Another JSP Bean assistance request 2

oaklandar · Apr 6, 2004

I am trying to get this JSP to work in the JSP Bean. Please advise what I am doing wrong?

Here is my Java file called myTherm.java which compiles with no problems:

Code:

package colors;

public class myTherm
{
private int temp;
private int maxTemp;
private int minTemp;


public myTherm()
{
this(34);
}

public myTherm(int temp)
{
this.temp = temp;
init();
}

public void setTemp(int temp)
{
this.temp = temp;
init();
}

public int getTemp()
{
return temp;
}

private void init()
{
maxTemp = this.temp + 10;
minTemp = this.temp = 20;
if(maxTemp > 150)
System.out.println("above");
else
System.out.println("below");
}
}

My JSP with the Bean call here:

Code:

<jsp:useBean id="myStat" class="colors.myTherm">

</jsp:useBean>
<html>
<body>

<% myTherm t = new myTherm(34); %>
The data is now <%= myStat.getTemp() %> data.

</body>
</html>

Error messages here:

Generated servlet error:
[javac] Compiling 1 source file

C:\jakarta-tomcat-4.1.27\work\Standalone\localhost\examples\jsp\colors\myTherm_jsp.java:55: cannot resolve symbol
symbol : class myTherm
location: class org.apache.jsp.myTherm_jsp
myTherm t = new myTherm(34);
^

An error occurred at line: 2 in the jsp file: /jsp/colors/myTherm.jsp

Generated servlet error:
C:\jakarta-tomcat-4.1.27\work\Standalone\localhost\examples\jsp\colors\myTherm_jsp.java:55: cannot resolve symbol
symbol : class myTherm
location: class org.apache.jsp.myTherm_jsp
myTherm t = new myTherm(34);
^
2 errors

sedj · Apr 6, 2004

Add this line at the top of your JSP :

<%@ page import="colors.*" %>

or change this line :

<% myTherm t = new myTherm(34); %>

to :

<% colors.myTherm t = new colors.myTherm(34); %>

Couple of things though -

why are you using the <jsp:useBean ...> tag and then creating a new "myTherm"" bean in the scriptlet ?

Java classes should be called naming conventions like "MyTherm" rather than "myTherm" - its not necessary but its good Java programming practice.

oaklandar · Apr 7, 2004

Thanks again for your assistance.

oaklandar · Apr 7, 2004

why are you using the <jsp:useBean ...> tag and then creating a new "myTherm"" bean in the scriptlet ?

I am still learning the bean part and not sure I assume there is a better way to do this?

sedj · Apr 7, 2004

You should be able to remove this line :

<% myTherm t = new myTherm(34); %>

because once the JSP is written into a servlet on before compilation, the <jsp:useBean ...> code will in effect become :

myTherm t = new myTherm(34);

Look in TOMCAT_HOME/work/* to find how your JSPs look once they are made into servlets and compiled - if you jsp is called "mypage.jsp" the servlet will be called something like "mypage_jsp.java".

oaklandar · Apr 7, 2004

Yes, that is exactly how it looks. Thanks for the explanations.

petey · Apr 7, 2004

It helps to understand what goes on under the sheets with these things, even though JSP is supposed to "insulate" you from it. The code:

Code:

<jsp:useBean id="myStat" class="colors.myTherm"/>

is basically equivalent to

Code:

<%
if (pageContext.getAttribute("myStat")==null) {
    myTherm foo = new myTherm();
    pageContext.setAttribute("myStat", foo);
}
%>

similarly, the code

Code:

<jsp:getProperty name="myStat" property="temp"/>

is essentially equivalent to

Code:

<%
out.print(((myTherm) pageContext.findAttribute("myStat")).getTemp());
%>

This hopefully shows how JSP beans work so you can use the tags more effectively in the future, and avoid typing some code.

http://www.drpeterjones.com/

News and views of some obscure guy

oaklandar · Apr 9, 2004

Thanks.

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Another JSP Bean assistance request 2

oaklandar

Technical User

sedj

Programmer

oaklandar

Technical User

oaklandar

Technical User

sedj

Programmer

oaklandar

Technical User

petey

Programmer

oaklandar

Technical User

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