1 /**
2 * Logback: the reliable, fast and flexible logging library for Java.
3 *
4 * Copyright (C) 1999-2006, QOS.ch
5 *
6 * This library is free software, you can redistribute it and/or modify it under
7 * the terms of the GNU Lesser General Public License as published by the Free
8 * Software Foundation.
9 */
10
11 package chapter3.calculator;
12
13
14
15 import java.util.EmptyStackException;
16
17 import org.xml.sax.Attributes;
18
19 import ch.qos.logback.core.joran.action.Action;
20 import ch.qos.logback.core.joran.spi.InterpretationContext;
21
22
23 /**
24 * This action adds the two integers at the top of the stack (they are removed)
25 * and pushes the result to the top the stack.
26 *
27 * @author Ceki Gülcü
28 */
29 public class AddAction extends Action {
30
31 public void begin(InterpretationContext ec, String name, Attributes attributes) {
32 int first = fetchInteger(ec);
33 int second = fetchInteger(ec);
34 // Push the result of the addition for the following actions.
35 ec.pushObject(new Integer(first + second));
36 }
37
38 /**
39 * Pop the Integer object at the top of the stack.
40 * This code illustrates usage of Joran's error handling paradigm.
41 */
42 int fetchInteger(InterpretationContext ec) {
43 int result = 0;
44
45 try {
46 // Pop the object at the top of the exection context stack.
47 Object o1 = ec.popObject();
48
49 if (o1 instanceof Integer) {
50 result = ((Integer) o1).intValue();
51 } else {
52 String errMsg =
53 "Object [" + o1
54 + "] currently at the top of the stack is not an integer.";
55 ec.addError(errMsg);
56 throw new IllegalArgumentException(errMsg);
57 }
58 } catch (EmptyStackException ese) {
59 ec.addError(("Expecting an integer on the execution stack."));
60 throw ese;
61 }
62 return result;
63 }
64
65 public void end(InterpretationContext ec, String name) {
66 // Nothing to do here.
67 // In general, the end() method of actions associated with elements
68 // having no children do not need to perform any processing in their
69 // end() method.
70 }
71 }