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<TITLE>Writing Advanced Applications, Chapter 8: Performance Techniques</TITLE>
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<FONT SIZE="-1"><A HREF="/developer/onlineTraining/index.html">Training Index</A></FONT>
<H2>Writing Advanced Applications<BR>
<FONT SIZE="3">Chapter 8 Continued: Connection Pooling </FONT></H2>
<FONT SIZE="-1">[<A HREF="perf.html"><<BACK</A>] [<A HREF="index.html#contents">CONTENTS</A>] [<A HREF="perf2.html">NEXT>></A>]</FONT></DIV>
<P>
If you have used a SQL or other similar tool to connect to a
database and act on the data, you probably know that
getting the connection and logging in is the part that takes
the most time. An application can easily spend several seconds
every time it needs to establish a connection.
<P>
In releases
prior to JDBC<FONT SIZE="-2"><SUP>TM</SUP></FONT> 2.0 every database session requires
a new connection and login even if the previous connection and
login used the same table and user account.
If you are using a JDBC release prior to 2.0 and want to
improve performance, you can cache JDBC connections instead.
<P>
Cached connections are kept in a runtime object pool and
can be used and reused as needed by the application.
One way to implement the object pool is to make a simple
hashtable of connection objects. However, a more flexible
way to do it is to write a wrapper JDBC <CODE>Driver</CODE>
that is an intermediary between the client application
and database.
<P>
The wrapper approach works particularly well in an Enterprise
Bean that uses Bean-managed persistence for two reasons: 1) Only
one <CODE>Driver</CODE> class is loaded per Bean, and 2) specific
connection details are handled outside the Bean.
<P>
This section explains how to write a wrapper JDBC <CODE>Driver</CODE>
class.
<UL>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<A HREF="#wrap">Wrapper Classes</A></FONT>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<A HREF="#drive">Connection Driver</A></FONT>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<A HREF="#pool">Connection Pool</A></FONT>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<A HREF="#dead">Deadlocks and Hangs</A></FONT>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<A HREF="#connect">Closing Connections</A></FONT>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<A HREF="#example">Example Application</A></FONT>
</UL>
<HR>
<A NAME="wrap"></A>
<H3>Wrapper Classes</H3>
The wrapper JDBC <CODE>Driver</CODE> created for this
examples consists of the following three classes:
<UL>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<CODE>JDCConnectionDriver</CODE></FONT>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<CODE>JDCConnectionPool</CODE></FONT>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">
<CODE>JDCConnection</CODE></FONT>
</UL>
<A NAME="drive"></A>
<H3>Connection Driver</H3>
The
<A HREF="./Code/JDCConnectionDriver.java">JDCConnectionDriver.java</A>
class implements the <CODE>java.sql.Driver</CODE> interface, which
provides methods to load drivers and create new
database connections.
<P>
A
<CODE>JDCConnectionManager</CODE> object is created by the application
seeking a database connection. The application provides the database
Uniform Resource Locator (URL) for the database, login user ID, and
login password.
<P>
The <CODE>JDCConnectionManager</CODE> constructor
does the following:
<UL>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">Registers the <CODE>JDCConnectionManager</CODE> object with the
<CODE>DriverManager</CODE>.</FONT>
<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">Loads the <CODE>Driver</CODE> class passed to the constructor
by the calling program. </FONT>
<P>
<LI><FONT FACE="Verdana, Arial, Helvetica, sans-serif">Initializes a <CODE>JDCConnectionPool</CODE> object for the
connections with the database URL, login user ID, and login password
passed to the constructor by the calling program. </FONT>
</UL>
</FONT>
<PRE>
public JDCConnectionDriver(String driver,
String url,
String user,
String password)
throws ClassNotFoundException,
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