getting java.sql.Connection error

[phamtranquocviet]

Hi,

I am getting this error:
[ERROR] Line 11: No source code is available for type
java.sql.SQLException; did you forget to inherit a required module?

when trying to check if an entered SSN is a duplicate via RPC. Here is
my RPC implementation:

package com.cadao.server;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import com.cadao.client.RegistrationService;
import com.google.gwt.user.server.rpc.RemoteServiceServlet;

public class RegistrationServiceImpl extends RemoteServiceServlet
implements RegistrationService
{
private static final long serialVersionUID = 1L;

public boolean isDuplicateSsn(String ssn) throws SQLException
{
String sql = "SELECT Ssn " +
"FROM User U JOIN Mem M ON U.UserId = M.UserId " +
"WHERE Ssn = '" + ssn + "'";
CadaoDb cadaoDb = new CadaoDb();
Connection connection = cadaoDb.getConnection();
Statement select = connection.createStatement();
ResultSet resultSet = select.executeQuery(sql);
resultSet.last();
if(resultSet.getRow() > 0)
return true;
return false;
}
}
============================================
package com.cadao.server;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;

public abstract class Db
{
private String driver = "com.mysql.jdbc.Driver";

/**
* Constructor
*/
public Db()
{ }

protected abstract String getUrl();
protected abstract String getDb();
protected abstract String getUser();
protected abstract String getPassword();

public final Connection getConnection()
{
String url = getUrl();
String db = getDb();
String user = getUser();
String password = getPassword();
Connection connection = null;
try
{
Class.forName(driver).newInstance();
connection = DriverManager.getConnection(url + db, user, password);
}
catch(Exception e)
{
System.err.println("Mysql Connection Error: ");
e.printStackTrace();
}
return connection;
}

protected static int getResultSetSize(ResultSet resultSet)
{
int size = -1;
try
{
resultSet.last();
size = resultSet.getRow();
resultSet.beforeFirst();
}
catch(SQLException e)
{ return size; }
return size;
}
}
======================================
I got this code from here:
http://gwt-examples.googlecode.com/svn/trunk/gwt-test-MySQLConn/src/com/tribling/gwt/test/mysqlconn/server/

Could somebody help me see what's missing? Thanks.

[Lothar Kimmeringer]

phamtranquocviet schrieb:

> public boolean isDuplicateSsn(String ssn) throws SQLException

You can't throw a SQLException from a method of a RemoteServiceServlet.
To be able to transport this exception to the client (where it is passed
as argument to the onFailure-method of the AsyncCallback, it's necessary
to extend it from SerializableException which SQLException clearly isn't.

I solved it that way, that I throw a RemoteServiceException where I add
the stacktrace of the causing exception as String, allowing to show the
error in a usual way (if you want to show that much information to an
user) without the need to create many many different exceptions.

Regards, Lothar

[Pham Tran Quoc Viet]

Thanks Lothar. I'll give it a try tonight and see what happens. Thanks again.
Viet Pham

[Pham Tran Quoc Viet]

Lothar,

Because I had isDuplicateSsn (on server) throw SQLException, I was forced to throw the same exception on RegistrationService, which is on client, which does not understand server language. That was the problem.

I fixed the code to catch SQLException instead of throwing it. This works for now, but I will probably log, then wrap it the way you suggested, and throw it again in a format that is serializable to be sent to client.

Thanks a bunch.

Viet Pham

[Pham Tran Quoc Viet]

Lothar,

By the way, I could not find RemoteServiceException in GWT doc. So, I assume it's your custom exception, right?

Thanks.

Viet Pham

[Lothar Kimmeringer]

Pham Tran Quoc Viet schrieb:

> By the way, I could not find RemoteServiceException in GWT doc. So, I
> assume it's your custom exception, right?

That's correct. But it's nothing very secret happening there so I
can post it here without being sent to the south-east-end of Cuba ;-)

------snip
/**
* Exception that will be thrown if there was an error while performing
* remote functions on the server
* @author "Lothar Kimmeringer" <lot...@kimmeringer.de>
*
*/
public class RemoteServiceException extends SerializableException {
private String stackTrace;
private String message;

private static final long serialVersionUID = 2L;

/**
* Creates a new instance of RemoteServiceException
*/
public RemoteServiceException() {
super();
}

/**
* Creates a new instance of RemoteServiceException
* @param message The message indicating the reason for the exception
* @param cause The cause leading to the exception
*/
public RemoteServiceException(String message, String cause) {
super(message);
this.message = message;
stackTrace = cause;
}

/**
* Creates a new instance of RemoteServiceException
* @param message The message indicating the reason for the exception
*/
public RemoteServiceException(String message) {
super(message);
this.message = message;
}

/**
* Returns the stacktrace of the cause
* @return The cause
*/
public String getCauseStackTrace() {
return stackTrace;
}

/**
* Returns the message of the exception
*/
public String getMessage(){
return message;
}
}
------snip

You can get the stacktrace as string doing the following:

StringWriter sw = new StringWriter();
throwable.printStackTrace(new PrintWriter(sw));
String stacktrace = sw.toString();

You have to do it outside the above exception, because the exception above
must be in a client-package, i.e. you are restricted to the GWT Java
ruling out PrintWriter at least.

Regards, Lothar

[Pham Tran Quoc Viet]

Thanks for taking the time to explain it so carefully. You are a good person.

Thanks again, Lothar.

Viet Pham