JDBC Interview Questions and Answers

How can I connect to an Excel spreadsheet file using jdbc?
Let's say you have created the following Excel spreadsheet in a worksheet called Sheet1 (the default sheet name). And you've saved the file in c:\users.xls.

USERID FIRST_NAME LAST_NAME
pkua Peter Kua
jlsmith John Smith
gh2312 Everett Johnson
chimera Faiz Abdullah
roy6943 Roy Sudirman

Since Excel comes with an ODBC driver, we'll use the JDBC-ODBC bridge driver that comes packaged with Sun's JDK to connect to our spreadsheet.
In Excel, the name of the worksheet is the equivalent of the database table name, while the header names found on the first row of the worksheet is the equivalent of the table field names. Therefore, when accessing Excel via jdbc, it is very important to place your data with the headers starting at row 1.
1. Create a new ODBC Data Source using the Microsoft Excel Driver. Name the DSN "excel", and have it point to c:\users.xls.
2. Type in the following code:

package classes;
import java.sql.*;

public class TestServer
{
static
{
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
}
catch (Exception e) {
System.err.println(e);
}
}

public static void main(String args[]) {
Connection conn=null;
Statement stmt=null;
String sql="";
ResultSet rs=null;

try {
conn=DriverManager.getConnection("jdbc:odbc:excel","","");
stmt=conn.createStatement();
sql="select * from [Sheet1$]";
rs=stmt.executeQuery(sql);

while(rs.next()){
System.out.println(rs.getString("USERID")+
" "+ rs.getString("FIRST_NAME")+" "+
rs.getString("LAST_NAME"));
}
}
catch (Exception e){
System.err.println(e);
}
finally {
try{
rs.close();
stmt.close();
conn.close();
rs=null;
stmt=null;
conn=null;
}
catch(Exception e){}
}
}
}

Notice that we have connected to the Excel ODBC Data Source the same way we would connect to any normal database server.
The only significant difference is in the SELECT statement. Although your data is residing in the worksheet called "Sheet1", you'll have to refer to the sheet as Sheet1$ in your SQL statements. And because the dollar sign symbol is a reserved character in SQL, you'll have to encapsulate the word Sheet1$ in brackets, as shown in the code.

How do I execute stored procedures?
Here is an example on how to execute a stored procedure with JDBC (to use this in a servlet is the same the only thing is that you create the connection and callable statement in the init() of the servlet):
package DBTest;
import java.sql.*;
public class JdbcTest {

private String msDbUrl = "jdbc:odbc:ms";
private String msJdbcClass = "sun.jdbc.odbc.JdbcOdbcDriver";
private Connection mcDbAccess;
private CallableStatement msProcedure;

public JdbcTest() {
try {
Class.forName( msDbUrl ).newInstance();
mcDbAccess = DriverManager.getConnection( msJdbcClass, "milestone", "milestone" );
msProcedure = mcDbAccess.prepareCall(
"{? = call sp_sav_Bom_Header( ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ? ) }"
);
msProcedure.registerOutParameter( 1, java.sql.Types.VARCHAR );
msProcedure.setInt( 2, -1 );
msProcedure.setInt( 3, 39 );
msProcedure.setString( 4, "format" );
long ltTest = new java.util.Date().getTime();
System.out.println( "Today: " + ltTest );
msProcedure.setTimestamp( 5, new Timestamp( ltTest ) );
msProcedure.setString( 6, "type" );
msProcedure.setString( 7, "submitter" );
msProcedure.setString( 8, "email" );
msProcedure.setString( 9, "phone" );
msProcedure.setString( 10, "comments" );
msProcedure.setString( 11, "label" );
msProcedure.setInt( 12, 52 );
msProcedure.setBoolean( 13, true );
msProcedure.setBoolean( 14, false );
msProcedure.setInt( 15, 53 );
msProcedure.setString( 16, "runtime" );
msProcedure.setString( 17, "configuration" );
msProcedure.setBoolean( 18, true );
msProcedure.setBoolean( 19, false );
msProcedure.setString( 20, "special instructions" );
msProcedure.setInt( 21, 54 );

ResultSet lrsReturn = null;
System.out.println( "Execute: " + (lrsReturn = msProcedure.executeQuery() ) );
while( lrsReturn.next() ) {
System.out.println( "Got from result set: " + lrsReturn.getInt( 1 ) );
}
System.out.println( "Got from stored procedure: " + msProcedure.getString( 1 ) );
} catch( Throwable e ) {
e.printStackTrace();
}
}

public static void main(String[] args) {
new JdbcTest();
}
}
I also tried it by using a native JDBC driver (i-net) and it also works fine. The only problem we encounter with JDBC-ODBC bridge is that a stored procedure pads spaces to the full length of a VARCHAR but the native JDBC behaves right. Therefore I suggest to use JDBC native drivers.
The above example uses the MS SQL Server.

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