Problem in usebean

[Betsy Camel]

hi
i am developing a application in jsp. & i am getting an error in tomcat server on using usebean

org.apache.jasper.JasperException: Unable to compile class for JSP

An error occurred at line: 36 in the jsp file: /tool/tool.jsp
Generated servlet error:
tool.connection.SqlConnect cannot be resolved or is not a type

An error occurred at line: 36 in the jsp file: /tool/tool.jsp
Generated servlet error:
tool.connection.SqlConnect cannot be resolved or is not a type


org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:84)
org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:328)
org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:389)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:288)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:267)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:255)
org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:556)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:296)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:245)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)




here is the code that i am using

<jsp:useBean id = "connect" scope = "session" type = "tool.connection.SqlConnect" />

its very urgent plz help

[David Ulicny]

I suppose that tool.connection.SqlConnect is not on the classpath. Try to fix it.

[Betsy Camel]

Can u plz explain that

[David Ulicny]

You need to have your packages somewhere on classpath. Easiest way is put them to WEB-INF/classes.

[Betsy Camel]

thanks david
that problem is solved but for each & every field in the bean class, i am getting this error
The field connect.stmt is not visible

where connect is the id name in the usebean & stmt is a field in the bean class.

[David Ulicny]

Must be public to be visible, but good practice is to use getters and setters for fields.

[Ben Souther]

Why don't you show us this SqlConnect object you're using?
Also describe how it's getting bound to session scope before your JSP is invoked.
[ September 20, 2005: Message edited by: Ben Souther ]

[Betsy Camel]

/* tool.connection.sqlconnect.java */
package tool.connection;

import java.sql.*;

public class SqlConnect
{
Connection conn = null;
Statement stmt = null;
//ResultSet rs = null;
public SqlConnect(){
try{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
conn = DriverManager.getConnection("jdbc dbc:mydsn","","");
stmt = conn.createStatement();
}catch(Exception e)
{
System.out.println(" e value is "+e);
}
}
}

[Betsy Camel]

can anyone help

[Ben Souther]

This class really isn't a bean.

In order to access a bean's fields from JSP using <jsp:getProperty or EL, the fields need to have accessors (getters). Even then, they will coerced into strings in the process.

A better approach would be to perform all of your JDBC operations in the bean, store the results in beans or lists of beans, bind the results to either request or session scope, THEN access the bean's fields from the JSP.

[ramprasad madathil]

Originally posted by Betsy
---------------------------
The field connect.stmt is not visible

From your posting of the code you use for the bean class, stmt is a variable of type Statement. Why do you try to access such variables from your useBean getProperty actions ?

Are you trying to get the statement object (in which case, what would you do with it ? ). You cannot set Statement objects using setProperty either. Your whole design needs another look. Perhaps it would help if you tell what you are trying to achieve.

cheers,
ram.

[Betsy Camel]

i have changed my code
<jsp:useBean id = "myclass" scope = "session" type = "tool.connection.SqlConnect" />

<%
java.sql.ResultSet res = myclass.selectQuery();
%>


and in the bean i have it

public static ResultSet selectQuery() throws SQLException
{
rs = stmt.executeQuery("select * from Machine_Details");
return rs;
}

& i am getting an error

java.lang.InstantiationException: bean myclass not found within scope
org.apache.jsp.tool.tool_jsp._jspService(org.apache.jsp.tool.tool_jsp:83)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:99)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:325)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:245)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

help needed immediately...

[ramprasad madathil]

Originally posted by Betsy
------------------------

<jsp:useBean id = "myclass" scope = "session" type = "tool.connection.SqlConnect" />

When you use useBean in this fashion (by defining the 'type' attribute rather than 'class'), the container will not instantiate a bean object for you. It would simply try to find an existing bean object in session scope (bound by an attribute name 'myclass') and give you a reference to that in the jsp. If it cannot find one, it throws an error , which's exactly what happened in your case. To put it short, the code above requires an object of SqlConnect bound to the session by an attribute name 'myclass', else it would fail.

To make it work, use the class attribute, which would do the same as above. Additionally if it does not find such a bean object, it would create one for you (and add it to that scope)

<jsp:useBean id = "myclass" scope = "session" class = "tool.connection.SqlConnect" />

<%
java.sql.ResultSet res = myclass.selectQuery();
%>

Here's the useBean syntax reference docs.

public static ResultSet selectQuery() throws SQLException
{
rs = stmt.executeQuery("select * from Machine_Details");
return rs;
}

Also, at some point you will have to do the above in a different way. A result set is alive only as long as the connection is - in the javabean you create a Connection, get a ResultSet and when you pass the result set to your front end, the associated Connection cannot be released until the 'view' is over with it. Also the clsoing of the ResultSet and Connection will have to occur in the 'view' because that's the place its used last. All this would result in quite unscalable code.

Solution :Use a DataTransferObject - when you get the ResultSet in your bean, populate the data into a model class (a POJO that follows JavaBean conventions) and then close the result set and connection. The view will now manipulate the model object rather than the result set.

Here's a sample -

public class MachineDetails{
  int id;
  String name;
  //all other properties of machine
 
  //add getter and setters for all props
}

And then in your Bean

public class SqlConnect {
 
   List machinesList = new ArrayList();
 
   public List getMachinesList(){ return machinesList;}
 
   public void selectQuery() throws SQLException
   {
       rs = stmt.executeQuery("select * from Machine_Details");
       while(rs.hasNext()){
           MachineDetails machine = new MachineDetails();
           //get data from rs, populate into machine object using the setter methods
           machinesList.add(machine);
       }
       rs.close();
   }
 
   //OTHER METHODS.
}
 

In your jsp

<jsp:useBean id = "myclass" scope = "session" class = "tool.connection.SqlConnect" />
 
<%myClass.selectQuery();%>
 
MachineDetails : <jsp:getProperty name = "myclass" property="machineDetails"/>

Hope that helps.
cheers,
ram.

[Betsy Camel]

i have implemented that..
but its giving an error..

java.lang.NoSuchMethodError: tool.connection.SqlConnect.selectQuery()Ljava/sql/ResultSet;
org.apache.jsp.tool.tool_jsp._jspService(org.apache.jsp.tool.tool_jsp:88)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:99)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:325)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:245)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

[Ben Souther]

Betsy,
I would strongly recommend that you find a JDBC tutorial and get your bean working as a standalone (command line) application.
In your main method, you should be able to:

Instanciate the bean,

Call a method the performs a database query and returns the data in something other than a resultSet (list of beans or multi dimensioned array).

Iterates over the data, printing it to the screen.

Once you've done this, you'll know that your database code is in good working order.
At that point look into what it will take to call this bean from a servlet or JSP and present the data in a browser.

One of server side Java's greatest strengths is that you can separate these concerns and not have to debug 15 different issues at the same time.

[ramprasad madathil]

Did you copy paste the code I posted ? Did the bean compile ?

I ask because

while(rs.hasNext()){

will not work (which is what's giving a NoSuchMethodError perhaps).

It ought to be

while(rs.next()){

Having said that, I think Ben's suggestion is very valid and should be the way to go for you. Your learning will be a lot more organized and less frsutrating (which means you can learn even more) that way.

cheers,
ram.

[Betsy Camel]

hi
i have dont that but facing another problem. i am able to get all the fields in the database into the list.while displaying i want it to be displayed exactly in the same way as in the database,which i am not able to implement using the arraylist.what other collection can i use ?
please help..

[Bear Bibeault]

i want it to be displayed exactly in the same way as in the database,which i am not able to implement using the arraylist

This tells us nothing. Firstly, DBs have no display, so the concept of having it display like it is in the DB makes no sense. What do you mean by that?

And what is it that the list isn't doing for you?

You'll get better answers to your questions if you take the time to explain what it is that you are after.

[Betsy Camel]

by using a list all the column values are displayed in a stretch. I need to display the values with respect to the columns.
eg

Name SerNo Marks

Tom 1 99
Jim 2 89


while i am able to get it in this manner

Name SerNo Marks
Tom
Jim
1
2
99
89

by using the above given code...
How to i align it....

[Ben Souther]

You could use nested lists or nested arrays to represent a two dimensional table. A better approach, if you know the column names and types, is to create a simple bean to represent a row in your table and return a List of those.

 
package com.mypackage;
 
public class MarksNumberRowBean{
    private String name;
    private String serialNo;
    private int    marks;
 
    public String getName(){
        return this.name;
    }
    public void setName(String name){
        this.name = name;
    }
........

Then, for each row in your resultSet, create and populate a MarksRowBean and add it to your List.

[Betsy Camel]

thats the problem...the column Number keeps changing & the user has rights to add a column...
this implies i cannot use the above method.
Can u tell me some other means

[Ben Souther]

I also mentioned in the last post that you can use nested arrays or lists to work with dynamic tables. You can use the methods found in ResultSetMetaData to determine how many columns you need to create.
http://java.sun.com/j2se/1.5.0/docs/api/java/sql/ResultSetMetaData.html