javax.script

The scripting API consists of interfaces and classes that define Java ^TM Scripting Engines and provides a framework for their use in Java applications. This API is intended for use by application programmers who wish to execute programs written in scripting languages in their Java applications. The scripting language programs are usually provided by the end-users of the applications.

The main areas of functionality of javax.script package include

1. Script execution: Scripts are streams of characters used as sources for programs executed by script engines. Script execution uses eval methods of ScriptEngine and methods of the Invocable interface.

2. Binding: This facility allows Java objects to be exposed to script programs as named variables. Bindings and ScriptContext classes are used for this purpose.

3. Compilation: This functionality allows the intermediate code generated by the front-end of a script engine to be stored and executed repeatedly. This benefits applications that execute the same script multiple times. These applications can gain efficiency since the engines' front-ends only need to execute once per script rather than once per script execution. Note that this functionality is optional and script engines may choose not to implement it. Callers need to check for availability of the Compilable interface using an instanceof check.

4. Invocation: This functionality allows the reuse of intermediate code generated by a script engine's front-end. Whereas Compilation allows entire scripts represented by intermediate code to be re-executed, Invocation functionality allows individual procedures/methods in the scripts to be re-executed. As in the case with compilation, not all script engines are required to provide this facility. Caller has to check for Invocable availability.

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 that is packaged in the jar file. ScriptEngineManager includes getEngineFactories method to get all ScriptEngineFactory instances discovered using this mechanism. ScriptEngineFactory has methods to query attributes about script engine.