java 使用ArrayList从数据库中检索数据并在JSP中显示
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Retrieving data from database using ArrayList and displaying it in JSP
提问by Gayathri Keerthana
MySQL DB server used. Database name: library, table name: book.
table contains the following columns with given type and order:
使用的 MySQL 数据库服务器。数据库名称：library，表名称：book。表包含具有给定类型和顺序的以下列：
title(varchar),
author(varchar),
book_id(int)- primary key,
count (int),
favs (int).
title(varchar),
author(varchar),
book_id(int)- primary key,
count (int),
favs (int).
I want to view all the records of this table using ArrayListin servletand JSP.
Here are my codes:
ViewBook (servlet)
我想使用ArrayListinservlet和来查看这个表的所有记录JSP。这是我的代码：ViewBook（servlet）
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import java.sql.*;
import p1.*;
public class ViewBook extends HttpServlet
{
public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException,IOException
{
PrintWriter out=res.getWriter();
try
{
Class.forName("com.mysql.jdbc.Driver");
Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3307/library", "root", "admin");
PreparedStatement ps=con.prepareStatement("select * from book");
ResultSet rs=ps.executeQuery();
ArrayList<Book> books=new ArrayList<Book>();
while(rs.next())
{
Book b= new Book();
b.bookID=rs.getInt(3);
b.bookTitle=rs.getString(1);
b.bookAuthor=rs.getString(2);
b.bookCopies=rs.getInt(4);
b.bookFavs=rs.getInt(5);
books.add(b);
}
req.setAttribute("bookslist",books);
con.close();
RequestDispatcher rd=req.getRequestDispatcher("/view_book.jsp");
rd.forward(req,res);
}
catch(Exception e)
{
out.println(e);
}
}
}
}
Package p1 contains the following class:
包 p1 包含以下类：
Book.java
书.java
package p1;
public class Book
{
public int bookFavs,bookID, bookCopies;
public String bookTitle;
public String bookAuthor;
}
The JSP to which the request is dispatched- view_book.jsp:
请求被分派到的 JSP-view_book.jsp：
<html>
<body>
<head>
<title>
View Books
</title>
</head>
<body>
<table border=2>
<tr>
<th>Book ID</th>
<th>Title</th>
<th>Author</th>
<th>No. of copies AVAILABLE</th>
<th>Number of favourites</th>
</tr>
<%
ArrayList<Book> dbooks=(ArrayList)request.getAttribute("bookslist");
Iterator it=dbooks.iterator();
while(it.hasNext())
{
Book b=(Book)it.next();
%>
<tr>
<td><%=b.bookID%></td>
<td><%=b.bookTitle%></td>
<td><%=b.bookAuthor%></td>
<td><%=b.bookCopies%></td>
<td><%=b.bookFavs%></td>
</tr>
<%
}
%>
</table>
</body>
</html>
The servlet and JSP aren't working. I know it's a vague question. Please point the blunders made. And solutions if possible!
servlet 和 JSP 不工作。我知道这是一个模糊的问题。请指出所犯的错误。以及可能的解决方案！
回答by chenchuk
The JSP file cant compile because the ArrayList needs an import directive :
JSP 文件无法编译，因为 ArrayList 需要导入指令：
<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>
<%@ page import="java.util.*" %>
回答by Srinu
You have to import your Bookand ArrayListand Iteratorin your JSP. Otherwise your JSPfile will not compile.
你必须导入Book并ArrayList和Iterator你的JSP。否则您的JSP文件将无法编译。
you can import multiple classes by using ,instead of ;like in the java. If you specify ;then you JSPwill throw Exception.
您可以通过使用,而不是;像在java.ini 中导入多个类。如果您指定，;那么您JSP将抛出异常。
<%@ page import="java.util.ArrayList,java.util.Iterator, p1.Book" %>
回答by Mwangi Thiga
Import java.util.*;to import the ArrayListclass in the jsp. Then, also import the required classes e.g. the Bookclass too. It should work.
Import java.util.*;ArrayList在jsp中导入类。然后，也导入所需的类，例如Book类。它应该工作。
回答by ElCalefactordeManchuri
The problem is quite simple: you don't execute the servlet anytime. You must to invoke the servlet from another .jsp then, inside that servlet, call the other jsp.
问题很简单：您不会在任何时候执行 servlet。您必须从另一个 .jsp 调用 servlet，然后在该 servlet 内调用另一个 jsp。
