简单的Java Web应用程序:表未在启动时加载

时间:2016-06-08 09:40:35

标签: java html mysql jsp

我正在使用Eclipse和Apache开发一个简单的应用程序,其中我使用Java,JSP和HTML显示使用MySQL创建的与产品(包含列ID,名称和价格)相关的表。我还有一个带有按钮的文本框,允许过滤表格,只显示价格高于文本框中插入价格的产品。

一切似乎都很好,包括过滤器。但是,当我第一次运行应用程序时,不会显示完整的表格。它仅在我使用过滤器时显示。我不确定,但是过滤器元素和表的scriptlet之间似乎存在一些冲突,因为如果我在JSP文件中注释过滤器元素的scriptlet,那么表就会在启动时加载它。

这是JSP类的代码,它加载表和搜索元素(带有一些Bootstrap样式):

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1" import="java.sql.Connection,java.sql.ResultSet,java.sql.DriverManager,project1.components.DBConnector, project1.components.Filter"%>
<!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">
<title>Product</title>
<style type="text/css">
    <%@include file="bootstrap/css/bootstrap.css" %>
    <%@include file="bootstrap/css/bootstrap-theme.css" %>
</style>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<script src="bootstrap/js/jquery.js"></script>
<script src="bootstrap/js/bootstrap.js"></script>
</head>
<body>
<% 
DBConnector dbc = new DBConnector();
Connection conn = dbc.connect();
String query = "select * from product";
%>
</body>

<form method="post">

<div class="col-xs-2 col-xs-offset-5">
<input type="text" class="form-control" name="value" value=<%=request.getParameter("firstinput")%>>
<br><br>
<input type="submit" class="form-control" name="submit" value="Filter">
<% 
    if(!request.getParameter("value").isEmpty()){
        String val = request.getParameter("value");
        Filter ft = new Filter();
        query = ft.filterByValue(val);
    }
%>
</div>
<br></br>
<table class = 'table table-hover'>
<tr>
<td>Id</td>
<td>Name</td>
<td>Product</td>
</tr>
<%
try
{               
    ResultSet rs = dbc.obtainTable(query);

    while(rs.next())
{

%><tr>
   <td><%=rs.getInt("ID") %></td>
   <td><%=rs.getString("NAME") %></td>
   <td><%=rs.getFloat("PRICE") %></td>
   </tr>     <%

}
%>
    </table>
    <%
    rs.close();
    conn.close();
    }
catch(Exception e)
{
    e.printStackTrace();
    }




%>

</form>

</html>

Java类,它连接到数据库并获取具有给定查询的数据,以便加载到上一个JSP文件中定义的表中:

package project1.components;

import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.Statement;

public class DBConnector {

    String url = "jdbc:mysql://localhost:3306/products?autoReconnect=true&useSSL=false";
    String user = "root";
    String pass = "root";

    public Connection connect() throws ClassNotFoundException, SQLException{
        Class.forName("com.mysql.jdbc.Driver");
        return (Connection) DriverManager.getConnection(url,user,pass); 
    }

    public ResultSet obtainTable(String query) throws ClassNotFoundException, SQLException{
        Connection cn = this.connect();
        Statement stmt= (Statement) cn.createStatement();
        return stmt.executeQuery(query);
    }
}

最后,过滤器本身在Java中定义:

package project1.components;

import java.sql.ResultSet;
import java.sql.SQLException;

public class Filter {

    public String filterByValue(String val) throws ClassNotFoundException, SQLException{
        int num = Integer.parseInt(val);
        String query = null;
        if(num >= 0){
            query = "select * from product where price >" + val;
        }
        else{
            query = "select * from product";
        }
        return query;
    }
}

任何帮助都会非常感激。

1 个答案:

答案 0 :(得分:0)

请您替换以下内容:

if(!request.getParameter("value").isEmpty()){

由:

if(request.getParameter("value")!=null && !request.getParameter("value").trim().isEmpty()){

并查看结果?