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| |
| <section> |
| <h2><a name="Writing_a_Custom_Mailet"></a>Writing a Custom Mailet</h2> |
| |
| |
| <p> |
| Implementing a custom mailet is generally a simple task, most of whose complexity |
| lies in coding the actual work to be done by the mailet. This is largely due to the |
| simplicity of the Mailet interface and the fact that a GenericMailet class is provided |
| as part of the Mailet package. |
| </p> |
| |
| |
| <p> |
| In this discussion we will assume that any mailet being implemented is a subclass of |
| GenericMailet. The GenericMailet class serves to abstract away of the configuration and |
| logging details. While it provides a noop implementation of the init() and destroy() methods, |
| these can be easily overridden to provide useful functionality. |
| </p> |
| |
| |
| <p> |
| In general, the only four methods that you should need to implement are init(), destroy(), |
| getMailetInfo(), and service(Mail). And only the last is required in all cases. |
| </p> |
| |
| <section> |
| <h3><a name="Configuration"></a>Configuration</h3> |
| |
| <p> |
| As described in the <a href="config-mailetcontainer.html">SpoolManager configuration |
| section</a>, mailets are configured with a set of String (name, value) pairs. These values are |
| passed into the Mailet upon initialization (although the details of this process are hidden by |
| the GenericMailet implementation). GenericMailet provides access to this configuration |
| information through use of the getInitParameter(String) method. Passing in the name of the |
| requested configuration value will yield the value if set, and null otherwise. Configuration |
| values are available inside the init(), destroy(), and service(Mail) methods. |
| </p> |
| </section> |
| |
| <section> |
| <h3><a name="Logging"></a>Logging</h3> |
| |
| |
| <p> |
| There is a simple logging mechanism provided by the Mailet API. It does not support |
| logging levels, so any log filtering will have to be implemented in the Mailet code. |
| Logging is done by calling one of the two logging methods on GenericMailet - log(String) |
| or log(String,Throwable). Logging is available inside the init(), destroy(), and service(Mail) |
| methods. |
| </p> |
| |
| <p> |
| Please note that the log() method logs with DEBUG level. You will need to define that DEBUG level |
| in the log4j.properties. |
| </p> |
| |
| <p> |
| The value of getMailetInfo() for the Mailet is prepended to the log entries for that |
| Mailet. So it may be desirable for you to override this method so you can distinguish mailet |
| log entries by Mailet. |
| </p> |
| |
| <p> |
| Alternatively, you can instantiate your own logger and log with different level, as show in the |
| following snippet (don't forget to update the log4j.properties so you log are taken into account). |
| </p> |
| |
| |
| <div class="source"> |
| <pre> |
| package com.test; |
| |
| import javax.mail.MessagingException; |
| |
| import org.apache.mailet.Mail; |
| import org.apache.mailet.base.GenericMailet; |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| public class MyMailet extends GenericMailet{ |
| private static final Logger logger = LoggerFactory.getLogger(MyMailet.class); |
| @Override |
| public void service(Mail mail) throws MessagingException { |
| log("log via mailet logger with INFO level"); |
| logger.info("Log via slf4j with INFO level !!! Add log4j.logger.com.test=INFO, CONS, FILE in the log4j.properties"); |
| logger.debug("Log via slf4j with DEBUG level !!! Add log4j.logger.com.test=DEBUG, CONS, FILE in the log4j.properties"); |
| } |
| } |
| </pre></div> |
| </section> |
| |
| <section> |
| <h3><a name="Initialization"></a>Initialization</h3> |
| |
| <p> |
| As part of the Mailet lifecycle, a Mailet is guaranteed to be initialized immediately after |
| being instantiated. This happens once and only once for each Mailet instance. The |
| Initialization phase is where configuration parsing and per-Mailet resource creation generally |
| take place. Depending on your Mailet, it may or may not be necessary to do any initialization |
| of the mailet. Initialization logic is implemented by overriding the init() method of |
| GenericMailet. |
| </p> |
| </section> |
| |
| <section> |
| <h3><a name="Servicing"></a>Servicing</h3> |
| |
| <p> |
| The bulk of the Mailet logic is expected to be invoked from the service(Mail) method. This |
| method is invoked each time a mail message is to be processed by the mailet. The message is |
| passed in as an instance of the Mail interface, which is part of the Mailet API.</p> |
| |
| <p>The Mail interface is essentially a light wrapper around JavaMail's MimeMessage class with a |
| few important differences. See the Javadoc for the interface for a description of the additional |
| methods available on this wrapper. |
| </p> |
| </section> |
| |
| <section> |
| <h3><a name="Destruction"></a>Destruction</h3> |
| |
| <p> |
| As part of the Mailet lifecycle, a Mailet is guaranteed to be destroyed when the container |
| cleans up the Mailet. This happens once and only once for each Mailet instance. The |
| Destruction phase is where per-Mailet resource release generally takes place. Depending |
| on your Mailet, it may or may not be necessary to do any destruction |
| of the mailet. Destruction logic is implemented by overriding the destroy() method of |
| GenericMailet. |
| </p> |
| </section> |
| |
| </section> |
| |
| <section> |
| <h2><a name="Deploying_a_Custom_Mailet"></a>Deploying a Custom Mailet</h2> |
| |
| |
| <p> |
| Once a Mailet has been successfully implemented there are only a couple of |
| additional steps necessary to actually deploy the Mailet. |
| </p> |
| |
| <section> |
| <h3><a name="Adding_Your_Mailet_to_the_Classpath"></a>Adding Your Mailet to the Classpath</h3> |
| |
| <p> |
| The Mailet must be added to James' classpath so that the Mailet can be loaded by James. There |
| are two ways to add a custom Mailet to the classpath so that James will be able to load the |
| Mailet. These are: |
| </p> |
| |
| <p> |
| 1a. Download the source distribution, add a jar file containing the custom files to the lib |
| directory of the unpacked source distribution, and build a new .tar.gz/zip file by following the |
| directions <a href="build-instructions.html">here</a>. This new tar.gz/zip file will now |
| include your custom classes. |
| </p> |
| |
| <p> |
| or |
| </p> |
| |
| <p> |
| 1b. Place a jar file containing the custom class files in |
| /path/to/james/conf/lib/ subdirectory with JAMES-Spring or /path/to/james/conf/extensions-jars/ subdirectory with JAMES-Guice. |
| </p> |
| |
| <p> |
| 2. The mailetpackages entity is no longer required, the class attribute of mailets and matchers now takes a fully qualified class name e.g. |
| |
| <p> |
| </p> |
| <div class="source"> |
| <pre> |
| <mailet match="All" class="com.your.company.MyMailet"/> |
| </pre></div> |
| |
| After that, restart James server. |
| |
| </section> |
| |
| <section> |
| <h3><a name="Add_custom_Guice_injections_for_extensions"></a>Add custom Guice injections for extensions</h3> |
| |
| <p>Upon injections, the user can reference additional guice modules, that are going to be used only upon extensions instantiation. |
| In order to do that:</p> |
| |
| <p> 1. Place the jar containing the guice module that should be used to instantiate your extensions within the /extensions-jars folder</p> |
| |
| <p> 2. Register your module fully qualified class name within <a class="externalLink" href="https://github.com/apache/james-project/blob/master/server/apps/distributed-app/sample-configuration/extensions.properties"> |
| extensions.properties</a> under the guice.extension.module key.</p> |
| </section> |
| |
| <section> |
| <h3><a name="James_Configuration"></a>James Configuration</h3> |
| |
| <p>Configuration of the processor chain is discussed |
| <a href="config-mailetcontainer.html">elsewhere</a> in this documentation. The |
| details of configuring mailet deployment is discussed at length. Here we will only comment |
| that it is important to add the appropriate mailet package for your custom mailet to the |
| <mailetpackages> list and that the name of your mailet should not conflict with any of |
| the mailets described <a href="dev-provided-mailets.html">here</a>. |
| </p> |
| </section> |
| |
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