DynaDTO Dynamic Data Transfer Objects

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DynaDTO Dynamic Data Transfer Objects

• Brian Sam-Bodden
• Integrallis Software, LLC.

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Presentation Contents

• J2EE Patterns
• Typical Patterns in a J2EE Web Application
• The Transfer Object Pattern
• The Transfer Object Assembler Pattern
• Transformation Layers in J2EE
• Typical DTO Strategies
• Problems with existing DTO strategies
• The DynaDTO strategy
• Typical Usage Scenarios
• Configuring DynaDTO
• Using DynaDTO

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J2EE Patterns

• Abstractions of a Solution (design) to a
  recurring problem
• Refactoring Good Design Time Design Pattern
• Patterns are discovered, not created
• J2EE Patterns are
• Strategies
• Interpretations
• Extensions
• of more general design patterns (GoF)

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J2EE Patterns

• Each pattern (design) can have multiple
  implementations (strategies)
• The trick is...
• ... finding the right granularity for your
  problem
• ... collaboration amongst patterns
• Pragmatic View
• A practical solution to a real world recurring
  problem and the guidelines of when and where to
  apply it

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J2EE Patterns

• J2EE Pattern Catalog Pattern Format
• Problem
• Forces
• Solution
• Structure
• Interaction
• Consequences
• Strategies

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J2EE Patterns

• J2EE Pattern Catalog classifies patterns by Tier
• Presentation Tier
• Business Tier
• Integration Tier

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Presentation Tier Patterns

• Intercepting Filter
• Front Controller
• Composite View
• View Helper
• Service to Worker
• Dispatcher View
• Context Object
• Application Controller

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Business Tier Patterns

• Business Delegate
• Session Facade
• Service Locator
• ? Transfer Object
• Composite Entity
• ? Transfer Object Assembler
• Value List Handler
• Business Object
• Application Service

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Integration Tier Patterns

• Data Access Object
• Service Activator
• Domain Store
• Web Service Broker

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J2EE Patterns
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Typical Patterns in a J2EE Web Application

• Presentation Tier
• MVC Model II OR Component-based MVC like
• JSPServlet, Struts, JSF, Tapestry and others
• Business Tier
• POJO Domain Model
• Domain Model persistence via DAO
• DAO wraps persistence mechanism (JDBC, CMP, JDO,
  Hibernate)
• Services in Session Façade
• Services return and take DTOs

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Typical Patterns in a J2EE Web Application

• Business Tier (cont.)
• DTOs are assembled from Domain Objects
• Assembly step is manual

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The Transfer Object Pattern

• Also known (old) as Value Object Pattern
• The Problem
• Coarse-grained Entities
• CMP EJBs not meant to leave the Tier they live in
• Each data access (method call) is a potentially
  remote call
• Performance degradation, portability problems,
  brittle architecture

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The Transfer Object Pattern

• The Problem (cont.)
• Fine-Grained Entities
• Domain Model should not be exposed to the client
• Client needs are temporal (application specific)
• Domain should outlive client needs and be
  reusable
• Anemic Domain Model (Fowler) results from Domain
  Model tainted by both Data Model and the User
  Interface Needs
• No separation of concerns, lack of encapsulation

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The Transfer Object Pattern

• The Problem (cont.)
• Bulk-Transfers
• Not only for the data of a single entity
• Collections Transfer
• Support for pagination schemes

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The Transfer Object Pattern

• The Forces
• Web Applications are typically read-mostly and
  save/update-occasionally
• Data Viewing requirements per page are
• Typically composed of multiple attributes
• Transformed for display purposes

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The Transfer Object Pattern

• Solution (typical)
• Transfer Object to encapsulate business data
• Single method call to transfer data of a business
  entity
• Business Tier Code (Enterprise Bean) constructs
  the Transfer Object, populate and pass it by
  value to the client

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The Transfer Object Pattern
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The Transfer Object Pattern
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The Transfer Object Pattern

• Strategies
• Updateable Transfer Objects Strategy
• Multiple Transfer Object Strategy
• Entity Inherits Transfer Object Strategy (1-to-1)
• Transfer Object Factory Strategy
• Custom Transfer Object Strategy
• Multiple Entity, Single Transfer Object

Not in the J2EE Pattern Catalog Entry
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Typical Implementation

• Developers manually create light(er) weight
  objects
• Populate them in code, near where they access the
  data
• Session Façade, Entity Bean, DAO
• Usually support strategies outlined poorly
• Requires a great deal of coding
• Muddles the business tier with transformation
  code
• Equivalent to having O/R mapping code

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Problems with the Typical Implementation

• Parallel-Object Hierarchy
• Parallel Hierarchy is hard to maintain
• in XP terms this is smelly
• Sign that domain has been flattened
• Code Overhead/Maintenance
• DTO classes
• Transformation Code

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Transformation Layers in J2EE

• In a typical 3 tier application there are 2
  transformation tiers
• Between the business tier and the
  data/integration tier
• Between the business tier and the presentation
  tier
• O/R Mapping Tools deal with the first
• DTO Pattern Implementations deal with the second
• Problem is that everyone starts from scratch

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The DynaDTO Solution

• Provide a solution to the screen/UI object lt--gt
  domain/data object transformation problem
• Solution similar to what Hibernate is to O/R
  Mapping
• XML configuration
• Factory-based design
• Smart defaults
• Supports all the strategies for the DTO pattern
  well
• Enables you to test outside of the container

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A DynaDTO Sample Usage Scenario

• We have a single object, want a mirror DTO
• A Quote object is the domain object
• The interface IQuouteDTO represents the DTO
• Client only reads IQuoteDTO

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A DynaDTO Sample Usage Scenario

• Quote.java
• public class Quote
• // fields
• private String title
• private Date date
• private String author
• String text
• // getters and setters

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A DynaDTO Sample Usage Scenario

• IQuoteDTO.java
• public interface IQuoteDTO extends DTO
• String getTitle()
• Date getDate()
• String getAuthor()
• String getText()

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A DynaDTO Sample Usage Scenario

• IQuoteDTO.dto.xml
• lt?xml version"1.0"?gt
• ltdtosgt
• ltdto targetIQuoteDTO"gt
• ltsourcesgt
• ltsource typeQuote" automap"true" /gt
• lt/sourcesgt
• lt/dtogt
• lt/dtosgt

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A DynaDTO Sample Usage Scenario - 2

• We have an object graph with 3 objects
• A Conference object
• A Conference has a Venue object
• A Conference has Tracks

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A DynaDTO Sample Usage Scenario - 2

• We want a IConferenceSummaryDTO interface
• Read only
• Some info from the Conference object
• The address, broken in two lines from the Venue
  object
• A List with the names of the Tracks

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A DynaDTO Sample Usage Scenario - 2

• IConferenceSummaryDTO.dto.xml Shell
• lt?xml version"1.0"?gt
• ltdtosgt
• ltdto targetIConferenceSummaryDTO"gt
• ltsourcesgt
• ltsource typeConference" gt
• ...INTERESTING STUFF GOES HERE
• lt/sourcegt
• lt/sourcesgt
• lt/dtogt
• lt/dtosgt

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A DynaDTO Sample Usage Scenario - 2

• IConferenceSummaryDTO.dto.xml
• ltsource type"Conference"gt
• lt!-- aliases, used by the expressions --gt
• ltalias source"venue" name"venue" /gt
• lt!-- mappings --gt
• ltmapping from"name" to"conferenceTitle" /gt
  
• ltmapping from"venue.name" to"venueName" /gt
• ltmapping from"venue.address.streetAddress
• to"venueAddressLine1" /gt
  
• lt/sourcegt

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A DynaDTO Sample Usage Scenario

• IConferenceSummaryDTO.dto.xml
• ltexpressionsgt
• ltexpression target"VenueAddressLine2
• value"venue.getAddress().getCity() ','
  util.space()
• venue.getAddress().getState()
  util.space()
• venue.getAddress().getZipCode()
  " /gt
• lt/expressionsgt

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Steps to use DynaDTO

• Define your DTO Interfaces
• Create mappings from Domain Object to DTO
  interfaces
• Reference the mapping in the dynadto.cfg.xml
• At runtime, initialize DynaDTO by reading
  dynadto.cfg.xml
• To create a DTO, use BuilderFactory to get a
  Builder for a given DTO interface or class
• Gather your source (domain objects)
• Pass them to the build method of the builder

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DynaDTO Sample Configuration File

• dynadto.cfg.xml
• lt?xml version"1.0" encoding"utf-8"?gt
• ltdynadto-configurationgt
• lt!-- mappings --gt
• ltmapping resource"ConferenceSummary.dto.xml" /gt
• lt/dynadto-configurationgt

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Initializing DynaDTO

• dynadto.cfg.xml
• try
• ConfigurationLoader.loadConfiguration("dynadto
  .cfg.xml")
• catch (ConfigurationException ce)
• ce.printStackTrace()

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Using DynaDTO

• Conference conf ...
• // build the DTO
• Builder builder BuilderFactory
• .getInstance()
  .getBuilder(IConferenceSummaryDTO.class)
• IConferenceSummaryDTO myDTO
• (IConferenceSummaryDTO) builder.build(conf)

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Conclusions

• DynaDTO simplifies implementation of DTO Pattern
• Supports all known strategies
• Supports complex expressions
• Supports nested DTOs
• Supports Collection Flattening/Transformation
• Allows you to use POJIs or POJOs as DTOs

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THANK YOU

• Questions?
• Feel free to email me at bsbodden_at_integrallis.com