A question ad JDK 9 or: how to make all javax.script engines available to all Java apps in JDK 9?

[Rony G. Flatscher]

Hi Rémi,

On 13.01.2015 09:18, Remi Forax wrote:
> does javax.script discovery implementation use java.util.ServiceLoader convention ?
The discovery mechanism relies on (cf.
<http://docs.oracle.com/javase/8/docs/api/javax/script/package-summary.html#package.description>):

    5. *Script engine discovery and Metadata*: Applications written to the Scripting API might have
    specific requirements on script engines. Some may require a specific scripting language and/or
    version while others may require a specific implementation engine and/or version. Script engines
    are packaged in a specified way so that engines can be discovered at runtime and queried for
    attributes. The Engine discovery mechanism is based on the Service discovery mechanism described
    in the *Jar File Specification*. Script engine implementing classes are packaged in jar files
    that include a text resource named *META-INF/services/javax.script.ScriptEngineFactory*. This
    resource must include a line for each |ScriptEngineFactory|
    <http://docs.oracle.com/javase/8/docs/api/javax/script/ScriptEngineFactory.html> that is
    packaged in the jar file. |ScriptEngineManager|
    <http://docs.oracle.com/javase/8/docs/api/javax/script/ScriptEngineManager.html> includes
    |getEngineFactories|
    <http://docs.oracle.com/javase/8/docs/api/javax/script/ScriptEngineManager.html#getEngineFactories-->
    method to get all |ScriptEngineFactory|
    <http://docs.oracle.com/javase/8/docs/api/javax/script/ScriptEngineFactory.html> instances
    discovered using this mechanism. |ScriptEngineFactory| has methods to query attributes about
    script engine. 

Not sure whether this matches the java.util.ServiceLoader convention.

> If the answer is yes, then it will work out of the box.
If the answer would be yes, how would one make access to such a scripting engine jar available (e.g.
to Java code running from the Oracle Java plugin in a browser), what needs to be configured where?

TIA,

---rony


>
> On 01/12/2015 05:09 PM, Rony G. Flatscher wrote:
>> Hi there,
>>
>> reading <http://openjdk.java.net/jeps/220 this is a question or maybe a request for information
>> regarding the removal of the "extension" mechanism and what can be used instead?
>>
>> There is one particular use-case that I regard to be of tremendeous importance for the Java world,
>> recognizing that many Java movers and shakers do not really realize ;) : making javax.script
>> scripting languages available to Java applications.
>>
>> Background: I served as an expert on JSR-223 which defined javax.script (personal background: Apache
>> Commons BSF scripting framework, BSF4ooRexx a JNI-bridge to the opensource ooRexx.org scripting
>> language, which itself is implemented in C++, creator of the Apache OpenOffice AOO ooRexx plugin
>> using the AOO Java scripting framework, teaching at a Business University among other things
>> scripting, ...).
>>
>> "javax.script" defines a discovery mechanism which allows a Java app to enumerate all available
>> scripting engines. This way all discoverable (= installed) javax.script engines are available to any
>> Java app and script/macro programmers. As a result the (end) users become able to pick the script
>> language they wish to use to create macros/scripts for their Java application. [An example would be
>> Apache OpenOffice (AOO), which allows using any script language, provided it is made available via
>> AOOs Java based scripting framework, like BeanShell, JavaScript, ooRexx, et.al.]
>>
>> Please note, that a Java application developer may not even (and need not) know in advance which
>> javax.script engines will be available on a target installation, just that it is rather easy to
>> enumerate the javax.script engines available to it and allow the (end) user programmer to pick one
>> for creating scripts targeted at the Java application.
>>
>> ---
>>
>> Currently (in pre-Java 9 environments), if one wishes to use javax.script engines (e.g. in web
>> browsers via the Oracle browser Java plugin and in parallel in other Java apps), one can make any
>> javax.script engine available by placing it in the Java "extension" directory, which works even
>> then, when Java apps (like the Oracle browser Java plugin or AOO) does not honor the CLASSPATH
>> environment variable.
>>
>> Now, having learned that JDK 9 will remove the "extension" mechanism, I am very interested in
>> learning what alternatives are discussed, planned for Java 9 to enable this particular important
>> use-case: making javax.script engines (packaged as jars) available to any Java app!
>>
>> TIA,
>>
>> ---rony