Hi all,
This is to give big thanks to all.
Erik - i will go thr it - i think i need some some time to grasp it.
Regards and Have a nice day,
Manisha
Erik Weber <[EMAIL PROTECTED]> wrote:
Manisha Sathe wrote:
>I am still new to struts and even servlets. Last time when i developed
>servlets, i created one common class method to get the connection (with
>regular JDBC call). All database related parameters i stored in a constant
>variable file.
>
>
That's the way I do it, with or without Struts, with or without a
DataSource that pools Connections. Make a ConnectionManager class with
either a static "getConnection" method, or an instance method if you are
using multiple DataSources and a singleton per DataSource. Then all the
rest of your app needs to know is ConnectionManager.getConnection(), or
ConnectionManager.getConnectionManager("config_name").getConnection().
Put the config data in a constant file or a properties file. Include
both the information needed to obtain a DataSource from the naming
server and (possibly) the information needed to obtain a Connection
directly from DriverManager. Write your ConnectionManager so that if it
can't find the DataSource or get a Connection from it, it will log an
alert and (possibly) get one from the DriverManager. If it finds the
DataSource and can get a Connection from it, it should cache the
DataSource reference so that it doesn't have to repeat the lookup:
protected DataSource dataSource;
protected void init() {
try {
InitialContext ic = new InitialContext();
//use JBoss' naming server
Object ds = ic.lookup("java:/MyDataSourceName");
//use Tomcat's naming server
//Object ds = ic.lookup("java:/comp/env/jdbc/MyDataSourceName");
dataSource = (DataSource) PortableRemoteObject.narrow(ds,
DataSource.class);
}
catch (Exception e) {
//problem!
}
}
public Connection getConnection() {
try {
return dataSource.getConnection();
}
catch (Exception e) {
//do something about it
return null;
}
}
Also consider including cleanup methods.
Your DAOs in any type of Servlet application can use this
ConnectionManager class, which has no knowledge of Struts (why should
it?). With that said, your DataSource implementation is much more
important than where in your code you configure your DataSource and
distribute your Connections (I have had problems with DBCP and leaks
which may or not be my fault; there are other open source DataSource
implementations). You don't gain anything that I know of by configuring
Struts to know about your DataSource.
Typically in Struts I do something like this:
Action.execute --> Manager.get or Manager.put --> DAO.query or
DAO.insert/update (using ConnectionManager).
Also, it's important to clean up connections properly, if you are using
a DataSource that pools connections. Use this idiom or similar:
Connection c = null;
PreparedStatement p = null;
ResultSet r = null;
ArrayList items = new ArrayList();
try {
c = ConnectionManager.getConnection();
if (c == null) throw new SystemException("no database connection
available");
String sql = SQLManager.getSQL(SQLManager.GUMMY_BEAR_FLAVORS_SELECT);
p = c.prepareStatement(sql);
r = p.executeQuery();
while (r.hasNext()) {
//add gummy bear flavors to list
}
p.close(); //also closes r
p = null;
c.close();
c = null;
return items;
}
//possibly catch and handle SQLExceptions, etc., here,
//throwing system Exceptions to your managers
finally {
//if an Exception was thrown during JDBC operations
//in the try clause, then the PreparedStatement and
//Connection possibly were instantiated but not closed,
//so this clause will close them;
//if not, this clause will do nothing;
//note: consider refactoring these lines into a
//ConnectionManager.cleanup method to eliminate
//duplicate code
try {
if (p != null) p.close();
}
catch (Exception e) {
//this would be a problem that should be handled
}
try {
if (c != null) c.close();
}
catch (Exception e) {
//this would be a problem that should be handled
}
}
See your J2EE server's documentation for how to configure the naming
server to instantiate a DataSource (it's well documented both for JBoss
and Tomcat). The advantage of using a DataSource that pools connections
is that your application doesn't have to suffer the overhead of
establishing a Socket connection, handshaking, authentication, etc.,
every time your application needs to use a Connection, as many
Connections are prepared and "held" waiting at DataSource initialization
time.
Erik
>
>Now in struts i found out that we can specify the datasource inside
>struts-config.xml.
>
>I want to know which methodology is better ? Can i continue with my existing
>method ? or struts database method is better ?
>
>regards
>Manisha
>
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