Does anyone know of any techniques that would allow a Database Access Object
(DAO) to be used from the various actions that make up a Struts application?
I have a DAO which, when instantiated, acquires a data source from the
servlet container (in this case, Apache Tomcat). Thereafter, I can execute
the various methods provided by the object which use the data source to
execute SQL queries/statements, and return usable data in the form of
Strings, Maps, Vectors etc, as appropriate.
Instantiating the DAO in the execute() method of each of my action's
however, seems a little inefficient. Does Struts provide any way to
instantiate the object once and then make it available for the lifetime of
the container (in a way that my Actions can access it)?
Note please that i'm well aware that this is a somewhat non-standard
approach to database interaction. I am intending to investigate Hibernate
(and like) at some point, but for the time being I want to avoid such.
This is the skeleton of the DAO I have in mind...
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import java.sql.*;
import javax.sql.*;
import javax.naming.*;
import javax.servlet.*;
public class MyDataAccessObject {
private DataSource dataSource;
private String SQL;
public MyDataAccessObject() throws Exception {
try {
Context init = new InitialContext();
Context ctx = (Context) init.lookup("java:comp/env");
dataSource = (DataSource) ctx.lookup("jdbc/mysqldb");
} catch (NamingException ne) {
throw new Exception("Cannot retrieve
java:comp/env/jdbc/mysqldb", ne);
}
SQL = null;
}
public String getValue(String name) {
Connection dbcon = null;
PreparedStatement pstmt = null;
ResultSet rs = null;
String value = null;
try {
dbcon = dataSource.getConnection();
SQL = "SELECT value FROM table WHERE name = ?";
pstmt = dbcon.prepareStatement(SQL);
pstmt.setString(1, name);
rs = pstmt.executeQuery();
while (rs.next()) {
value = rs.getString("value");
}
rs.close();
rs = null;
pstmt.close();
pstmt = null;
dbcon.close();
dbcon = null;
} catch (SQLException ex) {
log(ex);
} catch (Exception ex) {
log(ex);
} finally {
if (rs != null) {
try { rs.close(); } catch (Exception fe1) { log(fe1); }
rs = null;
}
if (pstmt != null) {
try { pstmt.close(); } catch (Exception fe2) { log(fe2); }
pstmt = null;
}
if (dbcon != null) {
try { dbcon.close(); } catch (Exception fe3) { log(fe3); }
dbcon = null;
}
}
SQL = null;
return value;
}
private void log(...) {
// Handle logging
}
}
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Thanks,
Jazz
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