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Tomcat example source code file (SymbolTable.java)

This example Tomcat source code file (SymbolTable.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

entry, entry, outer, outer, string, string, symboltable, symboltable, table_size

The Tomcat SymbolTable.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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, International
 * Business Machines, Inc., http://www.apache.org.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

package org.apache.jasper.xmlparser;

/**
 * This class is a symbol table implementation that guarantees that
 * strings used as identifiers are unique references. Multiple calls
 * to <code>addSymbol will always return the same string
 * reference.
 * <p>
 * The symbol table performs the same task as <code>String.intern()
 * with the following differences:
 * <ul>
 *  <li>
 *   A new string object does not need to be created in order to
 *   retrieve a unique reference. Symbols can be added by using
 *   a series of characters in a character array.
 *  </li>
 *  <li>
 *   Users of the symbol table can provide their own symbol hashing
 *   implementation. For example, a simple string hashing algorithm
 *   may fail to produce a balanced set of hashcodes for symbols
 *   that are <em>mostly unique. Strings with similar leading
 *   characters are especially prone to this poor hashing behavior.
 *  </li>
 * </ul>
 *
 * @author Andy Clark
 * @version $Id: SymbolTable.java 467222 2006-10-24 03:17:11Z markt $
 */
public class SymbolTable {

    //
    // Constants
    //

    /** Default table size. */
    protected static final int TABLE_SIZE = 101;

    //
    // Data
    //

    /** Buckets. */
    protected Entry[] fBuckets = null;

    // actual table size
    protected int fTableSize;

    //
    // Constructors
    //

    /** Constructs a symbol table with a default number of buckets. */
    public SymbolTable() {
        this(TABLE_SIZE);
    }

    /** Constructs a symbol table with a specified number of buckets. */
    public SymbolTable(int tableSize) {
        fTableSize = tableSize;
        fBuckets = new Entry[fTableSize];
    }

    //
    // Public methods
    //

    /**
     * Adds the specified symbol to the symbol table and returns a
     * reference to the unique symbol. If the symbol already exists,
     * the previous symbol reference is returned instead, in order
     * guarantee that symbol references remain unique.
     *
     * @param symbol The new symbol.
     */
    public String addSymbol(String symbol) {

        // search for identical symbol
        int bucket = hash(symbol) % fTableSize;
        int length = symbol.length();
        OUTER: for (Entry entry = fBuckets[bucket]; entry != null; entry = entry.next) {
            if (length == entry.characters.length) {
                for (int i = 0; i < length; i++) {
                    if (symbol.charAt(i) != entry.characters[i]) {
                        continue OUTER;
                    }
                }
                return entry.symbol;
            }
        }

        // create new entry
        Entry entry = new Entry(symbol, fBuckets[bucket]);
        fBuckets[bucket] = entry;
        return entry.symbol;

    } // addSymbol(String):String

    /**
     * Adds the specified symbol to the symbol table and returns a
     * reference to the unique symbol. If the symbol already exists,
     * the previous symbol reference is returned instead, in order
     * guarantee that symbol references remain unique.
     *
     * @param buffer The buffer containing the new symbol.
     * @param offset The offset into the buffer of the new symbol.
     * @param length The length of the new symbol in the buffer.
     */
    public String addSymbol(char[] buffer, int offset, int length) {

        // search for identical symbol
        int bucket = hash(buffer, offset, length) % fTableSize;
        OUTER: for (Entry entry = fBuckets[bucket]; entry != null; entry = entry.next) {
            if (length == entry.characters.length) {
                for (int i = 0; i < length; i++) {
                    if (buffer[offset + i] != entry.characters[i]) {
                        continue OUTER;
                    }
                }
                return entry.symbol;
            }
        }

        // add new entry
        Entry entry = new Entry(buffer, offset, length, fBuckets[bucket]);
        fBuckets[bucket] = entry;
        return entry.symbol;

    } // addSymbol(char[],int,int):String

    /**
     * Returns a hashcode value for the specified symbol. The value
     * returned by this method must be identical to the value returned
     * by the <code>hash(char[],int,int) method when called
     * with the character array that comprises the symbol string.
     *
     * @param symbol The symbol to hash.
     */
    public int hash(String symbol) {

        int code = 0;
        int length = symbol.length();
        for (int i = 0; i < length; i++) {
            code = code * 37 + symbol.charAt(i);
        }
        return code & 0x7FFFFFF;

    } // hash(String):int

    /**
     * Returns a hashcode value for the specified symbol information.
     * The value returned by this method must be identical to the value
     * returned by the <code>hash(String) method when called
     * with the string object created from the symbol information.
     *
     * @param buffer The character buffer containing the symbol.
     * @param offset The offset into the character buffer of the start
     *               of the symbol.
     * @param length The length of the symbol.
     */
    public int hash(char[] buffer, int offset, int length) {

        int code = 0;
        for (int i = 0; i < length; i++) {
            code = code * 37 + buffer[offset + i];
        }
        return code & 0x7FFFFFF;

    } // hash(char[],int,int):int

    /**
     * Returns true if the symbol table already contains the specified
     * symbol.
     *
     * @param symbol The symbol to look for.
     */
    public boolean containsSymbol(String symbol) {

        // search for identical symbol
        int bucket = hash(symbol) % fTableSize;
        int length = symbol.length();
        OUTER: for (Entry entry = fBuckets[bucket]; entry != null; entry = entry.next) {
            if (length == entry.characters.length) {
                for (int i = 0; i < length; i++) {
                    if (symbol.charAt(i) != entry.characters[i]) {
                        continue OUTER;
                    }
                }
                return true;
            }
        }

        return false;

    } // containsSymbol(String):boolean

    /**
     * Returns true if the symbol table already contains the specified
     * symbol.
     *
     * @param buffer The buffer containing the symbol to look for.
     * @param offset The offset into the buffer.
     * @param length The length of the symbol in the buffer.
     */
    public boolean containsSymbol(char[] buffer, int offset, int length) {

        // search for identical symbol
        int bucket = hash(buffer, offset, length) % fTableSize;
        OUTER: for (Entry entry = fBuckets[bucket]; entry != null; entry = entry.next) {
            if (length == entry.characters.length) {
                for (int i = 0; i < length; i++) {
                    if (buffer[offset + i] != entry.characters[i]) {
                        continue OUTER;
                    }
                }
                return true;
            }
        }

        return false;

    } // containsSymbol(char[],int,int):boolean

    //
    // Classes
    //

    /**
     * This class is a symbol table entry. Each entry acts as a node
     * in a linked list.
     */
    protected static final class Entry {

        //
        // Data
        //

        /** Symbol. */
        public String symbol;

        /**
         * Symbol characters. This information is duplicated here for
         * comparison performance.
         */
        public char[] characters;

        /** The next entry. */
        public Entry next;

        //
        // Constructors
        //

        /**
         * Constructs a new entry from the specified symbol and next entry
         * reference.
         */
        public Entry(String symbol, Entry next) {
            this.symbol = symbol.intern();
            characters = new char[symbol.length()];
            symbol.getChars(0, characters.length, characters, 0);
            this.next = next;
        }

        /**
         * Constructs a new entry from the specified symbol information and
         * next entry reference.
         */
        public Entry(char[] ch, int offset, int length, Entry next) {
            characters = new char[length];
            System.arraycopy(ch, offset, characters, 0, length);
            symbol = new String(characters).intern();
            this.next = next;
        }

    } // class Entry

} // class SymbolTable

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