//通过服务端

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.OutputStream;
import java.io.IOException;
import javax.servlet.http.HttpServletResponse;

public void down(String fileId,HttpServletResponse response) {
    	//文件路径存在db中
        String path = "D:/test/1.xlsx";
    	File file = new File(path);
		//创建文件输入流
	    try {
			FileInputStream in = new FileInputStream(file);
		} catch (IOException e) {
			e.printStackTrace();
		}
		//创建输出流
		OutputStream out = null;
		try {
			out = response.getOutputStream();
			response.reset();
                        String fileSuffix = null;
                        if(null != path||path.length!=0){
                            fileSuffix=path.substring(path.lastIndexOf(".")+1);
                        }
                response.setContentType(fileSuffix);
                String fileName = path.substring(path.lastIndexOf("\\")+1);
                response.setHeader("Content-Disposition", "attachment;filename="+fileName);
		} catch (IOException e) {
			e.printStackTrace();
		}
		downloadFile(file, out);
    	
    }

public void downloadFile(File file, OutputStream output){
         FileInputStream fileInputStream = null;
         BufferedInputStream inputStream = null;
	 try {
	      fileInputStream = new FileInputStream(file);
	      inputStream = new BufferedInputStream(fileInputStream);
	      byte[] buffer = new byte[8192];//1024*8
	      int i;
	      while ((i = inputStream.read(buffer)) != -1) {
	          output.write(buffer,0,i);
	       }
	  } catch (IOException e) {
	            e.printStackTrace();
	  } finally {
	       try {
	            if (inputStream != null)
	                inputStream.close();
	            if (fileInputStream != null)
	                fileInputStream.close();
	       }catch (IOException e) {
	                e.printStackTrace();
	       }
	  }

}