将BIRT整合到自己的Java项目中(二)

关于编写viewer，关键在于使用ReportEngine API，这个在birt官方文档上有很详细的描述。 这里将几个主要环节总结一下：

1. 启动ReportEngine
   这里需要注意启动ReportEngine的开销问题和图片链的协议的问题。使用IReportEngineFactory比每次new一个出来性能方面要好很多。使用HTMLEmitterConfig可以使得生成的HTML报表中的图片的src指向一个web资源而非file资源。
   
   public IReportEngine getEngine() ...{
       try ...{
         if(platformContext == null) ...{
            platformContext = new PlatformServletContext(servletContext);
          }
          engineConfig = new EngineConfig();
          engineConfig.setEngineHome(
              servletContext.getRealPath("/WEB-INF/platform/"));
         // 要求ENGINE HOME 位于WEB-INF/Platform
          engineConfig.setPlatformContext(platformContext);
         //This call sets the Log directory name and level
          engineConfig.setLogConfig(getLogDir(), Level.FINE);
         
         //设置Emitter，渲染HTML的时候，image的地址是HTTP协议而不是File协议
          HTMLEmitterConfig emitterConfig = new HTMLEmitterConfig( );
          emitterConfig.setActionHandler(new HTMLActionHandler());
          HTMLServerImageHandler imageHandler = new HTMLServerImageHandler();
          emitterConfig.setImageHandler(imageHandler);
          engineConfig.getEmitterConfigs().put("html", emitterConfig);
         
         //设置日志level
          engineConfig.setLogConfig(getLogDir(), Level.WARNING);
         //启动Platform，创建ReportEngine
          Platform.startup(engineConfig);
          IReportEngineFactory factory = (IReportEngineFactory) Platform
              .createFactoryObject(IReportEngineFactory.EXTENSION_REPORT_ENGINE_FACTORY);
          engine = factory.createReportEngine(engineConfig);
          engine.changeLogLevel(Level.WARNING);
         
          log.debug("A new engine startup.");
        } catch (BirtException e) ...{
          e.printStackTrace();
        }
   
       return engine;
      }
2. 运行报表
   我理解为编译报表文件。BIRT在渲染报表之前，要将报表编译为.rptdocument，再根据这个文件将报表渲染为HTML格式或PDF格式。编译报表使用IRunTask：
   
   protected void run(String rptDesign) ...{
       assert (context != null);
   
        IReportEngine engine = context.getEngine();
       // Open a report design
        IReportRunnable design = null;
       try ...{
          design = engine.openReportDesign(context
              .getFullRptDesignFilename(rptDesign));
         // Create task to run the report - use the task to
         // execute the report and save to disk.
          IRunTask task = engine.createRunTask(design);
          String doc = context.getFullRptDocumentFilename(rptDesign);
         // run the report and destroy the engine
          task.run(doc);
         
          log.debug("save rpt design to " + doc);
          task.close();
        } catch (EngineException e) ...{
          e.printStackTrace();
        }
      }