Tomcat example source code file (ExpressionTokenizer.java)

This example Tomcat source code file (ExpressionTokenizer.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Tomcat tags/keywords

less, string, string, token_end, token_eq, token_ge, token_ge, token_gt, token_gt, token_lbrace, token_le, token_le, token_lt, token_or

The Tomcat ExpressionTokenizer.java source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.catalina.ssi;


/**
 * Parses an expression string to return the individual tokens. This is
 * patterned similar to the StreamTokenizer in the JDK but customized for SSI
 * conditional expression parsing.
 * 
 * @version $Revision: 531303 $
 * @author Paul Speed
 */
public class ExpressionTokenizer {
    public static final int TOKEN_STRING = 0;
    public static final int TOKEN_AND = 1;
    public static final int TOKEN_OR = 2;
    public static final int TOKEN_NOT = 3;
    public static final int TOKEN_EQ = 4;
    public static final int TOKEN_NOT_EQ = 5;
    public static final int TOKEN_RBRACE = 6;
    public static final int TOKEN_LBRACE = 7;
    public static final int TOKEN_GE = 8;
    public static final int TOKEN_LE = 9;
    public static final int TOKEN_GT = 10;
    public static final int TOKEN_LT = 11;
    public static final int TOKEN_END = 12;
    private char[] expr;
    private String tokenVal = null;
    private int index;
    private int length;


    /**
     * Creates a new parser for the specified expression.
     */
    public ExpressionTokenizer(String expr) {
        this.expr = expr.trim().toCharArray();
        this.length = this.expr.length;
    }


    /**
     * Returns true if there are more tokens.
     */
    public boolean hasMoreTokens() {
        return index < length;
    }


    /**
     * Returns the current index for error reporting purposes.
     */
    public int getIndex() {
        return index;
    }


    protected boolean isMetaChar(char c) {
        return Character.isWhitespace(c) || c == '(' || c == ')' || c == '!'
                || c == '<' || c == '>' || c == '|' || c == '&' || c == '=';
    }


    /**
     * Returns the next token type and initializes any state variables
     * accordingly.
     */
    public int nextToken() {
        // Skip any leading white space
        while (index < length && Character.isWhitespace(expr[index]))
            index++;
        // Clear the current token val
        tokenVal = null;
        if (index == length) return TOKEN_END; // End of string
        int start = index;
        char currentChar = expr[index];
        char nextChar = (char)0;
        index++;
        if (index < length) nextChar = expr[index];
        // Check for a known token start
        switch (currentChar) {
            case '(' :
                return TOKEN_LBRACE;
            case ')' :
                return TOKEN_RBRACE;
            case '=' :
                return TOKEN_EQ;
            case '!' :
                if (nextChar == '=') {
                    index++;
                    return TOKEN_NOT_EQ;
                } else {
                    return TOKEN_NOT;
                }
            case '|' :
                if (nextChar == '|') {
                    index++;
                    return TOKEN_OR;
                }
                break;
            case '&' :
                if (nextChar == '&') {
                    index++;
                    return TOKEN_AND;
                }
                break;
            case '>' :
                if (nextChar == '=') {
                    index++;
                    return TOKEN_GE; // Greater than or equal
                } else {
                    return TOKEN_GT; // Greater than
                }
            case '<' :
                if (nextChar == '=') {
                    index++;
                    return TOKEN_LE; // Less than or equal
                } else {
                    return TOKEN_LT; // Less than
                }
            default :
                // Otherwise it's a string
                break;
        }
        int end = index;
        // If it's a quoted string then end is the next unescaped quote
        if (currentChar == '"' || currentChar == '\'') {
            char endChar = currentChar;
            boolean escaped = false;
            start++;
            for (; index < length; index++) {
                if (expr[index] == '\\' && !escaped) {
                    escaped = true;
                    continue;
                }
                if (expr[index] == endChar && !escaped) break;
                escaped = false;
            }
            end = index;
            index++; // Skip the end quote
        } else {
            // End is the next whitespace character
            for (; index < length; index++) {
                if (isMetaChar(expr[index])) break;
            }
            end = index;
        }
        // Extract the string from the array
        this.tokenVal = new String(expr, start, end - start);
        return TOKEN_STRING;
    }


    /**
     * Returns the String value of the token if it was type TOKEN_STRING.
     * Otherwise null is returned.
     */
    public String getTokenValue() {
        return tokenVal;
    }
}