Oracle ADF Architecture TV - Development - Error Handling


Real World ADF Design & Architecture Principles Error Handling

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15th Feb 2013 v1.0


Learning Objectives

•  At the end of this module you should be able to:

– Understand the ADF error handling architecture – Know the scope of an error handler – Distinguish between error handling and incident reporting

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Program Agenda •  Error Handling Introduction •  Handling ADF Lifecycle Errors •  ADF Business Components •  ADF Binding Layer •  ADF Controller

–  Bounded Task Flow –  Unbounded Task Flow

•  ADF View •  Servlet Container •  Summary


Fiction …

Wouldn't it be good if there was a single location to handle all application errors and exceptions?


… and Fact.

Not perfect, but a solution.


ADF Error Handling Hooks - Overview

ADF Faces (ADFv)

EJB/JPA ADF Business Components Java

ADF Model (ADFm)

JAX-WS

Unhandled exceptions

Servlet Container U

nhan

dled

exc

eptio

ns

Render Response

Propagates exceptions

ADF Controller (ADFc)

Business Service Layer

ADF Binding Layer Data Control


ADF Exception Handlers

•  ADFm Exception Handler – Error Handler (DCErrorHandler) in BindingContext

•  ADFc Exception Handler – Exception Handler activity in Task-Flow – Application wide Exception Handler

•  ADFv Exception Handler –  oracle.adf.view.rich.context.ExceptionHandler

•  Container, error-page in web.xml


ADF Error Handling Overview ADF Interaction in JSF Request Lifecycle


ADF Binding

JAX-WS

Restore View

Apply Request

Process Validation Update Model

Invoke Action

Render Response 1

2

3

4

5

6

JSF


oracle.jbo.JboException

•  JboException extends java.lang.RuntimeException –  Thus Business Component method can throw exceptions without

a throws clause in the method signature •  Translation of error messages occur by the client calling getLocalizedMessage() and not when an error is thrown

One Exception Super Class for All Exceptions


Bundled Exception Mode

•  Enabled by default •  Presents maximal set of failed validation exceptions •  Java supports single exception to be thrown at a time •  ADF BC moves all exceptions under a parent exception

–  Multiple entity attribute validation errors (ValidationException) are wrapped in RowValException parent exception

–  Multiple rows that fail validation performed during commit will have the RowValException wrapped in TxnValException object

–  You can recursively introspect exception by calling getDetails() on each exception

All Exceptions at Once

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Exceptions that are not handled in the business service propagate to the ADF model layer.

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ADF Model Error Handler

•  The ADF model error handler deals with – All ADF binding errors – Business service errors that occur when accessing a service

trough the ADF binding layer •  Formats and displays error message •  Default error handler skips the top-level JboException because it

only is a bundled exception wrapper for other business exceptions


Creating A Custom Error Handler

•  Extend oracle.adf.model.binding.DCErrorHandlerImpl and configure your custom error error handler in DataBindings.cpx

•  Override the following methods as needed –  reportException

• Override this method to analyze exceptions for errors you want to handle –  getDisplayMessage

• Override to change or suppress (null value) the displayed message –  getDetailedDisplayMessage

• Override this method to provide HTML markup formatted detail information –  skipException(Exception ex)

• Called by the framework to check if an exception should be ignored


Oracle JDeveloper 11g R2


Custom Error Handler Example Skip Exception for SQL Exceptions

public class CustomErrorHandler extends DCErrorHandlerImpl { ... protected boolean skipException(Exception ex) { if (ex instanceof DMLConstraintException) { return false; //don't show details of SQL exception } else if (ex instanceof SQLException) { return true; } else { return super.skipException(ex); } } )


Skip Exception Example SQLIntegrityConstraintViolationException

skipException == false skipException == true


The code is from a managed bean in our application. What happens in case of an

exception?

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OperationBinding operationBinding = null; operationBinding = getOperationBinding("UpdateOrder"); operationBinding.execute(); …


On a Related Note

•  It happens quite often that developers execute a client method directly on the Application Module –  BindingContext > findDataControl("...") > getDataProvider() –  Cast data provider to Application Module interface –  Execute client methods on it

•  The risk is that –  Exceptions thrown by the client interface logic are not handled by the

ADFm error handler if invoked directly –  Inconsistent error handling may occur


The ADF controller handles exceptions that occur during task flow execution



ADF Controller Exception Handling

•  Exceptions that may occur during task flow execution include –  Method call activity that throws an exception –  Task flow initialize or finalize methods throwing an exception –  Authorization failures when accessing an activity

•  Controller exceptions are handled by a task flow activity that is designated as an exception handler

•  When a task flow throws an exception, control flow is passed to the designated exception handling activity

Introduction


Exception Handler Activity How-to Define an Activity as the Exception Handler


Example: Method Error Handler

public void showErrorDialog() { ControllerContext context = ControllerContext.getInstance(); ViewPortContext currentViewPort = context.getCurrentViewPort(); if (currentViewPort.isExceptionPresent()) { FacesMessage fm = new FacesMessage( FacesMessage.SEVERITY_WARN, "Application Error", currentViewPort.getExceptionData().getMessage()); FacesContext fctx = FacesContext.getCurrentInstance(); fctx.addMessage("ApplicationInfo", fm); fctx.renderResponse(); } }


ADF Controller

•  Exceptions that occur in context of task flow are forwarded to exception handler activity

•  Best Practices - Define exception handling activity in each bounded and unbounded task flows

•  Define exception handler in task flow template for consistency

Exception Handler Activity


ADF Controller

•  AdfcExceptionHandler is the ADF controller internal framework class that passes control to the task flow's designated exception handler activity

•  If no exception handler activity exists, the control is passed the browser

•  Default exception handler does not handle exceptions thrown during RENDER_RESPONSE phase

Default Exception Handling


Customizing the Framework Error Handling

•  Configuration –  Create oracle.adf.view.rich.context.ExceptionHandler

text file and store it in .adf\META-INF\services –  you need to create the “services” folder –  Add the absolute name of your custom exception handler

•  Java class that extends ExceptionHandler

•  Configured for whole ADF application –  Deployed in EAR file

Add Your Own Exception Handler


import oracle.adf.view.rich.context.ExceptionHandler; public class CustomExceptionHandler extends ExceptionHandler { public CustomExceptionHandler() { super(); } public void handleException(FacesContext facesContext, Throwable throwable, PhaseId phaseId) throws Throwable{ if ( … Exception or Error to check …){ //handle issue } else { //pass error to default exception handler throw throwable; } } }

ADF Controller Overriding Default Exception Handler Class


Be thoughtful. Don't override the framework exception handler to eagerly or for no reason. Keep in mind that the error handler is not deployed with bounded task flows but deployed with the application.



Log Exceptions, Report Exceptions ..

•  Exception handler activities handle exceptions but don't report them –  No programming error fixes itself –  Log and report programming or system errors

•  Implement a exception handling, logging and reporting strategy that can be reused and that is declaratively applied

•  Report serious issues –  Considers weekends and vacations

•  Evaluate BPM (SOA Suite) Human Workflow integration –  In case of emergency, send mail or SMS


What Could Happen Task Flow Exception Propagation

Memory Stack

Current Task Flow

Task Flow 4

Task Flow 3

Task Flow 2

Task Flow 1

Task Flow 2 Call

Task Flow 3 Call

Task Flow 4 Call

!

!

View1

View2

View3

View4

Task Flow 1

Task Flow 2

Task Flow 3

Task Flow 4

EH

EH

Method Call

Current Task Flow

BANG!



Memory Stack

Current Task Flow

Task Flow 2

Task Flow 1

Task Flow 2 Call

Task Flow 3 Call

Task Flow 4 Call

Propagate Exception

Propagate Exception

!

!

View1

View2

View3

View4

Task Flow 1

Task Flow 2

Task Flow 3

Task Flow 4

EH

EH

Current Task Flow

Method Call

BANG!



!

!

View1

View2

Task Flow 1

Task Flow 2

EH

EH

Memory Stack

Current Task Flow

Task Flow 2

Task Flow 1

Task Flow 2 Call


Visual Example Exception Handler in Caller Task Flow

BANG!

!


Visual Example Exception Handler in Top Level Task Flow

BANG!

!


Every bounded task flow should have an error handler activity defined. Task flow templates help to configure error handlers consistent throughout an application.



Unbounded Task Flow

•  There always is a single unbounded task flow instance available for an application –  Independent of the number of adfc-config.xml files available in the

application class path •  Unbounded task flows cannot be based on task flow templates

Exception Handling Strategy


Unbounded Task Flow

•  To build "error handling templates" for unbounded task flows you use an unbounded task flow definitions in an ADF Library – Keep adfc-config.xml as the unbounded task flow definition file – Deploy error handling logic as managed bean within ADF library –  Load order of unbounded configuration files determines which

exception handler become active in cases of multiple defined handlers

– ADFc configuration files on the class path precede configurations in the application

Exception Handling Strategy


Exception Handling •  Typically, view layer exceptions occur because of

–  Failed execution of client logic in managed beans –  Failed access to the ADF binding layer

• EL references in page source • Java references in managed beans

–  Failed EL expressions • Typos in the object name • Missing objects (e.g. entity object references) • Failed type casting (e.g. oracle.jbo.domain.Number to Long)

– Expired session


Exception Raised In Managed Bean Example: Simulating A Problem


Exception Raised In Managed Bean Solution: Routing Exception To Binding Layer


Servlet Container

•  Handles all exceptions not handled by an application – Available to all Java EE applications

•  Looks in web.xml file for directive on how to handle a specific error code or the exception type

•  If nothing is set-up in web.xml, the exception terminates the user application session –  In Java, a stack trace is displayed in the browser, which exactly

what you don't want to happen


Java EE Exception Handling Last Resort

<error-page> <error-code> … http error code here (e.g 404)… </error-code> <location>/unhandled_error_page.html</location> </error-page> <error-page> <exception-type> … exception class here … (e.g. java.lang.Throwable) </exception-type> <location>/unhandled_exception_page.html</location> </error-page>



– Bounded Task Flow – Unbounded Task Flow



ADF Error Handling Summary Error Handling by Architecture Layers

•  try-catch block

•  ADFm Error Handler

•  Exception Handler Activity •  Custom ADFc Exception Handler

•  try-catch block

•  web.xml

ADF Faces


ADF Model

JAX-WS

Unhandled exceptions

Servlet Container

Unh

andl

ed e

xcep

tions

Render Response

Propagates exceptions

ADF Controller


Conclusion

•  Anticipate problems and work on a mitigation strategy – Only leave unexpected errors and errors you

want for pass through unhandled for the handlers –  Like for application security, perform a risk

analysis and identify threats (database down, WS not responsive, NPE …)

•  Define exception handling strategies and code them into custom standard exception handler classes

•  Log errors by severity


Conclusion

•  Access business service methods through the binding layer

•  Use try/catch blocks in any managed bean method –  Route managed bean exceptions to the binding layer

reportError() method •  Use custom task flow exception handler thoughful

–  .adf\META-INF\services –  Avoid new exceptions in your exception handler –  Keep in mind that this exception handler is on an

application level and not task flow / ADF library level


Further Reading

•  Oracle Magazine Article "Catch Me If You Can" –  http://www.oracle.com/technetwork/issue-archive/2013/13-mar/

o23adf-1897193.html

•  Oracle JDeveloper and ADF Documentation Library –  Fusion Developer Guide

•  "Handling and Displaying Exceptions in an ADF Application" •  "Customizing Business Components Error Messages"

•  How to log all errors to the database –  http://one-size-doesnt-fit-all.blogspot.de/2008/06/jdev-adf-how-to-log-all-

errors-to.html

Oracle ADF Architecture TV - Development - Error Handling

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