File	Doc	Category	Size	Date	Package
ExpressionParseTree.java	API Doc	Glassfish v2 API	12860	Fri May 04 22:32:20 BST 2007	org.apache.catalina.ssi

ExpressionParseTree

• java.lang.Object

Fields Summary
private LinkedList	nodeStack Contains the current set of completed nodes. This is a workspace for the parser.
private LinkedList	oppStack Contains operator nodes that don't yet have values. This is a workspace for the parser.
private Node	root The root node after the expression has been parsed.
private SSIMediator	ssiMediator The SSIMediator to use when evaluating the expressions.
private static final int	PRECEDENCE_NOT
private static final int	PRECEDENCE_COMPARE
private static final int	PRECEDENCE_LOGICAL

Constructors Summary
public ExpressionParseTree(String expr, SSIMediator ssiMediator) Creates a new parse tree for the specified expression. this.ssiMediator = ssiMediator; parseExpression(expr);

Methods Summary
public boolean	evaluateTree() Evaluates the tree and returns true or false. The specified SSIMediator is used to resolve variable references. return root.evaluate();
private void	parseExpression(java.lang.String expr) Parses the specified expression into a tree of parse nodes. StringNode currStringNode = null; // We cheat a little and start an artificial // group right away. It makes finishing easier. pushOpp(null); ExpressionTokenizer et = new ExpressionTokenizer(expr); while (et.hasMoreTokens()) { int token = et.nextToken(); if (token != ExpressionTokenizer.TOKEN_STRING) currStringNode = null; switch (token) { case ExpressionTokenizer.TOKEN_STRING : if (currStringNode == null) { currStringNode = new StringNode(et.getTokenValue()); nodeStack.add(0, currStringNode); } else { // Add to the existing currStringNode.value.append(" "); currStringNode.value.append(et.getTokenValue()); } break; case ExpressionTokenizer.TOKEN_AND : pushOpp(new AndNode()); break; case ExpressionTokenizer.TOKEN_OR : pushOpp(new OrNode()); break; case ExpressionTokenizer.TOKEN_NOT : pushOpp(new NotNode()); break; case ExpressionTokenizer.TOKEN_EQ : pushOpp(new EqualNode()); break; case ExpressionTokenizer.TOKEN_NOT_EQ : pushOpp(new NotNode()); // Sneak the regular node in. The NOT will // be resolved when the next opp comes along. oppStack.add(0, new EqualNode()); break; case ExpressionTokenizer.TOKEN_RBRACE : // Closeout the current group resolveGroup(); break; case ExpressionTokenizer.TOKEN_LBRACE : // Push a group marker pushOpp(null); break; case ExpressionTokenizer.TOKEN_GE : pushOpp(new NotNode()); // Similar stategy to NOT_EQ above, except this // is NOT less than oppStack.add(0, new LessThanNode()); break; case ExpressionTokenizer.TOKEN_LE : pushOpp(new NotNode()); // Similar stategy to NOT_EQ above, except this // is NOT greater than oppStack.add(0, new GreaterThanNode()); break; case ExpressionTokenizer.TOKEN_GT : pushOpp(new GreaterThanNode()); break; case ExpressionTokenizer.TOKEN_LT : pushOpp(new LessThanNode()); break; case ExpressionTokenizer.TOKEN_END : break; } } // Finish off the rest of the opps resolveGroup(); if (nodeStack.size() == 0) { throw new ParseException("No nodes created.", et.getIndex()); } if (nodeStack.size() > 1) { throw new ParseException("Extra nodes created.", et.getIndex()); } if (oppStack.size() != 0) { throw new ParseException("Unused opp nodes exist.", et.getIndex()); } root = (Node)nodeStack.get(0);
private void	pushOpp(org.apache.catalina.ssi.ExpressionParseTree$OppNode node) Pushes a new operator onto the opp stack, resolving existing opps as needed. // If node is null then it's just a group marker if (node == null) { oppStack.add(0, node); return; } while (true) { if (oppStack.size() == 0) break; OppNode top = (OppNode)oppStack.get(0); // If the top is a spacer then don't pop // anything if (top == null) break; // If the top node has a lower precedence then // let it stay if (top.getPrecedence() < node.getPrecedence()) break; // Remove the top node oppStack.remove(0); // Let it fill its branches top.popValues(nodeStack); // Stick it on the resolved node stack nodeStack.add(0, top); } // Add the new node to the opp stack oppStack.add(0, node);
private void	resolveGroup() Resolves all pending opp nodes on the stack until the next group marker is reached. OppNode top = null; while ((top = (OppNode)oppStack.remove(0)) != null) { // Let it fill its branches top.popValues(nodeStack); // Stick it on the resolved node stack nodeStack.add(0, top); }