jbpm4中不使用Spring, LazyInitializationException的处理

在使用jbpm4时, 如果没用应用spring框架, 就会经常出现LazyInitializationException.<init>:42 | could not initialize proxy - no Session 这个异常, 其实, 这个主要是hibernate懒加载造成的
解决方案一般有以下方式,
1.在相应的配置文件中配置lazy="false"
2. 在需要之前,采用Hibernate.initialize()事先加载
3. 自己写拦截器处理.
对于1,这个是很好处理的, 这里就不说了.
对于3. 这个我暂时还写不好.. , 这个应该是和spring中的那个OpenSessionInViewFilter类似的.
 
对于2, 这里就给个简单的例子来做说明
比如说想, 通过historyActivityInstanceQuery得到HistoryTaskInstanceImpl,再由HistoryTaskInstanceImpl得到HistoryTask.
如果直接获取, 就会报LazyInitializationException异常.
可以通过以下方式获得

// 测试例子
// list
HistoryActivityInstanceQuery haiQuery = new 
        HistoryActivityInstanceQueryImpl().executionId(piId);
List<HistoryActivityInstance> list = processEngine.get(CommandService.class).execute(
    new ListLoadImmediately<HistoryActivityInstance>((AbstractQuery) haiQuery) {
      private static final long serialVersionUID = 1L;

      @Override
      public void doLoad(HistoryActivityInstance datum) throws HibernateException {
        if (datum instanceof HistoryTaskInstanceImpl) {
          Hibernate.initialize(((HistoryTaskInstanceImpl) datum).getHistoryTask()); // 预先加载了
        }
      }
    });
for (HistoryActivityInstance hai : list) {
  if (hai instanceof HistoryTaskInstanceImpl) {
    HistoryTaskInstanceImpl hti = (HistoryTaskInstanceImpl) hai;
    System.out.println(">> " + hti.getHistoryTask().getAssignee());
  }
}
// UniqueResult
haiQuery = new HistoryActivityInstanceQueryImpl().executionId(piId).page(0, 1);
HistoryActivityInstance ai= processEngine.get(CommandService.class).execute(
    new UniqueLoadImmediately<HistoryActivityInstance>
       ((AbstractQuery) haiQuery) {
      private static final long serialVersionUID = 1L;

      @Override
      public void doLoad(HistoryActivityInstance datum) 
             throws HibernateException {
        if (datum instanceof HistoryTaskInstanceImpl) {
          Hibernate.initialize(
             ((HistoryTaskInstanceImpl) datum).getHistoryTask());// 预先加载了
        }
      }
    });
if (ai instanceof HistoryTaskInstanceImpl) {
  System.out.println(">> " + ((HistoryTaskInstanceImpl) ai).getHistoryTask()
            .getAssignee());
} else {
  System.out.println("not an instance of HistoryTaskInstance");
}
// 输出
// >> 王经理
// >> Sun Qi
// >> finance
// >> 张总
// >> 王经理

ListLoadImmediately.java

public abstract class ListLoadImmediately<T> implements Command<List<T>> {
  private static final long serialVersionUID = 1L;
  private AbstractQuery query;

  public ListLoadImmediately(AbstractQuery query) {
    this.query = query;
  }

  /* (non-Javadoc)
   * @see org.jbpm.api.cmd.Command#execute(org.jbpm.api.cmd.Environment)
   */
  @Override
  public List<T> execute(Environment environment) throws Exception {
    query.setCommandService(null); // 
    List<T> data = doExecute(environment);
    for (T datum : data) {
      doLoad(datum);
    }
    return data;
  }

  /**
   * 处理要加载的数据
   * 
   * @param datum
   * @throws HibernateException
   */
  public abstract void doLoad(T datum) throws HibernateException;

  @SuppressWarnings("unchecked")
  public List<T> doExecute(Environment environment) throws Exception {
    return (List<T>) query.execute(environment);
  }
}

UniqueLoadImmediately.java

/**
 * @author yeyong
 */
public abstract class UniqueLoadImmediately<T> implements Command<T> {
  private static final long serialVersionUID = 1L;
  private AbstractQuery query;

  public UniqueLoadImmediately(AbstractQuery query) {
    this.query = query;
  }

  /* (non-Javadoc)
   * @see org.jbpm.api.cmd.Command#execute(org.jbpm.api.cmd.Environment)
   */
  @Override
  public T execute(Environment environment) throws Exception {
    query.setCommandService(null); // 
    T data = doExecute(environment);
    doLoad(data);
    return data;
  }

  /**
   * 处理要加载的数据
   * 
   * @param data
   * @throws HibernateException
   */
  public abstract void doLoad(T data) throws HibernateException;

  @SuppressWarnings("unchecked")
  public T doExecute(Environment environment) throws Exception {
    List<T> list = (List<T>) query.execute(environment);
    if (list.isEmpty()) {
      return null;
    }
    if (list.size() > 1) {
      throw new JbpmException("result not unique: " + list.size());
    }
    return list.get(0);
  }
}