Chapter 4. Configuring Seam components - JBoss Seam 1.1.1 正式版英文参考手册

Seam components may be provided with configuration properties either via servlet context parameters, or via a properties file named seam.properties in the root of the classpath.

The configurable Seam component must expose JavaBeans-style property setter methods for the configurable attributes. If a seam component named com.jboss.myapp.settings has a setter method named setLocale(), we can provide a property named com.jboss.myapp.settings.locale in the seam.properties file or as a servlet context parameter, and Seam will set the value of the locale attribute whenever it instantiates the component.

The same mechanism is used to configure Seam itself. For example, to set the conversation timeout, we provide a value for org.jboss.seam.core.manager.conversationTimeout in web.xml or seam.properties. (There is a built-in Seam component named org.jboss.seam.core.manager with a setter method named setConversationTimeout().)

The components.xml file is a bit more powerful than property settings. It lets you:

A components.xml file may appear in one of three different places:

Usually, Seam components are installed when the deployment scanner discovers a class with a @Name annotation sitting in an archive with a seam.properties file or a META-INF/components.xml file. (Unless the component has an @Install annotation indicating it should not be installed by default.) The components.xml file lets us handle special cases where we need to override the annotations.

For example, the following components.xml file installs the JBoss Embeddable EJB3 container:

<components xmlns="http://jboss.com/products/seam/components" 
            xmlns:core="http://jboss.com/products/seam/core">
    <core:ejb/>
</components>

This example does the same thing:

<components>
    <component class="org.jboss.seam.core.Ejb"/>
</components>

This one installs and configures two different Seam-managed persistence contexts:

<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>

As does this one:

<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>

This example creates a session-scoped Seam-managed persistence context (this is not recommended in practice):

<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>

<components>
            
    <component name="productDatabase"
              scope="session"
              class="org.jboss.seam.core.ManagedPersistenceContext">
        <property name="persistenceUnitJndiName">java:/productEntityManagerFactory</property>
    </component>

</components>

The <factory> 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.

<components>

    <factory name="contact" method="#{contactManager.loadContact}" scope="CONVERSATION"/>

</components>

You can create an "alias" (a second name) for a Seam component like so:

<components>

    <factory name="user" value="#{actor}" scope="STATELESS"/>

</components>

You can even create an "alias" for a commonly used expression:

<components>

    <factory name="contact" value="#{contactManager.contact}" scope="STATELESS"/>

</components>

Sometimes we want to reuse the same components.xml file with minor changes during both deployment and testing. Seam lets you place wildcards of the form @wildcard@ in the components.xml file which can be replaced either by your Ant build script (at deployment time) or by providing a file named components.properties in the classpath (at development time). You'll see this approach used in the Seam examples.

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 components.xml into many small files. Seam lets you put configuration for a class named, for example, com.helloworld.Hello in a resource named com/helloworld/Hello.component.xml. (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 <components> or <component> element.

The first option lets you define multiple components in the file:

<components>
    <component class="com.helloworld.Hello" name="hello">
        <property name="name">#{user.name}</property>
    </component>
    <factory name="message" value="#{hello.message}"/>
</components>

The second option only lets you define or configure one component, but is less noisy:

<component name="hello">
    <property name="name">#{user.name}</property>
</component>

In the second option, the class name is implied by the file in which the component definition appears.

Alternatively, you may put configuration for all classes in the com.helloworld package in com/helloworld/components.xml.

Properties of string, primitive or primitive wrapper type may be configured just as you would expect:

org.jboss.seam.core.manager.conversationTimeout 60000

<core:manager conversation-timeout="60000"/>

<component name="org.jboss.seam.core.manager">
    <property name="conversationTimeout">60000</property>
</component>

Arrays, sets and lists of strings or primitives are also supported:

org.jboss.seam.core.jbpm.processDefinitions order.jpdl.xml, return.jpdl.xml, inventory.jpdl.xml

<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>

<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>

Even maps with String-valued keys and string or primitive values are supported:

<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>

Finally, you may wire together components using a value-binding expression. Note that this is quite different to injection using @In, 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.

<drools:managed-working-memory name="policyPricingWorkingMemory" rule-base="#{policyPricingRules}"/>

<component name="policyPricingWorkingMemory"
          class="org.jboss.seam.drools.ManagedWorkingMemory">
    <property name="ruleBase">#{policyPricingRules}</property>
</component>

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 components.xml file without namespaces. It uses the Seam Components DTD:

<?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>

As you can see, this is somewhat verbose. Even worse, the component and attribute names cannot be validated at development time.

The namespaced version looks like this:

<?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>

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 components.xml files much simpler.

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 <component> 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.

Any Java package can be associated with an XML namespace by annotating the package with the @Namespace annotation. (Package-level annotations are declared in a file named package-info.java in the package directory.) Here is an example from the seampay demo:

@Namespace(value="http://jboss.com/products/seam/examples/seampay")
package org.jboss.seam.example.seampay;

import org.jboss.seam.annotations.Namespace;

That is all you need to do to use the namespaced style in components.xml! Now we can write:

<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>

Or:

<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>

These examples illustrate the two usage models of a namespaced element. In the first declaration, the <pay:payment-home> references the paymentHome component:

package org.jboss.seam.example.seampay;
...
@Name("paymentHome")
public class PaymentController
    extends EntityHome<Payment>
{
    ... 
}

The element name is the hyphenated form of the component name. The attributes of the element are the hyphenated form of the property names.

In the second declaration, the <pay:payment> element refers to the Payment class in the org.jboss.seam.example.seampay package. In this case Payment is an entity that is being declared as a Seam component:

package org.jboss.seam.example.seampay;
...
@Entity
public class Payment
    implements Serializable
{
    ...
}

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.

The following are the the namespaces used by Seam: