The Java EE 5 Tutorial (PDF) - Oracle Software Downloads

Programming SimpleTag Handlers
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set, the handler retrieves the connection object from the page context. Otherwise, the tag
handler first retrieves the tag handler for the enclosing tag and then retrieves the connection
object from that handler.
public class QueryTag extends SimpleTagSupport {
public int doTag() throws JspException {
String cid = getConnectionId();
Connection connection;
if (cid != null) {
// there is a connection id, use it
connection =(Connection)pageContext.
getAttribute(cid);
} else {
ConnectionTag ancestorTag =
(ConnectionTag)findAncestorWithClass(this,
ConnectionTag.class);
if (ancestorTag == null) {
throw new JspTagException("A query without
a connection attribute must be nested
within a connection tag.");
}
connection = ancestorTag.getConnection();
...
}
}
}
The query tag implemented by this tag handler can be used in either of the following ways:
...
SELECT account, balance FROM acct_table
where customer_number = ?
SELECT account, balance FROM acct_table
where customer_number = ?
The TLD for the tag handler uses the following declaration to indicate that the connectionId
attribute is optional:
The Java EE 5Tutorial • June 2010