Walkthrough of Java APIs

Presented By Tracy Engwirda28 September, 2005

Overview

• Background

• Walk through of Java APIs– High level review of packages, patterns

• Building Block Overview

Audience

• Knowledge of Java programming

• People who want an overview of the entire range of functionality exposed – (without resorting to reading the docs)

• Thinking of building, don’t know what to look at first…

Design Goals – High Level

• Decouple persistence from data objects– XML and Database– Originally targeted for import/export– Database abstraction

• Iterative functionality– Start with simple objects, mapped to the legacy

schema

• Managed extensibility– System extensions and deployment model

A Little History…

Import/Export

R6 Portal

R6 Gradebook

R6 Assessment

Module Developer Kit

Building Blocks

Building Blocks Architecture

Core Services

Data Objects

Business Layer(JSP, Servlet, Struts)

View Layer(JSP, Servlet, Tag Library)

Log

Security

Config Persistence

Session

I18N VXI

Context Plug-ins

Road Map

• Data objects and packages– What data can I see?

• Persistence objects and packages– How do I get to the data?

• Service objects and packages– How do I log it, authenticate it, etc.?

• blackboard.* Building Block API

• blackboard.admin.* Release 6 Admin API

• com.blackboard.event.* Bb 5.5 Event API(deprecated)

Which API is that?

Building Block API Packages

blackboard.data.

blackboard.persist.

gradebook

calendar

announcement

content

user

role

navigation

course

gradebook

calendar

announcement

content

user

role

navigation

course

Building Block API Packages

blackboard.platform. session

context

persistence

blackboard.base.

blackboard.portal.

log

filesystem

plugin

blackboard.util.

Data Objects

blackboard.data

• Object view of the schema

• Typed to wrap legacy database constructs– Type-safe enumerations for constrained

database columns

• User.Role.SYSTEM_ADMIN

Data Objects – BbObject

• Base object for all data objects– Common attributes – Primary Key (Id), dates, etc.

• “Smart” attributes– Properties stored in an internal map, instead of

member variables– Smart load, dirty flag

• Id attribute helps define lifecycle– Id.UNSET_ID – default id for new objects

Data Objects – Content

blackboard.data.content

• Content is the root object that can be used in the “content” areas of a course– All other objects are simple subclasses of

Content that over-ride specific values

• Custom content types should create and manipulate Content objects; not CourseDocument objects.– CourseDocument can be used to manipulate

the base “Item” type

Data Objects – Content

• ContentHandler– Ties content to URI-based “handlers”– This is really the B2 “glue” for custom content

• IsFolder– Can the object contain other objects

• IsLesson– Should the contents be displayed sequentially

• Plus many more added in Bb 6.3

Data Objects – Content

Data Objects – Course

blackboard.data.course

• Course and Organization– Organization overrides course for specific

attributes

• Course Enrolment– CourseMembership– Enumerated roles

• CourseMembership.Role.INSTRUCTOR

• Course Groups and Group Enrolment

Data Objects – Gradebook

blackboard.data.gradebook

• LineItem– Defines the “columns” in a course

gradebook

• Score– Wraps the actual outcome for a given line

item

Data Objects – Misc.

• Announcement– Wraps announcements– Can be system or course level

• Calendar– Wrap entries in the calendar– Course and System level

Persistence Objects

• Intended to be decoupled from data objects

• Interfaces allow replaceable persistence implementations– Currently proprietary to Blackboard

• BbPersistenceManager– Ties together different aspects of persistence– Loader/Persister broker– Container

Persistence Objects – Id

• Used to encapsulate the unique identifier for each data object

• Primary key, and more…– Data type– Container (database)– GUIDs are not used, so keys can collide

Persistence Objects – Loaders

• Base interface to get at data– Roughly one-to-one correspondence to data objects

• All type-specific loaders are geared towards known predicates– loadById()– loadByUserIdandType()– Performance. Ad hoc queries can kill the system…– Schema stability

Persistence Objects – Persisters

• Perform any action that manipulates data– Again, one-to-one correspondence with data

objects

• “Smart” update– Id object state determines insert vs. update

Accessing Persisters and Loaders

• They’re interfaces, not directly instantiated by callers

• BbPersistenceManager is the broker

• Most have a Default object for direct accessContentDbLoader loader =

ContentDbLoader.Default.getInstance()

Putting It Together

Content content = new Content();content.setTitle();

// etc. . .

ContentDbPersister contentPersister = ContentDbPersister.Default.getInstance();

contentPersister.persist( content );

Putting It Together – v2

Content content = new Content();content.setTitle();

// etc. . .

// new reflection-based persistence methodscontent.persist();

Services

• Infrastructure for common utility functions

• Exposed as interfaces (mostly)

• Lookup via BbServiceManager

Service Lookups

LogService logService = BbServiceManager.getLogService();

LocaleManager locMgr = BbServiceManager.getLocaleManager();

ContextManager ctxMgr = (ContextManager)BbServiceManager .lookupService( ContextManager.class );

Services – Context

blackboard.platform.context

• Critical entry point that all code must call

• Context wraps information about current request to get the correct database connection

• Interact via ContextManager.setContext() and ContextManager.releaseContext()

Services – Session

blackboard.platform.session

• State for the current browser-based client– Stores authentication status

• Cookie-based session management– Database persistent to share between Perl and

Java processes– Some assembly required

• Not all HTTP-clients (e.g., media plugins for browsers) honor the host browser’s cookies

Services – Filesystem

blackboard.platform.filesystem

• FileSystemService - Broker different file system locations– Course and content– E.g., getContentDirectory()

Services – Log

blackboard.platform.log

• Simple write-only log implementation

• Supports configurable levels

• Written before log4j and JDK 1.4

Services – Security

blackboard.platform.security

• Authentication and Authorization– AccessManagerService

Package Base

• Mix of utility objects

• List functionality– BbList – should use List instead though– GenericFieldFilter – GenericFieldComparator

• Comparator implementation that can sort based on arbitrary properties

• Works with String, Boolean, Dates, and Comparable

Package Base

• BbEnum – base class for all type-safe enumerations

• FormattedText – encapsulation of text data entered via standard Text boxes– Defines enumeration for Smart, Plain, and HTML

text

• NestedRuntimeException/NestedException – pre-JDK 1.4 facility for chaining exceptions

Portal

blackboard.portal.external

• CustomData is all you’ll need…– getModuleData()– getModulePersonalizationData()

• Store name/value– Value can be string, or binary object

Administrative API Packages

blackboard.admin.data.

blackboard.admin.persist.

datasource

course

user

category

datasource

course

user

category

Administrative APIs

blackboard.admin.*

• APIs geared towards data integration– Formerly called the “Event” APIs– Repackaged to be more consistent with B2 APIs– Compatibility layer supported

• Base classes used in Snapshot

Administrative APIs

• Follows IMS Data Model

• Person, Course (Group), and Membership

• Additional objects for Blackboard usage– Category– Data Source

• Defines logically related entities that can be managed independently via Snapshot

Beyond APIs – UI Integration

• Tag Libraries

• Encapsulate re-usable UI components to capture the Blackboard look and feel

• Tag Library Descriptors– Re-use within individual web applications– .tld files

Beyond APIs - Deployment

• Not an API, per se

• Critical aspect of extension development– XML manifest used to generate records in the

database that define navigation, content brokering

Tying It All Together

• A Building Block may require touching several different APIs

1. Set context

2. Authorize current User

3. Load content object

4. Access Gradebook data

5. Perform custom calculation

6. Log result

7. Render results (bracketed via tags)

8. Release context

Thoughts

• There are a lot of classes to look at…– Focus on the type of Building Block you

need to build– Take it methodically, iteratively.

What’s your first goal? Second goal?

• Think of combining functions– What can I do using Content with

Gradebook?

Questions?