859 lines
34 KiB
Plaintext
859 lines
34 KiB
Plaintext
[[dynamic-language]]
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= Dynamic Language Support
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Spring provides comprehensive support for using classes and objects that have been
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defined by using a dynamic language (such as Groovy) with Spring. This support lets
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you write any number of classes in a supported dynamic language and have the Spring
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container transparently instantiate, configure, and dependency inject the resulting
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objects.
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Spring's scripting support primarily targets Groovy and BeanShell. Beyond those
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specifically supported languages, the JSR-223 scripting mechanism is supported
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for integration with any JSR-223 capable language provider (as of Spring 4.2),
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e.g. JRuby.
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You can find fully working examples of where this dynamic language support can be
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immediately useful in xref:languages/dynamic.adoc#dynamic-language-scenarios[Scenarios].
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[[dynamic-language-a-first-example]]
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== A First Example
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The bulk of this chapter is concerned with describing the dynamic language support in
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detail. Before diving into all of the ins and outs of the dynamic language support,
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we look at a quick example of a bean defined in a dynamic language. The dynamic
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language for this first bean is Groovy. (The basis of this example was taken from the
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Spring test suite. If you want to see equivalent examples in any of the other
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supported languages, take a look at the source code).
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The next example shows the `Messenger` interface, which the Groovy bean is going to
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implement. Note that this interface is defined in plain Java. Dependent objects that
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are injected with a reference to the `Messenger` do not know that the underlying
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implementation is a Groovy script. The following listing shows the `Messenger` interface:
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[source,java,indent=0,subs="verbatim,quotes",chomp="-packages"]
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----
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package org.springframework.scripting;
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public interface Messenger {
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String getMessage();
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}
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----
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The following example defines a class that has a dependency on the `Messenger` interface:
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[source,java,indent=0,subs="verbatim,quotes",chomp="-packages"]
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----
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package org.springframework.scripting;
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public class DefaultBookingService implements BookingService {
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private Messenger messenger;
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public void setMessenger(Messenger messenger) {
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this.messenger = messenger;
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}
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public void processBooking() {
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// use the injected Messenger object...
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}
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}
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----
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The following example implements the `Messenger` interface in Groovy:
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[source,groovy,indent=0,subs="verbatim,quotes",chomp="-packages",fold="none"]
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----
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package org.springframework.scripting.groovy
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// Import the Messenger interface (written in Java) that is to be implemented
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import org.springframework.scripting.Messenger
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// Define the implementation in Groovy in file 'Messenger.groovy'
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class GroovyMessenger implements Messenger {
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String message
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}
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----
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[NOTE]
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====
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To use the custom dynamic language tags to define dynamic-language-backed beans, you
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need to have the XML Schema preamble at the top of your Spring XML configuration file.
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You also need to use a Spring `ApplicationContext` implementation as your IoC
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container. Using the dynamic-language-backed beans with a plain `BeanFactory`
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implementation is supported, but you have to manage the plumbing of the Spring internals
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to do so.
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For more information on schema-based configuration, see xref:languages/dynamic.adoc#xsd-schemas-lang[XML Schema-based Configuration]
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.
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====
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Finally, the following example shows the bean definitions that effect the injection of the
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Groovy-defined `Messenger` implementation into an instance of the
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`DefaultBookingService` class:
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[source,xml,indent=0,subs="verbatim,quotes"]
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----
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<?xml version="1.0" encoding="UTF-8"?>
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<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xmlns:lang="http://www.springframework.org/schema/lang"
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xsi:schemaLocation="
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http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
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http://www.springframework.org/schema/lang https://www.springframework.org/schema/lang/spring-lang.xsd">
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<!-- this is the bean definition for the Groovy-backed Messenger implementation -->
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<lang:groovy id="messenger" script-source="classpath:Messenger.groovy">
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<lang:property name="message" value="I Can Do The Frug" />
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</lang:groovy>
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<!-- an otherwise normal bean that will be injected by the Groovy-backed Messenger -->
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<bean id="bookingService" class="x.y.DefaultBookingService">
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<property name="messenger" ref="messenger" />
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</bean>
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</beans>
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----
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The `bookingService` bean (a `DefaultBookingService`) can now use its private `messenger`
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member variable as normal, because the `Messenger` instance that was injected into it is
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a `Messenger` instance. There is nothing special going on here -- just plain Java and
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plain Groovy.
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Hopefully, the preceding XML snippet is self-explanatory, but do not worry unduly if it is not.
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Keep reading for the in-depth detail on the whys and wherefores of the preceding configuration.
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[[dynamic-language-beans]]
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== Defining Beans that Are Backed by Dynamic Languages
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This section describes exactly how you define Spring-managed beans in any of the
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supported dynamic languages.
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Note that this chapter does not attempt to explain the syntax and idioms of the supported
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dynamic languages. For example, if you want to use Groovy to write certain of the classes
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in your application, we assume that you already know Groovy. If you need further details
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about the dynamic languages themselves, see xref:languages/dynamic.adoc#dynamic-language-resources[Further Resources] at the end of
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this chapter.
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[[dynamic-language-beans-concepts]]
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=== Common Concepts
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The steps involved in using dynamic-language-backed beans are as follows:
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. Write the test for the dynamic language source code (naturally).
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. Then write the dynamic language source code itself.
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. Define your dynamic-language-backed beans by using the appropriate `<lang:language/>`
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element in the XML configuration (you can define such beans programmatically by
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using the Spring API, although you will have to consult the source code for
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directions on how to do this, as this chapter does not cover this type of advanced configuration).
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Note that this is an iterative step. You need at least one bean definition for each dynamic
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language source file (although multiple bean definitions can reference the same source file).
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The first two steps (testing and writing your dynamic language source files) are beyond
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the scope of this chapter. See the language specification and reference manual
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for your chosen dynamic language and crack on with developing your dynamic language
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source files. You first want to read the rest of this chapter, though, as
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Spring's dynamic language support does make some (small) assumptions about the contents
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of your dynamic language source files.
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[[dynamic-language-beans-concepts-xml-language-element]]
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==== The <lang:language/> element
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The final step in the list in the xref:languages/dynamic.adoc#dynamic-language-beans-concepts[preceding section]
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involves defining dynamic-language-backed bean definitions, one for each bean that you
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want to configure (this is no different from normal JavaBean configuration). However,
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instead of specifying the fully qualified class name of the class that is to be
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instantiated and configured by the container, you can use the `<lang:language/>`
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element to define the dynamic language-backed bean.
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Each of the supported languages has a corresponding `<lang:language/>` element:
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* `<lang:groovy/>` (Groovy)
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* `<lang:bsh/>` (BeanShell)
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* `<lang:std/>` (JSR-223, e.g. with JRuby)
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The exact attributes and child elements that are available for configuration depends on
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exactly which language the bean has been defined in (the language-specific sections
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later in this chapter detail this).
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[[dynamic-language-refreshable-beans]]
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==== Refreshable Beans
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One of the (and perhaps the single) most compelling value adds of the dynamic language
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support in Spring is the "`refreshable bean`" feature.
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A refreshable bean is a dynamic-language-backed bean. With a small amount of
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configuration, a dynamic-language-backed bean can monitor changes in its underlying
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source file resource and then reload itself when the dynamic language source file is
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changed (for example, when you edit and save changes to the file on the file system).
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This lets you deploy any number of dynamic language source files as part of an
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application, configure the Spring container to create beans backed by dynamic
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language source files (using the mechanisms described in this chapter), and (later,
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as requirements change or some other external factor comes into play) edit a dynamic
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language source file and have any change they make be reflected in the bean that is
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backed by the changed dynamic language source file. There is no need to shut down a
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running application (or redeploy in the case of a web application). The
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dynamic-language-backed bean so amended picks up the new state and logic from the
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changed dynamic language source file.
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NOTE: This feature is off by default.
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Now we can take a look at an example to see how easy it is to start using refreshable
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beans. To turn on the refreshable beans feature, you have to specify exactly one
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additional attribute on the `<lang:language/>` element of your bean definition. So,
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if we stick with xref:languages/dynamic.adoc#dynamic-language-a-first-example[the example] from earlier in
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this chapter, the following example shows what we would change in the Spring XML
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configuration to effect refreshable beans:
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[source,xml,indent=0,subs="verbatim,quotes"]
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----
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<beans>
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<!-- this bean is now 'refreshable' due to the presence of the 'refresh-check-delay' attribute -->
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<lang:groovy id="messenger"
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refresh-check-delay="5000" <!-- switches refreshing on with 5 seconds between checks -->
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script-source="classpath:Messenger.groovy">
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<lang:property name="message" value="I Can Do The Frug" />
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</lang:groovy>
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<bean id="bookingService" class="x.y.DefaultBookingService">
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<property name="messenger" ref="messenger" />
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</bean>
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</beans>
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----
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That really is all you have to do. The `refresh-check-delay` attribute defined on the
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`messenger` bean definition is the number of milliseconds after which the bean is
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refreshed with any changes made to the underlying dynamic language source file.
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You can turn off the refresh behavior by assigning a negative value to the
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`refresh-check-delay` attribute. Remember that, by default, the refresh behavior is
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disabled. If you do not want the refresh behavior, do not define the attribute.
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If we then run the following application, we can exercise the refreshable feature.
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(Please excuse the "`jumping-through-hoops-to-pause-the-execution`" shenanigans
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in this next slice of code.) The `System.in.read()` call is only there so that the
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execution of the program pauses while you (the developer in this scenario) go off
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and edit the underlying dynamic language source file so that the refresh triggers
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on the dynamic-language-backed bean when the program resumes execution.
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The following listing shows this sample application:
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[source,java,indent=0,subs="verbatim,quotes"]
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----
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import org.springframework.context.ApplicationContext;
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import org.springframework.context.support.ClassPathXmlApplicationContext;
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import org.springframework.scripting.Messenger;
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public final class Boot {
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public static void main(final String[] args) throws Exception {
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ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");
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Messenger messenger = (Messenger) ctx.getBean("messenger");
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System.out.println(messenger.getMessage());
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// pause execution while I go off and make changes to the source file...
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System.in.read();
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System.out.println(messenger.getMessage());
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}
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}
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----
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Assume then, for the purposes of this example, that all calls to the `getMessage()`
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method of `Messenger` implementations have to be changed such that the message is
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surrounded by quotation marks. The following listing shows the changes that you
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(the developer) should make to the `Messenger.groovy` source file when the
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execution of the program is paused:
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[source,groovy,indent=0,subs="verbatim,quotes",chomp="-packages"]
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----
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package org.springframework.scripting
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class GroovyMessenger implements Messenger {
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private String message = "Bingo"
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public String getMessage() {
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// change the implementation to surround the message in quotes
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return "'" + this.message + "'"
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}
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public void setMessage(String message) {
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this.message = message
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}
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}
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----
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When the program runs, the output before the input pause will be `I Can Do The Frug`.
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After the change to the source file is made and saved and the program resumes execution,
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the result of calling the `getMessage()` method on the dynamic-language-backed
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`Messenger` implementation is `'I Can Do The Frug'` (notice the inclusion of the
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additional quotation marks).
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Changes to a script do not trigger a refresh if the changes occur within the window of
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the `refresh-check-delay` value. Changes to the script are not actually picked up until
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a method is called on the dynamic-language-backed bean. It is only when a method is
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called on a dynamic-language-backed bean that it checks to see if its underlying script
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source has changed. Any exceptions that relate to refreshing the script (such as
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encountering a compilation error or finding that the script file has been deleted)
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results in a fatal exception being propagated to the calling code.
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The refreshable bean behavior described earlier does not apply to dynamic language
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source files defined with the `<lang:inline-script/>` element notation (see
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xref:languages/dynamic.adoc#dynamic-language-beans-inline[Inline Dynamic Language Source Files]). Additionally, it applies only to beans where
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changes to the underlying source file can actually be detected (for example, by code
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that checks the last modified date of a dynamic language source file that exists on the
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file system).
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[[dynamic-language-beans-inline]]
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==== Inline Dynamic Language Source Files
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The dynamic language support can also cater to dynamic language source files that are
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embedded directly in Spring bean definitions. More specifically, the
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`<lang:inline-script/>` element lets you define dynamic language source immediately
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inside a Spring configuration file. An example might clarify how the inline script
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feature works:
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[source,xml,indent=0,subs="verbatim,quotes"]
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----
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<lang:groovy id="messenger">
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<lang:inline-script>
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package org.springframework.scripting.groovy
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import org.springframework.scripting.Messenger
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class GroovyMessenger implements Messenger {
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String message
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}
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</lang:inline-script>
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<lang:property name="message" value="I Can Do The Frug" />
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</lang:groovy>
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----
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If we put to one side the issues surrounding whether it is good practice to define
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dynamic language source inside a Spring configuration file, the `<lang:inline-script/>`
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element can be useful in some scenarios. For instance, we might want to quickly add a
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Spring `Validator` implementation to a Spring MVC `Controller`. This is but a moment's
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work using inline source. (See xref:languages/dynamic.adoc#dynamic-language-scenarios-validators[Scripted Validators] for such an
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example.)
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[[dynamic-language-beans-ctor-injection]]
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==== Understanding Constructor Injection in the Context of Dynamic-language-backed Beans
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There is one very important thing to be aware of with regard to Spring's dynamic
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language support. Namely, you can not (currently) supply constructor arguments
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to dynamic-language-backed beans (and, hence, constructor-injection is not available for
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dynamic-language-backed beans). In the interests of making this special handling of
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constructors and properties 100% clear, the following mixture of code and configuration
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does not work:
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.An approach that cannot work
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[source,groovy,indent=0,subs="verbatim,quotes",chomp="-packages"]
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----
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package org.springframework.scripting.groovy
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import org.springframework.scripting.Messenger
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// from the file 'Messenger.groovy'
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class GroovyMessenger implements Messenger {
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GroovyMessenger() {}
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// this constructor is not available for Constructor Injection
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GroovyMessenger(String message) {
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this.message = message;
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}
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String message
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String anotherMessage
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}
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----
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[source,xml,indent=0,subs="verbatim,quotes"]
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----
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<lang:groovy id="badMessenger"
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script-source="classpath:Messenger.groovy">
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<!-- this next constructor argument will not be injected into the GroovyMessenger -->
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<!-- in fact, this isn't even allowed according to the schema -->
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<constructor-arg value="This will not work" />
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<!-- only property values are injected into the dynamic-language-backed object -->
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<lang:property name="anotherMessage" value="Passed straight through to the dynamic-language-backed object" />
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</lang>
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----
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In practice this limitation is not as significant as it first appears, since setter
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injection is the injection style favored by the overwhelming majority of developers
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(we leave the discussion as to whether that is a good thing to another day).
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[[dynamic-language-beans-groovy]]
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=== Groovy Beans
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This section describes how to use beans defined in Groovy in Spring.
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The Groovy homepage includes the following description:
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"`Groovy is an agile dynamic language for the Java 2 Platform that has many of the
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features that people like so much in languages like Python, Ruby and Smalltalk, making
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them available to Java developers using a Java-like syntax.`"
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If you have read this chapter straight from the top, you have already
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xref:languages/dynamic.adoc#dynamic-language-a-first-example[seen an example] of a Groovy-dynamic-language-backed
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bean. Now consider another example (again using an example from the Spring test suite):
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[source,java,indent=0,subs="verbatim,quotes",chomp="-packages"]
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----
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package org.springframework.scripting;
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public interface Calculator {
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int add(int x, int y);
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}
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----
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The following example implements the `Calculator` interface in Groovy:
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[source,groovy,indent=0,subs="verbatim,quotes",chomp="-packages"]
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----
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package org.springframework.scripting.groovy
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// from the file 'calculator.groovy'
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class GroovyCalculator implements Calculator {
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int add(int x, int y) {
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x + y
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}
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}
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----
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The following bean definition uses the calculator defined in Groovy:
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[source,xml,indent=0,subs="verbatim,quotes"]
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----
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<!-- from the file 'beans.xml' -->
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<beans>
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<lang:groovy id="calculator" script-source="classpath:calculator.groovy"/>
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</beans>
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----
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Finally, the following small application exercises the preceding configuration:
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[source,java,indent=0,subs="verbatim,quotes",chomp="-packages"]
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----
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package org.springframework.scripting;
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import org.springframework.context.ApplicationContext;
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import org.springframework.context.support.ClassPathXmlApplicationContext;
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public class Main {
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public static void main(String[] args) {
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ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");
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Calculator calc = ctx.getBean("calculator", Calculator.class);
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System.out.println(calc.add(2, 8));
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}
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}
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----
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The resulting output from running the above program is (unsurprisingly) `10`.
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(For more interesting examples, see the dynamic language showcase project for a more
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complex example or see the examples xref:languages/dynamic.adoc#dynamic-language-scenarios[Scenarios] later in this chapter).
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You must not define more than one class per Groovy source file. While this is perfectly
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legal in Groovy, it is (arguably) a bad practice. In the interests of a consistent
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approach, you should (in the opinion of the Spring team) respect the standard Java
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conventions of one (public) class per source file.
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[[dynamic-language-beans-groovy-customizer]]
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==== Customizing Groovy Objects by Using a Callback
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The `GroovyObjectCustomizer` interface is a callback that lets you hook additional
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creation logic into the process of creating a Groovy-backed bean. For example,
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implementations of this interface could invoke any required initialization methods,
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set some default property values, or specify a custom `MetaClass`. The following listing
|
||
shows the `GroovyObjectCustomizer` interface definition:
|
||
|
||
[source,java,indent=0,subs="verbatim,quotes"]
|
||
----
|
||
public interface GroovyObjectCustomizer {
|
||
|
||
void customize(GroovyObject goo);
|
||
}
|
||
----
|
||
|
||
The Spring Framework instantiates an instance of your Groovy-backed bean and then
|
||
passes the created `GroovyObject` to the specified `GroovyObjectCustomizer` (if one
|
||
has been defined). You can do whatever you like with the supplied `GroovyObject`
|
||
reference. We expect that most people want to set a custom `MetaClass` with this
|
||
callback, and the following example shows how to do so:
|
||
|
||
[source,java,indent=0,subs="verbatim,quotes"]
|
||
----
|
||
public final class SimpleMethodTracingCustomizer implements GroovyObjectCustomizer {
|
||
|
||
public void customize(GroovyObject goo) {
|
||
DelegatingMetaClass metaClass = new DelegatingMetaClass(goo.getMetaClass()) {
|
||
|
||
public Object invokeMethod(Object object, String methodName, Object[] arguments) {
|
||
System.out.println("Invoking '" + methodName + "'.");
|
||
return super.invokeMethod(object, methodName, arguments);
|
||
}
|
||
};
|
||
metaClass.initialize();
|
||
goo.setMetaClass(metaClass);
|
||
}
|
||
|
||
}
|
||
----
|
||
|
||
A full discussion of meta-programming in Groovy is beyond the scope of the Spring
|
||
reference manual. See the relevant section of the Groovy reference manual or do a
|
||
search online. Plenty of articles address this topic. Actually, making use of a
|
||
`GroovyObjectCustomizer` is easy if you use the Spring namespace support, as the
|
||
following example shows:
|
||
|
||
[source,xml,indent=0,subs="verbatim,quotes"]
|
||
----
|
||
<!-- define the GroovyObjectCustomizer just like any other bean -->
|
||
<bean id="tracingCustomizer" class="example.SimpleMethodTracingCustomizer"/>
|
||
|
||
<!-- ... and plug it into the desired Groovy bean via the 'customizer-ref' attribute -->
|
||
<lang:groovy id="calculator"
|
||
script-source="classpath:org/springframework/scripting/groovy/Calculator.groovy"
|
||
customizer-ref="tracingCustomizer"/>
|
||
----
|
||
|
||
If you do not use the Spring namespace support, you can still use the
|
||
`GroovyObjectCustomizer` functionality, as the following example shows:
|
||
|
||
[source,xml,indent=0,subs="verbatim,quotes"]
|
||
----
|
||
<bean id="calculator" class="org.springframework.scripting.groovy.GroovyScriptFactory">
|
||
<constructor-arg value="classpath:org/springframework/scripting/groovy/Calculator.groovy"/>
|
||
<!-- define the GroovyObjectCustomizer (as an inner bean) -->
|
||
<constructor-arg>
|
||
<bean id="tracingCustomizer" class="example.SimpleMethodTracingCustomizer"/>
|
||
</constructor-arg>
|
||
</bean>
|
||
|
||
<bean class="org.springframework.scripting.support.ScriptFactoryPostProcessor"/>
|
||
----
|
||
|
||
NOTE: You may also specify a Groovy `CompilationCustomizer` (such as an `ImportCustomizer`)
|
||
or even a full Groovy `CompilerConfiguration` object in the same place as Spring's
|
||
`GroovyObjectCustomizer`. Furthermore, you may set a common `GroovyClassLoader` with custom
|
||
configuration for your beans at the `ConfigurableApplicationContext.setClassLoader` level;
|
||
this also leads to shared `GroovyClassLoader` usage and is therefore recommendable in case of
|
||
a large number of scripted beans (avoiding an isolated `GroovyClassLoader` instance per bean).
|
||
|
||
|
||
|
||
[[dynamic-language-beans-bsh]]
|
||
=== BeanShell Beans
|
||
|
||
This section describes how to use BeanShell beans in Spring.
|
||
|
||
The https://beanshell.github.io/intro.html[BeanShell homepage] includes the following
|
||
description:
|
||
|
||
----
|
||
BeanShell is a small, free, embeddable Java source interpreter with dynamic language
|
||
features, written in Java. BeanShell dynamically runs standard Java syntax and
|
||
extends it with common scripting conveniences such as loose types, commands, and method
|
||
closures like those in Perl and JavaScript.
|
||
----
|
||
|
||
In contrast to Groovy, BeanShell-backed bean definitions require some (small) additional
|
||
configuration. The implementation of the BeanShell dynamic language support in Spring is
|
||
interesting, because Spring creates a JDK dynamic proxy that implements all of the
|
||
interfaces that are specified in the `script-interfaces` attribute value of the
|
||
`<lang:bsh>` element (this is why you must supply at least one interface in the value
|
||
of the attribute, and, consequently, program to interfaces when you use BeanShell-backed
|
||
beans). This means that every method call on a BeanShell-backed object goes through the
|
||
JDK dynamic proxy invocation mechanism.
|
||
|
||
Now we can show a fully working example of using a BeanShell-based bean that implements
|
||
the `Messenger` interface that was defined earlier in this chapter. We again show the
|
||
definition of the `Messenger` interface:
|
||
|
||
[source,java,indent=0,subs="verbatim,quotes",chomp="-packages"]
|
||
----
|
||
package org.springframework.scripting;
|
||
|
||
public interface Messenger {
|
||
|
||
String getMessage();
|
||
}
|
||
----
|
||
|
||
The following example shows the BeanShell "`implementation`" (we use the term loosely here)
|
||
of the `Messenger` interface:
|
||
|
||
[source,java,indent=0,subs="verbatim,quotes"]
|
||
----
|
||
String message;
|
||
|
||
String getMessage() {
|
||
return message;
|
||
}
|
||
|
||
void setMessage(String aMessage) {
|
||
message = aMessage;
|
||
}
|
||
----
|
||
|
||
The following example shows the Spring XML that defines an "`instance`" of the above
|
||
"`class`" (again, we use these terms very loosely here):
|
||
|
||
[source,xml,indent=0,subs="verbatim,quotes"]
|
||
----
|
||
<lang:bsh id="messageService" script-source="classpath:BshMessenger.bsh"
|
||
script-interfaces="org.springframework.scripting.Messenger">
|
||
|
||
<lang:property name="message" value="Hello World!" />
|
||
</lang:bsh>
|
||
----
|
||
|
||
See xref:languages/dynamic.adoc#dynamic-language-scenarios[Scenarios] for some scenarios where you might want to use
|
||
BeanShell-based beans.
|
||
|
||
|
||
|
||
|
||
[[dynamic-language-scenarios]]
|
||
== Scenarios
|
||
|
||
The possible scenarios where defining Spring managed beans in a scripting language would
|
||
be beneficial are many and varied. This section describes two possible use cases for the
|
||
dynamic language support in Spring.
|
||
|
||
|
||
|
||
[[dynamic-language-scenarios-controllers]]
|
||
=== Scripted Spring MVC Controllers
|
||
|
||
One group of classes that can benefit from using dynamic-language-backed beans is that
|
||
of Spring MVC controllers. In pure Spring MVC applications, the navigational flow
|
||
through a web application is, to a large extent, determined by code encapsulated within
|
||
your Spring MVC controllers. As the navigational flow and other presentation layer logic
|
||
of a web application needs to be updated to respond to support issues or changing
|
||
business requirements, it may well be easier to effect any such required changes by
|
||
editing one or more dynamic language source files and seeing those changes being
|
||
immediately reflected in the state of a running application.
|
||
|
||
Remember that, in the lightweight architectural model espoused by projects such as
|
||
Spring, you typically aim to have a really thin presentation layer, with all
|
||
the meaty business logic of an application being contained in the domain and service
|
||
layer classes. Developing Spring MVC controllers as dynamic-language-backed beans lets
|
||
you change presentation layer logic by editing and saving text files. Any
|
||
changes to such dynamic language source files is (depending on the configuration)
|
||
automatically reflected in the beans that are backed by dynamic language source files.
|
||
|
||
NOTE: To effect this automatic "`pickup`" of any changes to dynamic-language-backed
|
||
beans, you have to enable the "`refreshable beans`" functionality. See
|
||
xref:languages/dynamic.adoc#dynamic-language-refreshable-beans[Refreshable Beans] for a full treatment of this feature.
|
||
|
||
The following example shows an `org.springframework.web.servlet.mvc.Controller` implemented
|
||
by using the Groovy dynamic language:
|
||
|
||
[source,groovy,indent=0,subs="verbatim,quotes",chomp="-packages"]
|
||
----
|
||
package org.springframework.showcase.fortune.web
|
||
|
||
import org.springframework.showcase.fortune.service.FortuneService
|
||
import org.springframework.showcase.fortune.domain.Fortune
|
||
import org.springframework.web.servlet.ModelAndView
|
||
import org.springframework.web.servlet.mvc.Controller
|
||
|
||
import jakarta.servlet.http.HttpServletRequest
|
||
import jakarta.servlet.http.HttpServletResponse
|
||
|
||
// from the file '/WEB-INF/groovy/FortuneController.groovy'
|
||
class FortuneController implements Controller {
|
||
|
||
@Property FortuneService fortuneService
|
||
|
||
ModelAndView handleRequest(HttpServletRequest request,
|
||
HttpServletResponse httpServletResponse) {
|
||
return new ModelAndView("tell", "fortune", this.fortuneService.tellFortune())
|
||
}
|
||
}
|
||
----
|
||
|
||
[source,xml,indent=0,subs="verbatim,quotes"]
|
||
----
|
||
<lang:groovy id="fortune"
|
||
refresh-check-delay="3000"
|
||
script-source="/WEB-INF/groovy/FortuneController.groovy">
|
||
<lang:property name="fortuneService" ref="fortuneService"/>
|
||
</lang:groovy>
|
||
----
|
||
|
||
|
||
|
||
[[dynamic-language-scenarios-validators]]
|
||
=== Scripted Validators
|
||
|
||
Another area of application development with Spring that may benefit from the
|
||
flexibility afforded by dynamic-language-backed beans is that of validation. It can
|
||
be easier to express complex validation logic by using a loosely typed dynamic language
|
||
(that may also have support for inline regular expressions) as opposed to regular Java.
|
||
|
||
Again, developing validators as dynamic-language-backed beans lets you change
|
||
validation logic by editing and saving a simple text file. Any such changes is
|
||
(depending on the configuration) automatically reflected in the execution of a
|
||
running application and would not require the restart of an application.
|
||
|
||
NOTE: To effect the automatic "`pickup`" of any changes to dynamic-language-backed
|
||
beans, you have to enable the 'refreshable beans' feature. See
|
||
xref:languages/dynamic.adoc#dynamic-language-refreshable-beans[Refreshable Beans] for a full and detailed treatment of this feature.
|
||
|
||
The following example shows a Spring `org.springframework.validation.Validator`
|
||
implemented by using the Groovy dynamic language (see xref:core/validation/validator.adoc[Validation using Spring’s Validator interface]
|
||
for a discussion of the
|
||
`Validator` interface):
|
||
|
||
[source,groovy,indent=0,subs="verbatim,quotes"]
|
||
----
|
||
import org.springframework.validation.Validator
|
||
import org.springframework.validation.Errors
|
||
import org.springframework.beans.TestBean
|
||
|
||
class TestBeanValidator implements Validator {
|
||
|
||
boolean supports(Class clazz) {
|
||
return TestBean.class.isAssignableFrom(clazz)
|
||
}
|
||
|
||
void validate(Object bean, Errors errors) {
|
||
if(bean.name?.trim()?.size() > 0) {
|
||
return
|
||
}
|
||
errors.reject("whitespace", "Cannot be composed wholly of whitespace.")
|
||
}
|
||
}
|
||
----
|
||
|
||
|
||
|
||
|
||
[[dynamic-language-final-notes]]
|
||
== Additional Details
|
||
|
||
This last section contains some additional details related to the dynamic language support.
|
||
|
||
|
||
|
||
[[dynamic-language-final-notes-aop]]
|
||
=== AOP -- Advising Scripted Beans
|
||
|
||
You can use the Spring AOP framework to advise scripted beans. The Spring AOP
|
||
framework actually is unaware that a bean that is being advised might be a scripted
|
||
bean, so all of the AOP use cases and functionality that you use (or aim to use)
|
||
work with scripted beans. When you advise scripted beans, you cannot use class-based
|
||
proxies. You must use xref:core/aop/proxying.adoc[interface-based proxies].
|
||
|
||
You are not limited to advising scripted beans. You can also write aspects themselves
|
||
in a supported dynamic language and use such beans to advise other Spring beans.
|
||
This really would be an advanced use of the dynamic language support though.
|
||
|
||
|
||
|
||
[[dynamic-language-final-notes-scopes]]
|
||
=== Scoping
|
||
|
||
In case it is not immediately obvious, scripted beans can be scoped in the same way as
|
||
any other bean. The `scope` attribute on the various `<lang:language/>` elements lets
|
||
you control the scope of the underlying scripted bean, as it does with a regular
|
||
bean. (The default scope is xref:core/beans/factory-scopes.adoc#beans-factory-scopes-singleton[singleton],
|
||
as it is with "`regular`" beans.)
|
||
|
||
The following example uses the `scope` attribute to define a Groovy bean scoped as
|
||
a xref:core/beans/factory-scopes.adoc#beans-factory-scopes-prototype[prototype]:
|
||
|
||
[source,xml,indent=0,subs="verbatim,quotes"]
|
||
----
|
||
<?xml version="1.0" encoding="UTF-8"?>
|
||
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
|
||
xmlns:lang="http://www.springframework.org/schema/lang"
|
||
xsi:schemaLocation="
|
||
http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
|
||
http://www.springframework.org/schema/lang https://www.springframework.org/schema/lang/spring-lang.xsd">
|
||
|
||
<lang:groovy id="messenger" script-source="classpath:Messenger.groovy" scope="prototype">
|
||
<lang:property name="message" value="I Can Do The RoboCop" />
|
||
</lang:groovy>
|
||
|
||
<bean id="bookingService" class="x.y.DefaultBookingService">
|
||
<property name="messenger" ref="messenger" />
|
||
</bean>
|
||
|
||
</beans>
|
||
----
|
||
|
||
See xref:core/beans/factory-scopes.adoc[Bean Scopes] in xref:web/webmvc-view/mvc-xslt.adoc#mvc-view-xslt-beandefs[The IoC Container]
|
||
for a full discussion of the scoping support in the Spring Framework.
|
||
|
||
|
||
|
||
[[xsd-schemas-lang]]
|
||
=== The `lang` XML schema
|
||
|
||
The `lang` elements in Spring XML configuration deal with exposing objects that have been
|
||
written in a dynamic language (such as Groovy or BeanShell) as beans in the Spring container.
|
||
|
||
These elements (and the dynamic language support) are comprehensively covered in
|
||
xref:languages/dynamic.adoc[Dynamic Language Support]. See that section
|
||
for full details on this support and the `lang` elements.
|
||
|
||
To use the elements in the `lang` schema, you need to have the following preamble at the
|
||
top of your Spring XML configuration file. The text in the following snippet references
|
||
the correct schema so that the tags in the `lang` namespace are available to you:
|
||
|
||
[source,xml,indent=0,subs="verbatim,quotes"]
|
||
----
|
||
<?xml version="1.0" encoding="UTF-8"?>
|
||
<beans xmlns="http://www.springframework.org/schema/beans"
|
||
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
|
||
xmlns:lang="http://www.springframework.org/schema/lang"
|
||
xsi:schemaLocation="
|
||
http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
|
||
http://www.springframework.org/schema/lang https://www.springframework.org/schema/lang/spring-lang.xsd">
|
||
|
||
<!-- bean definitions here -->
|
||
|
||
</beans>
|
||
----
|
||
|
||
|
||
|
||
|
||
[[dynamic-language-resources]]
|
||
== Further Resources
|
||
|
||
The following links go to further resources about the various dynamic languages referenced
|
||
in this chapter:
|
||
|
||
* The https://www.groovy-lang.org/[Groovy] homepage
|
||
* The https://beanshell.github.io/intro.html[BeanShell] homepage
|
||
* The https://www.jruby.org[JRuby] homepage
|