spring-integration/src/reference/asciidoc/scripting.adoc

[[scripting]]
=== Scripting support

With Spring Integration 2.1 we've added support for the http://jcp.org/aboutJava/communityprocess/pr/jsr223/[JSR223 Scripting for Java specification], introduced in Java version 6.
This allows you to use scripts written in any supported language including Ruby/JRuby, Javascript and Groovy to provide the logic for various integration components similar to the way the Spring Expression Language (SpEL) is used in Spring Integration.
For more information about JSR223 please refer to the http://java.sun.com/developer/technicalArticles/J2SE/Desktop/scripting/[documentation]

IMPORTANT: Note that this feature requires Java 6 or higher.
Sun developed a JSR223 reference implementation which works with Java 5 but it is not officially supported and we have not tested it with Spring Integration.

In order to use a JVM scripting language, a JSR223 implementation for that language must be included in your class path.
Java 6 natively supports Javascript.
The http://www.groovy-lang.org/[Groovy] and http://jruby.org/[JRuby] projects provide JSR233 support in their standard distribution.
Other language implementations may be available or under development.
Please refer to the appropriate project website for more information.

IMPORTANT: Various JSR223 language implementations have been developed by third parties.
A particular implementation's compatibility with Spring Integration depends on how well it conforms to the specification and/or the implementer's interpretation of the specification.

TIP: If you plan to use Groovy as your scripting language, we recommended you use <<groovy,Spring-Integration's Groovy Support>> as it offers additional features specific to Groovy.
_However you will find this section relevant as well_.

[[scripting-config]]
==== Script configuration

Depending on the complexity of your integration requirements scripts may be provided inline as CDATA in XML configuration or as a reference to a Spring resource containing the script.
To enable scripting support Spring Integration defines a `ScriptExecutingMessageProcessor` which will bind the Message Payload to a variable named `payload` and the Message Headers to a `headers` variable, both accessible within the script execution context.
All that is left for you to do is write a script that uses these variables.
Below are a couple of sample configurations:

_Filter_
[source,xml]
----
<int:filter input-channel="referencedScriptInput">
   <int-script:script lang="ruby" location="some/path/to/ruby/script/RubyFilterTests.rb"/>
</int:filter>

<int:filter input-channel="inlineScriptInput">
     <int-script:script lang="groovy">
     <![CDATA[
     return payload == 'good'
   ]]>
  </int-script:script>
</int:filter>
----

Here, you see that the script can be included inline or can reference a resource location via the `location` attribute.
Additionally the `lang` attribute corresponds to the language name (or JSR223 alias)

Other Spring Integration endpoint elements which support scripting include _router_, _service-activator_, _transformer_, and _splitter_.
The scripting configuration in each case would be identical to the above (besides the endpoint element).

Another useful feature of Scripting support is the ability to update (reload) scripts without having to restart the Application Context.
To accomplish this, specify the `refresh-check-delay` attribute on the _script_ element:
[source,xml]
----
<int-script:script location="..." refresh-check-delay="5000"/>
----

In the above example, the script location will be checked for updates every 5 seconds.
If the script is updated, any invocation that occurs later than 5 seconds since the update will result in execution of the new script.
[source,xml]
----
<int-script:script location="..." refresh-check-delay="0"/>
----

In the above example the context will be updated with any script modifications as soon as such modification occurs, providing a simple mechanism for 'real-time' configuration.
Any negative number value means the script will not be reloaded after initialization of the application context.
This is the default behavior.

IMPORTANT: Inline scripts can not be reloaded.

[source,xml]
----
<int-script:script location="..." refresh-check-delay="-1"/>
----

_Script variable bindings_

Variable bindings are required to enable the script to reference variables externally provided to the script's execution context.
As we have seen, `payload` and `headers` are used as binding variables by default.
You can bind additional variables to a script via `<variable>` sub-elements:
[source,xml]
----
<script:script lang="js" location="foo/bar/MyScript.js">
    <script:variable name="foo" value="foo"/>
    <script:variable name="bar" value="bar"/>
    <script:variable name="date" ref="date"/>
</script:script>
----

As shown in the above example, you can bind a script variable either to a scalar value or a Spring bean reference.
Note that `payload` and `headers` will still be included as binding variables.

With _Spring Integration 3.0_, in addition to the `variable` sub-element, the `variables` attribute has been introduced.
This attribute and `variable` sub-elements aren't mutually exclusive and you can combine them within one `script` component.
However variables must be unique, regardless of where they are defined.
Also, since _Spring Integration 3.0_, variable bindings are allowed for inline scripts too:
[source,xml]
----
<service-activator input-channel="input">
    <script:script lang="ruby" variables="foo=FOO, date-ref=dateBean">
        <script:variable name="bar" ref="barBean"/>
        <script:variable name="baz" value="bar"/>
        <![CDATA[
            payload.foo = foo
            payload.date = date
            payload.bar = bar
            payload.baz = baz
            payload
        ]]>
    </script:script>
</service-activator>
----

The example above shows a combination of an inline script, a `variable` sub-element and a `variables` attribute.
The `variables` attribute is a comma-separated value, where each segment contains an '=' separated pair of the variable and its value.
The variable name can be suffixed with `-ref`, as in the `date-ref` variable above.
That means that the binding variable will have the name `date`, but the value will be a reference to the `dateBean` bean from the application context.
This may be useful when using _Property Placeholder Configuration_ or command line arguments.

If you need more control over how variables are generated, you can implement your own Java class using the `ScriptVariableGenerator` strategy:
[source,java]
----
public interface ScriptVariableGenerator {

    Map<String, Object> generateScriptVariables(Message<?> message);

}
----

This interface requires you to implement the method `generateScriptVariables(Message)`.
The Message argument allows you to access any data available in the Message payload and headers and the return value is the Map of bound variables.
This method will be called every time the script is executed for a Message.
All you need to do is provide an implementation of `ScriptVariableGenerator` and reference it with the `script-variable-generator` attribute:
[source,xml]
----
<int-script:script location="foo/bar/MyScript.groovy"
        script-variable-generator="variableGenerator"/>

<bean id="variableGenerator" class="foo.bar.MyScriptVariableGenerator"/>
----

If a `script-variable-generator` is not provided, script components use `DefaultScriptVariableGenerator`, which merges any provided `<variable>` s with _payload_ and _headers_ variables from the `Message` in its `generateScriptVariables(Message)` method.

IMPORTANT: You cannot provide both the `script-variable-generator` attribute and `<variable>` sub-element(s) as they are mutually exclusive.