[jboss-cvs] jboss-seam/doc/reference/en/modules ...
Gavin King
gavin.king at jboss.com
Wed Nov 29 16:53:11 EST 2006
User: gavin
Date: 06/11/29 16:53:11
Added: doc/reference/en/modules xml.xml
Log:
new chapter
Revision Changes Path
1.1 date: 2006/11/29 21:53:11; author: gavin; state: Exp;jboss-seam/doc/reference/en/modules/xml.xml
Index: xml.xml
===================================================================
<chapter id="xml">
<title>Configuring Seam components</title>
<para>
The philosophy of minimizing XML-based configuration is extremely strong in Seam. Nevertheless,
there are various reasons why we might want to configure a Seam component using XML: to isolate
deployment-specific information from the Java code, to enable the creation of re-usable frameworks,
to configure Seam's built-in functionality, etc.
Seam provides two basic approaches to configuring components: configuration via property settings in a
properties file or <literal>web.xml</literal>, and configuration via <literal>components.xml</literal>.
</para>
<sect1>
<title>Configuring components via property settings</title>
<para>
Seam components may be provided with configuration properties either via servlet context parameters,
or via a properties file named <literal>seam.properties</literal> in the root of the classpath.
</para>
<para>
The configurable Seam component must expose JavaBeans-style property setter methods for the
configurable attributes. If a seam component named <literal>com.jboss.myapp.settings</literal> has a
setter method named <literal>setLocale()</literal>, we can provide a property named
<literal>com.jboss.myapp.settings.locale</literal> in the <literal>seam.properties</literal> file or
as a servlet context parameter, and Seam will set the value of the <literal>locale</literal> attribute
whenever it instantiates the component.
</para>
<para>
The same mechanism is used to configure Seam itself. For example, to set the conversation timeout, we
provide a value for <literal>org.jboss.seam.core.manager.conversationTimeout</literal> in
<literal>web.xml</literal> or <literal>seam.properties</literal>. (There is a built-in Seam
component named <literal>org.jboss.seam.core.manager</literal> with a setter method named
<literal>setConversationTimeout()</literal>.)
</para>
</sect1>
<sect1>
<title>Configuring components via <literal>components.xml</literal></title>
<para>
The <literal>components.xml</literal> file is a bit more powerful than property settings. It lets
you:
</para>
<itemizedlist>
<listitem>
<para> Configure components that have been installed automatically—including both built-in
components, and application components that have been annotated with the
<literal>@Name</literal> annotation and picked up by Seam's deployment scanner. </para>
</listitem>
<listitem>
<para> Install classes with no <literal>@Name</literal> annotation as Seam components—this
is most useful for certain kinds of infrastructural components which can be installed multiple
times different names (for example Seam-managed persistence contexts). </para>
</listitem>
<listitem>
<para> Install components that <emphasis>do</emphasis> have a <literal>@Name</literal> annotation
but are not installed by default because of an <literal>@Install</literal> annotation that
indicates the component should not be installed. </para>
</listitem>
<listitem>
<para> Override the scope of a component. </para>
</listitem>
</itemizedlist>
<para>
A <literal>components.xml</literal> file may appear in one of three different places:
</para>
<itemizedlist>
<listitem>
<para>The <literal>WEB-INF</literal> directory of a <literal>war</literal>.</para>
</listitem>
<listitem>
<para>The <literal>META-INF</literal> directory of a <literal>jar</literal>.</para>
</listitem>
<listitem>
<para>
Any directory of a <literal>jar</literal> that contains classes with an
<literal>@Name</literal> annotation.
</para>
</listitem>
</itemizedlist>
<para>
Usually, Seam components are installed when the deployment scanner discovers a class with a
<literal>@Name</literal> annotation sitting in an archive with a <literal>seam.properties</literal>
file or a <literal>META-INF/components.xml</literal> file. (Unless the component has an
<literal>@Install</literal> annotation indicating it should not be installed by default.)
The <literal>components.xml</literal> file lets us handle special cases where we need
to override the annotations.
</para>
<para>
For example, the following <literal>components.xml</literal> file installs the JBoss Embeddable
EJB3 container:
</para>
<programlisting><![CDATA[<components xmlns="http://jboss.com/products/seam/components"
xmlns:core="http://jboss.com/products/seam/core">
<core:ejb/>
</components>]]></programlisting>
<para>
This example does the same thing:
</para>
<programlisting><![CDATA[<components>
<component class="org.jboss.seam.core.Ejb"/>
</components>]]></programlisting>
<para>
This one installs and configures two different Seam-managed persistence contexts:
</para>
<programlisting><![CDATA[<components xmlns="http://jboss.com/products/seam/components"
xmlns:core="http://jboss.com/products/seam/core"
<core:managed-persistence-context name="customerDatabase"
persistence-unit-jndi-name="java:/customerEntityManagerFactory"/>
<core:managed-persistence-context name="accountingDatabase"
persistence-unit-jndi-name="java:/accountingEntityManagerFactory"/>
</components>]]></programlisting>
<para>
As does this one:
</para>
<programlisting><![CDATA[<components>
<component name="customerDatabase"
class="org.jboss.seam.core.ManagedPersistenceContext">
<property name="persistenceUnitJndiName">java:/customerEntityManagerFactory</property>
</component>
<component name="accountingDatabase"
class="org.jboss.seam.core.ManagedPersistenceContext">
<property name="persistenceUnitJndiName">java:/accountingEntityManagerFactory</property>
</component>
</components>]]></programlisting>
<para>
This example creates a session-scoped Seam-managed persistence context (this is not recommended in
practice):
</para>
<programlisting><![CDATA[<components xmlns="http://jboss.com/products/seam/components"
xmlns:core="http://jboss.com/products/seam/core"
<core:managed-persistence-context name="productDatabase" scope="session"
persistence-unit-jndi-name="java:/productEntityManagerFactory"/>
</components>]]></programlisting>
<programlisting><![CDATA[<components>
<component name="productDatabase"
scope="session"
class="org.jboss.seam.core.ManagedPersistenceContext">
<property name="persistenceUnitJndiName">java:/productEntityManagerFactory</property>
</component>
</components>]]></programlisting>
<para>
The <literal><factory></literal> declaration lets you specify a value or method binding
expression that will be evaluated to initialize the value of a context variable when it is first
referenced.
</para>
<programlisting><![CDATA[<components>
<factory name="contact" method="#{contactManager.loadContact}" scope="CONVERSATION"/>
</components>]]></programlisting>
<para>
You can create an "alias" (a second name) for a Seam component like so:
</para>
<programlisting><![CDATA[<components>
<factory name="user" value="#{actor}" scope="STATELESS"/>
</components>]]></programlisting>
<para>
You can even create an "alias" for a commonly used expression:
</para>
<programlisting><![CDATA[<components>
<factory name="contact" value="#{contactManager.contact}" scope="STATELESS"/>
</components>]]></programlisting>
<para>
Sometimes we want to reuse the same <literal>components.xml</literal> file with minor changes during
both deployment and testing. Seam lets you place wildcards of the form <literal>@wildcard@</literal> in
the <literal>components.xml</literal> file which can be replaced either by your Ant build script (at
deployment time) or by providing a file named <literal>components.properties</literal> in the classpath
(at development time). You'll see this approach used in the Seam examples.
</para>
</sect1>
<sect1>
<title>Fine-grained configuration files</title>
<para>
If you have a large number of components that need to be configured in XML, it makes much more sense
to split up the information in <literal>components.xml</literal> into many small files. Seam lets
you put configuration for a class named, for example, <literal>com.helloworld.Hello</literal> in a
resource named <literal>com/helloworld/Hello.component.xml</literal>. (You might be familiar with this
pattern, since it is the same one we use in Hibernate.) The root element of the file may be either a
<literal><components></literal> or <literal><component></literal>
element. </para>
<para>
The first option lets you define multiple components in the file:
</para>
<programlisting><![CDATA[<components>
<component class="com.helloworld.Hello" name="hello">
<property name="name">#{user.name}</property>
</component>
<factory name="message" value="#{hello.message}"/>
</components>]]></programlisting>
<para>
The second option only lets you define or configure one component, but is less noisy:
</para>
<programlisting><![CDATA[<component name="hello">
<property name="name">#{user.name}</property>
</component>]]></programlisting>
<para>
In the second option, the class name is implied by the file in which the component definition
appears.
</para>
<para>
Alternatively, you may put configuration for all classes in the <literal>com.helloworld</literal>
package in <literal>com/helloworld/components.xml</literal>.
</para>
</sect1>
<sect1>
<title>Configurable property types</title>
<para>
Properties of string, primitive or primitive wrapper type may be configured just as you would expect:
</para>
<programlisting><![CDATA[org.jboss.seam.core.manager.conversationTimeout 60000]]></programlisting>
<programlisting><![CDATA[<core:manager conversation-timeout="60000"/>]]></programlisting>
<programlisting><![CDATA[<component name="org.jboss.seam.core.manager">
<property name="conversationTimeout">60000</property>
</component>]]></programlisting>
<para>
Arrays, sets and lists of strings or primitives are also supported:
</para>
<programlisting><![CDATA[org.jboss.seam.core.jbpm.processDefinitions order.jpdl.xml, return.jpdl.xml, inventory.jpdl.xml]]></programlisting>
<programlisting><![CDATA[<core:jbpm>
<core:process-definitions>
<value>order.jpdl.xml</value>
<value>return.jpdl.xml</value>
<value>inventory.jpdl.xml</value>
</core:process-definitions>
</core:jbpm>]]></programlisting>
<programlisting><![CDATA[<component name="org.jboss.seam.core.jbpm">
<property name="processDefinitions">
<value>order.jpdl.xml</value>
<value>return.jpdl.xml</value>
<value>inventory.jpdl.xml</value>
</property>
</component>]]></programlisting>
<para>
Even maps with String-valued keys and string or primitive values are supported:
</para>
<programlisting><![CDATA[<component name="issueEditor">
<property name="issueStatuses">
<key>open</key> <value>open issue</value>
<key>resolved</key> <value>issue resolved by developer</value>
<key>closed</key> <value>resolution accepted by user</value>
</property>
</component>]]></programlisting>
<para>
Finally, you may wire together components using a value-binding expression. Note that this is quite
different to injection using <literal>@In</literal>, since it happens at component instantiation time
instead of invocation time. It is therefore much more similar to the dependency injection facilities
offered by traditional IoC containers like JSF or Spring.
</para>
<programlisting><![CDATA[<drools:managed-working-memory name="policyPricingWorkingMemory" rule-base="#{policyPricingRules}"/>]]></programlisting>
<programlisting><![CDATA[<component name="policyPricingWorkingMemory"
class="org.jboss.seam.drools.ManagedWorkingMemory">
<property name="ruleBase">#{policyPricingRules}</property>
</component>]]></programlisting>
</sect1>
<sect1>
<title>Using XML Namespaces</title>
<para>
Throughout the examples, there have been two competing ways of declaring components: with and without
the use of XML namespaces. The following shows a typical <literal>components.xml</literal> file
without namespaces. It uses the Seam Components DTD:
</para>
<programlisting><![CDATA[<?xml version="1.0" encoding="UTF-8">
<!DOCTYPE components PUBLIC "-//JBoss/Seam Component Configuration DTD 1.1//EN"
"http://jboss.com/products/seam/components-1.1.dtd">
<components>
<component class="org.jboss.seam.core.init">
<property name="debug">true</property>
<property name="jndiPattern">@jndiPattern@</property>
</component>
<component name="org.jboss.sean.core.ejb" installed="@embeddedEjb@" />
</components>]]></programlisting>
<para>
As you can see, this is somewhat verbose. Even worse, the component and attribute names cannot be
validated at development time.
</para>
<para>The namespaced version looks like this:</para>
<programlisting><![CDATA[<?xml version="1.0" encoding="UTF-8"?>
<components xmlns="http://jboss.com/products/seam/components"
xmlns:core="http://jboss.com/products/seam/core"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation=
"http://jboss.com/products/seam/core http://jboss.com/products/seam/core-1.1.xsd
http://jboss.com/products/seam/components http://jboss.com/products/seam/components-1.1.xsd">
<core:init debug="true" jndi-pattern="@jndiPattern@"/>
<core:ejb installed="@embeddedEjb@"/>
</components>]]></programlisting>
<para>
Even though the schema declarations are verbose, the actual XML content is lean and easy to understand.
The schemas provide detailed information about each component and the attributes available, allowing XML
editors to offer intelligent autocomplete. The use of namespaced elements makes generating and
maintaining correct <literal>components.xml</literal> files much simpler.
</para>
<para>
Now, this works great for the built-in Seam components, but what about user components? There are two options.
First, Seam supports mixing the two models, allowing the use of the generic <literal><component></literal>
declarations for user components, along with namespaced declarations for built-in components. But even better,
Seam allows you to quickly declare namespaces for your own components.
</para>
<para>
Any Java package can be associated with an XML namespace by annotating the package with the
<literal>@Namespace</literal> annotation. (Package-level annotations are declared in a file named
<literal>package-info.java</literal> in the package directory.) Here is an example from the seampay demo:
</para>
<programlisting>@Namespace(value="http://jboss.com/products/seam/examples/seampay")
package org.jboss.seam.example.seampay;
import org.jboss.seam.annotations.Namespace;</programlisting>
<para>
That is all you need to do to use the namespaced style in <literal>components.xml</literal>!
Now we can write:
</para>
<programlisting><![CDATA[<components xmlns="http://jboss.com/products/seam/components"
xmlns:pay="http://jboss.com/products/seam/examples/seampay"
... >
<pay:payment-home new-instance="#{newPayment}"
created-message="Created a new payment to #{newPayment.payee}" />
<pay:payment name="newPayment"
payee="Somebody"
account="#{selectedAccount}"
payment-date="#{currentDatetime}"
created-date="#{currentDatetime}" />
...
</components>]]></programlisting>
<para>Or:</para>
<programlisting><![CDATA[<components xmlns="http://jboss.com/products/seam/components"
xmlns:pay="http://jboss.com/products/seam/examples/seampay"
... >
<pay:payment-home>
<pay:new-instance>"#{newPayment}"</pay:new-instance>
<pay:created-message>Created a new payment to #{newPayment.payee}</pay:created-message>
</pay:payment-home>
<pay:payment name="newPayment">
<pay:payee>Somebody"</pay:payee>
<pay:account>#{selectedAccount}</pay:account>
<pay:payment-date>#{currentDatetime}</pay:payment-date>
<pay:created-date>#{currentDatetime}</pay:created-date>
</pay:payment>
...
</components>]]></programlisting>
<para>
These examples illustrate the two usage models of a namespaced element. In the first declaration,
the <literal><pay:payment-home></literal> references the <literal>paymentHome</literal>
component:
</para>
<programlisting><![CDATA[package org.jboss.seam.example.seampay;
...
@Name("paymentHome")
public class PaymentController
extends EntityHome<Payment>
{
...
}]]></programlisting>
<para>
The element name is the hyphenated form of the component name. The attributes of the element are
the hyphenated form of the property names.
</para>
<para>
In the second declaration, the <literal><pay:payment></literal> element refers to the
<literal>Payment</literal> class in the <literal>org.jboss.seam.example.seampay</literal> package.
In this case <literal>Payment</literal> is an entity that is being declared as a Seam component:
</para>
<programlisting><![CDATA[package org.jboss.seam.example.seampay;
...
@Entity
public class Payment
implements Serializable
{
...
}]]></programlisting>
<para>
If we want validation and autocompletion to work for user-defined components, we will need a schema.
Seam does not yet provide a mechanism to automatically generate a schema for a set of components, so
it is necessary to generate one manually. The schema definitions for the standard Seam packages can
be used for guidance.
</para>
</sect1>
</chapter>
More information about the jboss-cvs-commits
mailing list