Seam

Introduction

Seam manages components, that means it manages the complete lifecycle and scope of the components (inversion of control principle), named as context of a component. Thereto it injects dependencies to the components (dependency injection).

Most Seam application use session beans as JSF action listeners.

Seam lets you use a JSF EL expression inside EJB-QL. Under the covers, this results in an ordinary JPA setParameter() call on the standard JPA Query object.

Seam integrates Hibernate Validator and lets you use it for data validation (even if you are not using Hibernate for persistence).

Installation and Configuration

• download jboss-seam-2.0.2.SP1.zip and extract to <ECLIPSE_WORKSPACE>
• add jboss.home to <SEAM_DIR>\build.properties

Libs

jboss-seam.jar	Provides the Seam container, Seam annotations, bijection, extended JSF life cycle, CRUD framework, security, jBPM integration, Drools integration, web services, page flows, asynchronous support, conversations, extended EL, managed transactions and persistence, and the integration test framework.
jboss-seam-remoting.jar	Supports invoking Seam components using Ajax requests and allows JavaScript to listen for messages on JMS queues and topics
jboss-seam-ui.jar	Includes the Seam JSF components, file upload capability, graphics generation, Facelet integration, and conversation controls
jboss-seam-debug.jar	Activates the hot deployment classloader and provides a Seam debug page and developer-oriented error page
jboss-seam-ioc.jar	Provides integration with Spring and other IoC containers
jboss-seam-pdf.jar	Has support for generating PDF files using Facelet templates and a document storage mechanism for pushing binary files
jboss-seam-mail.jar	Provides email integration and supports creating emails from Facelet templates

Annotations

Seam defines own annotations and uses some other annotations.

org.hibernate.validator.Length

@org.hibernate.validator.Length(min=<Number>, max=<Number>)
<attribute declaration>

for length validation.

org.hibernate.validator.NotNull

@org.hibernate.validator.NotNull
<attribute declaration>

for validation.

org.jboss.seam.annotations.datamodel.DataModel

@org.jboss.seam.annotations.datamodel.DataModel[(scope=ScopeType.<TYPE>)]
<attribute declaration>

The @DataModel annotation exposes an attibute of type java.util.List to the JSF page as an instance of javax.faces.model.DataModel. This allows us to use the list in a JSF <h:dataTable> with clickable links for each row. In this case, the DataModel is made available in a session context variable named messageList.

org.jboss.seam.annotations.datamodel.DataModelSelection

@org.jboss.seam.annotations.datamodel.DataModelSelection
<attribute declaration>

The @DataModelSelection annotation tells Seam to inject the List element that corresponded to the clicked link.

org.jboss.seam.annotations.Factory

@org.jboss.seam.annotations.Factory("<context variable name>")
<method_declaration>

The @Factory annotation tells Seam to create an instance of the bean and invoke the method to initialize the value. We call method a factory method. Marks a method as a factory method for a context variable. A factory method is called whenever no value is bound to the named context variable, and is expected to initialize the value of the context variable. There are two kinds of factory methods. Factory methods with void return type are responsible for outjecting a value to the context variable. Factory methods which return a value do not need to explicitly ouject the value, since Seam will bind the returned value to the specified scope. This annotation supports use of the Seam "factory component" pattern.

org.jboss.seam.annotations.In

@org.jboss.seam.annotations.In
<attribute_declaration>

The attribute is injected by Seam. Examples for injections are EntityManager or FacesMessages.

org.jboss.seam.annotations.Logger

@org.jboss.seam.annotations.Logger

The annotation is used to inject the component's Log instance. The logger has a specialised syntax e.g.

log.info("creating component '#0' on #1", name(), date());
log.info("#{<object>.<attribute>}");

org.jboss.seam.annotations.Name

@org.jboss.seam.annotations.Name("<Name>")
<class_declaration>

specifies the name of the Seam component. This name must be unique within the Seam application. When JSF asks Seam to resolve a context variable with a name that is the same as a Seam component name, and the context variable is currently undefined (null), Seam will instantiate that component, and bind the new instance to the context variable.

org.jboss.seam.annotations.Out

@org.jboss.seam.annotations.Out
<attribute_declaration>

The @Out annotation then exposes the selected value directly to the page. So ever time a row of the clickable list is selected, the row object is injected to the attribute of the stateful bean, and the subsequently outjected to the event context variable named as the attribute name.

org.jboss.seam.annotations.Scope

@org.jboss.seam.annotations.Scope(org.jboss.seam.ScopeType.<SCOPE_TYPE>)
<class_declaration>

specifies the scope of a seam component. Each Seam component type has a default scope. Types are:

Type	Description	Default for
APPLICATION
BUSINESS_PROCESS
CONVERSATION	The conversation scope maintains data for a single user across a well-defined series of pages	entities
EVENT	the component lives only for one method call	JavaBeans
METHOD
PAGE
SESSION
STATELESS
UNSPECIFIED

Standard components

Identiy

@In
Identity idendity;

is a standard component of the Seam security model und lives as long as the session.

API

FacesMessages

FacesMessages.instance().add("...");

Seam tags

Seam use Facelets for the user interface. An example of an xhtml file is

<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:s="http://jboss.com/products/seam/taglib"
      xmlns:h="http://java.sun.com/jsf/html"
      xmlns:f="http://java.sun.com/jsf/core">

validateAll

This JSF component tells JSF to validate all contained input fields against the Hibernate Validator annotations specified in the entitiy bean.

Applications

• s. JBoss

Reources

• Seam in Action by Dan Allen in C:\Uwes\Documents\Software_Development\Programming\Frameworks\Seam\SeaminAction.pdf, Source code extracted to <ECLIPSE_WORKSPACE>/seaminaction