千万不要忘了，否则复制的文件超大            writer.write(buffer ,0 , len);            writer.flush();        }        System.out.println("复制成功");        writer.close();        reader.close();    }}

 2.优化复制文件

public static void main(String[] args) throws Exception {        File src = new File("d:/Evernote_6.1.2.2292.exe");        File des = new File("e:\\NEW_Evernote_6.1.2.2292.exe");        copyFile(src,des);    }    private static void copyFile(File src, File des) throws  Exception{        FileInputStream reader = new FileInputStream(src);        FileOutputStream writer = new FileOutputStream(des);        int len = 0;        byte[] buffer = new byte[1024*1024];//1MB缓存        while((len = reader.read(buffer))!=-1){ //len = reader.read(buffer) buffer千万不要忘了，否则复制的文件超大，陷入死循环            writer.write(buffer ,0 , len);            writer.flush();        }        System.out.println("复制成功");        writer.close();        reader.close();    }

 3.下载文件三要素: contentType, contentLength, setHeader-"Content-Disposition"　　　　

　　

File f = new File("d:/photo_04.jpg");			response.setHeader("Content-Disposition", "attachment; filename="+f.getName());			response.setContentType("image/jpeg");				FileInputStream fis = new FileInputStream(f);			response.setContentLength(fis.available());			byte[] buf = new byte[1024];			int len = 0;			while((len = fis.read(buf))!=-1){				response.getOutputStream().write(buf, 0, len);			}

　　4.优化: 在doGet方法中调用即可!

private static Map
     
       imageContentType = new HashMap
      
       ();	static{        imageContentType.put("jpg", "image/jpeg");        imageContentType.put("jpeg", "image/jpeg");        imageContentType.put("png", "image/png");        imageContentType.put("tif", "image/tiff");        imageContentType.put("tiff", "image/tiff");        imageContentType.put("ico", "image/x-icon");        imageContentType.put("bmp", "image/bmp");        imageContentType.put("gif", "image/gif");	}		public static void writeImgToResponse(File image, HttpServletResponse response) throws Exception{		FileInputStream fis = new FileInputStream(image);		response.setContentLength(fis.available());				String filename = image.getName();		response.setHeader("Content-Disposition", "attachment; filename=" + filename);				String type_key = filename.substring(filename.lastIndexOf(".") + 1).toLowerCase();		response.setContentType(imageContentType.get(type_key));				byte[] buf = new byte[1024*1024];		int len = 0;		while((len = fis.read(buf)) != -1){			response.getOutputStream().write(buf, 0, len);		}		}
      
     

　　5.继续优化:当用到框架的时候,不懂为什么不设置下载头?

public static void writeImgToResponse(File image, HttpServletResponse response) throws Exception {        FileInputStream inputStream = new FileInputStream(image);        int length = inputStream.available();        byte data[] = new byte[length];        response.setContentLength(length);        String fileName = image.getName();        String fileType = fileName.substring(fileName.lastIndexOf(".") + 1).toLowerCase();        response.setContentType(imageContentType.get(fileType));        inputStream.read(data);        OutputStream toClient = response.getOutputStream();        toClient.write(data);        toClient.flush();        IOUtils.closeQuietly(toClient);        IOUtils.closeQuietly(inputStream);    }