Question

我有一个从数据库生成的表。该表格将以表格形式附上。以下是浏览器的结果：

http://i.imgur.com/NLZzgwP.png（低代表问题）

下面是JSP / JSTL代码：

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/sql" prefix="sql" %>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Issues</title>
<style type="text/css">
table {
border-collapse: collapse;
}
table, th, td {
border: 1px solid black;
}
td {
padding: 10px;
}
</style>
</head>
<body>
<sql:setDataSource
var="myDS"
driver="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/pdfdb"
user="user" password="*******"
/>
<sql:query var="listIssues" dataSource="${myDS}">
 SELECT BookId from Book;
</sql:query>

    <form method="get" action="fileDownload">
        <div align="center">
            <table>
                <caption>List of Issues</caption>
                    <tr>
                        <th>Magazine Issue #</th>
                        <th>Download</th>
                    </tr>
                    <c:forEach var="issue" items="${listIssues.rows}">
                    <tr>
                        <td><c:out value="${issue.BookId}" /></td>
                        <td><input name='<c:out value="${issue.BookId}" />' type="submit" value="Download"></td>        
                    </tr>
                    </c:forEach>
            </table>
        </div>
    </form>
</body>
</html>

现在，我想要的是下载按钮与id / Issue编号链接，该ID与按钮位于同一行，这样，当用户点击下载按钮时，它会传递id /杂志向网址发出号码告诉浏览器用户想要下载点击该按钮的相应杂志发行号。下面是我用来实现这个的servlet：

package com.mypackage.fileDownload;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;



/**
* Servlet implementation class FileDownloadServlet
 */
@WebServlet("/fileDownload")
public class FileDownloadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

//size of byte buffer to send file
private static final int BUFFER_SIZE = 4096;

//database connection settings
private String dbUrl = "jdbc:mysql://localhost:3306/pdfdb";
private String dbUser = "user";
private String dbPass = "******";

/**
 * @see HttpServlet#doGet(HttpServletRequesrequest,HttpServletResponse response)
 */
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //get upload id from URL's parameters
    String uploadId = request.getParameter("name");

    Connection con = null; //connects to the database

    try {
        //connects to the database
        Class.forName("com.mysql.jdbc.Driver");
        con = DriverManager.getConnection(dbUrl, dbUser, dbPass);

        //queries the database
        String sql = "SELECT * FROM Book WHERE BookId = ?";
        PreparedStatement pstmt = con.prepareStatement(sql);
        pstmt.setString(1, uploadId);

        ResultSet result = pstmt.executeQuery();
        if(result.next()) {
            //gets file name and file blob data
            String fileId = result.getString("BookId");
            Blob blob = result.getBlob("BookContent");
            InputStream inputStream = blob.getBinaryStream();
            int fileLength = inputStream.available();

            System.out.println("File length = " + fileLength);
            ServletContext context = getServletContext();

            //Sets MIME type for the file download
            String mimeType = context.getMimeType(fileId);
            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\"", fileId);

            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: " + uploadId);
        }
    } catch(SQLException ex) {
        ex.printStackTrace();
        response.getWriter().print("SQL Error: " + ex.getMessage());
    } catch(IOException ex) {
        ex.printStackTrace();
        response.getWriter().print("IO Error: " + ex.getMessage());
    } catch(ClassNotFoundException ex) {
        ex.printStackTrace();
        response.getWriter().print("Class Missing Error: " + ex.getMessage());
    }
        finally {
        if(con != null) {
            //closes the database connection 
            try {
                con.close();
            } catch(SQLException ex) {
                ex.printStackTrace();
               }
            }
        }
    }

}

嗯，从我这样做的方式来看，它并没有按照我想要的方式工作。例如，如果您在服务器上运行此代码并单击任何下载按钮，则该URL将类似于

issue.jsp？1 =下载

这很奇怪。它也会在浏览器上显示

找不到id：null
的文件

我希望（在网址上）

issue.jsp？下载= 1

其中1是要下载的问题。我的数据库有两列：IssueId和fileContent（存储在BLOB中的文件内容）。

我想我已经解释得足够清楚了。任何帮助将不胜感激，这是我可以使用我的代码＆amp;研究。谢谢！

Answer 1

最简单的方法是在表格中移动表单并执行多种形式：

    <div align="center">
        <table>
            <caption>List of Issues</caption>
                <tr>
                    <th>Magazine Issue #</th>
                    <th>Download</th>
                </tr>
                <c:forEach var="issue" items="${listIssues.rows}">
                <tr>
                    <td><c:out value="${issue.BookId}" /></td>
                    <td>
                        <form method="get" action="fileDownload">
                           <input type='hidden' name='bookid' value='<c:out value="${issue.BookId}" />' />
                           <input type="submit" value="Download">
                        </form>
                   </td>        
                </tr>
                </c:forEach>
        </table>
    </div>

您还需要将值移出按钮的name属性，并进入隐藏输入的value属性。隐藏的输入需要name来获取servlet中的值：request.getParameter("bookid");

使用JSP和Servlet处理多个提交按钮

1 个答案: