The BIStateServlet
class demonstrates state handling. The state
of an application includes state strings that represent the state of the thin
beans in the application and state strings that represent application state.
The state strings can be placed onto the URLs/Forms that an application generates,
so that the application can re-establish the thin-bean's state from a request's
URL. This placing of an application's state onto the URL enables an application
to re-establish application state from a bookmark.
To demonstrate the state handling, drill down on one dimension of the crosstab and use the browser's back button to go back to the initial state. Then, drill down on another dimension. You will notice that the application is able to identify the state of the application immediately before the second drill so that it just drills down the second dimension. Without state handling, the application would have drilled down on both the first and second dimensions.
The following section provides a walkthrough and explanations of the code fragments:
The processRequest
method is called by the base class after a successful
user login. The first step of the application is to initialize the thin beans.
The following code initializes a crosstab thin bean.
presentation = new Presentation(ViewTypeTool.CROSSTAB);
presentation.setThinBeanName(PRESENTATION_NAME);
ThinDataviewCommon crosstab = presentation.getView();
crosstab.setPagingControlVisible(true);
crosstab.setDataSource(dataSource);
handler.registerThinBean(presentation);
Register the thin bean with the BIAdvancedStateManager
object.
BIAdvancedStateManager stateManager = biHttpSession.getStateManager();
stateManager.registerTransientStateBean(presentation);
Establish the base state from which state changes that are included in the state string are tracked. This call clears the thin-bean's current state string.
presentation.setBaseState();
The application delegates to the ServletRequestHandler
for handling
thin-bean events.
ServletRequestHandler
handler = biHttpSession.getServletRequestHandler ( );
ServletQueryParameterProvider
provider = new ServletQueryParameterProvider ( request, response );
handler.handleRequest
( provider );
The application can render the HTML using a combination of raw HTML and thin
beans. For rendering HTML, the application can retrieve the PrintWriter
from the HttpResponse
object and use println
statements
to output HTML to the client.
response.setContentType (
"text/html" );
PrintWriter out = response.getWriter ( );
The thin beans are added to a FormBean
UIX component.
FormBean
rootNode = new FormBean ( FORM_NAME );
ThinCrosstab crosstab = ( ThinCrosstab
) handler.getThinBean ( CROSSTAB_NAME );
if ( crosstab != null ) {
CrosstabBean crosstabBean = new CrosstabBean ( crosstab );
rootNode.addIndexedChild ( crosstab );
}
The application calls the computeCurrentState
method on the BIAdvancedStateManager
object to update the state for each thin bean that is registered with it. The
states of thin beans are then added to the UIX component tree as hidden form
fields.
stateManager.computeCurrentState();
FormValueBean formValue = null;
String transientStateId = stateManager.getCurrentTransientStateID();
if (transientStateId != null) {
formValue = new FormValueBean(BIAdvancedStateManager.TRANSIENT_STATE_ID, transientStateId);
form.addIndexedChild(formValue);
}
String savedStateId = stateManager.getCurrentSavedStateID();
if (savedStateId != null) {
formValue = new FormValueBean(BIAdvancedStateManager.SAVED_STATE_ID, savedStateId);
form.addIndexedChild(formValue);
}
String stateString = stateManager.getCurrentBeanStates();
if (stateString != null) {
formValue = new FormValueBean(BIAdvancedStateManager.STATE_ID, stateString);
form.addIndexedChild(formValue);
}
The thin beans in a FormBean
UIX component are rendered as follows:
ServletRenderingContext renderingContext
= new ServletRenderingContext( this, request, response, out );
rootNode.render ( renderingContext );
While the code cleans up the BIHttpSession
that is related to
a client, the resources allocated by the servlet need to be cleaned up. This
includes beans that the servlet allocates for the session. The close
method (implemented by QueryClient
) should be called to release
resources that are related to the data source. The cleanUp
method
should be called on the ThinGraph
to release Graph-related resources.
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