Oracle ADF Architecture TV - Development - Error Handling

Real World ADF Design & Architecture Principles
Error Handling
ORACLE
PRODUCT
LOGO
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.

Program Agenda
•  ADF View
•  Summary

ADF Error Handling Hooks - Overview
ADF Faces (ADFv)
EJB/JPAADF Business Components Java
ADF Model (ADFm)
JAX-WS
Unhandled exceptions
Servlet Container
Unhandledexceptions
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 ValidationUpdate Model
Invoke Action
Render Response
1
2
3
4
5
6
JSF

Program Agenda
•  ADF View
•  Summary

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

14 Copyright © 2013, Oracle and/or its affiliates. All rights reserved.14 Copyright © 2013, Oracle and/or its affiliates. All rights reserved.
Exceptions that are not handled in the business
service propagate to the ADF model layer.
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Program Agenda
•  ADF View
•  Summary

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

Program Agenda
•  ADF View
•  Summary

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 .adfMETA-INFservices
–  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

Program Agenda
•  ADF View
•  Summary

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!

What Could Happen
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!

What Could Happen
!
!
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.

Program Agenda
•  ADF View
•  Summary

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

Program Agenda
•  ADF View
•  Summary

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

Program Agenda
•  ADF View
•  Summary

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>

Program Agenda
•  ADF View
•  Summary

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
Unhandledexceptions
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
–  .adfMETA-INFservices
–  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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