Set Ant build properties from JSON

Readme.md

Example:

Jeffreys-MacBook-Air$ ant example
Buildfile: /Users/jsambells/Documents/example/build.xml
    [echo] Parsing properties
    [echo] greeting=Hello
    [echo] audience=world
example:
    [echo] Hello world

build.xml

<?xml version="1.0" encoding="UTF-8"?>
<project name="JSON Example" basedir=".">
    <script language="javascript">

        importClass(java.io.File);
        importClass(java.io.FileReader);
        importClass(java.io.BufferedReader);
        importClass(java.io.FileWriter);
        importClass(java.io.BufferedWriter);

        echo = project.createTask("echo");
        echo.setMessage("Parsing properties");
        echo.perform();

        var file = new File("properties.json");
        fr = new FileReader(file);
        br = new BufferedReader(fr);

        // Read the file. 
        // This assumes the file has no line breaks and is one line.
        var json = br.readLine();

        // Evaluate the JSON.
        var struct = eval("(" + json + ")");

        // Set each property in the project environment.
        for (i in struct) {
            echo = project.createTask("echo");
            echo.setMessage(i + "=" + struct[i]);
            echo.perform();
            project.setProperty(i,struct[i]);
        }

    </script>

    <target name="example">
        <echo>${greeting} ${audience}</echo>
    </target>

</project>

properties.json

{"greeting":"Hello","audience":"world"}

It's useful , hope Ant can provide 'json-parse / json-stringify' task

I can't seem to get it to work correctly. It seems to parse correctly because it echos it out, but I can't access the property.

I'm getting:

javax.script.ScriptEngineFactory: Provider com.sun.phobos.script.javascript.RhinoScriptEngineFactory could not be instantiated

How did you setup ant to start running tasks like this?