在JBoss AS7中使用WS-AT

WS-AT全称Web Services Atomic Transaction，是基于SOAP的事务解决方案。JBoss AS7默认支持WS-AT，本文介绍使用方法。首先从JBoss AS的网站下载JBoss AS7和quickstart：



在quickstart当中，有一个wsat-simple项目，我们要使用这个项目做为demo。下面是对这个项目的简单讲解。这个项目实现了一个饭店的订位服务：

public interface RestaurantServiceAT {

    /**
     * Create a new booking
     */
    @WebMethod
    public void makeBooking() throws RestaurantException;

    /**
     * obtain the number of existing bookings
     * 
     * @return the number of current bookings
     */
    @WebMethod
    public int getBookingCount();

    /**
     * Reset the booking count to zero
     */
    @WebMethod
    public void reset();

}

可以看到包含业务包含makeBooking，getBookingCount和reset，都很好理解，即订位，获得已订位数，重置订位数。以下是整个项目的设计：



接下来我们要部署并运行这个例子，我们要使用standalone-xts.xml来启动AS7，在这套配置里面，包含了对WS-AT的支持。这个配置文件位于AS7的example目录当中：

为了正确启动，我们要将这个配置copy到standalone的配置目录中：

weli@power:~/projs/jboss-as-7.1.1.Final$ find .  | grep xts
./docs/examples/configs/standalone-xts.xml

weli@power:~/projs/jboss-as-7.1.1.Final$ cp docs/examples/configs/standalone-xts.xml standalone/configuration/

在这个配置文件中，增加了对xts模块的配置：

<extension module="org.jboss.as.xts"/>

以及xts模块的配置:

<subsystem xmlns="urn:jboss:domain:xts:1.0">
    <xts-environment url="http://${jboss.bind.address:127.0.0.1}:8080/ws-c11/ActivationService"/>
</subsystem>

接下来我们用standalone-xts.xml这个配置来启动AS7：



启动成功后，进到wsat-simple项目中，执行maven命令进行编译，部署，测试：



可以看到，通过使用JBoss Arquillian的Maven插件，项目的编译、部署、打包是一次完成的。如果你成功执行了上面的命令，那么从AS7的目录里面会看到项目部署，运行过程，卸载的全部日志。下面对提取出来的日志进行分段讲解。

首先是xts模块的启动过程：

11:02:55,303 INFO  [org.jboss.as.webservices] (MSC service thread 1-14) JBAS015539: Starting service jboss.ws.endpoint-publish.ws-t11-participant
11:02:55,304 INFO  [org.jboss.as.webservices] (MSC service thread 1-7) JBAS015539: Starting service jboss.ws.endpoint-publish.ws-t11-client
11:02:55,303 INFO  [org.jboss.as.webservices] (MSC service thread 1-13) JBAS015539: Starting service jboss.ws.endpoint-publish.ws-t11-coordinator
11:02:55,304 INFO  [org.jboss.as.webservices] (MSC service thread 1-16) JBAS015539: Starting service jboss.ws.endpoint-publish.ws-c11

从日志中，你可以看到xts模块会默认注册多个WebService，用于支持WS-AT事务流。在WS-AT标准定义的事务中，包括Participant，Client，Coordinator这几个角色。

项目的执行过程分为testCommit()和testRollback()两部分。我们先从testCommit看起：

Starting 'testCommit'. This test invokes a WS within an AT. The AT is later committed, which causes the back-end resource(s) to be committed.
[CLIENT] Creating a new WS-AT User Transaction
[CLIENT] Beginning Atomic Transaction (All calls to Web services that support WS-AT wil be included in this transaction)
[CLIENT] invoking makeBooking() on WS
[SERVICE] Restaurant service invoked to make a booking
[SERVICE] Enlisting a Durable2PC participant into the AT
[SERVICE] Invoking the back-end business logic
[SERVICE] makeBooking called on backend resource.
[CLIENT] committing Atomic Transaction (This will cause the AT to complete successfully)
Prepare called on participant, about to prepare the back-end resource
prepare called on backend resource.
back-end resource prepared, participant votes prepared
all participants voted 'prepared', so coordinator tells the participant to commit
commit called on backend resource.

我将上面的过程，做成时序图，程序的执行过程如下：



我们可以看到WS-AT定义的事务是一个2-Phase-Commit，事务先由Participant进入Prepare阶段，如果准备就绪，则Commit事务。

以下是rollback的日志输出：

Starting 'testRollback'. This test invokes a WS within an AT. The AT is later rolled back, which causes the back-end resource(s) to be rolled back.
[CLIENT] Creating a new WS-AT User Transaction
[CLIENT] Beginning Atomic Transaction (All calls to Web services that support WS-AT wil be included in this transaction)
[CLIENT] invoking makeBooking() on WS
[SERVICE] Restaurant service invoked to make a booking
[SERVICE] Enlisting a Durable2PC participant into the AT
[SERVICE] Invoking the back-end business logic
[SERVICE] makeBooking called on backend resource.
[CLIENT] rolling back Atomic Transaction (This will cause the AT and thus the enlisted back-end resources to rollback)
one or more participants voted 'aborted' or a failure occurred, so coordinator tells the participant to rollback
rollback called on backend resource.

注意到rollback测试最终的结果是事务回滚了：

[SERVICE] one or more participants voted 'aborted' or a failure occurred, so coordinator tells the participant to rollback

通过上面的流程，我们可以看到，WS-AT的特色就是客户端和服务端共同参与事务。事务的开始，提交，回滚，都是由客户端发起的：

public class ClientTest {
   
    /**
     * Test the simple scenario where a booking is made and then committed.
     * 
     * @throws Exception if something goes wrong.
     */
    @Test
    public void testCommit() throws Exception {

        UserTransaction ut = UserTransactionFactory.userTransaction();
        try {
            ut.begin();

        } finally {
            rollbackIfActive(ut);
            client.reset();
        }
    }

    /**
     * Tests the scenario where a booking is made and the transaction is later rolledback.
     * 
     * @throws Exception if something goes wrong
     */
    @Test
    public void testRollback() throws Exception {

        UserTransaction ut = UserTransactionFactory.userTransaction();
        try {
            ut.begin();

        } finally {
            rollbackIfActive(ut);
            client.reset();
        }
    }

    /**
     * Utility method for rolling back a transaction if it is currently active.
     * 
     * @param ut The User Business Activity to cancel.
     */
    private void rollbackIfActive(UserTransaction ut) {
        try {
            ut.rollback();
        } catch (Throwable th2) {
            // do nothing, not active
        }
    }
}

而事务的参与，执行，则在服务端完成。这是WS-AT的真正Power所在。如果你对WS-AT的实现感兴趣，可以参考具体协议标准：

Web Services Atomic Transaction (WS-AtomicTransaction) Version 1.2