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Add my own class to JSP - ResultSet cannot be resolved to a type

Greenhorn

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posted 10 years ago

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Hi,

I am trying to use a custom class in a .jsp page, as part of a course I am taking on Web Technologies.

The original version of the jsp page was working fine, until I moved part of the Java code to a separate class.

Here is the original .jsp code that is working:

<!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="javax.naming.*,java.sql.*,javax.sql.*" %>
			<%
					Context init = new InitialContext();
					Context env = (Context) init.lookup("java:/comp/env/");
					DataSource data = (DataSource) env.lookup("jdbc/mydb");
					Connection conn = data.getConnection();
					Statement stmt = conn.createStatement();

String sqlStr = "SELECT * FROM Posts ORDER BY Id ASC";

ResultSet rset = stmt.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>

<%
		      rset.close();
		      stmt.close();
		      conn.close();
		 %>

</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 hijacking </h1>
			        <p> Do not hijack someone else's thread and interrupt a topic of discussion. </p>
			    </section>
			</aside>
		</div>

<%@ include file="footer.html" %>
	
</body>
</html>

Here is the Java class I created:

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 executeUpdate(String sqlStr)
	{
	    try {
	        stmt.executeUpdate(sqlStr);
	    }
	    catch (SQLException e)
	    {
	        System.out.println("Cannot execute query");
	    }
	}

public void closeAll()
	{
	    try {
	        rset.close();
	        stmt.close();
	        conn.close();                       
	    }
	    catch (SQLException e)
	    {
	        System.out.println("Cannot close connection");
	    }
	}
}

And here is the .jsp page after I replaced part of the code with the Java class:

<!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);
			%>

<% dbConnection.closeAll(); %>

</div>

<%@ include file="footer.html" %>

</body>
</html>

Here is the error message I get:

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: 38 in the jsp file: /forum.jsp
ResultSet cannot be resolved to a type
35: 			<%
36: 				DbConnect dbConnection = new DbConnect();
37: 	      		String sqlStr = "SELECT * FROM Posts ORDER BY Id ASC";
38: 				ResultSet rset = dbConnection.executeQuery(sqlStr);
39: 			%>
40: 
41: 			<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.

Finally, I attach a screenshot of my file manager, to show that I did save the class under the appropriate folder: ROOT/WEB-INF/classes/com/stocktails/DbConnect.class

Filename: screenshot.tiff

File size: 131 Kbytes

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Surendra Kumar

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Posts: 236

posted 10 years ago

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It's not a good practice to have Java code in JSP. Create a servlet and do all processing there and then return results to be used in JSP.

In your case right now, you have ResultSet class used in your JSP, but you removed the import statement, hence the error.

Paul Clapham

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posted 10 years ago

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Is your course really teaching you to put scriplets into a JSP??? That's been an obsolete technology for a decade now.

I suppose it's true that it might be helpful to know how that works, in the likely case that you get stuck cleaning up some old application. But the course really ought to be telling you seriously not to use scriptlets in new code. Hopefully that's the case.

Anyway... you have to import the ResultSet class into the JSP, just like you have to import it into Java code which uses it. You haven't done that. Sorry, I can't tell you how to do it because I haven't written JSP code with scriptlets for years now but it should be covered in your course material somewhere.

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Lienol Crazel

Greenhorn

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Surendra, I thank you for your reply. I cannot use servlets for this coursework, as it was discouraged by our professor who expressly requested that we use Java in .jsp pages instead. I do think your point is valid, as I have repeatedly seen the same remark elsewhere.

Coming back to my problem, I get a different error when I add <%@ page import="java.sql.ResultSet" %> to my .jsp page, as suggested by you:

After I posted my initial message, I created another much more simple .jsp page, to try to isolate the problem. It does seem that the problem lies with the class DbConnect.

This results in the following error:

HTTP Status 500 - An exception occurred processing JSP page /test.jsp at line 15

type Exception report

message An exception occurred processing JSP page /test.jsp at line 15

description The server encountered an internal error that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: An exception occurred processing JSP page /test.jsp at line 15

12: 	<%@ include file="navigation.html" %>
13: 			<%@ page import="com.stocktails.*" %>
14: 			
15: 			<%DbConnect dbConnection = new DbConnect();%>
16: 
17: </body>
18: </html>

Stacktrace:
	org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:455)
	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)
root cause

javax.servlet.ServletException: java.lang.NoClassDefFoundError: DbConnect
	org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:916)
	org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:845)
	org.apache.jsp.test_jsp._jspService(test_jsp.java:105)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
	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)
root cause

java.lang.NoClassDefFoundError: DbConnect
	org.apache.jsp.test_jsp._jspService(test_jsp.java:95)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
	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)
root cause

java.lang.ClassNotFoundException: DbConnect
	org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1718)
	org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1569)
	org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:126)
	org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:63)
	org.apache.jsp.test_jsp._jspService(test_jsp.java:95)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
	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.

Surendra Kumar

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Posts: 236

posted 10 years ago

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You created DbConnect class but what package is it in? Use the same one in your JSP too.

Lienol Crazel

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Surendra,

I saved the class under ROOT/WEB-INF/classes/com/stocktails/DbConnect.java and I then compiled it from ROOT/WEB-INF/

LC

Lienol Crazel

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By the way, I attach some extracts from my course's slides where it says not to use servlets. Personally, I am new to JSP and I therefore do not have a view of my own. But I see the consensus seems to be that servlets are the better solution.

LC

Filename: servlets2.tiff

File size: 182 Kbytes

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Filename: servlet.tiff

File size: 142 Kbytes

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Bear Bibeault

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In the real world, it's never a question using one of servlets or JSP; servlets and JSP are always used together. Each is a tool used for its own strengths, just like a carpenter will use both a saw and a drill to get a job done.

In an academic environment things are different to focus effort on a single concept.

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Lienol Crazel

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Bear, I thank you for your comment. It helps me put these slides in a new light. Once I am done with my studies, I will need to pursue my education Web Technologies. I will then have a look into this in more detail. This trimester, I have to learn Java, Web Technologies (HTML, CSS, Javascript, Tomcat, JSP) and SQL all at the same time. No need to say, I lack perspective on what I am learning...

LC

Surendra Kumar

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In your DbConnect class code you posted, I don't see package statement.
Is it not copied here while posting or you don't have it in the class?

Lienol Crazel

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Surendra,

The tutorial I use says I have two options:

1) not to create a package but save the class under ROOT/WEB-INF/classes/com/stocktails/DbConnect.java and compile it from ROOT/WEB-INF/
$ javac com/stocktails/DbConnect.java

=> this is what I did until now

2) to create a package:

$ javac com/stocktails/DbConnect.java
$ jar -cf stocktails.jar com/stocktails/*.class

I then moved the package under ROOT/WEB-INF/lib

Finally, I added the following line to DbConnect.java:
package com.stocktails;

I just tried the second solution, but unfortunately, I still get the same error message.

LC

Bear Bibeault

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I finally took a look at those slides. Egads! Be sure to take them with a grain of salt -- I disagree with almost everything they say.

In fact, the statement about always using JSP is so wrong as to be almost criminally negligent.

Please be advised.

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Bear Bibeault

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P.S. If you want to "read ahead" check out this article which gives you an overview of how web apps in the real world are constructed.

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Lienol Crazel

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Bear, thank you for sharing this article. It is very instructive. I see there is so much to learn...

LC

Lienol Crazel

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Surendra,

It now works! I tried again using the second solution and the JSP page now functions.

I thank you very much for your guidance and your patience.

Best regards,

LC

Paul Clapham

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Lienol Crazel wrote:I see there is so much to learn...

Yeah, Java + HTML + CSS + JavaScript + SQL + JSP does look like quite a dog's breakfast, doesn't it? But nevertheless that's what we're stuck with when creating Web applications.

Lienol Crazel

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Should I also consider learning a Web Development framework (such as Play, since we are talking Java)? I am still unsure how these frameworks relate to what I am learning now.

LC

Bear Bibeault

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Learn the basic first, before diving off into any frameworks.

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