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

• Contact me at rharrop@interface21.com

Agenda

• Tools for Web Development

• Getting Started

• Basic User Interactions

• Handling Site Formatting

• User Conversations with Web Flow

• Adding Security

• Handling Exceptions

• Interception and Filtering

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

• Maven is a good tool for managing Jetty

Tools for Web Development

• Spring and Spring Web Flow

• Site Formatting

– SiteMesh

– Tiles

• CSS Framework

– ContentWithStyle.co.uk

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

– Data for that view

View Resolution

• Typically views are represented as String

names

– Decoupled from the actual view

implementation

– Easy to test

View Resolution

• These names are mapped to concrete views using a ViewResolver:

– InternalResourceViewResolver

– BeanNameViewResolver

– VelocityViewResolver

• Many applications have multiple

ViewResolvers configured in a chain

Mapping Controllers to URIs

• Controllers are configured as beans in the web application config file

– Can have injected dependencies

– Declarative services

Mapping Controllers to URIs

• These Controller beans are mapped to

URIs using a HandlerMapping:

– SimpleUrlHandlerMapping

– BeanNameHandlerMapping

• HandlerMappings are also configured

in the web application config file

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

SiteMesh1. Configure the SiteMesh filter

2. Create a decorators.xml file

1. Define your page decorators

3. Create your decorator(s)

DEMO:

SiteMesh in Action

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

– Exception 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

Actions before proceeding to another State

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

– Registry of flow definitions

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

flow

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>

Flows are XML files stored in /WEB-INF/flows

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

– Spring HandlerExceptionResolvers

Handling Exceptions

• HandlerExceptionResolver allows for:

– Last ditch processing

– Same contract as a Controller

– Access to thrown Exception

– Auto detected from the ApplicationContext

Handling Exceptions

• Spring provides SimpleMappingExceptionResolver

– Configurable mapping of Exception type to

error view name

DEMO:

Configuring a HandlerExceptionResolver

Interception and Filtering

• Spring web applications have three

options for interception:

– Servlet Filters

– Spring HandlerInterceptors

– AOP

Interception and Filtering

• All three options can be treated as normal

Spring beans:

– Dependency Injection

– Remote/JMX exposure

Uses for Interception and Filtering

• Conditional request processing

–Maintenance mode

– Redirect based on user type

• Tracing and profiling

• Thread local management

DEMO:

Filtering and Interception in

Action

Further Information

• Blog - http://blog.interface21.com/

• SiteMesh -

http://www.opensymphony.com/sitemes

h

• ContentWithStyle -

http://www.contentwithstyle.co.uk

Q&A