import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class DownLoadServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String path = "C:/file";
        String fileName = request.getParameter("filename");
        File file = new File(path + "/" + fileName);
        //如果文件存在
        if (file.exists()) {
            //设置响应类型及响应头
            response.setContentType("application/x-msdownload");
            response.addHeader("Content-Disposition", "attachment; filename=\""
                    + fileName + "\"");
            //读取文件
            InputStream inputStream = new FileInputStream(file);
            BufferedInputStream bis = new BufferedInputStream(inputStream);
            byte[] bytes = new byte[1024];
            ServletOutputStream outStream = response.getOutputStream();
            BufferedOutputStream bos = new BufferedOutputStream(outStream);
            int readLength = 0;
            while ((readLength = bis.read(bytes)) != -1) {
                bos.write(bytes, 0, readLength);
            }
            //释放资源
            inputStream.close();
            bis.close();
            bos.flush();
            outStream.close();
            bos.close();
        }
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}