Java ResultSet 无法解析为类型
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/22685651/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
提示：将鼠标放在中文语句上可以显示对应的英文。显示中英文
时间：2020-08-13 17:16:27 来源:igfitidea点击:
ResultSet cannot be resolved to a type
提问by lcazarre
I am refactoring two .jsp pages to place some common code to a Java class. The purpose of the common code is to connect to a database.
我正在重构两个 .jsp 页面以将一些公共代码放置到 Java 类中。公共代码的目的是连接到数据库。
Both pages were working well before the change. But I now get an "ResultSet cannot be resolved to a type" error on one page, whereas the other page runs without error. I do not understand why, as I think I made similar changes to both pages.
两个页面在更改前都运行良好。但是我现在在一个页面上收到“ResultSet 无法解析为类型”错误，而另一页运行时没有错误。我不明白为什么，因为我认为我对两个页面都做了类似的更改。
Could anyone help me explain why the first page does not work, while the first one does?
谁能帮我解释为什么第一页不起作用，而第一页却起作用？
Here is the page that no longer works after the change:
这是更改后不再有效的页面：
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" lang="en-GB" xml:lang="en-GB">
<%@page pageEncoding="utf-8" %>
<head>
<meta charset="UTF-8" />
<title>Forum</title>
<link rel="stylesheet" type="text/css" href="stocktails.css" />
</head>
<body>
<%@ include file="navigation.html" %>
<div id="maindiv">
<header>
<h1> Discussion forum </h1>
<p>Bounce your investing ideas off the community</p>
</header>
<div class="left-col">
<div id='post'>
<form action='post.jsp' method="get">
User name: <input type="text" name="userName"><br>
Password: <input type="password" name="pwd">
<textarea id="postText" name="textarea" rows="10" cols="50">Type here</textarea>
<input type="submit" value="Submit">
</form>
</div>
<%@ page import="com.stocktails.*" %>
<%
dbConnect dbConnection = new dbConnect();
String sqlStr = "SELECT * FROM Posts ORDER BY Id ASC";
ResultSet rset = dbConnection.executeQuery(sqlStr);
%>
<div id="tablePlaceholder">
<form method="get" action="forum.jsp">
<table class='forumTable'>
<%
while (rset.next()) {
%>
<tr>
<td class="postDate">Posted on: <%= rset.getDate("Date") %></td>
<td class="postId">Post #<%= rset.getInt("Id") %></td>
</tr>
<tr>
<td class="postMember"><%= rset.getString("Member") %></td>
<td class="postText"><%= rset.getString("Text") %></td>
</tr>
<tr>
<td class="postEmpty"></td>
</tr>
<%
}
%>
</table>
<br>
</form>
</div>
<% dbConnection.closeAll(); %>
</div>
<div class="right-col">
<aside class="aside-forum">
<header>
<h1> Forum etiquette </h1>
<p> Thou shall not troll </p>
</header>
<section>
<h1> No promotion </h1>
<p> Do not use this forum to promote your own business. </p>
</section>
<section>
<h1> Keep calm and carry on </h1>
<p> Be courteous. Personal disagreements should be handled through email and not through public posts. </p>
</section>
<section>
<h1> No hiHymaning </h1>
<p> Do not hiHyman someone else's thread and interrupt a topic of discussion. </p>
</section>
<section>
<h1> You say /t??me?to?/, we say /t??mɑ?t??/ </h1>
<p> Please refrain from using American spelling. </p>
</section>
</aside>
</div>
<div class="clear"></div>
</div>
<%@ include file="footer.html" %>
</body>
</html>
Here is the error message if get:
如果获取，这是错误消息：
HTTP Status 500 - Unable to compile class for JSP:
type Exception report
message Unable to compile class for JSP:
description The server encountered an internal error that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: Unable to compile class for JSP:
An error occurred at line: 37 in the jsp file: /forum.jsp
ResultSet cannot be resolved to a type
34: <%
35: dbConnect dbConnection = new dbConnect();
36: String sqlStr = "SELECT * FROM Posts ORDER BY Id ASC";
37: ResultSet rset = dbConnection.executeQuery(sqlStr);
38: %>
39:
40: <div id="tablePlaceholder">
Stacktrace:
org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:103)
org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:366)
org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:468)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:378)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:353)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:340)
org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:657)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:357)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.52 logs.
Here is the other page that still works even after I moved some code to a separate class:
这是另一个页面，即使在我将一些代码移动到单独的类后仍然有效：
<html>
<head>
<title>Quote Query</title>
</head>
<body>
<h1>retrieve stock quotes</h1>
<h3>Choose Ticker(s):</h3>
<form method="get">
<input type="checkbox" name="ticker" value="AAPL">AAPL
<input type="checkbox" name="ticker" value="MSFT">MSFT
<input type="submit" value="Query">
</form>
<%
String[] tickers = request.getParameterValues("ticker");
if (tickers != null) {
%>
<%@ page import="com.stocktails.*" %>
<%
dbConnect dbConnection = new dbConnect();
String sqlStr = "SELECT * FROM Quotes WHERE Ticker IN (";
sqlStr += "'" + tickers[0] + "'"; // First ticker
for (int i = 1; i < tickers.length; ++i) {
sqlStr += ", '" + tickers[i] + "'"; // Subsequent tickers need a leading commas
}
sqlStr += ") ORDER BY Date ASC";
// for debugging
System.out.println("Query statement is " + sqlStr);
ResultSet rset = dbConnection.executeQuery(sqlStr);
%>
<hr>
<form method="get" action="quotes.jsp">
<table border=1 cellpadding=5>
<tr>
<th>Ticker</th>
<th>Date</th>
<th>PriceOpen</th>
<th>PriceHigh</th>
<th>PriceLow</th>
<th>PriceClose</th>
<th>Volume</th>
<th>PriceAdjClose</th>
</tr>
<%
while (rset.next()) {
%>
<tr>
<td><%= rset.getString("Ticker") %></td>
<td><%= rset.getString("Date") %></td>
<td>$<%= rset.getInt("PriceOpen") %></td>
<td><%= rset.getInt("PriceHigh") %></td>
<td><%= rset.getString("PriceLow") %></td>
<td><%= rset.getString("PriceClose") %></td>
<td>$<%= rset.getInt("Volume") %></td>
<td><%= rset.getInt("PriceAdjClose") %></td>
</tr>
<%
}
%>
</table>
<br>
<input type="submit" value="Order">
<input type="reset" value="Clear">
</form>
<a href="<%= request.getRequestURI() %>"><h3>Back</h3></a>
<%
dbConnection.closeAll();
}
%>
<%@ include file="footer.html" %>
</body>
</html>
Here is the Java class:
这是Java类：
import javax.naming.*;
import java.sql.*;
import javax.sql.*;
public class dbConnect
{
private Context init;
private Context env;
private DataSource data;
private Connection conn;
private Statement stmt;
private ResultSet rset;
public dbConnect()
{
try {
init = new InitialContext();
}
catch (NamingException e)
{
System.out.println("Cannot create initial environment");
};
try {
env = (Context) init.lookup("java:/comp/env/");
}
catch (NamingException e)
{
System.out.println("Cannot create context");
};
try {
data = (DataSource) env.lookup("jdbc/mydb");
}
catch (NamingException e)
{
System.out.println("Cannot create data source");
};
try {
conn = data.getConnection();
}
catch (SQLException e)
{
System.out.println("Cannot get connection");
}
try {
stmt = conn.createStatement();
}
catch (SQLException e)
{
System.out.println("Cannot create statement");
}
}
public ResultSet executeQuery(String sqlStr)
{
try {
rset = stmt.executeQuery(sqlStr);
}
catch (SQLException e)
{
System.out.println("Cannot execute query");
}
return rset;
}
public void closeAll()
{
try {
rset.close();
stmt.close();
conn.close();
}
catch (SQLException e)
{
System.out.println("Cannot close connection");
}
}
}
采纳答案by Charaf JRA
You should also import java.sql.ResultSetclass in your JSP :
您还应该java.sql.ResultSet在 JSP 中导入类：
<%@ page import="java.sql.ResultSet" %>
make sure that you included the jdbc JAR.
确保包含 jdbc JAR。
PS:You should learn how to organize your code , never access database through JSP,Read more about RequestDispatcher,request.setAttribute..., Google about MVC.
PS：你应该学习如何组织你的代码，永远不要通过 JSP 访问数据库，阅读更多关于RequestDispatcher，request.setAttribute...，谷歌关于MVC。
