###前提・実現したいこと
エラーが出てしまう
重大: Servlet.service() for servlet [servlet.book_lend] in context with path [/Library] threw exception [java.lang.NullPointerException] with root cause
###JSP
<%@ page contentType="text/html; charset=UTF-8" import="java.sql.*,javax.naming.*,javax.sql.*,java.text.*,java.util.Date,java.util.Calendar"%> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%> <%@ taglib prefix="sql" uri="http://java.sun.com/jsp/jstl/sql"%> <html> <sql:setDataSource var="db" driver="com.mysql.jdbc.Driver" url="jdbc:mysql://localhost/Library" user="root" password="" /> <sql:query var="rs" dataSource="${db}"> SELECT book.book_no,book.book_name,book.state,genre.genre_no,genre.genre_name,user.user_no,user.user_id, lend.lend_date,lend.return_date FROM book LEFT JOIN lend ON book.book_no = lend.book_no LEFT JOIN user ON user.user_no = lend.user_no LEFT JOIN genre ON book.genre_no = genre.genre_no <c:if test="${!empty param['genreNo']}"> where book.genre_no = ? <sql:param value="${param['genreNo']}" /> ORDER BY book.book_no asc; </c:if> </sql:query> <sql:query var="rs1" dataSource="${db}"> select * from genre </sql:query> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <link rel="stylesheet" type="text/css" href="css/Lending.css"> <title>書籍貸出画面</title> </head> <body> <h2>書籍貸出画面</h2> <br> <form method="POST" action="book_lend.jsp"> <p> ジャンル <select name="genreNo"> <option value="">全て</option> <c:forEach var="row" items="${rs1.rows}"> <option value=${row.genre_no}>${row.genre_name}</option> </c:forEach> </select> </p> <INPUT style="color:white; background-color:D57200;" type="submit" value="絞り込む" /> </form> <br> <table border="1"> <tr> <th>ID</th> <th>書籍名</th> <th>ジャンル</th> <th>貸出日</th> <th>返却予定日</th> <th>状態</th> <th>貸出/返却</th> <th>貸りた人</th> </tr> <c:forEach var="row" items="${rs.rows}"> <tr> <td>${row.book_no}</td> <td>${row.book_name}</td> <td>${row.genre_name}</td> <td> <c:if test="${empty row.lend_date}">-</c:if> ${row.lend_date } </td> <td> <c:if test="${empty row.lend_date}">-</c:if> ${row.return_date } </td> <td> <c:if test="${row.state == 2}" > <span class="fontRed">貸出不可</span> </c:if> <c:if test="${row.state == 1 }"> <c:if test="${empty row.lend_date}"> 貸出可能 </c:if> <c:if test="${!empty row.lend_date}"> <c:set var= "today" value="<%=new Date()%>"/> <c:if test="${today > row.return_date}"> 返却遅延 </c:if> <c:if test="${today <= row.return_date}"> 貸出中 </c:if> </c:if> </c:if> </td> <td> <c:if test="${empty row.lend_date}"> <c:if test="${row.state == 2}">-</c:if> <c:if test="${row.state == 1}"> <form method="POST" action="book_lend"> <input type="hidden" value="${row.book_no}" name="book_no"> <input type="hidden" value="${row.genre_no}" name="genre_no"> <INPUT style="color:white; background-color:D57200; width:60px; height:40px;" type="submit" value="貸出" /> </form> </c:if> </c:if> <c:if test="${!empty row.lend_date}"> <form method="GET" action="book_lend"> <input type="hidden" value=${row.book_no} name="book_no" /> <INPUT style="color:white; background-color:AFD170; width:60px; height:40px;" type="submit" value="返却" /> </form> </c:if> </td> <td> <c:if test="${!empty row.lend_date}"> <option value=${row.user_no}>${row.user_id}</option> </c:if> </td> </c:forEach> </table> <br> <form action="kanri_mypage.jsp"> <input style="color:white; background-color:D57200;" type="submit" name="mypage" value="TOPページ"> </form> </body> </html>
###servlet
package servlet; import java.io.IOException; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import javax.naming.InitialContext; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import javax.sql.DataSource; @WebServlet("/book_lend") public class book_lend extends HttpServlet { private static final long serialVersionUID = 1L; protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); String bookNo = request.getParameter("book_no"); HttpSession session = request.getSession(); Boolean userResult = (Boolean) session.getAttribute("userResult"); Connection con = null; PreparedStatement ps = null; String sql = null; ResultSet rs = null; if(session.getAttribute("userResult")!=null) { userResult = (boolean)session.getAttribute("userResult"); } if(userResult) { try{ InitialContext initContext = new InitialContext(); DataSource ds = (DataSource) initContext.lookup("java:comp/env/jdbc/Library"); con = ds.getConnection(); sql = "delete from lend where book_no = ?"; ps = con.prepareStatement(sql); ps.setString(1, bookNo); ps.executeUpdate(); }catch(Exception e){ throw new ServletException(e); }finally{ try{ if(rs != null){ rs.close(); } if(con != null){ con.close(); } if(ps != null){ ps.close(); } }catch(Exception e){ } this.getServletContext().getRequestDispatcher("/book_lend.jsp").forward(request, response); } } } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); String genreNo = request.getParameter("genre_no"); String bookNo = request.getParameter("book_no"); HttpSession session = request.getSession(); Boolean userResult = false; Connection con = null; PreparedStatement ps = null; String sql = null; ResultSet rs = null; if(session.getAttribute("userResult")!=null) { userResult = (boolean)session.getAttribute("userResult"); } if(userResult) { try{ InitialContext initContext = new InitialContext(); DataSource ds = (DataSource) initContext.lookup("java:comp/env/jdbc/Library"); con = ds.getConnection(); sql = "insert into lend (user_no,book_no,lend_date,return_date,genre_no) values (?,?,cast(now() as date) ,cast((now() + interval 6 day) as date),?)"; ps = con.prepareStatement(sql); Integer a =(Integer)session.getAttribute("user_no"); ps.setInt(1, a); ps.setString(2, bookNo); ps.setString(3, genreNo); ps.executeUpdate(); }catch(Exception e){ throw new ServletException(e); }finally{ try{ if(rs != null){ rs.close(); } if(con != null){ con.close(); } if(ps != null){ ps.close(); } }catch(Exception e){ } this.getServletContext().getRequestDispatcher("/book_lend.jsp").forward(request, response); } } } }
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