Download - W&L CS Web Application Server

Using AOP to Ease Evolution
Presented by David Shepherd (QLI & UD)
Co-Authors: Thomas Roper (QLI) and Lori Pollock (UD)
Motivation for Evolution in the Field
Databases with
Records Of Cars
Making a Distributed Database Application
 Issue: Stale Data
DB
Data
DB
North Carolina
Detective
Delaware
?
notify
Data
Clerk App.
Detective App.
Update car data
Non-Trivial Data Mining
DB
Update
Hawaii
DMV
2
Desired Evolution Task
Notification Scheme
DMV App
DB
Server
Who is
interested in
these records?
Can a database support
this functionality?
DetectApp
Interesting Update
Return Results
Send Primary Keys
Query DB
Return Results
No
3
Software Evolution Problem
Have
Open-Source Software (OSS) App
Need to Modify Application
Adding Feature(s)
Open Source
Software X
Additional
Feature(s)
Issues
OSS evolves independently
Injection of feature
Maintenance of feature
Potential Solutions
OOP vs. Aspect-Oriented Programming (AOP)
4
New
Version of OSS Available
Overview of Evolution
Process
AOP Process
Original
Open
Source
Software
1
1
OOP Process
Feature
Feature
Feature
Original
Open
Source
Software
New
Version
OSS
New
Version
OSS2
Augmented
Open
Source
Software
2
2
Augmented
New Version
OSS
Augmented
New
Version
OSS2
5
Possible OOP Solution
SQLQuery
DbServer
notifyObservers
executeQuery
openConnection
parseQuery
getQuery
executes
notifies
commitQuery
addObserver
SQLQuery
DBObserver
Notifies
listeners
addVar
Original OSS Code
Add Code into method
try{
// Evaluate the sql query
Table result =
sql_executor.
execute(db_conn, query);
query.notifyObservers(result);
error = false;
return t;
}
Original
OSS Code
Clear …
Add Code into method
Add methods
public class SQLQuery implements Subject{
...
public void notifyObservers(Table result){
//Get the primary keys, table, etc.
ResultInfo resultInfo =...
//Get query info from the query
QueryInfo queryInfo =...
//update all ...
}
public SQLQuery(){
addObserver(DatabaseDistributedNotifier.
getInstance());
...
New Feature Code
Add interface
Add implementation of interface
Public interface DBObserver{
…
…
}
Public class MckoiDBObserver
implements DBObserver {
…
…
}
6
An Outcome of OOP Solution
2 packages
3 classes
Blue lines represent
our feature’s implementation
This represents one .java file
Taller = Longer file *needs to be
Crosscutting Concern
(CCC)
added here
7
Another Outcome of OOP Solution
Tangling
 Statement level
 Method level
8
AOP Solution
ObserverProtocol
SQLQuery
execute
Pointcut SubjectChange
Prepare
Pointcut updateObserver
SQLQuery
Pointcut registration
DBObserver
update
KeyPointcut
Feature:
Only loosely
coupled with
OriginalPointcut
OSS
Pointcut
DBObserverProtocol
Pointcut subjectChange
Pointcut updateObserver
Key
Pointcut registration
Declare Subject
Original Code
Base
Declare Observer
Feature 2:
Observer
concern
modularized
Feature Implementation
9
Finding Code Insertion Points
A First Step in implementation (for both methods)
Database Codebase
10
Finding Insertion Point – A Closer Look
Statement “Select”’s evaluate method
/**
* Evaluates the select statement with the given Database context.
*/
public Table evaluate() throws DatabaseException {
Which place is better?
DatabaseQueryContext context = new DatabaseQueryContext(database);
// Check the permissions for this user to select from the tables in the
Snippet from JDBCDatabaseInterface’s execQuery method . . .
// given plan.
…
checkUserSelectPermissions(context, user, plan);
try {
boolean error = true;
try {
Table t = plan.evaluate(context);
error = false;
return t;
}
// Evaluate the sql query.
Table result =
sql_executor.execute(database_connection,
query);
// Put the result in the result cache... This will lock this object
// until it is removed from the result set cache. Returns an id that
// uniquely identifies this result set in future communication.
// NOTE: This locks the roots of the table so that its contents
// may not be altered.
result_set_info = new ResultSetInfo(query, result);
result_id = addResultSet(result_set_info);
11
OOP Process – Find Insertion Point
1
Answer Co-Worker’s
Insert in most likely
Continue Cutting and Pasting
2 Test
3 –
4Fail 5 Code
Question About Another
Remove
place
...
Project
We
removed
an extra
statement
Ponder, where was I?
(what is my working set)
Causing
two errors
12
AOP Process – Find Insertion Point
1
Answer Co-Worker’s
Set Pointcut
toContinue
Most
Changing Pointcut .
Change
Pointcut
5
2 Test
3 – 4Fail
Question About Another
Likely Place . .
Project
Only working with one file:
Easy to remember working set
13
New OSS Version Available
AOP Process
Original
Open
Source
Software
OOP Process
Feature
Feature
Feature
Original
Open
Source
Software
New
Version
OSS
New
Version
OSS2
Augmented
Open
Source
Software
2
2
Augmented
New Version
OSS
Augmented
New
Version
OSS2
14
OOP Solution another outcome
1. Find Feature Code
Process with OOP
2. Extract Feature Code
3. Find new insertion points
4. Insert Feature code
Database Codebase
New Database
Codebase
15
Evolution of Codebase: AOP Solution
New Code Well-Modularized
 Separate from main code base
AOP: At worst,
realign pointcut
references
 Refers to main code base
Database Codebase
New Database
Codebase
16
Concluding Remarks - Lessons Learned
AOP saves effort when adapting an open-source project
Eases Initial Maintenance Task - Add New Feature
 Non-Invasive Change
 Maintaining Working Set
Eases Evolution - Adapt to OSS Change
 Finding the Feature
 Only Re-Align Pointcuts
Status
 Working Implementation
 Continue to use in ongoing industry research
AOP is AOK!
17
18
Slide graveyard
19
AOP Process – Find Insertion Point
Snippet from JDBCDatabaseInterface’s execQuery method . . .
…
try {
// Evaluate the sql query.
Table result = sql_executor.execute(database_connection, query);
query.notification(result);
error=false;
// Put the result in the result cache... This will lock this object
// until it is removed from the result set cache. Returns an id that
// uniquely identifies this result set in future communication.
// NOTE: This locks the roots of the table so that its contents
// may not be altered.
result_set_info = new ResultSetInfo(query, result);
result_id = addResultSet(result_set_info);
}
…
20
21
com.mckoi.jfccontrols
com.mckoi.database.sql
com.mckoi.database.jdbc
com.mckoi.store
com.mckoicom.mckoi.database
com.mckoi.database.control
com.mckoi.debug
com.mckoi.database.interpret
com.mckoi.database.global
com.mckoi.toolscom.mckoi.util
com.mckoi.database.jdbcserver
com.mckoi.database.procedure
com.mckoi.database.regexbridge
com.mckoi.runtime
com.mckoi
com.mckoi.database
com.mckoi.database.control
com.mckoi.database.global
com.mckoi.database.interpret
com.mckoi.database.jdbc
com.mckoi.database.jdbcserver
com.mckoi.database.procedure
com.mckoi.database.regexbridge
com.mckoi.database.sql
com.mckoi.debugc
om.mckoi.jfccontrols
22
Possible Solutions
Can a database support
this functionality?
SQLQuery
notifyObservers
DbServer
executeQuery
openConnection
parseQuery
commitQuery
…
try{
// Evaluate the sql query
Table result =
sql_executor.execute(db_conn, query);
query.notifyObservers(result);
error = false;
return t;
}
getQuery
addObserver
removerObserver
SQLQuery
addVar
translateObjectType
clear
public class SQLQuery implements Subject{
...
public void notifyObservers(Table result){
//Get the primary keys, table, etc. from results
ResultInfo resultInfo =...
//Get query info from the query
QueryInfo queryInfo =...
for(Iterator e = observers.iterator();
e.hasNext(); ){
((DBObserver)e.next()).
update(resultInfo,queryInfo);
}
}
…
public SQLQuery(){
addObserver(DatabaseDistributedNotifier.
getInstance());
...
}
23
Quantum Leap Innovations – Business
Model
Technology
Differentiated
Products &
Services
Pioneering
Software
Technologies
Research
Programs
Gov’t Agencies
Partners
End Users
What We Do
We create pioneering technologies that are used by our
partners to build innovative products and services.
How We Do It
We support our partners as a team member by providing
our unique IP, software technologies and people.
Tom, am I allowed to show this? It was from the
Template.ppt in J:\Presentations.
24