如何在servlet中读取href参数.地址栏上的

Question

：http://localhost:8080/tryupload/downloadservlet?bookid=15bkbookid=15bk（15bk是我通过servlet上的getString从数据库上的bookid获得的）

然后，下面是我在servlet（而不是jsp）上的显示

out.println("<TD><a href=downloadservlet?bookId=" + rs.getString(1)+ ">Download</A></TD>");

然后它转到downloadservlet.java//，但它不起作用。空白页。

如何阅读此链接中的"boookid"http://localhost:8080/tryupload/downloadservlet?bookid=15bk到我的servlet？并在我的downloadservlet.java上执行？

下载servlet.java

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
                String bookId = request.getParameter("bookId");
        Connection conn = null; // connection to the database
        try (PrintWriter out = response.getWriter()) {
            /* TODO output your page here. You may use following sample code. */
            DriverManager.registerDriver(new com.mysql.jdbc.Driver());
            conn = DriverManager.getConnection(dbURL, dbUser, dbPass);
            // queries the database
            String sql = "SELECT * FROM books WHERE bookId = ?";
            PreparedStatement statement = conn.prepareStatement(sql);
            statement.setString(1, bookId);
            ResultSet result = statement.executeQuery();
            if (result.next()) {
                // gets file name and file blob data
                String fileName = result.getString("BookContent");
                Blob blob = result.getBlob("BookContent");
                InputStream inputStream = blob.getBinaryStream();
                int fileLength = inputStream.available();
                System.out.println("fileLength = " + fileLength);
                ServletContext context = getServletContext();
                // sets MIME type for the file download
                String mimeType = context.getMimeType(fileName);
                if (mimeType == null) {        
                    mimeType = "application/octet-stream";
                }              
                // set content properties and header attributes for the response
                response.setContentType(mimeType);
                response.setContentLength(fileLength);
                String headerKey = "Content-Disposition";
                String headerValue = String.format("attachment; filename="%s"", fileName);
                response.setHeader(headerKey, headerValue);
                // writes the file to the client
                OutputStream outStream = response.getOutputStream();
                byte[] buffer = new byte[BUFFER_SIZE];
                int bytesRead = -1;
                while ((bytesRead = inputStream.read(buffer)) != -1) {
                    outStream.write(buffer, 0, bytesRead);
                }
                inputStream.close();
                outStream.close();             
            } else {
                // no file found
                response.getWriter().print("File not found for the id: " + bookId);  
            }
        } catch (SQLException ex) {
            ex.printStackTrace();
            response.getWriter().print("SQL Error: " + ex.getMessage());
        } catch (IOException ex) {
            ex.printStackTrace();
            response.getWriter().print("IO Error: " + ex.getMessage());
        } finally {
            if (conn != null) {
                // closes the database connection
                try {
                    conn.close();
                } catch (SQLException ex) {
                    ex.printStackTrace();
                }
            }          
        }

    }

Answer 1

使用正确读取参数

request.getParameter("bookid")

然而，当您读取15bk时，您不能直接应用Integer.parseInt，因为它不是整数，如果您需要15bk中的15，则需要额外的解析步骤。

在你上次编辑之后，也是同样的问题-你不能进行

statement.setInt(1, bookid);

bookid不会是int。你需要解析，不确定，但例如，如果你想消除最后2个字符，你可以进行

bookIntId = bookId.substrings(0, bookId.length - 2)

Answer 2

String bookId = request.getParameter("bookid");

如果你的参数值是15bk，那么你的代码行：

int bookid = Integer.parseInt(request.getParameter("bookid"));

将抛出NumberFormatException，因为bk无法转换为整数值。