WebContextFactory是工厂，方法都是静态的，持有一个Builder实例和Builder的接口
WebContextBuilder是产品的制造机器，他的实现类可以自定义，不同的实现类，对应不同的产品制造方式。
WebContext 是产品
WebContextFactory对WebContextBuilder进行了封装，让购买者和产品的生产进行解耦
public class WebContextFactory
{
public static WebContext get()
{
if (builder == null)
{
log.warn("Missing WebContextBuilder. Is DWR setup properly?");
return null;
}
return builder.get();
}
private static WebContextBuilder builder = null;
//此方法在容器启动时调用，所以WebContextBuilder的实现类可以自己定义，在启动时注入
public static void attach(Container container)
{
WebContextFactory.builder = container.getBean(WebContextBuilder.class);
}
public interface WebContextBuilder
{
WebContext get();
void engageThread(Container container,HttpServletRequest request,HttpServletResponse response);
void disengageThread();
}
/**
* The log stream
*/
private static final Log log = LogFactory.getLog(WebContextFactory.class);
}
DwrServlet 类webContextBuilder 的使用
doPost方法里使用构建器webContextBuilder负责本线程webContext对象的生产和销毁
在后面Handler方法里使用工厂WebContextFactory生产产品
public void init(ServletConfig servletConfig) throws servletexception
{
super.init(servletConfig);
try
{
StartupUtil.logStartup(getClass().getSimpleName(),servletConfig);
container = createContainer(servletConfig);
//DwrServlet启动的时候赋予webContextBuilder的实现类对象
webContextBuilder = container.getBean(WebContextBuilder.class);
configureContainer(container,servletConfig);
}
catch (servletexception ex)
{
throw ex;
}
catch (Exception ex)
{
log.fatal("init Failed",ex);
throw new servletexception(ex);
}
finally
{
if (webContextBuilder != null)
{
webContextBuilder.disengageThread();
}
}
}
@Override
public void doPost(HttpServletRequest request,HttpServletResponse response) throws IOException,servletexception
{
try
{
//由webContextBuilder生产一个webContext对象，
//此webContext对象在此线程的后面整个请求处理的过程中都能通过WebContextFactory.get()访问到
//webContextBuilder内部使用ThreadLocal来保存webContext对象，所以只用本线程能访问
webContextBuilder.engageThread(container,request,response);
UrlProcessor processor = container.getBean(UrlProcessor.class);
processor.handle(request,response);
}
finally
{ //由webContextBuilder回收一个webContext产品
webContextBuilder.disengageThread();
}
}