Passing Parameters to Scripts - Scripting in Java: Integrating with Groovy and JavaScript - page 31

Putting Them Together
In this section, I will show you how instances of Bindings and their scopes,
ScriptContext , ScriptEngine , ScriptEngineManager , and the host application work
together. The focus will be on how to manipulate the key-value pairs stored in Bindings
in different scopes using a ScriptEngine and a ScriptEngineManager .
A ScriptEngineManager maintains a set of key-value pairs in a Bindings . It lets you
manipulate those key-value pairs using the following four methods:

•

void put(String key, Object value)

•

Object get(String key)

•

void setBindings(Bindings bindings)

Bindings getBindings()
The put() method adds a key-value pair to the Bindings . The get() method returns
the value for the specified key; it returns null if the key is not found. The Bindings for an
engine manager can be replaced using the setBindings() method. The getBindings()
method returns the reference of the Bindings of the ScriptEngineManager .
Every ScriptEngine , by default, has a ScriptContext known as its default context.
Recall that, besides readers and writers, a ScriptContext has two Bindings : one in the
engine scope and one in the global scope. When a ScriptEngine is created, its engine
scope Bindings is empty and its global scope Bindings refers to the Bindings of the
ScriptEngineManager that created it.
By default, all instances of the ScriptEngine created by a ScriptEngineManager
share the Bindings of the ScriptEngineManager . It is possible to have multiple instances
of ScriptEngineManager in the same Java application. In that case, all instances of
ScriptEngine created by the same ScriptEngineManager share the Bindings of the
ScriptEngineManager as their global scope Bindings for their default contexts.
The following snippet of code creates a ScriptEngineManager , which is used to
create three instances of ScriptEngine :

•

// Create a ScriptEngineManager
ScriptEngineManager manager = new ScriptEngineManager();

// Create three ScriptEngines using the same ScriptEngineManager
ScriptEngine engine1 = manager.getEngineByName("JavaScript");
ScriptEngine engine2 = manager.getEngineByName("JavaScript");
ScriptEngine engine3 = manager.getEngineByName("JavaScript");

Now, let's add three key-value pairs to the Bindings of the ScriptEngineManager
and two key-value pairs to the engine scope Bindings of each ScriptEngine :

// Add three key-value pairs to the Bindings of the manager
manager.put("K1", "V1");
manager.put("K2", "V2");
manager.put("K3", "V3");