java，

java，

查看占用的内存

JAVA虚拟机占用的内存(试图使用的最大内存量): Runtime.getRuntime().maxMemory() 
JAVA虚拟机中的空闲内存量: Runtime.getRuntime().freeMemory() 
JAVA虚拟机中的内存总量: Runtime.getRuntime().totalMemory()

文件读取

		File file = new File("D:/1.txt");
		//FileUtils
		List<String> list = FileUtils. readLines(file, "UTF-8");
		System.out.println(list.get(0));
		
		//BufferedReader
		InputStream in = new FileInputStream(file);
		BufferedReader reader = new BufferedReader(new InputStreamReader(in));
		String str = reader.readLine();
		while(str!=null) {
			System.out.println(str);
			str = reader.readLine();
		}
		reader.close();		
		//InputStream
		in = new FileInputStream(file);
		byte[] b = new byte[1024];
		int len = -1;
		while ((len = in.read(b)) != -1) {
			System.out.println(new String(b, 0, len, "utf-8"));
		}
		in.close();

文件下载

@RequestMapping(value = "/download", method = RequestMethod.POST)
	public ModelAndView download(String url, ModelMap modelMap,
			HttpServletRequest request, 
			HttpServletResponse response)
			throws IOException {
		String filename = url.substring(url.lastIndexOf("/")+1);
		filename = URLEncoder.encode(filename, "UTF-8"); 
        response.reset();  
        response.setHeader("Content-Disposition", "attachment; filename="+filename);  
        response.setContentType("application/octet-stream; charset=utf-8");
        URL u = new URL(url); // 图片地址
        InputStream is = u.openStream();
        // 循环取出流中的数据
        byte[] b = new byte[1024];
        int len;
        try {
            while ((len = is.read(b)) > 0) {
                response.getOutputStream().write(b, 0, len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            is.close();
        }
		return null;
	}

@RequestMapping(value = "/download", method = RequestMethod.GET)
	public void download(String url, ModelMap modelMap, HttpServletRequest request,  HttpServletResponse response)
			throws IOException {
        URL u = new URL(url); // 图片地址
        InputStream is = new BufferedInputStream(u.openStream());
        byte[] buffer = new byte[is.available()];
        is.read(buffer);
        is.close();
        
		String filename = url.substring(url.lastIndexOf("/")+1);
		filename = URLEncoder.encode(filename, "UTF-8"); 
        response.reset();  
        response.setHeader("Content-Disposition", "attachment; filename="+filename);  
        response.setContentType("application/octet-stream; charset=utf-8");
        response.setContentLength(buffer.length);
        response.addHeader("Content-Length", buffer.length +"");
        OutputStream out = new BufferedOutputStream(response.getOutputStream());
        out.write(buffer);
        out.flush();
	}

redirect