Walkthrough of Java APIs Presented By Tracy Engwirda 28 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 ConfigPersistence Session I18NVXI ContextPlug-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 access ContentDbLoader 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 methods content.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?