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Annotations in JBoss Deployment

在我们书写EJB代码时，为了简化配置，我们使用了注解而不是xml配置文件。那么，JBoss（或者说Wildfly）是如何利用这些注解，在合适的时候调用了我们的代码呢？换句话说，jboss从启动到输出像这样的jndi设置信息的部署过程究竟发生了什么？今天我们就通过分析其源代码简单探讨一下这个问题。

从annotations讲起

在开发过程中, 我们也时常会在应用代码中会看到这些看上去比较奇怪的@开头的东西，例如@Override, @Deprecated。他们的作用到底是什么？又是如何实现的呢？我们稍稍介绍以一跟我们今天内容相关的背景。

注解，根据其寿命长短，可以分为三类：

  1. Source：只存在于源代码中，在编译后便被丢弃。所以说他的作用范围便是编译时。
  2. Class：在class文件中，但不在VM中。貌似没有什么卵用
  3. Runtime：一直存活到VM中，即可以通过反射获得注释信息（用大白话说就是，当你程序跑起来之后，还可以获取注解的内容）。

所以，联想到我们在使用EJB的过程：先写好源代码，再编译，再打包，再交给jboss部署，jboss再调用我们的代码。我们可以明白，诸如@Stateless, @EJB这样的注解都是第三类注解。

JBoss部署

在上面讲的使用EJB的过程中，jboss的部署其实还是一个黑盒，所以当我们把我们的jar包部署到JBoss时究竟发生了什么？
让我们通过源代码(org/jboss/as/server/deployment/Phase.java)把部署过程理一理：

/**
 * This phase creates the initial root structure.  Depending on the
 * service for this phase will ensure that the
 * deployment unit's initial root structure is available and accessible.
 * Upon entry, this phase performs the following actions:
 * <ul>
 * <li>The primary deployment root is mounted (during {@link #STRUCTURE_MOUNT})</li>
 * <li>Other internal deployment roots are mounted (during {@link #STRUCTURE_NESTED_JAR})</li>
 * </ul>
 */
STRUCTURE(null),
/**
 * This phase assembles information from the root structure to prepare
 * for adding and processing additional external
 * structure, such as from class path entries and other similar 
 * mechanisms.
 * Upon entry, this phase performs the following actions:
 * <ul>
 * <li>The root content's MANIFEST is read and made available during
 * {@link #PARSE_MANIFEST}.</li>
 * <li>The annotation index for the root structure is calculated during 
 * {@link #STRUCTURE_ANNOTATION_INDEX}.</li>
 * </ul>
 */
PARSE(null),
/**
 * In this phase parsing of deployment metadata is complete and the 
 * component may be registered with the subsystem.
 * This is prior to working out the components dependency and equivalent 
 * to the OSGi INSTALL life cycle.
 */
REGISTER(null),
/**
 * In this phase, the full structure of the deployment unit is made 
 * available and module dependencies may be assembled.
 * Upon entry, this phase performs the following actions:
 * <ul>
 * <li>Any additional external structure is mounted during {@link #XXX}</li>
 * </ul>
 */
DEPENDENCIES(null),
CONFIGURE_MODULE(null),
/**
 * Processors that need to start/complete before the deployment 
 * classloader is used to load application classes,
 * belong in the FIRST_MODULE_USE phase.
 */
FIRST_MODULE_USE(null),
POST_MODULE(null),
INSTALL(null),
CLEANUP(null),
;

当然，这只是对部署过程的概览，其实每一个步骤下都有许多小的步骤，非常复杂，要理解注解的角色，我们从jboss启动开始讲起。

首先JBoss启动–>注册processor->DeploymentUnitPhaseService.start()->processor.deploy()开始逐层调用各个步骤的processor以完成不同阶段的功能 – 下面列举了一些：

// create the index of annotations:读取类文件，抽象成Index对象
//（类似于class类，读取annotation，method，field。。。）
DeployerChainAddHandler.addDeploymentProcessor(SERVER_NAME, 
Phase.STRUCTURE, Phase.STRUCTURE_ANNOTATION_INDEX, new 
AnnotationIndexProcessor());

// create composite index：用list集中管理
DeployerChainAddHandler.addDeploymentProcessor(SERVER_NAME, Phase.PARSE,
 Phase.PARSE_COMPOSITE_ANNOTATION_INDEX, new CompositeIndexProcessor());

// process annotations：开始处理,解析
//（分成SessionBean，MessageDrivenBean分别处理）
processorTarget.addDeploymentProcessor(EJB3Extension.SUBSYSTEM_NAME, 
Phase.PARSE, Phase.PARSE_CREATE_COMPONENT_DESCRIPTIONS, new 
AnnotatedEJBComponentDescriptionDeploymentUnitProcessor(appclient));

// make jndi binding：注册JNDI，然后输出一段熟悉的注册信息(如下）
processorTarget.addDeploymentProcessor(EJB3Extension.SUBSYSTEM_NAME, 
Phase.POST_MODULE, Phase.POST_MODULE_EJB_JNDI_BINDINGS, new 
EjbJndiBindingsDeploymentUnitProcessor(appclient));
java:global/learnEJB/HelloBean!first.HelloBean
java:app/learnEJB/HelloBean!first.HelloBean
java:module/HelloBean!first.HelloBean
java:global/learnEJB/HelloBean!first.HelloBeanRemote
java:app/learnEJB/HelloBean!first.HelloBeanRemote
java:module/HelloBean!first.HelloBeanRemote
java:jboss/exported/learnEJB/HelloBean!first.HelloBeanRemote

Ref:

  1. RetentionPolicy.CLASS
  2. JBoss VFS

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