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：
-
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;
}
-
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();
}
}
