jetty mysql database connection pooling

Question

I'm trying to do something seemingly simple: set up a small pool of database connections so that a servlet (just the one) doesn't create my server at 1 connection per second.

On Ubuntu 10.04, with the latest upgrade/update, I'm using Eclipse Jetty 8.1.5.v20120716. I'm trying to connect to a MySQL 5.1 server.

My servlet is called gcm, so in ${jetty}/contexts, I have this gcm.xml file:

<?xml version="1.0"  encoding="ISO-8859-1"?>
<!DOCTYPE Configure PUBLIC "-//Jetty//Configure//EN" "http://www.eclipse.org/jetty/configure.dtd">
<Configure id="wac" class="org.eclipse.jetty.webapp.WebAppContext">
  <New id="jdbc/myds" class="org.eclipse.jetty.plus.jndi.Resource">
    <Arg></Arg>
    <Arg>jdbc/myds</Arg>
    <Arg>
      <New class="com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource">
        <Set name="Url">jdbc:mysql://localhost:3306/chat</Set>
        <Set name="User">root</Set>
        <Set name="Password">sillyness</Set>
      </New>
    </Arg>
  </New>
  <Set name="contextPath">/</Set>
  <Set name="war"><SystemProperty name="jetty.home" default="."/>/webapps/gcm</Set>
  <Set name="extractWAR">true</Set>
</Configure>

When I start Jetty with java -jar start.jar -port=8080, everything starts fine until I try to hit the database from my servlet. The code handling part of the request looks like this:

 public static List<String> getDevices()
    throws javax.naming.NamingException, java.sql.SQLException {
    synchronized (regIds) {
        InitialContext ctx = new InitialContext();
        DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/myds");
        Connection conn = null;
        Statement stmt = null;

        try {
            conn = ds.getConnection();

            stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery("select * from chatdevice");

        //blah,blah,blah...

The error I get is:

    javax.naming.NameNotFoundException; remaining name 'jdbc/myds'
        at org.eclipse.jetty.jndi.NamingContext.lookup(NamingContext.java:500)
        at org.eclipse.jetty.jndi.NamingContext.lookup(NamingContext.java:531)
        at org.eclipse.jetty.jndi.NamingContext.lookup(NamingContext.java:531)
        at org.eclipse.jetty.jndi.NamingContext.lookup(NamingContext.java:546)
        at org.eclipse.jetty.jndi.java.javaRootURLContext.lookup(javaRootURLContext.java:112)
        at javax.naming.InitialContext.lookup(InitialContext.java:409) 
        at com.google.android.gcm.demo.server.Datastore.getDevices(Datastore.java:98)

How to get Jetty to find the database code?

Solution

In my case, I went to the jetty mailing list (https://dev.eclipse.org/mailman/listinfo/jetty-users) to ask my question.

A very smart person (Hi Jan!) wrote and answered like this:

There are generally many different ways to acheive the same outcome in jetty, so that's probably why you've seen different ways documented. Generally having options is a good thing

In case there's any confusion, this is the definitive page: http://wiki.eclipse.org/Jetty/Feature/JNDI If there's something missing, then please let us know so we can update the page.

Your case is a little out-of-the-ordinary in that you are using javaee-style features, but without a web.xml. This is not something I've encountered before, but it sounds like something I should add to the documentation.

I would recommend (as does the page above) that you put any jndi definitions into a WEB-INF/jetty-env.xml file and not the context xml file. If you do that, then you can effectively do what a web.xml element would do and bind your datasource into the java:comp/env namespace by defining your resource and binding it into java:comp/env in the one go (note this will NOT work in a context xml file, it must be jetty-env.xml):

So do the following in WEB-INF/jetty-env.xml:

 <New  id="jdbc/myds"  class="org.eclipse.jetty.plus.jndi.Resource">
  <Arg></Arg>
  <Arg>jdbc/myds</Arg>
  <Arg>
    <New  class="com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource">
      <Set  name="Url">jdbc:mysql://localhost:3306/chat</Set>
      <Set  name="User">root</Set>
      <Set  name="Password">sillyness</Set>
    </New>
  </Arg>
  <Call name="bindToENC">
     <Arg>jdbc/myds</Arg>
  </Call>   
 </New>

In the call to bindToENC bind whatever name you want to look up as the suffix to java:comp/env. Eg if you want to lookup java:comp/env/my/foo then the bindToENC argument would be "my/foo".

-- Jan Bartel www.webtide.com – Developer advice, services and support from the Jetty & CometD experts. _______________________________________________ jetty-users mailing list [email protected] https://dev.eclipse.org/mailman/listinfo/jetty-users

Now, that wasn't quite enough (I'm a jetty newbie). The WEB-INF referred to was the WEB-INF inside the war file for my servlet...so I extracted the contents of the war file into a directory, and then I could easily put the jetty-env.xml file in the WEB-INF directory.

This was critical too:

OK, I assumed a little jetty knowledge there, and thought you'd know that what I posted was merely a snippet from what you'd need to have for a complete jetty-env.xml file.

The wiki page for the jetty-env.xml file is here: http://wiki.eclipse.org/Jetty/Reference/jetty-env.xml

So wrap the root element as shown on that page around the snippet I posted and you should be good.

Now /that/ got the database connection to be attempted. Then I was getting connection refused from 127.0.0.1 errors in /var/log/auth.log.

Turns out for that I had denyhosts running, and sure enough someone had put ALL: 127.0.0.1 in there... which meant connections to my local machine were denied.

Once that detail was fixed, the servlet can finally reach MySQL on my server.