从javascript表达式获取变量（Rhino）

Question

I'm using Rhino to evaluate js expressions, by putting all the possible variable values in the scope and evaluating an anonymous function. However the expressions are fairly simple and I would like to put only the values used in the expression, for performance.

Code sample:

    Context cx = Context.enter();

    Scriptable scope = cx.initStandardObjects(null);

    // Build javascript anonymous function
    String script = "(function () {" ;

    for (String key : values.keySet()) {
        ScriptableObject.putProperty(scope, key, values.get(key));
    }
    script += "return " + expression + ";})();";

    Object result = cx.evaluateString(scope, script, "<cmd>", 1, null);

I want to get all the tokens from the expressions that are variable names.

For instance, if the expression is

(V1ND < 0 ? Math.abs(V1ND) : 0)

it will return V1ND .

Answer 1

Rhino 1.7 R3 introduced an AST package which can be used to find names:

import java.util.*;
import org.mozilla.javascript.Parser;
import org.mozilla.javascript.ast.*;

public class VarFinder {
  public static void main(String[] args) throws IOException {
    final Set<String> names = new HashSet<String>();
    class Visitor implements NodeVisitor {
      @Override public boolean visit(AstNode node) {
        if (node instanceof Name) {
          names.add(node.getString());
        }
        return true;
      }
    }
    String script = "(V1ND < 0 ? Math.abs(V1ND) : 0)";
    AstNode node = new Parser().parse(script, "<cmd>", 1);
    node.visit(new Visitor());
    System.out.println(names);
  }
}

Output:

[V1ND, abs, Math]

However, I'm not sure this will help much with efficiency unless the expressions are amenable to caching. You would be parsing the code twice and if you need to disambiguate a variable abs from the function on Math further inspection will be required.