Java
Building Web Apps with Spring Rob Harrop, Interface21 Ltd.
About the Speaker
• VP at Interface21
• Core Developer on Spring
• Founder of Spring Modules
• JMX 2.0 Expert Group Member
• Author of Pro Spring
Agenda
• Tools for Web Development
• Getting Started
• Basic User Interactions
• Handling Site Formatting
• User Conversations with Web Flow
• Adding Security
• Handling Exceptions
Tools for Web Development
• Get a good IDE:
– IntelliJ IDEA
– Eclipse with WTP
– NetBeans
• Consider using Jetty for development
– Rapid turn around
– Easy to edit view files, flow definitions etc
Tools for Web Development
• Spring and Spring Web Flow
• Site Formatting
– SiteMesh
– Tiles
• CSS Framework
Getting Started
1.Create basic web application skeleton
1.Consider Maven as a kick start
2.Configure Spring's
DispatcherServlet
3.Create a Spring Web Application config file
4.Configure ContextLoaderListener
and middle tier configuration files as needed
DEMO:
Basic Web Application
Configuration
Basic User Interactions
• Logic encapsulated in Controllers
– Implement Controller directly
– Extend AbstractController, MultiActionController or SimpleFormController
Basic User Interactions
• Controllers return a ModelAndView
which describes:
– The view to render
View Resolution
• Typically views are represented as String names
– Decoupled from the actual view implementation
View Resolution
• These names are mapped to concrete views using a ViewResolver:
– InternalResourceViewResolver
– BeanNameViewResolver
– VelocityViewResolver
• Many applications have multiple
Mapping Controllers to URIs
• Controllers are configured as beans in
the web application config file
– Can have injected dependencies
Mapping Controllers to URIs
• These Controller beans are mapped to
URIs using a HandlerMapping:
– SimpleUrlHandlerMapping
– BeanNameHandlerMapping
• HandlerMappings are also configured
DEMO:
Creating and Configuring a
Controller
Site-Wide Formatting
• Most web applications require consistent formatting across the site
– Headers
– Navigation
– Footers
– Ads
• Adding this by hand can be painful and error-prone
Handling Site-Wide Formatting
• Site-wide formatting can be applied automatically
– Do not cut and paste across pages!
• Use a pre-built tool
– SiteMesh and Tiles are good candidates
• Couple this with a strong CSS-based layout
– I use a pre-built CSS framework from ContentWithStyle
Site-Wide Formatting with
SiteMesh
1. Configure the SiteMesh filter
2. Create a decorators.xml file
1. Define your page decorators
DEMO:
User Conversations with Web
Flow
• Web Flow provides a sophisticated
mechanism for controlling long running user interactions
• Conversations are mapped as fa low using standard state machines concepts
User Conversations with Web
Flow
• Web Flow is integrated with Spring MVC
– View resolution works the same way
Web Flow Concepts
• State
– A single stage in the execution of a flow
• Action
– A piece of logic that can be executed a various points during the flow
Web Flow Concepts
• Event
– A user or action initiated event such as “submit” or “process”
• Transition
– A movement from one state to another in response to some event
Web Flow Concepts
• View State
– A state that constitutes a pause in the flow execution and renders a view for the user
• Action State
– A state type that executes one or more
Web Flow Concepts
• Flow Executor
– Manages flow execution. Resumes and pauses flows as they proceed
• Flow Repository
– Store in-progress flow execution state
– Simple and continuation-based implementations provided
Web Flow Concepts
• Flow Registry
Getting Started with Web Flow
1.Configure Flow Registry
2.Configure Flow Executor
3.Optionally configure Flow Repository
4.Create Flow Definition
5.Configure a FlowController for your
Configuring Web Flow
• Configure the FlowExecutor and FlowRegistry
• <flow:executor id="flowExecutor"
• registry-ref="flowRegistry"/>
• <flow:registry id="flowRegistry">
• <flow:location path="/WEB-INF/flows/**.xml"/>
• </flow:registry>
Configuring a
FlowController
• <bean name="/checkout.html" class="o.s.w.ex.mvc.FlowController"> • <property name="flowExecutor" • ref="flowExecutor"/> • <property name="defaultFlowId" • value="checkout"/> • </bean>DEMO:
Order Process with Spring Web
Flow
Handling Exceptions
• Exceptions that cannot be handled should be allowed to propagate
• These can be handled by some last-ditch process
– Servlet error pages
Handling Exceptions
• HandlerExceptionResolver allows for:
– Last ditch processing
– Same contract as a Controller
– Access to thrown Exception
– Auto detected from the
Handling Exceptions
• Spring provides
SimpleMappingExceptionResolver
– Configurable mapping of Exception type to error view name
DEMO:
Configuring a
Interception and Filtering
• Spring web applications have three options for interception:
– Servlet Filters
– Spring HandlerInterceptors
Interception and Filtering
• All three options can be treated as normal Spring beans:
– Dependency Injection
Uses for Interception and
Filtering
• Conditional request processing
– Maintenance mode
– Redirect based on user type
• Tracing and profiling
