Sometimes it is useful to pass configuration information to a webapp at runtime that you either cannot or cannot conveniently code into a web.xml env-entry. In such cases, you can use org.eclipse.jetty.plus.jndi.EnvEntry, and even override an entry of the same name in web.xml.

<New class="org.eclipse.jetty.plus.jndi.EnvEntry">
  <Arg></Arg>
  <Arg>mySpecialValue</Arg>
  <Arg type="java.lang.Integer">4000</Arg>
  <Arg type="boolean">true</Arg>
</New>   

This example defines a virtual env-entry called mySpecialValue with value 4000 that is scoped to the JVM. It is put into JNDI at java:comp/env/mySpecialValue for every web app deployed. Moreover, the boolean argument indicates that this value overrides an env-entry of the same name in web.xml. If you don't want to override, omit this argument, or set it to false.

The Servlet Specification allows binding only the following object types to an env-entry:

That being said, Jetty is a little more flexible and allows you to also bind custom POJOs, javax.naming.References and javax.naming.Referenceables. Be aware that if you take advantage of this feature, your web application is not portable.

To use the env-entry configured above, use code in your servlet/filter/etc., such as:

import javax.naming.InitialContext;

public class MyClass {

  public void myMethod() {

    InitialContext ic = new InitialContext();
    Integer mySpecialValue = (Integer)ic.lookup("java:comp/env/mySpecialValue");
    ...
  }
}   

You can configure any type of resource that you want to refer to in a web.xml file as a resource-ref or resource-env-ref, using the org.eclipse.jetty.plus.jndi.Resource type of naming entry. You provide the scope, the name of the object (relative to java:comp/env) and a POJO instance or a javax.naming.Reference instance or javax.naming.Referenceable instance.

The J2EE Specification recommends storing DataSources in java:comp/env/jdbc, JMS connection factories under java:comp/env/jms, JavaMail connection factories under java:comp/env/mail and URL connection factories under java:comp/env/url. For example:

Here is an example of configuring a javax.sql.DataSource. Jetty can use any DataSource implementation available on its classpath. In this example, the DataSource is from the Derby relational database, but you can use any implementation of a javax.sql.DataSource. This example configures it as scoped to a web app with the id of wac:

<Configure id='wac' class="org.eclipse.jetty.webapp.WebAppContext">
  <New id="myds" class="org.eclipse.jetty.plus.jndi.Resource">
    <Arg><Ref refid="wac"/></Arg>
    <Arg>jdbc/myds</Arg>
    <Arg>
      <New class="org.apache.derby.jdbc.EmbeddedDataSource">
        <Set name="DatabaseName">test</Set>
        <Set name="createDatabase">create</Set>
      </New>
    </Arg>
  </New>
</Configure>

The code above creates an instance of org.apache.derby.jdbc.EmbeddedDataSource, calls the two setter methods setDatabaseName("test"), and setCreateDatabase("create"), and binds it into the JNDI scope for the web app. If you do not have the appropriate resource-ref set up in your web.xml, it is available from application lookups as java:comp/env/jdbc/myds.

Here's an example web.xml declaration for the datasource above:

<resource-ref>
  <res-ref-name>jdbc/myds</res-ref-name>
  <res-type>javax.sql.DataSource</res-type>
  <res-auth>Container</res-auth>
</resource-ref>  

To look up your DataSource in your servlet/filter/etc.:

import javax.naming.InitialContext;
import javax.sql.DataSource;

public class MyClass {

  public void myMethod() {

    InitialContext ic = new InitialContext();
    DataSource myDS = (DataSource)ic.lookup("java:comp/env/jdbc/myds");     

    ...
  }
}

For more examples of datasource configurations, see Datasource Examples.

Jetty can bind any implementation of the JMS destinations and connection factories. You just need to ensure the implementation Jars are available on Jetty's classpath. Here is an example of binding an ActiveMQ in-JVM connection factory:

<Configure id='wac' class="org.eclipse.jetty.webapp.WebAppContext">
  <New id="cf" class="org.eclipse.jetty.plus.jndi.Resource">
    <Arg><Ref refid='wac'/></Arg>
    <Arg>jms/connectionFactory</Arg>
    <Arg>
      <New class="org.apache.activemq.ActiveMQConnectionFactory">
        <Arg>vm://localhost?broker.persistent=false</Arg>
      </New>
    </Arg>
  </New>
</Configure>

The entry in web.xml would be:

<resource-ref>
  <res-ref-name>jms/connectionFactory</res-ref-name>
  <res-type>javax.jms.ConnectionFactory</res-type>
  <res-auth>Container</res-auth>
</resource-ref>

TODO: put in an example of a QUEUE from progress demo

Jetty also provides infrastructure for access to javax.mail.Sessions from within an application:

<Configure id='wac' class="org.eclipse.jetty.webapp.WebAppContext">
  <New id="mail" class="org.eclipse.jetty.plus.jndi.Resource">
    <Arg><Ref refid="wac"/></Arg>
    <Arg>mail/Session</Arg>
    <Arg>
      <New class="org.eclipse.jetty.jndi.factories.MailSessionReference">
        <Set name="user">fred</Set>
        <Set name="password">OBF:1xmk1w261z0f1w1c1xmq</Set>
        <Set name="properties">
          <New class="java.util.Properties">
            <Put name="mail.smtp.host">XXX</Put>
            <Put name="mail.from">me@me</Put>
            <Put name="mail.debug">true</Put>
          </New>
        </Set>
      </New>
    </Arg>
  </New>
</Configure>     

This setup creates an instance of the org.eclipse.jetty.jndi.factories.MailSessionReference class, calls its setter methods to set up the authentication for the mail system, and populates a set of Properties, setting them on the MailSessionReference instance. The result is that an application can look up java:comp/env/mail/Session  at runtime and obtain access to a javax.mail.Session  that has the necessary configuration to permit it to send email via SMTP.

If you want to perform distributed transactions with your resources, you need a transaction manager that supports the JTA interfaces, and that you can look up as java:comp/UserTransaction in your webapp. Jetty does not ship with one as standard, but you can plug in the one you prefer. You can configure a transaction manager using the JNDI Transaction object in a Jetty config file. The following example configures the Atomikos transaction manager:

<New id="tx" class="org.eclipse.jetty.plus.jndi.Transaction">
  <Arg>
    <New class="com.atomikos.icatch.jta.J2eeUserTransaction"/>
  </Arg>
</New>

Generally, the name you set for your Resource should be the same name you use for it in web.xml. For example:

In a context xml file:

<Configure id='wac' class="org.eclipse.jetty.webapp.WebAppContext">
  <New id="myds" class="org.eclipse.jetty.plus.jndi.Resource">
    <Arg><Ref refid="wac"/></Arg>
    <Arg>jdbc/mydatasource</Arg>
    <Arg>
      <New class="org.apache.derby.jdbc.EmbeddedDataSource">
        <Set name="DatabaseName">test</Set>
        <Set name="createDatabase">create</Set>
      </New>
    </Arg>
  </New>
</Configure>

In web.xml:

<resource-ref>
  <res-ref-name>jdbc/mydatasource</res-ref-name>
  <res-type>javax.sql.DataSource</res-type>
  <res-auth>Container</res-auth>
  <injection-target>
    <injection-target-class>com.acme.JNDITest</injection-target-class>
    <injection-target-name>myDatasource</injection-target-name>
  </injection-target>
</resource-ref>

However, you can refer to it in web.xml by a different name, and link it to the name in your org.eclipse.jetty.plus.jndi.Resource by using an org.eclipse.jetty.plus.jndi.Link. For the example above, you can refer to the jdbc/mydatasource resource as jdbc/mydatasource1 as follows:

In a context xml file declare jdbc/mydatasource:

<Configure id='wac' class="org.eclipse.jetty.webapp.WebAppContext">
  <New id="myds" class="org.eclipse.jetty.plus.jndi.Resource">
    <Arg><Ref refid="wac"/></Arg>
    <Arg>jdbc/mydatasource</Arg>
    <Arg>
      <New class="org.apache.derby.jdbc.EmbeddedDataSource">
        <Set name="DatabaseName">test</Set>
        <Set name="createDatabase">create</Set>
      </New>
    </Arg>
  </New>
</Configure>

Then in a WEB-INF/jetty-env.xml file, link the name jdbc/mydatasource to the name you want to reference it as in web.xml, which in this case is jdbc/mydatasource1:

<New id="map1" class="org.eclipse.jetty.plus.jndi.Link">
  <Arg><Ref refid='wac'/></Arg>
  <Arg>jdbc/mydatasource1</Arg> <!-- name in web.xml -->
  <Arg>jdbc/mydatasource</Arg>  <!-- name in container environment -->
</New>

Now you can refer to jdbc/mydatasource1 in the web.xml like this:

<resource-ref>
  <res-ref-name>jdbc/mydatasource1</res-ref-name>
  <res-type>javax.sql.DataSource</res-type>
  <res-auth>Container</res-auth>
  <injection-target>
    <injection-target-class>com.acme.JNDITest</injection-target-class>
    <injection-target-name>myDatasource</injection-target-name>
  </injection-target>
</resource-ref>

This can be useful when you cannot change a JNDI resource directly in the web.xml but need to link it to a specific resource in your deployment environment.