stringutils.java

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 *    any, must include the following acknowledgement:
 *       "This product includes software developed by the
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package org.apache.commons.lang;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * <p>Operations on {@link java.lang.String} that are 
 * <code>null</code> safe.</p>
 * 
 * <ul>
 *  <li><b>IsEmpty/IsBlank</b>
 *      - checks if a String contains text</li>
 *  <li><b>Trim/Strip</b>
 *      - removes leading and trailing whitespace</li>
 *  <li><b>Equals</b>
 *      - compares two strings null-safe</li>
 *  <li><b>IndexOf/LastIndexOf/Contains</b>
 *      - null-safe index-of checks
 *  <li><b>IndexOfAny/LastIndexOfAny/IndexOfAnyBut/LastIndexOfAnyBut</b>
 *      - index-of any of a set of Strings</li>
 *  <li><b>ContainsOnly/ContainsNone</b>
 *      - does String contains only/none of these characters</li>
 *  <li><b>Substring/Left/Right/Mid</b>
 *      - null-safe substring extractions</li>
 *  <li><b>SubstringBefore/SubstringAfter/SubstringBetween</b>
 *      - substring extraction relative to other strings</li>
 *  <li><b>Split/Join</b>
 *      - splits a String into an array of substrings and vice versa</li>
 *  <li><b>Replace/Delete/Overlay</b>
 *      - Searches a String and replaces one String with another</li>
 *  <li><b>Chomp/Chop</b>
 *      - removes the last part of a String</li>
 *  <li><b>LeftPad/RightPad/Center/Repeat</b>
 *      - pads a String</li>
 *  <li><b>UpperCase/LowerCase/SwapCase/Capitalize/Uncapitalize</b>
 *      - changes the case of a String</li>
 *  <li><b>CountMatches</b>
 *      - counts the number of occurrances of one String in another</li>
 *  <li><b>IsAlpha/IsNumeric/IsWhitespace</b>
 *      - checks the characters in a String</li>
 *  <li><b>DefaultString</b>
 *      - protects against a null input String</li>
 *  <li><b>Reverse/ReverseDelimited</b>
 *      - reverses a String</li>
 *  <li><b>Abbreviate</b>
 *      - abbreviates a string using ellipsis</li>
 *  <li><b>Difference</b>
 *      - compares two Strings and reports on their differences</li>
 *  <li><b>LevensteinDistance</b>
 *      - the number of changes needed to change one String into another</li>
 * </ul>
 *
 * <p>The <code>StringUtils</code> class defines certain words related to
 * String handling.</p>
 * 
 * <ul>
 *  <li>null - <code>null</code></li>
 *  <li>empty - a zero-length string (<code>""</code>)</li>
 *  <li>space - the space character (<code>' '</code>, char 32)</li>
 *  <li>whitespace - the characters defined by {@link Character#isWhitespace(char)}</li>
 *  <li>trim - the characters &lt;= 32 as in {@link String#trim()}</li>
 * </ul>
 * 
 * <p><code>StringUtils</code> handles <code>null</code> input Strings quietly.
 * That is to say that a <code>null</code> input will return <code>null</code>.
 * Where a <code>boolean</code> or <code>int</code> is being returned
 * details vary by method.</p>
 * 
 * <p>A side effect of the <code>null</code> handling is that a 
 * <code>NullPointerException</code> should be considered a bug in
 * <code>StringUtils</code> (except for deprecated methods).</p>
 * 
 * <p>Methods in this class give sample code to explain their operation.
 * The symbol <code>*</code> is used to indicate any input including <code>null</code>.</p>
 *
 * @see java.lang.String
 * @author <a href="http://jakarta.apache.org/turbine/">Apache Jakarta Turbine</a>
 * @author GenerationJavaCore
 * @author <a href="mailto:[e-mail]">Jon S. Stevens</a>
 * @author <a href="mailto:[e-mail]">Daniel Rall</a>
 * @author <a href="mailto:[e-mail]">Greg Coladonato</a>
 * @author <a href="mailto:[e-mail]">Henri Yandell</a>
 * @author <a href="mailto:[e-mail]">Ed Korthof</a>
 * @author <a href="mailto:[e-mail]">Rand McNeely</a>
 * @author Stephen Colebourne
 * @author <a href="mailto:[e-mail]">Fredrik Westermarck</a>
 * @author Holger Krauth
 * @author <a href="mailto:[e-mail]">Alexander Day Chaffee</a>
 * @author <a href="mailto:[e-mail]">Henning P. Schmiedehausen</a>
 * @author Arun Mammen Thomas
 * @author Gary Gregory
 * @author Phil Steitz
 * @since 1.0
 * @version $Id: StringUtils.java,v 1.107 2003/08/23 10:39:20 scolebourne Exp $
 */
public class StringUtils {
    // Performance testing notes (JDK 1.4, Jul03, scolebourne)
    // Whitespace:
    // Character.isWhitespace() is faster than WHITESPACE.indexOf()
    // where WHITESPACE is a string of all whitespace characters
    // 
    // Character access:
    // String.charAt(n) versus toCharArray(), then array[n]
    // String.charAt(n) is about 15% worse for a 10K string
    // They are about equal for a length 50 string
    // String.charAt(n) is about 4 times better for a length 3 string
    // String.charAt(n) is best bet overall
    //
    // Append:
    // String.concat about twice as fast as StringBuffer.append
    // (not sure who tested this)
    
    /**
     * The empty String <code>""</code>.
     * @since 2.0
     */
    public static final String EMPTY = "";
    
    /**
     * <p>The maximum size to which the padding constant(s) can expand.</p>
     */
    private static final int PAD_LIMIT = 8192;

    /**
     * <p>An array of <code>String</code>s used for padding.</p>
     *
     * <p>Used for efficient space padding. The length of each String expands as needed.</p>
     */
    private static final String[] PADDING = new String[Character.MAX_VALUE];
    
    static {
        // space padding is most common, start with 64 chars
        PADDING[32] = "                                                                ";
    }

    /**
     * <p><code>StringUtils</code> instances should NOT be constructed in
     * standard programming. Instead, the class should be used as
     * <code>StringUtils.trim(" foo ");</code>.</p>
     *
     * <p>This constructor is public to permit tools that require a JavaBean
     * instance to operate.</p>
     */
    public StringUtils() {
    }

    // Empty checks
    //-----------------------------------------------------------------------
    /**
     * <p>Checks if a String is empty ("") or null.</p>
     * 
     * <pre>
     * StringUtils.isEmpty(null)      = true
     * StringUtils.isEmpty("")        = true
     * StringUtils.isEmpty(" ")       = false
     * StringUtils.isEmpty("bob")     = false
     * StringUtils.isEmpty("  bob  ") = false
     * </pre>
     *
     * <p>NOTE: This method changed in Lang version 2.0.
     * It no longer trims the String.
     * That functionality is available in isBlank().</p>
     * 
     * @param str  the String to check, may be null
     * @return <code>true</code> if the String is empty or null
     */
    public static boolean isEmpty(String str) {
        return (str == null || str.length() == 0);
    }

    /**
     * <p>Checks if a String is not empty ("") and not null.</p>
     * 
     * <pre>
     * StringUtils.isNotEmpty(null)      = false
     * StringUtils.isNotEmpty("")        = false
     * StringUtils.isNotEmpty(" ")       = true
     * StringUtils.isNotEmpty("bob")     = true
     * StringUtils.isNotEmpty("  bob  ") = true
     * </pre>
     *
     * @param str  the String to check, may be null
     * @return <code>true</code> if the String is not empty and not null
     */
    public static boolean isNotEmpty(String str) {
        return (str != null && str.length() > 0);
    }

    /**
     * <p>Checks if a String is whitespace, empty ("") or null.</p>
     * 
     * <pre>
     * StringUtils.isBlank(null)      = true
     * StringUtils.isBlank("")        = true
     * StringUtils.isBlank(" ")       = true
     * StringUtils.isBlank("bob")     = false
     * StringUtils.isBlank("  bob  ") = false
     * </pre>
     *
     * @param str  the String to check, may be null
     * @return <code>true</code> if the String is null, empty or whitespace
     * @since 2.0
     */
    public static boolean isBlank(String str) {
        int strLen;
        if (str == null || (strLen = str.length()) == 0) {
            return true;
        }
        for (int i = 0; i < strLen; i++) {
            if ((Character.isWhitespace(str.charAt(i)) == false) ) {
                return false;
            }
        }
        return true;
    }

    /**
     * <p>Checks if a String is not empty (""), not null and not whitespace only.</p>
     * 
     * <pre>
     * StringUtils.isNotBlank(null)      = false
     * StringUtils.isNotBlank("")        = false
     * StringUtils.isNotBlank(" ")       = false
     * StringUtils.isNotBlank("bob")     = true
     * StringUtils.isNotBlank("  bob  ") = true
     * </pre>
     *
     * @param str  the String to check, may be null
     * @return <code>true</code> if the String is 
     *  not empty and not null and not whitespace
     * @since 2.0
     */
    public static boolean isNotBlank(String str) {
        int strLen;
        if (str == null || (strLen = str.length()) == 0) {
            return false;
        }
        for (int i = 0; i < strLen; i++) {
            if ((Character.isWhitespace(str.charAt(i)) == false) ) {
                return true;
            }
        }
        return false;
    }

    // Trim
    //-----------------------------------------------------------------------
    /**
     * <p>Removes control characters (char &lt;= 32) from both
     * ends of this String, handling <code>null</code> by returning
     * an empty String ("").</p>
     * 
     * <pre>
     * StringUtils.clean(null)          = ""
     * StringUtils.clean("")            = ""
     * StringUtils.clean("abc")         = "abc"
     * StringUtils.clean("    abc    ") = "abc"
     * StringUtils.clean("     ")       = ""
     * </pre>
     *
     * @see java.lang.String#trim()
     * @param str  the String to clean, may be null
     * @return the trimmed text, never <code>null</code>
     * @deprecated Use the clearer named {@link #trimToEmpty(String)}.
     *             Method will be removed in Commons Lang 3.0.
     */
    public static String clean(String str) {
        return (str == null ? EMPTY : str.trim());
    }

    /**
     * <p>Removes control characters (char &lt;= 32) from both
     * ends of this String, handling <code>null</code> by returning
     * <code>null</code>.</p>
     * 
     * <p>The String is trimmed using {@link String#trim()}.
     * Trim removes start and end characters &lt;= 32.