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357 lines
14 KiB
HTML
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="Generator" content="Microsoft Word 97">
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<meta name="GENERATOR" content="Mozilla/4.75 [en] (WinNT; U) [Netscape]">
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<title>Embedding Rhino</title>
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</head>
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<body>
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<center><font size=+4>Tutorial: Embedding Rhino</font></center>
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<p>Embedding Rhino can be done simply with good results. With more effort
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on the part of the embedder, the objects exposed to scripts can be customized
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further.
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<p>This tutorial leads you through the steps from a simple embedding to
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more customized, complex embeddings. Fully compilable examples are provided
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along the way.
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<p>The examples live in the <tt>rhino/examples</tt> directory in the distribution
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and in <tt>mozilla/js/rhino/examples</tt> in cvs. This document will link
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to them using <a href="http://lxr.mozilla.org/">lxr</a>.
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<p>In this document, JavaScript code will be in <font color="#006600">green</font>,
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Java code will be in <font color="#006600">green</font>, and shell logs
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will be in <font color="#663366">purple</font>.
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<h3>
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<font size=+3>Contents</font></h3>
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<ul>
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<li>
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<font size=+1><a href="#RunScript">RunScript: A simple embedding</a></font></li>
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<ul>
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<li>
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<font size=+1><a href="#EnteringContext">Entering a Context</a></font></li>
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<li>
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<font size=+1><a href="#initializing">Initializing standard objects</a></font></li>
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<li>
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<font size=+1><a href="#Collecting">Collecting the arguments</a></font></li>
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<li>
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<font size=+1><a href="#Evaluating">Evaluating a script</a></font></li>
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<li>
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<font size=+1><a href="#Print">Print the result</a></font></li>
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<li>
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<font size=+1><a href="#Exit">Exit the Context</a></font></li>
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</ul>
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<li>
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<font size=+1><a href="#Expose">Expose Java APIs</a></font></li>
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<ul>
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<li>
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<font size=+1><a href="#UseJava">Use Java APIs</a></font></li>
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<li>
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<font size=+1><a href="#ImplementingInterfaces">Implementing interfaces</a></font></li>
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<li>
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<font size=+1><a href="#AddJava">Add Java objects</a></font></li>
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</ul>
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<li>
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<font size=+1><a href="#UsingJSObjs">Using JavaScript objects from Java</a></font></li>
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<ul>
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<li>
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<font size=+1><a href="#UsingJSvars">Using JavaScript variables</a></font></li>
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<li>
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<font size=+1><a href="#CallingJSfuns">Calling JavaScript functions</a></font></li>
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</ul>
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<li>
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<font size=+1><a href="#JavaScriptHostObjects">JavaScript host objects</a></font></li>
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<ul>
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<li>
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<font size=+1><a href="#DefiningHostObjects">Defining Host Objects</a></font></li>
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<li>
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<font size=+1><a href="#Counter">Counter example</a></font></li>
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<ul>
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<li>
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<font size=+1><a href="#CounterCtors">Counter's constructors</a></font></li>
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<li>
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<font size=+1><a href="#classname">Class name</a></font></li>
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<li>
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<font size=+1><a href="#Dynamic">Dynamic properties</a></font></li>
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<li>
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<font size=+1><a href="#DefiningMethods">Defining JavaScript "methods"</a></font></li>
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<li>
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<font size=+1><a href="#AddingCounter">Adding Counter to RunScript</a></font></li>
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</ul>
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</ul>
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</ul>
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<hr WIDTH="100%">
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<br><a NAME="RunScript"></a><font size=+3>RunScript: A simple embedding</font>
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<p>About the simplest embedding of Rhino possible is the <a href="http://lxr.mozilla.org/mozilla/source/js/rhino/examples/RunScript.java">RunScript
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example</a>. All it does it read a script from the command line, execute
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it, and print a result.
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<p>Here's an example use of RunScript from a shell command line:
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<blockquote>
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<pre><font color="#663366">$ java RunScript "Math.cos(Math.PI)"
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-1
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$ java RunScript 'function f(x){return x+1} f(7)'
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8</font></pre>
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</blockquote>
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Note that you'll have to have both the Rhino classes and the RunScript
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example class file in the classpath. Let's step through the body of <tt>main</tt>
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one line at time.
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<p><a NAME="EnteringContext"></a><font size=+2>Entering a Context</font>
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<p>The code
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<blockquote>
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<pre><font color="#006600">Context cx = Context.enter();</font></pre>
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</blockquote>
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Creates and enters a <tt>Context. </tt>A <tt>Context</tt> stores information
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about the execution environment of a script.
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<br>
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<p><a NAME="initializing"></a><font size=+2>Initializing standard objects</font>
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<p>The code
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<blockquote>
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<pre><font color="#006600">Scriptable scope = cx.initStandardObjects();</font></pre>
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</blockquote>
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Initializes the standard objects (<tt>Object</tt>,
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<tt>Function</tt>, etc.)
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This must be done before scripts can be executed. The <tt>null</tt> parameter
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tells <tt>initStandardObjects</tt> to create and return a scope object
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that we use in later calls.
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<p><a NAME="Collecting"></a><font size=+2>Collecting the arguments</font>
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<p>This code is standard Java and not specific to Rhino. It just collects
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all the arguments and concatenates them together.
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<blockquote>
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<pre style="color: #006600">
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String s = "";
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for (int i=0; i < args.length; i++) {
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s += args[i];
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}
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</pre>
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</blockquote>
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<p><br><a NAME="Evaluating"></a><font size=+2>Evaluating a script</font>
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<p>The code
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<blockquote>
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<pre><font color="#006600">Object result = cx.evaluateString(scope, s, "<cmd>", 1, null);</font></pre>
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</blockquote>
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uses the Context <tt>cx</tt> to evaluate a string. Evaluation of the script
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looks up variables in <tt>scope</tt>, and errors will be reported with
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the filename <tt><cmd></tt> and line number 1.
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<br>
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<p><a NAME="Print"></a><font size=+2>Print the result</font>
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<p>The code
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<blockquote>
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<pre><font color="#006600">System.out.println(cx.toString(result));</font></pre>
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</blockquote>
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prints the result of evaluating the script (contained in the variable <tt>result</tt>).
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<tt>result</tt>
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could be a string, JavaScript object, or other values..The
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<tt>toString</tt>
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method converts any JavaScript value to a string.
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<br>
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<p><a NAME="Exit"></a><font size=+2>Exit the Context</font>
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<p>The code
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<blockquote>
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<pre style="color: #006600">
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} finally {
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Context.exit();
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}
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</pre>
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</blockquote>
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exits the Context. This removes the association between the Context and
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the current thread and is an essential cleanup action. There should be
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a call to <tt>exit</tt> for every call to <tt>enter</tt>. To make sure that it is called even if an exception is thrown, it is put into the finally block corresponding to the try block starting after <tt>Context.enter()</tt>.
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<br>
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<dir> </dir>
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<a NAME="Expose"></a><font size=+3>Expose Java APIs</font>
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<p><a NAME="UseJava"></a><font size=+2>Use Java APIs</font>
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<p>No additional code in the embedding needed! The JavaScript feature called
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<i>LiveConnect</i>
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allows JavaScript programs to interact with Java objects:
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<dir><tt><font color="#663366">$ java RunScript 'java.lang.System.out.println(3)'</font></tt>
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<br><tt><font color="#663366">3.0</font></tt>
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<br><tt><font color="#663366">undefined</font></tt></dir>
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<a NAME="ImplementingInterfaces"></a><font size=+2>Implementing interfaces</font>
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<p>Using Rhino, JavaScript objects can implement arbitrary Java interfaces.
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There's no Java code to write--it's part of Rhino's LiveConnect implementation.
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For example, we can see how to implement java.lang.Runnable in a Rhino
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shell session:
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<blockquote>
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<pre><font color="#663366">js> obj = { run: function() { print('hi'); } }
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[object Object]
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js> obj.run()
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hi
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js> r = new java.lang.Runnable(obj);
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[object Object]
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js> t = new java.lang.Thread(r)
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Thread[Thread-0,5,main]
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js> t.start()
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hi</font></pre>
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</blockquote>
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<a NAME="AddJava"></a><font size=+2>Add Java objects</font>
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<p>The next example is <a href="http://lxr.mozilla.org/mozilla/source/js/rhino/examples/RunScript2.java">RunScript2</a>.
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This is the same as RunScript, but with the addition of two extra lines
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of code:
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<dir><tt><font color="#006600">Object wrappedOut = Context.javaToJS(System.out, scope);</font></tt>
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<br><tt><font color="#006600">ScriptableObject.putProperty(scope, "out", wrappedOut);</font></tt></dir>
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These lines add a global variable <tt>out</tt> that is a JavaScript reflection
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of the <tt>System.out</tt> variable:
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<dir><tt><font color="#663366">$ java RunScript2 'out.println(42)'</font></tt>
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<br><tt><font color="#663366">42.0</font></tt>
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<br><tt><font color="#663366">undefined</font></tt></dir>
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<p><br><a NAME="UsingJSObjs"></a><font size=+3>Using JavaScript objects
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from Java</font>
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<p>After evaluating a script it's possible to query the scope for variables
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and functions, extracting values and calling JavaScript functions. This
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is illustrated in the <a href="http://lxr.mozilla.org/mozilla/source/js/rhino/examples/RunScript3.java">RunScript3</a>
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example. This example adds the ability to print the value of variable <tt>x</tt>
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and the result of calling function <tt>f</tt>. Both <tt>x</tt> and <tt>f</tt>
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are expected to be defined by the evaluated script. For example,
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<blockquote>
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<pre style="color: #663366">
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$ java RunScript3 'x = 7'
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x = 7
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f is undefined or not a function.
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$ java RunScript3 'function f(a) { return a; }'
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x is not defined.
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f('my args') = my arg
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</pre>
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</blockquote>
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<a NAME="UsingJSvars"></a><font size=+2>Using JavaScript variables</font>
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<p>To print out the value of <tt>x</tt>, we add the following code.
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<blockquote>
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<pre style="color: #006600">
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Object x = scope.get("x", scope);
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if (x == Scriptable.NOT_FOUND) {
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System.out.println("x is not defined.");
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} else {
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System.out.println("x = " + Context.toString(x));
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}
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</pre>
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</blockquote>
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<a NAME="CallingJSfuns"></a><font size=+2>Calling JavaScript functions</font>
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<p>To get the function <tt>f</tt>, call it, and print the result, we add
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this code:
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<blockquote>
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<pre style="color: #006600">
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Object fObj = scope.get("f", scope);
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if (!(fObj instanceof Function)) {
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System.out.println("f is undefined or not a function.");
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} else {
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Object functionArgs[] = { "my arg" };
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Function f = (Function)fObj;
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Object result = f.call(cx, scope, scope, functionArgs);
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String report = "f('my args') = " + Context.toString(result);
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System.out.println(report);
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}
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</pre>
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</blockquote>
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<p><br><a NAME="JavaScriptHostObjects"></a><font size=+3>JavaScript host
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objects</font>
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<p><a NAME="DefiningHostObjects"></a><font size=+2>Defining Host Objects</font>
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<p>Custom host objects can implement special JavaScript features like dynamic
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properties.
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<p><a NAME="Counter"></a><font size=+2>Counter example</font>
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<p>The <a href="http://lxr.mozilla.org/mozilla/source/js/rhino/examples/Counter.java">Counter
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example</a> is a simple host object. We'll go through it method by method
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below.
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<p>It's easy to try out new host object classes in the shell using its
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built-in <tt>defineClass</tt> function. We'll see how to add it to RunScript
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later. (Note that because the <tt>java -jar</tt> option preempts the rest
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of the classpath, we can't use that and access the <tt>Counter</tt> class.)
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<blockquote>
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<pre style="color: #663366">
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$ java -cp 'js.jar;examples' org.mozilla.javascript.tools.shell.Main
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js> defineClass("Counter")
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js> c = new Counter(7)
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[object Counter]
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js> c.count
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7
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js> c.count
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8
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js> c.count
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9
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js> c.resetCount()
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js> c.count
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0
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</pre>
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</blockquote>
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<a NAME="CounterCtors"></a><font size=+2>Counter's constructors</font>
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<p>The zero-argument constructor is used by Rhino runtime to create instances.
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For the counter example, no initialization work is needed, so the implementation
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is empty.
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<dir><tt><font color="#006600">public Counter () { }</font></tt></dir>
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The method <tt>jsConstructor</tt> defines the JavaScript constructor that
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was called with the expression <tt>new Counter(7)</tt> in the JavaScript
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code above.
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<dir><tt><font color="#006600">public void jsConstructor(int a) { count
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= a; }</font></tt></dir>
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<a NAME="classname"></a><font size=+2>Class name</font>
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<p>The class name is defined by the <tt>getClassName</tt> method. This
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is used to determine the name of the constructor.
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<dir><tt><font color="#006600">public String getClassName() { return "Counter";
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}</font></tt></dir>
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<a NAME="Dynamic"></a><font size=+2>Dynamic properties</font>
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<p>Dynamic properties are defined by methods beginning with <tt>jsGet_</tt>
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or <tt>jsSet_</tt>. The method <tt>jsGet_count</tt> defines the <i>count</i>
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property.
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<dir><tt><font color="#006600">public int jsGet_count() { return count++;
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}</font></tt></dir>
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The expression <tt>c.count</tt> in the JavaScript code above results in
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a call to this method.
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<p><a NAME="DefiningMethods"></a><font size=+2>Defining JavaScript "methods"</font>
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<p>Methods can be defined using the <tt>jsFunction_ prefix</tt>. Here we
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define <tt>resetCount</tt> for JavaScript.
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<dir><tt><font color="#006600">public void jsFunction_resetCount() { count
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= 0; }</font></tt></dir>
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The call <tt>c.resetCount()</tt> above calls this method.
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<p><a NAME="AddingCounter"></a><font size=+2>Adding Counter to RunScript</font>
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<p>Now take a look at the <a href="http://lxr.mozilla.org/mozilla/source/js/rhino/examples/RunScript4.java">RunScript4
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example</a>. It's the same as RunScript except for two additions. The method
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<tt>ScriptableObject.defineClass</tt>
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uses a Java class to define the Counter "class" in the top-level scope:
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<dir><tt><font color="#006600">ScriptableObject.defineClass(scope, Counter.class);</font></tt></dir>
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Now we can reference the <tt>Counter</tt> object from our script:
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<dir><tt><font color="#663366">$ java RunScript4 'c = new Counter(3); c.count;
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c.count;'</font></tt>
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<br><tt><font color="#663366">4</font></tt></dir>
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It also creates a new instance of the <tt>Counter</tt> object from within
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our Java code, constructing it with the value 7, and assigning it to the
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top-level variable <tt>myCounter</tt>:
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<blockquote>
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<pre style="color: #006600">
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Object[] arg = { new Integer(7) };
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Scriptable myCounter = cx.newObject(scope, "Counter", arg);
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scope.put("myCounter", scope, myCounter);
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</pre>
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</blockquote>
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Now we can reference the <tt>myCounter</tt> object from our script:
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<blockquote>
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<pre style="color: #663366">
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$ java RunScript3 'RunScript4 'myCounter.count; myCounter.count'
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8
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</pre>
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</blockquote>
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</body>
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</html>
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