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<title>Scripting Java</title>
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Scripting Java</h1></center>
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<p>It's possible to use Rhino just for scripting Java. You don't have to
write any additional Java code; just use the existing Rhino shell and then
make calls into Java.
<br>&nbsp;
<h2>
Rhino Shell</h2>
The Rhino shell allows you to run scripts from files or interactively at
a command line.
<p>If you download the zip file for rhino, it will contain a single JAR
file, <tt>js.jar</tt>. If you add the JAR file to your class path, you
can start the Rhino shell using the command
<pre>&nbsp;&nbsp;&nbsp; java org.mozilla.javascript.tools.shell.Main</pre>
or if you have Java 2 (JDK 1.2), you can avoid changing your classpath
and simply use the command
<pre>&nbsp;&nbsp;&nbsp; java -jar js.jar</pre>
Unfortunately the <tt>-jar</tt> option to <tt>java</tt> will overwrite
your existing classpath. The shell's interactive mode is a good way to
begin exploring Rhino.
<p><i>Note: Earlier versions of Rhino have two JAR files, js.jar and jstools.jar,
and don't support the -jar option. Both JAR files must be added to the
class path to start the shell</i>.
<p>You can execute a JavaScript file by putting the file name as an argument
to the shell class:
<pre>&nbsp;&nbsp;&nbsp; java org.mozilla.javascript.tools.shell.Main myScript.js</pre>
There are a number of options for evaluating scripts using the shell. See
the <a href="http://www.mozilla.org/rhino/shell.html">command description</a>
for more information.
<br>&nbsp;
<h2>
LiveConnect: Communicating with Java from JavaScript</h2>
If you are planning to script Java using Rhino, you'll want to use LiveConnect,
which allows you to create Java classes and call Java methods from within
JavaScript. For example, here's a log from an interactive session. If you
type it in, you'll see a window with a button filling it.
<center>
<p><img SRC="scriptjavaframe.jpg" height=100 width=200>
<br><i><font size=-1>A Java frame created from the Rhino shell.</font></i></center>
<pre>$ java org.mozilla.javascript.tools.shell.Main
js> importPackage(java.awt);
js> frame = new Frame("JavaScript")
java.awt.Frame[frame0,0,0,0x0,invalid,hidden,layout=java.awt.BorderLayout,resizable,title=JavaScript]
js> frame.show()
js> frame.setSize(new Dimension(200,100))
js> button = new Button("OK")
java.awt.Button[button0,0,0,0x0,invalid,label=OK]
js> frame.add(button)
java.awt.Button[button0,0,0,0x0,invalid,label=OK]
js> frame.show()
js> quit()
$</pre>
If you wish to load classes from JavaScript that aren't in the <tt>java</tt>
package, you'll need to prefix the package name with "<tt>Packages.</tt>".
For example:
<pre>$ java org.mozilla.javascript.tools.shell.Main
js> cx = Packages.org.mozilla.javascript.Context.enter()
org.mozilla.javascript.Context@25980b44
js> cx.evaluateString(this, "3+2", null, 0, null)
5.0
js> quit()
$</pre>
<h2>
Accessing JavaBean Properties</h2>
Java classes can define JavaBean properties using getter and setter methods.
For example, the following class defines two properties:
<p><tt>public class Me {</tt>
<br><tt>&nbsp;&nbsp;&nbsp; public int getAge() { return age; }</tt>
<br><tt>&nbsp;&nbsp;&nbsp; public void setAge(int anAge) { age = anAge;
}</tt>
<br><tt>&nbsp;&nbsp;&nbsp; public String getSex() { return "male"; }</tt>
<br><tt>&nbsp;&nbsp;&nbsp; private int age;</tt>
<br><tt>};</tt>
<p>The two properties defined are <i>age</i> and <i>sex</i>. The <i>sex</i>
property is read-only: it has no setter.
<p>Using Rhino we can access the bean properties as if they where JavaScript
properties. We can also continue to call the methods that define the property.
<p><tt>js> me = new Packages.Me();</tt>
<br><tt>Me@93</tt>
<br><tt>js> me.getSex()</tt>
<br><tt>male</tt>
<br><tt>js> me.sex</tt>
<br><tt>male</tt>
<br><tt>js> me.age = 33;</tt>
<br><tt>33</tt>
<br><tt>js> me.age</tt>
<br><tt>33</tt>
<br><tt>js> me.getAge()</tt>
<br><tt>33</tt>
<br><tt>js></tt>
<p>Since the <i>sex</i> property is read-only, we are not allowed to write
to it.
<p><i>Note: JavaBean reflection is not available in versions of Rhino before
1.5.</i>
<br><tt></tt>&nbsp;
<h2>
Importing Java Classes and Packages</h2>
Above we saw the use of the <tt>importPackage</tt> function to import all
the classes from a particular Java package. There is also <tt>importClass</tt>,
which imports a single class:
<pre>$ java org.mozilla.javascript.tools.shell.Main
js> importClass(Packages.org.mozilla.javascript.Context)
js> cx = Context.enter()
org.mozilla.javascript.Context@25980d62
js> cx.evaluateString(this, "3+2", null, 0, null)
5.0
js> quit()
$</pre>
<h2>
Extending Java Classes and Implementing Java Interfaces with JavaScript</h2>
Starting from the example above of creating a Java frame using JavaScript,
we can add a listener for the button. Once we call <tt>addActionListener</tt>
we can then click on the button to get the current date printed out:
<pre>$ java org.mozilla.javascript.tools.shell.Main
js> importPackage(java.awt);
js> frame = new Frame("JavaScript")
java.awt.Frame[frame0,0,0,0x0,invalid,hidden,layout=java.awt.BorderLayout,resizable,title=JavaScript]
js> button = new Button("OK")
java.awt.Button[button0,0,0,0x0,invalid,label=OK]
js> frame.setSize(new Dimension(200,100))
js> frame.add(button)
java.awt.Button[button0,0,0,0x0,invalid,label=OK]
js> frame.show()
js> function printDate() { print(new Date()) }
js> printDate()
Wed Mar 15 15:42:20 GMT-0800 (PST) 2000
js> o = { actionPerformed: printDate }
[object Object]
js> o.actionPerformed()
Wed Mar 15 15:42:39 GMT-0800 (PST) 2000
js> buttonListener = java.awt.event.ActionListener(o)
adapter0@6acc0f66
js>&nbsp; button.addActionListener(buttonListener)
js> Wed Mar 15 15:43:05 GMT-0800 (PST) 2000
Wed Mar 15 15:43:05 GMT-0800 (PST) 2000
Wed Mar 15 15:43:08 GMT-0800 (PST) 2000
quit()
$</pre>
When we type <tt>buttonListener = java.awt.event.ActionListener(o)</tt>,
Rhino actually creates a new Java class that implements <tt>ActionListener</tt>
and forwards calls from that class to the JavaScript object. So when you
click on the button, the <tt>printDate</tt> method is called.
<br>&nbsp;
<h2>
JavaAdapter constructor</h2>
Another way to create a JavaAdapter is to call the JavaAdapter constructor
explicitly. Using the JavaAdapter constructor gives you additional features
that cannot be had by "constructing" a Java interface as was done above.
<p>Instead of writing
<pre>&nbsp;&nbsp;&nbsp; buttonListener = java.awt.event.ActionListener(o)</pre>
above we can also write
<pre>&nbsp;&nbsp;&nbsp; buttonListener = new JavaAdapter(java.awt.event.ActionListener, o)</pre>
which is equivalent. If we also wanted to extend class <tt>Foo</tt>, while
also implementing <tt>java.lang.Runnable</tt>, we would write
<pre>&nbsp;&nbsp;&nbsp; buttonListener = new JavaAdapter(Packages.Foo,&nbsp;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; java.awt.event.ActionListener,
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; java.lang.Runnable, o)</pre>
In general the syntax is
<p>&nbsp;&nbsp;&nbsp; <tt>new JavaAdapter(</tt><i>java-class</i>, [<i>java-class</i>,
...] <i>javascript-object</i><tt>)</tt>
<p>where at most one <i>java-class</i> is a Java class and the remaining
<i>java-class</i>es
are interfaces. The result will be a Java adapter that extends any specified
Java class, implements the Java interfaces, and forwards any calls to the
methods of the <i>javascript-object</i>.
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