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Sisu/PlexusMigration

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<ac:macro ac:name="toc" />

Overview

This document provides some details on how to convert Sonatype Nexus legacy Plexus components into modern Sisu/Guice JSR-330 components.

Annotations

For brevity of examples imports are omitted.  The following table defines the meanings and fully-qualified-class-names of the annotations references in the following examples.

<tbody> </tbody>
Annotation Class Description
@Component org.codehaus.plexus.component.annotations.Component Legacy Plexus component annotation
@Requirement org.codehaus.plexus.component.annotations.Requirement Legacy Plexus injection annotation
@Configuration org.codehaus.plexus.component.annotations.Configuration Legacy Plexus configuration annotation
@Named javax.inject.Named Standard JSR-330 annotation to provide component name
@Singleton javax.inject.Singleton Standard JSR-330 annotation to mark component as singleton
@Typed javax.enterprise.inject.Typed JavaEE annotation to mark component type
@Description org.sonatype.inject.Description Sisu-specific annotation to provide a description for a component
@Parameters org.sonatype.inject.Parameters Sisu-specific annotation to mark Map<String,String> injection as container context parameters.
@Inject javax.inject.Inject Standard JSR-330 annotation to mark field, parameter, method for injection
@Nullable javax.annotation.Nullable Standard JSR-305 annotation to mark field, parameter, result value as potentially returning null value
<ac:macro ac:name="warning"><ac:parameter ac:name="title">javax.inject vs. com.google.inject</ac:parameter><ac:rich-text-body>

There are com.google.inject flavors of @Inject, @Named and @Singleton which should NOT be used.

Prefer the standard javax.inject versions.

</ac:rich-text-body></ac:macro>

References

<a href="http://www.jcp.org/en/jsr/detail?id=330">JSR-330</a>

<a href="http://www.jcp.org/en/jsr/detail?id=330">JSR-305</a>

@Component

Plexus @Component annotations are replaced by standard @Named@Singleton, etc annotations.

Singletons

For example this Plexus component:

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my")

public class MyComponent

   implements Component

{ }]]></ac:plain-text-body></ac:macro>

can be converted to:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{ }]]></ac:plain-text-body></ac:macro><ac:macro ac:name="tip"><ac:parameter ac:name="title">Naming Varients</ac:parameter><ac:rich-text-body>

Components which are not directly looked up by names, or otherwise used in a context where the name is important you can omit the value for @Named and the full-qualified-class-name of the component will be used as the name instead.

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[package components;

@Named @Singleton public class MyComponent

   implements Component

{ }]]></ac:plain-text-body></ac:macro>

Results in a component with implicit name of "components.MyComponent"

Additionally the Sisu Plexus integration has special handling for Plexus default components. Many Plexus applications define objects like:

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class)

public class DefaultComponent

   implements Component

{ }]]></ac:plain-text-body></ac:macro>

The Default prefix on the component implementation class causes the binding to be translated to @Named("default"), so the conversion would look like:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[package components;

@Named @Singleton public class DefaultComponent

   implements Component

{ }]]></ac:plain-text-body></ac:macro>

BUT the name bound for this component would be "default".

</ac:rich-text-body></ac:macro>

Instance

By default in Plexus, components are singletons, but this is not the case for every component.  This Plexus component is not a singleton:

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my", instantiationStrategy="per-lookup")

public class MyComponent

   implements Component

{ }]]></ac:plain-text-body></ac:macro>

and is converted to:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

public class MyComponent

   implements Component

{ }]]></ac:plain-text-body></ac:macro>

Notice this is the same as the example above, except with-out the @Singleton annotation.

<ac:macro ac:name="warning"><ac:rich-text-body>

Only per-lookup and singleton instantiation strategies have reasonable mappings into Sisu. The keep-alive and poolable strategies are not supported.

Additionally other Plexus-specific component configuration such as lifecycle-handlers, factories, composer, configurator, alias, version, profile, isolatedRealm are NOT supported.

</ac:rich-text-body></ac:macro>

 

Type Override

By default the type of the component is determined automatically, though in some rare cases an explicit type is required.  To specify the explicit binding type use the @Typed annotation:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Typed(Component.class) public class MyComponent

   extends SomeSupportClassHardToGuessTypeFrom

{ }]]></ac:plain-text-body></ac:macro>

Descriptions

In some cases component descriptions are required.  There is no standard annotation to provide this, however Sisu provides a custom annotation for this.

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my", description="My custom component")

public class MyComponent

   implements Component

{ }]]></ac:plain-text-body></ac:macro>

becomes:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton @Description("My custom component") public class MyComponent

   implements Component

{ }]]></ac:plain-text-body></ac:macro>

@Requirement

Basics

@Requirement defines injection points for legacy Plexus components.  These more-or-less line-up directly with replacement with @Inject, though there are more options available as @Inject is support for fields, constructors and methods, where @Requirement only worked with fields.  The recommended option is to replace legacy Plexus injection with constructor injection where possible.

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my")

public class MyComponent

   implements Component

{

   @Requirement
   private AnotherComponent another;

}]]></ac:plain-text-body></ac:macro>

becomes:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted using recommended constructor injection</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{

   private final AnotherComponent another;

   @Inject
   public MyComponent(final AnotherComponent another) {
       this.another = another;
   }

}]]></ac:plain-text-body></ac:macro>

Use of constructor injection in this fashion has some impact on replacing legacy Plexus lifecycle Initializable and Contextualizable  interfaces, which often only exist to perform setup once injection is performed.

Alternatives

Other options for conversions using field injection:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted using field injection</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{

   @Inject
   private AnotherComponent another;

}]]></ac:plain-text-body></ac:macro><ac:macro ac:name="warning"><ac:rich-text-body>

This is not recommended, as it makes it difficult to UNIT test the code w/o a full container to provide injection, which in itself can be problematic for UNIT testing. We highly recommend this form of injection NOT BE USED.

</ac:rich-text-body></ac:macro>

 

or method injection:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted using method injection</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{

   private AnotherComponent another;

   @Inject
   public setAnotherComponent(final AnotherComponent another) {
       this.another = another;
   }

}]]></ac:plain-text-body></ac:macro>

Optional

Optional components are configured to be @Nullable

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my")

public class MyComponent

   implements Component

{

   @Requirement(optional=true)
   private AnotherComponent another;

}]]></ac:plain-text-body></ac:macro>

becomes:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{

   private final AnotherComponent another;

   @Inject
   public MyComponent(final @Nullable AnotherComponent another) {
       this.another = another;
   }

}]]></ac:plain-text-body></ac:macro>

Names and Hints

Legacy Plexus component hints become @Named:

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my")

public class MyComponent

   implements Component

{

   @Requirement(hint="foo")
   private AnotherComponent another;

}]]></ac:plain-text-body></ac:macro>

becomes:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{

   private final AnotherComponent another;

   @Inject
   public MyComponent(final @Named("foo") AnotherComponent another) {
       this.another = another;
   }

}]]></ac:plain-text-body></ac:macro>

Types

Legacy Plexus component roles, which are normally only used for collection types are generally not needed:

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my")

public class MyComponent

   implements Component

{

   @Requirement(role=AnotherComponent.class)
   private List<AnotherComponent> components;

}]]></ac:plain-text-body></ac:macro>

becomes:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{

   private final List<AnotherComponent> components;

   @Inject
   public MyComponent(final List<AnotherComponent> components) {
       this.components = components;
   }

}]]></ac:plain-text-body></ac:macro>

@Configuration

Plexus configuration injection is handled by @Inject @Named("${expression}") injection.

Basics

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my")

public class MyComponent

   implements Component

{

   @Configuration(name="configDir")
   private File configDir;

}]]></ac:plain-text-body></ac:macro>

becomes:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{

   private final File configDir;

   @Inject
   public MyComponent(final @Named("${configDir}") configDir) {
       this.configDir = configDir;
   }

}]]></ac:plain-text-body></ac:macro>

Defaults

Default values are provided by expression syntax.

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my")

public class MyComponent

   implements Component

{

   @Configuration(name="configDir", value="defaultDir")
   private File configDir;

}]]></ac:plain-text-body></ac:macro>

becomes:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{

   private final File configDir;

   @Inject
   public MyComponent(final @Named("${configDir:-defaultDir}") configDir) {
       this.configDir = configDir;
   }

}]]></ac:plain-text-body></ac:macro>

Lifecycle Support

This section is specific to how to adapter legacy Plexus component lifecycle interfaces to use inside of Sonatype Nexus.  There is no hard-fast way to adapt these, but there are some guidelines to follow.

<tbody> </tbody>
Interface Class Description
Initializable org.codehaus.plexus.personality.plexus.lifecycle.phase.Initializable

Hook was used to inform a component once its injection has been performed.

Contextualizable org.codehaus.plexus.personality.plexus.lifecycle.phase.Contextualizable

Similar to Initializable but passes in the container context.

Startable org.codehaus.plexus.personality.plexus.lifecycle.phase.Startable Allows components to be started and stopped.
Disposable org.codehaus.plexus.personality.plexus.lifecycle.phase.Disposable Hook used to inform a component that it is no longer available in the container.

Initializable

By and far this can be replaced by using constructor-inject, and performing the initialize() at the end of the constructor.

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my")

public class MyComponent

   implements Component, Initializable

{

   @Requirement
   private AnotherComponent another;

   public initialize() throws InitializationException {
       another.init();
   }

}]]></ac:plain-text-body></ac:macro>

becomes:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{

   private final AnotherComponent another;

   @Inject
   public MyComponent(final AnotherComponent another) {
       this.another = another;
       another.init();
   }

}]]></ac:plain-text-body></ac:macro>

Contextualizable

Similar to Initializable, though if the context is needed you can inject the container context parameters with:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named("my")

@Singleton public class MyComponent

   implements Component

{

   @Inject
   public MyComponent(final @Parameters Map<String,String> params) {

// do something with _context_ params

   }

} ]]></ac:plain-text-body></ac:macro>

Startable

There is no natural correlating container feature in Sisu presently (or maybe ever) which supports this Plexus lifecycle.  To work around, use the Nexus EventBus and handle events to replace start/stop behavior.

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my")

public class MyComponent

   implements Component, Startable

{

   public start() throws StartingException {
       // do something to "start"
   }

   public stop() throws StoppingException {
       // do something to "stop"
   }

}]]></ac:plain-text-body></ac:macro>

becomes:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[import org.sonatype.sisu.goodies.eventbus.EventBus;

import com.google.common.eventbus.Subscribe;

@Named("my") @Singleton public class MyComponent

   implements Component

{

   private final EventBus eventBus;

   @Inject
   public MyComponent(final EventBus eventBus) {
       this.eventBus = eventBus;
       eventBus.register(this);
   }

   @Subscribe
   public on(final NexusStartedEvent event) throws Exception {
       // do something to "start"
   }

   @Subscribe
   public on(final NexusStoppedEvent event) throws Exception {
       // do something to "stop"

       eventBus.unregister(this);
   }

}]]></ac:plain-text-body></ac:macro>

Disposable

Similar to Startable use of events are used to handle replacement for Disposable components.

<ac:macro ac:name="code"><ac:parameter ac:name="title">plexus</ac:parameter><ac:plain-text-body><![CDATA[@Component(role=Component.class, hint="my")

public class MyComponent

   implements Component, Disposable

{

   public dispose() {
       // do something to "dispose"
   }

}]]></ac:plain-text-body></ac:macro>

becomes:

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[import org.sonatype.sisu.goodies.eventbus.EventBus;

import com.google.common.eventbus.Subscribe;

@Named("my") @Singleton public class MyComponent

   implements Component

{

   private final EventBus eventBus;

   @Inject
   public MyComponent(final EventBus eventBus) {
       this.eventBus = eventBus;
       eventBus.register(this);
   }

   @Subscribe
   public on(final NexusStoppedEvent event) throws Exception {
       // do something to "dispose"

       eventBus.unregister(this);
   }

}]]></ac:plain-text-body></ac:macro>

Custom Bindings

Plugins which require additional custom bindings can provide a @Named Guice module to configure components bindings further.

Sisu will automatically load modules which are @Named and apply them to the injectors bindings.  These modules are really no different than normal Guice modules, except that they need to have the @Named annotation on them so that Sisu can locate them when initializing.

<ac:macro ac:name="code"><ac:parameter ac:name="title">converted</ac:parameter><ac:plain-text-body><![CDATA[@Named

public class MyPluginModule

   extends com.google.inject.AbstractModule

{

   public void configure() {
       bind(Component.class).to(MyComponent.class);
   }

}]]></ac:plain-text-body></ac:macro>