SeamFramework.orgCommunity Documentation

Chapter 3. Developing a Plugin

3.1. Referencing the Forge APIs
3.1.1. Using Forge
3.1.2. With Maven
3.2. Implementing the Plugin interface
3.3. Naming your plugin
3.4. Add commands to your plugin
3.4.1. Default commands
3.4.2. Named commands
3.5. Understanding command @Options
3.5.1. --named options
3.5.2. Ordered options
3.5.3. Combining --named and ordered options
3.6. Piping output between plugins
3.7. Ensure all referenced libraries are on the CLASSPATH
3.8. Make your Plugin available to Forge
3.8.1. As local source files (for development)
3.8.2. As a git repository
3.8.3. As a Maven artifact
3.8.4. As a local distributable JAR file
3.8.5. As a remote distributable JAR file
3.9. Removing a plugin from Forge

Part of Forge's architecture is to allow extensions to be created with extreme ease. This is done using the same programming model that you would use for any CDI or Java EE application, and you should quickly recognize the annotation-driven patterns and practices applied.

A Forge plugin could be as simple as a tool to print files to the console, or as complex as deploying an application to a server, 'tweet'ing the status of your latest source-code commit, or even sending commands to a home-automation system; the sky is the limit!

Because Forge is based on Maven, the easiest way to get started quickly writing a plugin is to create a new maven Java project. This can be done by hand, or using Forge's build in plugin project facet.

In two short steps, you can have a new plugin-project up and running; this can be done using Forge itself!

That's it! Now your project is ready to be compiled and installed in Forge, but you may still want to create some Plugins.


If you do not wish to create a new plugin project using Forge itself, you will need to manually include the Forge-API dependencies. For purposes of simplicity, we have pasted a sample Maven POM file which can be used as a starting point for a new plugin:

NOTE: You must also create a beans.xml file in the src/main/resources/META-INF/ directory of your project, or your plugin will not be detected by Forge.

<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                             http://maven.apache.org/xsd/maven-4.0.0.xsd" 
    xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.example.plugin</groupId>
  <artifactId>example</artifactId>
  <version>1.0.0-SNAPSHOT</version>

  <properties>
    <forge.api.version>[1.0.0-SNAPSHOT,)</forge.api.version>
  </properties>
  
  <dependencies>
    <dependency>
      <groupId>org.jboss.seam.forge</groupId>
      <artifactId>forge-shell-api</artifactId>
      <version>${forge.api.version}</version>
    </dependency>
  </dependencies>
  
  <repositories>
    <repository>
      <id>jboss</id>
      <url>https://repository.jboss.org/nexus/content/groups/public/</url>
    </repository>
  </repositories>
  
  <build>
    <plugins>
      <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.6</source>
          <target>1.6</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

The first thing you must do in order to create a forge plugin, is create a new class and implement the org.jboss.seam.forge.shell.plugins.Plugin interface. Notice that the interface has no methods, this is because you will be adding your own custom commands later.

import org.jboss.seam.forge.shell.plugins.Plugin;
         
public class ExamplePlugin implements Plugin {
}

Each plugin should be given a name. This is done by adding the @org.jboss.seam.forge.shell.plugins.Alias annotation to your plugin class. By default, if no @Alias annotation is found, the lower-case Class name will be used; for instance, our ExamplePlugin, above, would be executed by typing:
$ exampleplugin 
Now we will add a name to our plugin.
@Alias("example")
public class ExamplePlugin implements Plugin {
   // commands
}
Our named @Alias("example") ExamplePlugin would be executed by typing:
$ example 

Now that you have implemented the Plugin interface, it's time to add some functionality. This is done by adding "Commands" to your plugin class. Commands are plain Java methods in your plugin Class. Plugin methods must be annotated as either a @DefaultCommand, the method to be invoked if the plugin is called by name (with no additional commands), or @Command("..."), in which case the plugin name and command name must both be used to invoke the method.

Commands also accept @Options parameters as arguments. These are described in detail later in this section.

Once we have a command or two in our Plugin, it's time to give our users some control over what it does; to do this, we use @Option params; options enable users to pass information of various types into our commands.

Options can be named, in which case they are set by passing the --name followed immediately by the value, or if the option is a boolean flag, simply passing the flag will signal a `true` value. Named parameters may be passed into a command in any order, while unnamed parameters must be passed into the command in the order with which they were defined.

In addition to --named option parameters, as described above, parameters may also be passed on the command line by the order in which they are entered. These are called "ordered option parameters", and do not require any parameters other than help or description information.

@Option String value

The order of the options in the method signature controls how values are assigned from parsed Forge shell command statements.

For example, the following command accepts several options, named 'one', and 'two':

public class ExamplePlugin implements Plugin {
   @Command("perform")
   public void exampleCommand( 
                  @Option String one,
                  @Option String two,
                  PipeOut out) {
       out.println(">> option one equals: " + one);
       out.println(">> option two equals: " + two);
   }
}

The above command, when executed, would produce the following output:

$ exampleplugin perform cat dog 
>> option one equals: cat
>> option two equals: dog

Both --named and ordered option parameters can be mixed in the same command; there are some constraints on how commands must be typed, but there is a great deal of flexibility as well.

@Option String value,
@Option(name="num") int number

The order of ordered options in the method signature controls how values are assigned from the command line shell, whereas the named options have no bearing on the order in which inputs are provided on the command line.

For example, the following command accepts several options, named 'one', 'two', and several more options that are not named:

public class ExamplePlugin implements Plugin {
   @Command("perform")
   public void exampleCommand( 
                  @Option(name="one") String one,
                  @Option(name="two") String two,
                  @Option String three,
                  @Option String four,
                  PipeOut out) {
       out.println(">> option one equals: " + one);
       out.println(">> option two equals: " + two);
       out.println(">> option three equals: " + three);
       out.println(">> option four equals: " + four);
   }
}

The above command, when executed, would produce the following output:

$ exampleplugin perform --one cat --two dog bird lizard  
>> option one equals: cat
>> option two equals: dog 
>> option three equals: bird
>> option four equals: lizard

However, we could also achieve the same result by re-arranging parameters, and as long as the name-value pairs remain together, and the ordered values are passed in the correct order, interpretation will remain the same:

$ exampleplugin --two dog bird --one cat lizard  
>> option one equals: cat
>> option two equals: dog 
>> option three equals: bird
>> option four equals: lizard

Much like a standard UNIX-style shell, the Forge shell supports piping IO between executables; however in the case of forge, piping actually occurs between plugins, commands, for example:

$ cat /home/username/.forge/config | grep automatic 
@/* Automatically generated config file */;

This might look like a typical BASH command, but if you run forge and try it, you may be surprised to find that the results are the same as on your system command prompt, and in this example, we are demonstrating the pipe: '|'

In order to enable piping in your plugins, you must use one or both of the @PipeIn InputStream stream or PipeOut out command arguments. Notice that PipeOut is a java type that must be used as a Method parameter, whereas @PipeIn is an annotation that must be placed on a Java @PipeIn InputStream stream or @PipeIn String in Method parameter.

`PipeOut out` - by default - is used to print output to the shell console; however, if the plugin on the left-hand-side is piped to a secondary plugin on the command line, the output will be written to the `@PipeIn InputStream stream` of the plugin on the right-hand-side:

$ left | right

Or in terms of pipes, this could be thought of as a flow of data from left to right:

$ PipeOut out -> @PipeIn InputStream stream

Notice that you can pipe output between any number of plugins as long as each uses both a @PipeIn InputStream and PipeOut:

$ first command | second command | third command



Take the 'grep' command itself, for example, which supports two methods of invocation: Invocation on one or more Resource<?> objects, or invocation on a piped InputStream.

Tip

If no piping is invoked (e.g: via standalone execution of the plugin), a piped InputStream will be null. In addition, piped InputStreams do not need to be closed; Forge will handle cleanup of these streams.

@Alias("grep")
@Topic("File & Resources")
@Help("print lines matching a pattern")
public class GrepPlugin implements Plugin
{
   @DefaultCommand
   public void run(
         @PipeIn final InputStream pipeIn,
         @Option(name = "ignore-case", shortName = "i", flagOnly = true) boolean ignoreCase,
         @Option(name = "regexp", shortName = "e") String regExp,
         @Option(description = "PATTERN") String pattern,
         @Option(description = "FILE ...") Resource<?>[] resources, 
         final PipeOut pipeOut
   ) throws IOException 
   {
      Pattern matchPattern = /* determine pattern (omitted for space) */;

      if (resources != null) {
      
         /* User passed file(s) on the command line; grep those. */
      
         for (Resource<?> r : resources) {
            InputStream inputStream = r.getResourceInputStream();
            try {
               match(inputStream, matchPattern, pipeOut, ignoreCase);
            }
            finally {
               inputStream.close();
            }
         }
      }
      else if (pipeIn != null) {
      
         /* No files were passed on the command line; check for a 
          * piped InputStream and use that.
          */
      
         match(pipeIn, matchPattern, pipeOut, ignoreCase);
      }
      else {
      
         /* No input was passed to the plugin. */
      
         throw new RuntimeException("Error: arguments required");
      }
   }

   private void match(InputStream instream, Pattern pattern, PipeOut pipeOut, boolean caseInsensitive) throws IOException {
      StringAppender buf = new StringAppender();

      int c;
      while ((c = instream.read()) != -1) { /* Read from the given stream. */
         switch (c) {
         case '\r':
         case '\n':
            String s = caseInsensitive ? buf.toString().toLowerCase() : buf.toString();

            if (pattern.matcher(s).matches()) {
               pipeOut.println(s); /* Write to the output pipe. */
            }
            buf.reset();
            break;
         default:
            buf.append((char) c);
            break;
         }
      }
   }
}

If your Plugin depends on classes or libraries that are not provided by Forge, then you must either package those classes in the JAR file containing your Plugin (for instance, using the maven shade plugin), or you must ensure that the required dependencies are also placed on the CLASSPATH (typically in the $FORGE_HOME/lib folder,) otherwise your plugin will *not* be loaded.

Warning

NOTE: This is required even if dependencies are specified directly in your pom.xml file. Transitive dependencies WILL NOT BE INSTALLED with your plugin; they must be packaged via shade.


Warning

Do NOT include Forge provided libraries with shade, or you will very likely create a non-functional plugin.

It it also recommended, however, to relocate shaded class files to a new package. Your code will access the bundled code at this new location, and will prevent version conflicts if another plugin bundles a different version of the same library. For this, we use the following command.

$ shade relocate --pattern {ORIGINAL PGK} --shadedPattern {NEW PKG} --excludes {EXCLUDED PKGS...}

For the purposes of this example, let us assume that our Plugin depends on the Apache Commons Collections library (org.apache.commons.collections), and we want to make sure that no conflicts occur.

[example-plugin] example-plugin $ shade relocate --pattern org.apache.commons.collections --shadedPattern ~.shaded.apache.collections
***SUCCESS*** Relocating [org.apache.commons.collections] to [com.example.forge.plugin.shaded.apache.collections]
[example-plugin] example-plugin $ 
      	

This should be repeated for each dependency as necessary. Notice that our POM has been updated with the configuration:

   <plugin>
     <artifactId>maven-shade-plugin</artifactId>
     <version>1.4</version>
     <executions>
       <execution>
         <phase>package</phase>
         <goals>
           <goal>shade</goal>
         </goals>
         <configuration>
           <artifactSet>
             <includes>
               <include>commons-collections:commons-collections</include>
             </includes>
           </artifactSet>
           <relocations>
             <relocation>
               <pattern>org.apache.commons.collections</pattern>
               <shadedPattern>com.example.forge.plugin.shaded.apache.collections</shadedPattern>
             </relocation>
           </relocations>
         </configuration>
       </execution>
     </executions>
   </plugin>

When you build your plugin, you should see confirmation output from the Maven Shade Plugin looking something like this:
[INFO] --- maven-shade-plugin:1.4:shade (default) @ example-plugin ---
[INFO] Excluding org.jboss.seam.forge:forge-shell-api:jar:{version} from the shaded jar.
[INFO] Excluding org.jboss.seam.forge:forge-parser-java-api:jar:{version} from the shaded jar.
[INFO] Excluding org.jboss.seam.forge:forge-parser-xml:jar:{version} from the shaded jar.
[INFO] Excluding org.jboss.shrinkwrap.descriptors:shrinkwrap-descriptors-api:jar:{version} from the shaded jar.
[INFO] Excluding javax.enterprise:cdi-api:jar:{version} from the shaded jar.
[INFO] Excluding org.jboss.spec.javax.interceptor:jboss-interceptors-api:jar:{version} from the shaded jar.
[INFO] Excluding javax.annotation:jsr250-api:jar:{version} from the shaded jar.
[INFO] Excluding javax.inject:javax.inject:jar:{version} from the shaded jar.

[INFO] Including commons-collections:commons-collections:jar:3.2.1 in the shaded jar.

[INFO] Replacing original artifact with shaded artifact.
[INFO] Replacing ~/Desktop/example-plugin/target/example-plugin-1.0.0-SNAPSHOT.jar 
   with ~/Desktop/example-plugin/target/example-plugin-1.0.0-SNAPSHOT-shaded.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------

After following all of the steps in this section, you should now be ready to install your Plugin into the Forge environment. There are several methods for installing and distributing your plugin; these methods are described in this section.

All plugin installation should take place using the '$ forge' meta-command. For more information on this command, type:

$ help forge

Tip

After installation, Forge automatically hot-loads plugin classes and makes them available for use. There is no need to restart Forge when installing or updating plugins.

Perhaps the simplest form of plugin installation is when the plugin source files are stored locally in a project on the local computer. If a plugin project is already checked out locally, it may be built and installed using the following command:

$ forge source-plugin {PATH}

Example 3.5. Installing a local plugin project

[no project] Desktop $ forge source-plugin ~/Desktop/example-plugin/
***INFO*** Invoking build with underlying build system.
[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building example-plugin 1.0.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] Compiling 1 source file to ~/Desktop/example-plugin/target/classes
[INFO] 

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
There are no tests to run.

[INFO] --- maven-jar-plugin:2.3.1:jar (default-jar) @ example-plugin ---
[INFO] Building jar: /home/lb3/Desktop/example-plugin/target/example-plugin-1.0.0-SNAPSHOT.jar
[INFO] 
[INFO] --- maven-shade-plugin:1.4:shade (default) @ example-plugin ---
[INFO] Excluding org.jboss.seam.forge:forge-shell-api:jar:1.0.0-SNAPSHOT from the shaded jar.
[INFO] Excluding org.jboss.seam.forge:forge-parser-java-api:jar:1.0.0-SNAPSHOT from the shaded jar.
[INFO] Excluding org.jboss.seam.forge:forge-parser-xml:jar:1.0.0-SNAPSHOT from the shaded jar.
[INFO] Excluding org.jboss.shrinkwrap.descriptors:shrinkwrap-descriptors-api:jar:0.1.4 from the shaded jar.
[INFO] Excluding javax.enterprise:cdi-api:jar:1.0-SP4 from the shaded jar.
[INFO] Excluding org.jboss.spec.javax.interceptor:jboss-interceptors-api_1.1_spec:jar:1.0.0.Beta1 from the shaded jar.
[INFO] Excluding javax.annotation:jsr250-api:jar:1.0 from the shaded jar.
[INFO] Excluding javax.inject:javax.inject:jar:1 from the shaded jar.
[INFO] Including commons-collections:commons-collections:jar:3.2.1 in the shaded jar.
[INFO] Replacing original artifact with shaded artifact.
[INFO] Replacing /home/lb3/Desktop/example-plugin/target/example-plugin-1.0.0-SNAPSHOT.jar with /home/lb3/Desktop/example-plugin/target/example-plugin-1.0.0-SNAPSHOT-shaded.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
***SUCCESS*** Build successful.
If you are installing an updated version of an existing plugin, Forge will prompt for confirmation to continue installation.
An existing version of this plugin was found. Replace it? [Y/n] y
***INFO*** Installing plugin artifact.
Wrote ~/.forge/plugins/com.example.forge.plugin$example-plugin$1$1.0.0-SNAPSHOT.jar
***SUCCESS*** Installed from [example-plugin] successfully.
[no project] Desktop $
Your plugin is now installed and ready to use:
$ exampleplugin perform --one cat --two dog bird lizard
>> option one equals: cat
>> option two equals: dog 
>> option three equals: bird
>> option four equals: lizard

Plugins may be installed directly from a Git repository. This feature simply automates the source code checkout and installation, much like the $ forge source-plugin command. Your plugin will be built and installed while Forge runs.

$ forge git-plugin git://github.com/username/repository.git --ref 1.0.0.Alpha1

Notice that a --ref may be specified if a specific branch or tag should be built. This is recommended, since snapshots are more likelty to contain unstable code.

In order to remove plugins, you must shut down Forge and delete the plugin files from the forge plugin directory (usually ~/.forge/plugins/). To see a list of which plugins are installed, and where they are stored, type the following command:

[no project] Desktop $ forge list-plugins --all

[installed plugins]
org.jboss.errai.forge : forge-errai : 1.0.0-SNAPSHOT
com.ocpsoft.forge.prettyfaces : prettyfaces-forge-plugin : 1.0.0.Alpha2
com.example.forge.plugin : example-plugin : 1.0.0-SNAPSHOT

[no project] Desktop $