OFBiz中services调用机制_genericdispatcher.runsync

http://www.cnblogs.com/Ivan-j2ee/archive/2012/04/13/2445414.html

OFBiz业务方法里面，当执行一个service的时候，通常采用如下的方式：

     LocalDispatcher dispatcher = dctx.getDispatcher();
     Map<String, Object> result = dispatcher.runSync(getServiceName(), getContext());

LocalDispatcher是本地调度器，实现服务的同步异步调度和定时任务的调度。与服务调度相关的类图如下：



LocalDispatcher是一个接口，实例化的都是GenericDispatcher类，ContextFilter实现了Servlet Filter，会初始化一个GenericDispatcher,并将其存放在ServletContext中，以备整个应用使用。
在请求处理过程中，如果遇到service的event，那么EventHandler会使用LocalDispatcher执行service。
实际上GenericDispatcher只是一个Proxy，自己并不处理相关的调度工作，真正最苦最累的调度工作是由ServiceDispatcher完成的。下面具体研究一下Dispatcher同步和异步调用方法的实现代码：

1.同步调用

通过dispatcher调用runSync方法，也即是调用GenericDispatcher的runSync方法：
    
         /**
          * @see org.ofbiz.service.LocalDispatcher#runSync(java.lang.String, java.util.Map)
          */
         public Map<String, Object> runSync(String serviceName, Map<String, ? extends Object> context)
         throws ServiceValidationException, GenericServiceException
         {
             ModelService service = ctx.getModelService(serviceName);
             return dispatcher.runSync(this.name, service, context);
         }

dispatcher实际是ServiceDispatcher对象。ServiceDispatcher的runSync方法有三百多行，比较复杂，
但最终调用service的是GenericEngine。

     GenericEngine engine = this.getGenericEngine(modelService.engineName);
     ……
    
     Map<String, Object> invokeResult = engine.runSync(localName, modelService, context);
   
GenericEngine是其工厂类GenericEngineFactory获取的，这个Factory类非常简单：

public class GenericEngineFactory {

     protected ServiceDispatcher dispatcher = null;
     protected Map<String, GenericEngine> engines = null;

     public GenericEngineFactory(ServiceDispatcher dispatcher) {
         this.dispatcher = dispatcher;
         engines = FastMap.newInstance();
     }

     /**
      * Gets the GenericEngine instance that corresponds to given the name
      *@param engineName Name of the engine
      *@return GenericEngine that corresponds to the engineName
      */
     public GenericEngine getGenericEngine(String engineName) throws GenericServiceException {
         Element rootElement = null;

         try {
             rootElement = ServiceConfigUtil.getXmlRootElement();
         } catch (GenericConfigException e) {
             throw new GenericServiceException("Error getting Service Engine XML root element", e);
         }
         Element engineElement = UtilXml.firstChildElement(rootElement, "engine", "name", engineName);

         if (engineElement == null) {
             throw new GenericServiceException("Cannot find a service engine definition for the engine name [" + engineName + "] in the serviceengine.xml file");
         }

         String className = engineElement.getAttribute("class");

         GenericEngine engine = engines.get(engineName);

         if (engine == null) {
             synchronized (GenericEngineFactory.class) {
                 engine = engines.get(engineName);
                 if (engine == null) {
                     try {
                         ClassLoader loader = Thread.currentThread().getContextClassLoader();
                         Class<?> c = loader.loadClass(className);
                         Constructor cn = c.getConstructor(ServiceDispatcher.class);
                         engine = (GenericEngine) cn.newInstance(dispatcher);
                     } catch (Exception e) {
                         throw new GenericServiceException(e.getMessage(), e);
                     }
                     if (engine != null) {
                         engines.put(engineName, engine);
                     }
                 }
             }
         }

         return engine;
     }
}

从配置文件serviceengine.xml文件中获取相应的engine子类，如java的是org.ofbiz.service.engine.StandardJavaEngine
bsh的是org.ofbiz.service.engine.BeanShellEngine。

Java的StandardJavaEnignerunSync方法采用的是反射来执行相应的方法，如下：

         Class<?> c = cl.loadClass(this.getLocation(modelService));
             Method m = c.getMethod(modelService.invoke, DispatchContext.class, Map.class);
             result = m.invoke(null, dctx, context);
            
不同的Engine实现的方式不一样。

2. 异步调用

异步调用怎么实现的呢？实现异步的原理就是启动一个线程来执行相应的业务逻辑，原方法直接返回，从而实现异步。具体实现的时候可以根据实际情况而定，比如 将业务逻辑封装成一个任务，将此任务放到一个任务链中，线程池采用先进先出的方式来选择任务进行执行。OFBiz中怎么实现呢？具体查看 GenericAsyncEngine的runAsync方法发现是通过一个生成一个Job来实现的：

         job = new GenericServiceJob(dctx, jobId, name, modelService.name, context, requester);
         try {
             dispatcher.getJobManager().runJob(job);
         } catch (JobManagerException jse) {
             throw new GenericServiceException("Cannot run job.", jse);
         }