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Using a bean in jsp

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rj2046

rj2046

Programmer
Dec 15, 2004
14
US
Hi, I'm trying to learn jsp for a possible job interview.

I'm trying to use a jsp page to access a class that I intend to use to retrieve data from a database.

This code is my first step so that I can at least get a bean to return data to a jsp.

Can anyone tell me why tomcat is throwing an exception?

Thank you very much.

MY BEAN
Code: 
package DB;

import java.beans.*;

public class DBBean  {
    
  public String INFO_STRING;
    
  public DBBean( ) 
  {
    INFO_STRING="Info string";
  }
       
public String getInfo(){
      return INFO_STRING;
  }
   
}


MY JSP
Code: 
<%@page contentType="text/html"%>

<%@page import="java.text.*, DB.*, java.sql.*"%>

<html>
<head><title>JSP Page</title></head>
<body>

<jsp:useBean id="DB" scope="session" class="DBBean" />
<%-- <jsp:getProperty name="beanInstanceName"  property="propertyName" /> --%>


<CENTER>
<TABLE WIDTH=60% BGCOLOR=yellow CELLPADDING=15>
<TR>
<TD ALIGN=CENTER> DBData<%= DB.getInfo() %></TD>
</TR>
</TABLE>


</body>
</html>


ERROR MESSAGE
Code: 
Apache Tomcat/4.0.6 - HTTP Status 500 - Internal Server Error

--------------------------------------------------------------------------------

type Exception report

message Internal Server Error

description The server encountered an internal error (Internal Server Error) that prevented it from fulfilling this request.

exception 

javax.servlet.ServletException: DBBean
	at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:471)
	at org.apache.jsp.FxJsp$jsp._jspService(FxJsp$jsp.java:125)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:107)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
	at org.netbeans.modules.tomcat.tomcat40.runtime.IDEJspServlet$JspServletWrapper.service(IDEJspServlet.java:173)
	at org.netbeans.modules.tomcat.tomcat40.runtime.IDEJspServlet.serviceJspFile(IDEJspServlet.java:246)
	at org.netbeans.modules.tomcat.tomcat40.runtime.IDEJspServlet.service(IDEJspServlet.java:339)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
	at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:226)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:243)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:190)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at org.apache.catalina.valves.CertificatesValve.invoke(CertificatesValve.java:246)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at org.netbeans.modules.web.monitor.catalina.MonitorValve.invoke(MonitorValve.java:148)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2347)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:170)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:170)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:468)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at org.apache.catalina.connector.http.HttpProcessor.process(HttpProcessor.java:1027)
	at org.apache.catalina.connector.http.HttpProcessor.run(HttpProcessor.java:1125)
	at java.lang.Thread.run(Thread.java:534)


root cause 

java.lang.InstantiationException: DBBean
	at org.apache.jsp.FxJsp$jsp._jspService(FxJsp$jsp.java:83)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:107)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
	at org.netbeans.modules.tomcat.tomcat40.runtime.IDEJspServlet$JspServletWrapper.service(IDEJspServlet.java:173)
	at org.netbeans.modules.tomcat.tomcat40.runtime.IDEJspServlet.serviceJspFile(IDEJspServlet.java:246)
	at org.netbeans.modules.tomcat.tomcat40.runtime.IDEJspServlet.service(IDEJspServlet.java:339)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
	at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:226)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:243)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:190)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at org.apache.catalina.valves.CertificatesValve.invoke(CertificatesValve.java:246)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at org.netbeans.modules.web.monitor.catalina.MonitorValve.invoke(MonitorValve.java:148)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2347)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:170)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:170)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:468)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
	at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
	at org.apache.catalina.connector.http.HttpProcessor.process(HttpProcessor.java:1027)
	at org.apache.catalina.connector.http.HttpProcessor.run(HttpProcessor.java:1125)
	at java.lang.Thread.run(Thread.java:534)
 
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If you change your useBean line to :

<jsp:useBean id="DB" scope="session" class="DB.DBBean"/>

then it should work ... why it doesn't when you import the "DB" package though, I have no idea.

Butm this is not my biggest concern. If you are going for an interview - you need to sharpen up your style considerably. Your code really is bad programming : poorly capitalized html code, badly named variables, package names that are capitalized, importing packages you don't use etc etc. Plus your "bean" is not a "bean" - in that it does not conform to the JavaBean standard even closely (and capitalized variables are generally reserved for static final variables).

Below is a better example of your code :

Code: 
<%@page contentType="text/html"%>

<html>
<head><title>JSP Page</title></head>
<body>

<jsp:useBean id="testBean" scope="session" class="com.acme.beans.TestBean"/>

<table>
	<tr>
		<td>
			<jsp:getProperty name="testBean"  property="info" />	
		</td>
	</tr>
</table>

</body>
</html>

And the bean :

Code: 
package com.acme.beans;

public class TestBean  {

  	public String info;

	public TestBean() {
		this.info = "Info string";
	}

	public void setInfo(String info) {
		this.info = info;
	}

	public String getInfo(){
		return this.info;
  	}

}

Good luck !

--------------------------------------------------
Free Database Connection Pooling Software
 
Upvote 0 Downvote

Thank you very much! It did indeed work.

And I appreciate your comments on style.
 
Upvote 0 Downvote
Can I ask why "this." is required ?

I guess it implies I can reference the same variable in other instances, or global scope.

Do you have a link to documentation for this?

Thanks again.
 
Upvote 0 Downvote
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