ioannis cherouvim

When writing Java code you must follow the Code Conventions for the Java Programming Language. It’s a document written by Sun back in 1997. Why should you read such an ancient (in computer science terms) document?

Code conventions are important to programmers for a number of reasons:

* 80% of the lifetime cost of a piece of software goes to maintenance.
* Hardly any software is maintained for its whole life by the original author.
* Code conventions improve the readability of the software, allowing engineers to understand new code more quickly and thoroughly.

Some people tell me that they cannot change their style, because that’s how they are used to coding. Fair enough. Do whatever you want when coding alone, in your home. But not in a professional environment. If you can’t be bothered, do us a favour and leave. Resign. Start selling popcorn. Whatever.

I have a serious problem working with people who commit Java code which looks like this:

public class persons {

public void PersonSave(persons p) {

package foo.bar.personUtils;

public static final String foo = "whatever";

whatever()
{
  // do stuff
}

Seriously, please try to read the following piece of code found in a real life project. Does this look like Java?

if(e<0.0)d= -d;
if(d!=0.0)for(int i=0;i<dim;i++)this.n[i] = this.n[i]/d;
else this.tW.writeString("normalise: non simplex");
Object leftList = null, rightList = null;
try{ leftList = c.newInstance();}
catch(Exception e){tW.writeString("sort:error1 ");return null;};

OK, this style might have been good in an Obfuscated Code Contest, but it definitely does not get you going in the workplace.

Good luck

You are building a webapp. You want database connectivity. You want pooling (because its an expensive resource). You start building your own database connection pool. STOP!!!

Who told you that you can do it well? Why did you hack your own connection pool implementation, which is seriously broken, spawns thousands of threads and turns the server into a miserable piece of shit that needs restart every 24h?

Wrong choice my friend. Next time do us all a favour and use one of the following:

• DBCP
• c3p0
• proxool

And don’t forget: The standard idiom for releasing a connection is to close (return) the connection in a finally block.

Connection con = getPooledConnectionFromSomewhere();
try {
  // do stuff with connection
} catch (SQLException e) {
  // handle problems
} finally {
  con.close();
}

Of course, closing the connection can throw an SQLException, but it’s up to you on how you will handle it.

Good luck

You are building a webapp and you want database connection pooling. Your container can help you manage this javax.sql.DataSource by configuring it and exposing it through the JNDI tree.

Containers usually come with Jakarta Commons DBCP out of the box. In order to use it edit the context.xml file of your webapp and set your datasource there.

<?xml version="1.0" encoding="UTF-8"?>
 <Context path="/foo-app">

 <!-- TOMCAT 5.5.xx DESCRIPTOR -->
 <Resource name="foo"
  auth="Container"
  type="javax.sql.DataSource"
  maxActive="1"
  maxIdle="1"
  maxWait="3000"
  username="user"
  password="pass"
  driverClassName="net.sourceforge.jtds.jdbc.Driver"
  url="jdbc:jtds:sqlserver://localhost:1433;DatabaseName=foobar;charset=utf8"
 />

 <!-- TOMCAT 5.0.28 DESCRIPTOR -->
 <!--
  <Resource name="foo" type="javax.sql.DataSource"/>
  <ResourceParams name="foo">
   <parameter><name>maxActive</name><value>1</value></parameter>
   <parameter><name>maxIdle</name><value>1</value></parameter>
   <parameter><name>maxWait</name><value>3000</value></parameter>
   <parameter><name>username</name><value>user</value></parameter>
   <parameter><name>password</name><value>pass</value></parameter>
   <parameter><name>driverClassName</name><value>net.sourceforge.jtds.jdbc.Driver</value></parameter>
   <parameter><name>url</name><value>jdbc:jtds:sqlserver://localhost:1433;DatabaseName=foobar;charset=utf8</value></parameter>
  </ResourceParams>
  -->

</Context>

Tomcat 5.0.xx and 5.5.xx uses different xml syntax for most of it’s configuration. Here I’m presenting both with 5.0.xx’s block commented out.

So, you’ve got your app called “foo-app”. Next time you’ll deploy it, tomcat will copy context.xml to ${catalina.home}/conf/localhost/foo-app.xml where from it will be reading the configuration on each context or container initialization. Your Datasource is called “foo”.
In your java code now, what you need to get a reference to “foo” is:

Context ctx = new InitialContext();
DataSource ds = (DataSource)ctx.lookup("java:comp/env/foo");

And then something along the lines:

Connection con = ds.getConnection();

Happy coding.