View source for Clad User Manual - How to Implement a Command Line Application

=Internal=

* [[Clad_User_Manual#Subjects|clad User Manual]]

=Overview=

=Declare the Maven Dependency=

<pre>
<dependency>
    <groupId>io.novaordis.clad</groupId>
    <artifactId>novaordis-clad</artifactId>
    <version>...</version>
</dependency>
</pre>

=Provide an ApplicationRuntime Implementation=

Extend  <tt>[https://github.com/NovaOrdis/clad/blob/master/src/main/java/io/novaordis/clad/application/ApplicationRuntimeBase.java ApplicationRuntimeBase]</tt>, into a "clad" sub-package of your project. This is the recommended approach. If you need more flexibility, you can implement <tt>[https://github.com/NovaOrdis/clad/blob/master/src/main/java/io/novaordis/clad/application/ApplicationRuntime.java ApplicationRuntime]</tt> interface.

The application runtime functionality is related to the following aspects:

==Specify a Default Command==

To provide a default command, implement <tt>public String getDefaultCommandName()</tt>. For more details on the default command, see "[[Clad_User_Manual_-_Concepts#Default_Command|Default Command]]" section.

==Define Global Options==

For more details on the default command, see "[[Clad_User_Manual_-_Concepts#Global_Options|Global Options]]" section.

=Logging=

==Console Output==

<font color=red>
TODO
</font>


==Debug Logging==

<font color=red>
TODO
</font>



==SLF4J Binding==

clad relies on SLF4J API, but does not enforce any binding. It is up to your application to define a binding among its dependencies. For more details see [[Slf4j#No_StaticLoggerBinder|SLF4J - No StaticLoggerBinder]].

<pre>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.7.12</version>
</dependency>
</pre>

<font color=red>TODO: Come up with a deterministic way to specify the slf4j-log4j12 version, in relation to the slf4j-api version used by clad.</font>

=Log4j=

<font color=red>

Come up with a solution for:

<pre>
log4j:WARN No appenders could be found for logger (io.novaordis.clad.configuration.ConfigurationImpl).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
</pre>


For the time being I worked around the issue by placing a src/main/resources/log4j.xml. Example: [[Simple_log4j.xml_Example|simple log4j.xml]].
</font>

=Wrapper=


java -cp ... io.novaordis.clad.CommandLineApplication

==Application Name==

The application name should be provided as a system property argument to java, in the wrapper:


-Dapplication.name=Release


<font color=red>


Package the application runtime implementation class and the commands in a JAR (or place them in a directory).

Set “<tt>application.name</tt>” as a system property. If the application runtime implementation class is <tt>BlueApplicationRuntime</tt>, the application.name must be “blue”.

Make sure the JAR or the directory is first on the class path (otherwise other <tt><your-command-name>Command.class</tt>, if exist, will be instantiated first).

</font>