带有 Servlet、JSP 和 MySQL 的 Java 中的 CRUD Web 应用程序，没有 DAO
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【中文标题】带有 Servlet、JSP 和 MySQL 的 Java 中的 CRUD Web 应用程序，没有 DAO【英文标题】：CRUD web application in Java with Servlet,JSP and MySQL without DAO 【发布时间】：2017-06-12 23:11:14 【问题描述】：我正在使用 Java EE、Servlet、JSP 和 mysql 开发一个简单的家庭图书馆 Web 应用程序。我的创建、读取和删除工作正常，但更新不工作。我没有使用任何形式的设计模式，只是使用了 servlet 和 POJO。我尝试学习的所有示例似乎都使用了 MVC 和 DAO 设计模式。有什么方法可以实现 CRUD 应用程序不使用 MVC 和 DAO 模式？对于这样一个简单的应用程序，推荐和最佳做法是什么？
代码如下： UpdateBook.jsp
<%@ page language="java" contentType="text/html; charset=gbk"
pageEncoding="gbk"%>
<%@ page import ="java.util.ArrayList"%>
<%@page import="book.Book"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gbk">
<link rel="stylesheet" type="text/css" href="../css/styles.css" />
<title>Updated Library Collection</title>
</head>
<body>
<div id="container">
<div id="header"><h1 align="center" style="color:blue">Edit Library Collection</h1></div>
<div id="wrapper">
<div id="content" align="center">
<%
request.setCharacterEncoding("gbk");
String ISBN=request.getParameter("Isbn");
String BookTitle=request.getParameter("Title");
String BookAuthor=request.getParameter("Author");
String Category=request.getParameter("Category");
String Description=request.getParameter("Description");
%>
<table border="0" cellspacing="0" cellpadding="4" align="center" >
<tr>
<td bgcolor="#EAEAEA" colspan="2">
<form name="bookUpdate" action="/homelibrary/UpdateBookServlet" method="POST">
<p>
<label for="Isbn">ISBN: </label>
<input type="text"readonly name="Isbn" id="Isbn" value=<%=ISBN%> >
<br><br>
<label for="Title">Title: </label>
<input type="text" name="Title" id="Title" value=<%=BookTitle%>>
<br><br>
<label for="Author">Author: </label>
<input type="text" name="Author" id="Author" value=<%=BookAuthor%>>
<br><br>
<label for="Category">Category: </label>
<input type="text" name="Category" id="Category" value=<%=Category%>>
<br><br>
<label for="Description">Description: </label>
<input type="text" name="Description" id="Description" value=<%=Description%>>
<br><br>
<p>
<input type="submit" name="Submit" value="Submit" onclick="goto">
<input type="button" name="Cancel" value="Cancel" onclick="javascript:history.go(-1);">
</p>
</form>
</td>
</tr>
</table>
</div>
</div>
<div id="footer" align="center">
<p>© Home Library</p>
</div>
</body>
</html>
UpdateBookServlet.java
package book;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/UpdateBookServlet")
public class UpdateBookServlet extends HttpServlet
private static final long serialVersionUID = 1L;
public UpdateBookServlet()
super();
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
//String forward="";
String action = request.getParameter("action");
if (action == ("edit"))
String Isbn = request.getParameter("Isbn");
Book book = null;
try
book = this.getBookByIsbn(Isbn);
catch (ClassNotFoundException e)
// TODO Auto-generated catch block
e.printStackTrace();
request.setAttribute("book", book);
RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("/Book/UpdateBook.jsp");
dispatcher.forward(request,response);
//@SuppressWarnings("unused")
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
Book book = new Book();
response.setContentType("text/html");
request.setCharacterEncoding("gbk");
//Get data from form data
String ISBN = request.getParameter("Isbn");
String BookTitle = request.getParameter("Title");
String BookAuthor = request.getParameter("Author");
String Category = request.getParameter("Category");
String Description = request.getParameter("Description");
//@SuppressWarnings("unused")
//PreparedStatement preStmt = null;
//Connection cn =null;
try
//Create a java MySQL database connection
Class.forName("com.mysql.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/ebookstore";
Connection cn = DriverManager.getConnection(url, "admin", "admin");
PreparedStatement prepStmt= null;
if(ISBN != null)
// create the java MySQL update PreparedStatement
prepStmt = cn.prepareStatement("UPDATE book SET Title=?,Author=?,Category=?,Description=? "+" where Isbn=?");
//String update = "UPDATE book SET Title=?,Author=?,Category=?,Description=? "+" where Isbn=1111";
//prepStmt = cn.prepareStatement(update);
prepStmt.setString(1, book.getTitle());
prepStmt.setString(2, book.getAuthor());
prepStmt.setString(3, book.getCategory());
prepStmt.setString(4, book.getDescription());
prepStmt.setInt(5, Integer.parseInt(book.getISBN()));
//execute the java preparedStatment
prepStmt.executeUpdate();
cn.close();
prepStmt.close();
catch (Exception e)
System.err.println("Got an exception! ");
System.err.println(e.getMessage());
//forwarding from Servlet to a JSP
RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("/Book/QueryBook.jsp");
dispatcher.forward(request,response);
public Book getBookByIsbn(String isbn) throws ClassNotFoundException
Book book = new Book();
try
//Create a java MySQL database connection
Class.forName("com.mysql.jdbc.Driver");
String url = "jdbc:mysql://localhost:3306/homelib";
Connection cn = DriverManager.getConnection(url, "root", "admin");
PreparedStatement preparedStatement = cn.
prepareStatement("SELECT * FROM book where Isbn=?");
preparedStatement.setString(1, isbn);
ResultSet rs = preparedStatement.executeQuery();
if (rs.next())
book.setISBN(rs.getString("Isbn"));
book.setTitle(rs.getString("Title"));
book.setAuthor(rs.getString("Author"));
book.setCategory(rs.getString("Category"));
book.setDescription(rs.getString("Description"));
catch (SQLException e)
e.printStackTrace();
return book;
QueryBook.jsp中的按钮
<td><a href="/homelibrary/UpdateBookServlet?action=edit&Isbn=<c:out value="$book.Isbn"/>">Update</a></td>
【问题讨论】：
推荐的做法是使用适当的设计模式。也就是说，是否使用设计模式本身并不影响数据库更新是否有效。如果您需要这方面的帮助，您必须提供 minimal reproducible example。 有我的servlet和jsp页面。更新页面的所有值都返回 null。 【参考方案1】：你在评论中说：
更新页面的所有值都返回 null。
也就是说，因为您在 UpdateBookServlet.java 中实例化了 Book 对象
Book book = new Book();
但是您将请求参数设置为单独的字符串对象：
String ISBN = request.getParameter("Isbn");
String BookTitle = request.getParameter("Title");
String BookAuthor = request.getParameter("Author");
String Category = request.getParameter("Category");
String Description = request.getParameter("Description");
但永远不要使用它们。相反，您从空 Book 对象添加数据：
prepStmt.setString(1, book.getTitle());
prepStmt.setString(2, book.getAuthor());
prepStmt.setString(3, book.getCategory());
prepStmt.setString(4, book.getDescription());
prepStmt.setInt(5, Integer.parseInt(book.getISBN()));
【讨论】：
【参考方案2】：此示例用于在用户登录会话时更新图书信息
在你的 JSP 顶部插入这个来识别会话中的用户
if (session!=null && request.getSession().getAttribute("loggedin") != null)
if (request.getSession().getAttribute("role").equals("Student"))
response.sendRedirect("index.jsp");
return;
else
response.sendRedirect("index.jsp");
return;
%>
<% if (request.getSession().getAttribute("loggedin") == null)
response.sendRedirect("index.jsp");
return;
BookDTO dto = (BookDTO) request.getSession().getAttribute("book");
然后在下面的 JSP 中插入这段代码以将新数据发布到 servlet
<form method="POST" action="EditBookServlet">
<div class="form-submit">
My Information
<div class="submit">
<div class="form-row">
<div class="x">
<label>Name</label>
<input type="text" class="form" value="<%= dto.getName()%>" name="name">
</div>
<div class="x">
<label>Author</label>
<input type="author" class="form" value="<%= dto.getAuthor()%>" name="author">
</div>
<div class="form x">
<button class="btn" type="submit">Save Changes</button>
</div>
</div>
</div>
</form>
在 EditBookServlet 中，插入此代码
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
try
BookDB db = new BookDB();
BookDTO dto = db.getBookByID(((BookDTO)
request.getSession().getAttribute("book")).getId());
dto.setName(request.getParameter("name"));
dto.setAuthor(request.getParameter("author"));
db.updateBook(dto);
request.getSession().setAttribute("book", dto);
在 StudentDB java 文件中插入这个以通过 Id 查找图书，然后更新图书 sql 文件
public BookDTO getBookByID(int id)
BookDTO obj = null;
String query = "Select * from book where id=?";
PreparedStatement pst = null;
ResultSet rs = null;
try
pst = conn.prepareStatement(query);
pst.setInt(1,id);
rs = pst.executeQuery();
if (rs != null)
if (rs.next())
obj = new BookDTO();
obj.setId(rs.getInt(1));
obj.setName(rs.getString(2));
obj.setAuthor(rs.getAuthor(3));
catch (SQLException ex)
Logger.getLogger(BookDB.class.getName()).log(Level.SEVERE, null, ex);
finally
if (rs != null)
try
rs.close();
catch (SQLException ex)
Logger.getLogger(BookDB.class.getName()).log(Level.SEVERE, null, ex);
public boolean updateBook(BookDTO obj)
int affectedRows = 0;
String query = "update `book` set name=? , author=lower(?) where id=?";
PreparedStatement pst = null;
try
pst = conn.prepareStatement(query);
pst.setString(1,obj.getName());
pst.setString(2,obj.getAuthor());
pst.setInt(10, obj.getId());
System.out.println(pst);
affectedRows = pst.executeUpdate();
catch (SQLException ex)
Logger.getLogger(Book.class.getName()).log(Level.SEVERE, null, ex);
return affectedRows > 0;
【讨论】：
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