Java MVC JSP从JavaBean获取连接和值
[英]Java MVC JSP get Connection and Values from JavaBean
问题描述
我试图从JavaBean ProductDataBean.java中获取ShowProductCatalog.jsp中的值（列表productList = data.getProductList（）;）。 我收到错误nullpointerexception。 请帮忙！ 您的帮助将不胜感激。
*编辑：我意识到在getProductList（）中的ProductDataBean.java中获得的连接为空。 现在的问题是，如何进行更改以插入值？ 如果我将整个连接放在getProductList（）中，则会出现错误消息。 “找不到合适的驱动程序。”
**ShowProductCatalog.jsp**
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ page import = "java.util.*" import="cart.*,java.net.*,java.text.*"%>
<jsp:useBean id="data" scope="session" class="cart.ProductDataBean" />
<!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=ISO-8859-1">
</head>
<body>
<%
List productList = data.getProductList();
Iterator prodListIterator = productList.iterator();
%>
**ProductDataBean.java**
package cart;
import java.io.*;
import java.sql.*;
import java.util.*;
public class ProductDataBean implements Serializable{
private static Connection connection;
private PreparedStatement addRecord, getRecords;
public ProductDataBean(){
try{
// Step1: Load JDBC Driver
Class.forName("com.mysql.jdbc.Driver");
// Step 2: Define Connection URL
String connURL ="jdbc:mysql://localhost/onlineshop?user=root&password=teck1577130713";
// Step 3: Establish connection to URL
connection = DriverManager.getConnection(connURL);
}catch(Exception e){e.printStackTrace();}
}
public static Connection getConnection(){
return connection;
}
public ArrayList getProductList() throws SQLException{
ArrayList productList = new ArrayList();
Statement statement = connection.createStatement();
ResultSet results = statement.executeQuery("SELECT * FROM products");
while (results.next()){
DVD movie = new DVD();
movie.setMovie(results.getString("movieName"));
movie.setRating(results.getString("movieRate"));
movie.setYear(results.getString("movieYear"));
movie.setPrice(results.getDouble("moviePrice"));
productList.add(movie);
}
return productList;
}
}
2 个解决方案
解决方案1
0 2014-02-08 11:48:44
您的JSP页面运行正常，没有错误。 检查您的数据库，并确认您在产品表内有行。 空指针异常发生，因为方法getProductList()没有返回ArrayList 。
解决方案2
0 已采纳 2014-02-08 12:04:05
检查您的构建路径mySql驱动程序已添加。 并请为您得到的问题添加例外，然后轻松回答。
mysql-connector-java-5.1.24-bin.jar
你可以从这里得到
看看这样如何避免在jsp中的Java代码
我建议您使用Servlets而不是在jsp中编写Java代码。 如果您使用Servlet编写代码，则可以轻松地测试/调试代码。
回答： how can I make the changes to insert the value?
使用sql插入查询创建PreparedStatement obj，然后调用[executeUpdate()][3]执行INSERT ， UPDATE或DELETE操作。
将这段代码添加到ProductDataBean类中，以将新记录添加到表中。
public static void addRecord(DVD dvd) throws SQLException{
PreparedStatement pStatement =
getConnection().prepareStatement("insert into products(movieName, movieRate, movieYear, moviePrice) values(?,?,?,?)");
pStatement.setString(1, dvd.getMovie());
pStatement.setString(2, dvd.getRating());
pStatement.setString(3, dvd.getYear());
pStatement.setDouble(4, dvd.getPrice());
pStatement.executeUpdate();
}
使您的DVD类像POJO
package cart;
public class DVD {
private String movie;
private String rating;
private String year;
private Double price;
public DVD(){}
public DVD(String movie, String rating, String year, Double price) {
this.movie = movie;
this.rating = rating;
this.year = year;
this.price = price;
}
public String getMovie() {
return movie;
}
public void setMovie(String movie) {
this.movie = movie;
}
public String getRating() {
return rating;
}
public void setRating(String rating) {
this.rating = rating;
}
public String getYear() {
return year;
}
public void setYear(String year) {
this.year = year;
}
public Double getPrice() {
return price;
}
public void setPrice(Double price) {
this.price = price;
}
@Override
public String toString() {
return "DVD [movie=" + movie + ", rating=" + rating + ", year=" + year
+ ", price=" + price + "]";
}
}
并在您的jsp页面中调用servlet url模式以执行GET和POST，并在jsp用户标准标签lib jstl1.2.jar呈现所有产品，您可以从此处获取它，因此将jsp文件替换为：
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!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=ISO-8859-1">
</head>
<body>
<c:url value="/Product" var="pdctServletUrl"/>
Product Page
<form method="post" action="${pdctServletUrl}">
<h4>Enter New Movie details:</h4>
<label>Name</label>
<input type="text" name="movie"/>
<label>Rating</label>
<input type="text" name="rating"/>
<label>Year</label>
<input type="text" name="year"/>
<label>Price</label>
<input type="text" name="price"/>
<input type="submit" value="save movie"/>
</form>
<br/>
To get a list of products click
<a href="${pdctServletUrl}">Get Products</a>
<c:if test="${not empty products}">
<h4>Available Products.</h4>
<table>
<tr>
<th>Movie Name</th>
<th>Rating</th>
<th>Year</th>
<th>Price</th>
</tr>
<c:forEach items="${products}" var="pd">
<tr>
<td>${pd.movie}</td>
<td>${pd.rating}</td>
<td>${pd.year}</td>
<td>${pd.price}</td>
</tr>
</c:forEach>
</table>
</c:if>
</body>
</html>
一个处理GET和POST请求以及将数据传输到客户端等的servlet。
产品.java
package cart;
import java.io.IOException;
import java.sql.SQLException;
import java.util.List;
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 Product
*/
@WebServlet("/Product")
public class Product extends HttpServlet {
private static final long serialVersionUID = 1L;
private ProductDataBean pDataBean = new ProductDataBean();
public Product() {
super();
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
List<Product> products;
try {
products = pDataBean.getProductList(); // Obtain all products.
request.setAttribute("products", products); // Store products in request scope.
request.getRequestDispatcher("/test.jsp").forward(request, response); // Forward to JSP page to display them in a HTML table.
} catch (SQLException e) {
e.printStackTrace();
}
}
/* (non-Javadoc)
* @see javax.servlet.http.HttpServlet#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
*/
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
String movie = req.getParameter("movie");
String rating = req.getParameter("rating");
String year = req.getParameter("year");
Double price = Double.valueOf(req.getParameter("price"));
if(movie!=null && rating!=null && year!=null && price!=null)
try {
ProductDataBean.addRecord(new DVD(movie, rating, year, price));
} catch (SQLException e) {
e.printStackTrace();
}
doGet(req, resp);
}
}
我认为这可以帮助您理解。
Java MVC JSP从JavaBean获取连接和数据
声明:本站的技术帖子网页，遵循CC BY-SA 4.0协议，如果您需要转载，请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.