jBPM的Scheduler模块和Spring集成失败

我的Web系统中使用了jBPM，并使用Spring来管理bean，并使用Spring＋JTOM组合来管理来自多个数据库的事务（有Oracle9i，Microsoft SQL Server 2000）。但是没有使用jBPM的Scheduler。系统运行很好。
最近由于业务需要，我在jBPM中添加了timer。这样，就需要配置一个Scheduler了。而我的麻烦也从此开始。

我一开始使用jBPM提供的那个SchedulerServlet，可是发现这个Servlet会去自动加载jBPM的默认配置，也就是在default.jbpm.ctf.xml中配置的属性，特别是数据库的配置。这样，我的Spring就无法管理它的事务了。
我查看了它的源代码，发现其代码如下（省略了不相干代码）：

public class SchedulerServlet extends HttpServlet {

  private static final long serialVersionUID = 1L;
  
  Scheduler scheduler = null;

  public void init() throws ServletException {
    // create a new scheduler
    scheduler = new Scheduler();

    // start the scheduler
    scheduler.start();
  }
  ...
}

public class Scheduler {
  
  SchedulerThread schedulerThread = null;
  ...
  public void start() {
    log.debug("starting the scheduler");
    schedulerThread = new SchedulerThread();
    schedulerThread.setInterval(interval);
    schedulerThread.addListener(new HistoryListener());
    schedulerThread.start();
  }
  ...
}

public class SchedulerThread extends Thread {

  JbpmConfiguration jbpmConfiguration = null;
  String jbpmContextName = null;
  ...

  public SchedulerThread() {
    this(JbpmConfiguration.getInstance(), JbpmContext.DEFAULT_JBPM_CONTEXT_NAME);
  }
  ...
}

我查找了相关资源，发现没有现成的和Spring集成的工具。（jBPM的核心引擎已经有spring-module提供了集成工具）。我想，那我自己覆盖这个SchedulerServlet，让这个SchedulerThread使用Spring管理下的JbpmConfiguration实例，那不就可以达到目的了吗？于是动手。

可是这时候才发现，这个jBPM提供的Scheduler对象，根本就没有可以让我能够向SchedulerThread注射入JbpmConfiguration的入口。而且这个类是default的可见范围，连继承扩展都做不到。迫于无奈，我在Scheduler的相同package下，建了一个子类，来提供注入Spring管理的JbpmConfiguration实例的能力，然后自己写了一个ServletContextListener来加载这个监听线程。
代码如下：

package org.jbpm.scheduler.impl;
...

public class SpringAwareScheduler extends Scheduler {
    
    private static final Log log = LogFactory.getLog(SpringAwareScheduler.class);

    protected JbpmConfiguration jbpmConfiguration;
    
    public SpringAwareScheduler() {
        this(null);
    }
    
    public SpringAwareScheduler(JbpmConfiguration jbpmConfiguration) {
        super();
        this.jbpmConfiguration = jbpmConfiguration;
    }
    
    /**
     * @param jbpmConfiguration the jbpmConfiguration to set
     */
    public void setJbpmConfiguration(JbpmConfiguration jbpmConfiguration) {
        this.jbpmConfiguration = jbpmConfiguration;
    }
    
    public void start() {
      log.debug("starting the scheduler");
      schedulerThread = new SchedulerThread(this.jbpmConfiguration);
      schedulerThread.setInterval(interval);
      schedulerThread.addListener(new HistoryListener());
      schedulerThread.start();
    }
}

这里是用来取代SchedulerServlet的ServletContextListener：

public class SpringAwareJbpmSchedulerListener implements ServletContextListener {

    private Scheduler scheduler = null;
    
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        scheduler.stop();
    }

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        // create a new scheduler
        String beanName = sce.getServletContext().getInitParameter("jbpmConfigurationBeanName");
        if (StringUtils.isBlank(beanName)) {
            beanName = "jbpmConfiguration";
        }
        WebApplicationContext wac = WebApplicationContextUtils.getRequiredWebApplicationContext(sce.getServletContext());
        JbpmConfiguration jbpmConfiguration = (JbpmConfiguration) wac.getBean(beanName);
        scheduler = new SpringAwareScheduler(jbpmConfiguration);
        
        JbpmContext jbpmContext = jbpmConfiguration.createJbpmContext(JbpmContext.DEFAULT_JBPM_CONTEXT_NAME);
        SessionFactory sessionFactory = jbpmContext.getSessionFactory();
        assert sessionFactory != null;
        
        // initialize it with the servlet init parameters 
        int interval = 5000;
        if (!StringUtils.isBlank(sce.getServletContext().getInitParameter("interval"))) {
            interval = Integer.parseInt(sce.getServletContext().getInitParameter("interval"));
        }
        scheduler.setInterval(interval);
        
        int historyMaxSize = 50;
        if (!StringUtils.isBlank(sce.getServletContext().getInitParameter("historyMaxSize"))) {
            historyMaxSize = Integer.parseInt(sce.getServletContext().getInitParameter("historyMaxSize"));
        }
        scheduler.setHistoryMaxSize(historyMaxSize);
        
        // put the scheduler in the web app context
        sce.getServletContext().setAttribute("scheduler", scheduler);
        
        // start the scheduler
        scheduler.start();
    }
}

好了，以为现在在web.xml中配置好了以后，总该可以了吧？可是不然。问题又来了。发现系统在启动的过程中，根本没有使用在JbpmConfiguration实例中配置的SessionFactory，而是继续使用根据default.jbpm.cfg.xml中的配置生成的那个SessionFactory实例。
我单步跟踪了一下代码，发现之所以会去加载根据default.jbpm.cfg.xml中的配置生成的那个SessionFactory实例，原因是在DbPersistenceService在获取SessionFactory实例的时候，发现为空，所以就按照默认配置去创建一个新的SessionFactory实例。异常信息如下：

10:19:32,939 FATAL [org.hibernate.connection.DatasourceConnectionProvider] - Could not find datasource: java:/DefaultDS
javax.naming.NameNotFoundException
	at org.objectweb.carol.jndi.enc.java.CompNamingContext.lookupCtx(CompNamingContext.java:689)
	at org.objectweb.carol.jndi.enc.java.CompNamingContext.lookup(CompNamingContext.java:179)
	at org.objectweb.carol.jndi.enc.java.JavaURLContext.lookup(JavaURLContext.java:138)
	at javax.naming.InitialContext.lookup(InitialContext.java:392)
	at org.hibernate.connection.DatasourceConnectionProvider.configure(DatasourceConnectionProvider.java:52)
	at org.hibernate.connection.ConnectionProviderFactory.newConnectionProvider(ConnectionProviderFactory.java:124)
	at org.hibernate.connection.ConnectionProviderFactory.newConnectionProvider(ConnectionProviderFactory.java:56)
	at org.hibernate.cfg.SettingsFactory.createConnectionProvider(SettingsFactory.java:414)
	at org.hibernate.cfg.SettingsFactory.buildSettings(SettingsFactory.java:62)
	at org.hibernate.cfg.Configuration.buildSettings(Configuration.java:2009)
	at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1292)
	at org.jbpm.persistence.db.DbPersistenceServiceFactory.getSessionFactory(DbPersistenceServiceFactory.java:91)
	at org.jbpm.persistence.db.DbPersistenceService.getSessionFactory(DbPersistenceService.java:76)
	at org.jbpm.persistence.db.DbPersistenceService.getSession(DbPersistenceService.java:80)
	at org.jbpm.persistence.db.DbPersistenceService.getSchedulerSession(DbPersistenceService.java:261)
	at org.jbpm.JbpmContext.getSchedulerSession(JbpmContext.java:531)
	at org.jbpm.scheduler.impl.SchedulerThread.executeTimers(SchedulerThread.java:104)
	at org.jbpm.scheduler.impl.SchedulerThread.run(SchedulerThread.java:71)

可是，明明DbPersistenceService的实例是根据JbpmContext创建的，而JbpmContext又是根据JbpmConfiguration实例创建的。也就是说，DbPersistenceService使用的SessionFactory的实例应该是来自JbpmConfiguration的实例中的那个。为什么实际上却为空呢？

现在我晕掉了。到底错误在那里呢？