JUEL mathematics

Question

I'm programming server on java, and I need to use math with the help of JUEL.

For example 2*2+2 and it will print out the result 6. The problem is, it doesn't work.

Here is a method for mathematics:

public static void Math(String operation){

    ValueExpression expr = f.createValueExpression(cont, "${" + operation + "}", Object.class);
    out.print(expr);

}

So, I take an operation as String "8+5+4"and print out result on conlsole.

May be I use JUEL in a wrong way?

try{
        while ((newLine = in.readLine()) != null) {
            try {
               Pattern patternMath = Pattern.compile("<MATH>(\\s*?)(\\d+)(\\s*?)([-+/\\*])(\\s*?)(\\d+)");
               Matcher matcher = patternMath.matcher(newLine);

                Pattern pattCSEN = Pattern.compile("<RU-EN>(.*)");
                Matcher matCSEN = pattCSEN.matcher(newLine);

                Pattern pattENCS = Pattern.compile("<EN-RU>(.*)");
                Matcher matENCS = pattENCS.matcher(newLine);




                if (matENCS.find()) {out.println("<TRANSLATION> " + ENGtoCZ(matENCS.group(1)));}
                else if (matCSEN.find()) {out.println("<TRANSLATION> " + CZtoENG(matCSEN.group(1)));}
               else if (newLine.equals("<BYE>")) {
                    clientSocket.close();

                }
                else  if (matcher.find()) {

               Math(newLine);

                } else {
                    out.println("<FAIL>");
                    clientSocket.close();

                }
            }catch(Exception ex){
                clientSocket.close();;
            }}
            } catch (Exception e) {
                out.println("<FAIL>");
                clientSocket.close();
            }
        }

Answer 1

Here are the following lines to always make sure that you have in your code. Make sure you have the context set up something like the following:

SimpleContext context = new SimpleContext();

You expression object should be of the Implemented class, something like the following:

ExpressionFactory factory = new ExpressionFactoryImpl();

JUEL Api

Secondly put your ValueExpression in a try block, in case anything goes wrong, you will know the problem from the caught exception.

Check how expression is entered with a System.out as in:

Object display = expr.getValue(context);
System.out.println("> " + display);

Some additional reference is Here