Resin's configuration files provide support for certain control tags for conditional processing.

Control Structures

The resin.conf and web.xml configuration files can use control structures. The syntax of the control structures is deliberately similar to the control structures used in JSTL.

These can be useful to create a resin.conf which works for both testing and deployment, depending on an environment parameter. When possible, users should avoid using the control tags when possible to keep their configuration files as simple as possible.

<web-app xmlns="http://caucho.com/ns/resin"
            xmlns:resin="http://caucho.com/ns/resin/core">
  <resin:choose>
  <resin:when test="\${mode='development'}">
    <resin:log>Development Mode</resin:log> 
  </resin:when>
  <resin:when test="\${mode='deploy'}">
    <resin:log>Deployment Mode</resin:log> 
  </resin:when>
  <resin:otherwise>
    <resin:log>Unknown Mode \${mode}</resin:log>
  </resin:otherwise>
  <resin:choose>
</web-app>

The source code for the control elements is found in com.caucho.config.core.

resin:set

resin:set adds an EL variable to the current context.

<resin:set var="name" value="\${value}"/>

<resin xmlns="http://caucho.com/ns/resin"
          xmlns:resin="http://caucho.com/ns/resin/core">
  <resin:set name="root" value="/var/www">

  <cluster id="app-tier">
    <root-directory>${root}</root-directory>

    ...
  </cluster>
</resin>

resin:if

resin:if executes part of the configuration file conditionally.

<resin:if test="\${expr}">
  ...
<resin:if>

resin:choose

resin:choose implements an if, elsif, else.

<resin:choose>
  <resin:when test="\${expr1}">
    ...
  </resin:when>

  <resin:when test="\${expr2}">
    ...
  </resin:when>

  <resin:otherwise>
    ...
  </resin:otherwise>
<resin:choose>

resin:when

<resin:when> conditionally configures a block within a <resin:choose> block. If the test matches, Resin will use the enclosed configuration.

resin:otherwise

<resin:otherwise> is the catch-all configuration for a <resin:choose> block when none of the <resin:when> items match.

Special Directives

resin:log

Logs a message to the given log file. The content of the element is the message.

<web-app xmlns="http://caucho.com/ns/resin">

  <resin:log>Starting server \${server.name}</resin:log>
</web-app>

resin:import

resin:import is used to read configuration information from another file. The target file is validated by a schema where the schema depends on the location of the resin:import. A resin:import in <server> will have a target with a top-level of <server>.

<resin xmlns="http://caucho.com/ns/resin"
          xmlns:resin="http://caucho.com/ns/resin/core">
  <cluster id="app-tier">

    <web-app-default>
      <resin:import path="WEB-INF/web.xml" optional="true"/>
      <resin:import path="WEB-INF/resin-web.xml" optional="true"/>
    </web-app-default>

  </cluster>
</resin>

resin:env

resin:env creates a new environment for a section of the configuration file. Some users may want to use this to create resources or databases with custom <class-loader> tags.

resin:env is tricky and only required for some extraordinary circumstances. Using it correctly requires a good understanding of classloaders.

Here is an example of a solution for the situation where a custom access logging class requires an old version of a jar that the web application uses as well. The requirement is that the example.MyAccessLog use an old version of the classes in Foo.jar, webapps use a newer version of the jar.

In a normal circumstance, access-log is used in the <host> environment. If the example.MyAccessLog uses a class from a jar file oldversion-Foo.jar, oldversion-Foo.jar needs to available to the classloader for the <host> environment. Because a %lt;web-app> inherits the classes of the <host>, the webapp will end up with the Foo.jar classes from the host's classloader; WEB-INF/lib/Foo.jar will not provide the classes because they have already been defined in the parent (host) classloader.

The following example solves the problem by using resin:env to create an environment just for the instantiation of the example.MyAccessLog class.

<host id=''>
  <resin:env>
   <class-loader>
     <library-loader path="/opt/lib/oldversion-Foo.jar"/>
   </class-loader>

   <access-log resin:type="example.MyAccessLog"/>
  </resin:env>

  ...

  <web-app>
    <!-- WEB-INF/lib can contain Foo.jar and the classes are not overridden 
         by the classes in oldversion-Foo.jar.
       -->
    ...
  </web-app>
</host>