Do you use a bean for creating database connection?

[Raghavan Chockalingam]

I am wondering whether people develop a bean for making a database connection. I was thinking of creating of a bean that would return a Connection or Statement object and I came up with this java program but there is a problem when I try to include the bean in my jsp program.

java program...DbBean.java...placed in web-inf/classes/Utilities

 
package Utilities;
 
import java.sql.*;
import java.io.*;
 
class DbBean{
Connection connection;
Statement stmt;

void makeConnection(){
try
{
Class.forName("org.gjt.mm.mysql.Driver").newInstance();
try
{
this.connection = 
 
DriverManager.getConnection("jdbc:mysql://localhost:3306/fortrial","root","rootPassword");
}
catch (SQLException s)
{
System.out.println(s.toString());
}
}
catch (Exception e)
{
System.out.println(e.toString());
        }
 
}
 
void makeStatement(){
try{
this.stmt = connection.createStatement();
}catch(Exception e){
System.out.println("Unable to create statement");
}
}

 
Connection getConnection(){
return this.connection;
}

Statement getStatement(){
return this.stmt;
}
 
/*void setConnection(String str){
}
 
void setStatement(String str){
}*/
 
 
}

Jsp file...carBean.jsp

  
<jsp:useBean id="myConnection" class="Utilities.DbBean" />

Errors....taken from log file..

  
 
2006-01-03 11:48:21 StandardWrapperValve[jsp]: Servlet.service() for servlet jsp threw exception
org.apache.jasper.JasperException: /forums/carBean.jsp(15,0) The value for the useBean class attribute Utilities.DbBean is invalid.
at org.apache.jasper.compiler.DefaultErrorHandler.jspError(DefaultErrorHandler.java:39)
at org.apache.jasper.compiler.ErrorDispatcher.dispatch(ErrorDispatcher.java:409)
at org.apache.jasper.compiler.ErrorDispatcher.jspError(ErrorDispatcher.java:150)
at org.apache.jasper.compiler.Generator$GenerateVisitor.visit(Generator.java:1227)
at org.apache.jasper.compiler.Node$UseBean.accept(Node.java:1116)
at org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2163)
at org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2213)
at org.apache.jasper.compiler.Node$Visitor.visit(Node.java:2219)
at org.apache.jasper.compiler.Node$Root.accept(Node.java:456)
at org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2163)
at org.apache.jasper.compiler.Generator.generate(Generator.java:3272)
at org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:244)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:470)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:451)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:439)
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:511)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:295)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:118)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)
at java.lang.Thread.run(Thread.java:595)
 
 
 

[ January 03, 2006: Message edited by: Raghavan Chockalingam ]

[Balasubramani Dharmalingam]

Raghav,
you have used default access to DbBean class so it is not visible to the JSP. so change access specifier for DbBean class as public.

[Raghavan Chockalingam]

Sorry about that...now I have changed it to public and compiled again but I have the same error even then...

I want to know the .java file is a valid bean???

  
package Utilities;
 
import java.sql.*;
import java.io.*;
 
public class DbBean{
Connection connection;
Statement stmt;

void makeConnection(){.......

[ January 03, 2006: Message edited by: Raghavan Chockalingam ]

[Balasubramani Dharmalingam]

Raghav,
I tried the samething here. I am also getting same error.But after changing the access as public the error has gone.
did u restart the server after compiling the DbBean class ?

[Amarender Reddy]

Raghavan,
Can you make sure that the given error is thrown excatly the line :

 
<jsp:useBean id="myConnection" class="Utilities />

cheers

[Raghavan Chockalingam]

Thanks both of you guys for your help and I did not know earlier that I should restart the server.

1. Is it always necessary to restart the server whenever there is a revision with the bean class?

2. I now have a logical problem, if the bean creates a Connection or a Statement object then how do I use those objects in the .jsp file???

For example....
<jsp:getProperty name="myConnection" property="stmt" />

the above statement gives a Statement object but how do I assign this object to a Statement object created in jsp scriptlet.

 
<jsp:useBean id="myConnection" class="Utilities.DbBean" />
<% 
Statement stmt = 
%><jsp:getProperty name="myConnection" property="stmt" />
 
<%
ResultSet rs = stmt.executeQuery("select * from Forum_db.Forums_tbl");
%>
 

If you think I am totally wrong with the way I am thinking, can you tell me how do you establish/ use database connections in your applications. It would be very kind if you can me a working example of yours...thank you...

[Ulf Dittmer]

to 1) It is not necessary to restart the server if a class changes, but it is necessary to restart the web app that contains that class.

to 2) It is considered bad design to be using java.sql objects in a JSP page (and has practical drawbacks as well, like making exception handling hard). At a minimum, perform all the DB access in the bean class, and just retrieve the results from it in the JSP.

[Raghavan Chockalingam]

Thanks Ulf for your advice, can you tell me how to restart the Web application alone???

[Ben Souther]

Originally posted by Raghavan Chockalingam:
Thanks Ulf for your advice, can you tell me how to restart the Web application alone???

The Manager app that ships with Tomcat can be used for restarting applications.
http://tomcat.apache.org/tomcat-5.5-doc/manager-howto.html