001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache license, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the license for the specific language governing permissions and
015 * limitations under the license.
016 */
017package org.apache.logging.log4j.util;
018
019/**
020 * <em>Consider this class private.</em>
021 * 
022 * @see <a href="http://commons.apache.org/proper/commons-lang/">Apache Commons Lang</a>
023 */
024public final class Strings {
025
026    /**
027     * The empty string.
028     */
029    public static final String EMPTY = "";
030
031    private Strings() {
032        // empty
033    }
034
035    /**
036     * Returns a double quoted string.
037     * 
038     * @param str a String
039     * @return {@code "str"}
040     */
041    public static String dquote(final String str) {
042        return Chars.DQUOTE + str + Chars.DQUOTE;
043    }
044
045    /**
046     * Checks if a String is blank. A blank string is one that is {@code null}, empty, or when trimmed using
047     * {@link String#trim()} is empty.
048     *
049     * @param s the String to check, may be {@code null}
050     * @return {@code true} if the String is {@code null}, empty, or trims to empty.
051     */
052    public static boolean isBlank(final String s) {
053        return s == null || s.trim().isEmpty();
054    }
055
056    /**
057     * <p>
058     * Checks if a CharSequence is empty ("") or null.
059     * </p>
060     *
061     * <pre>
062     * Strings.isEmpty(null)      = true
063     * Strings.isEmpty("")        = true
064     * Strings.isEmpty(" ")       = false
065     * Strings.isEmpty("bob")     = false
066     * Strings.isEmpty("  bob  ") = false
067     * </pre>
068     *
069     * <p>
070     * NOTE: This method changed in Lang version 2.0. It no longer trims the CharSequence. That functionality is
071     * available in isBlank().
072     * </p>
073     *
074     * <p>
075     * Copied from Apache Commons Lang org.apache.commons.lang3.StringUtils.isEmpty(CharSequence)
076     * </p>
077     *
078     * @param cs the CharSequence to check, may be null
079     * @return {@code true} if the CharSequence is empty or null
080     */
081    public static boolean isEmpty(final CharSequence cs) {
082        return cs == null || cs.length() == 0;
083    }
084
085    /**
086     * Checks if a String is not blank. The opposite of {@link #isBlank(String)}.
087     *
088     * @param s the String to check, may be {@code null}
089     * @return {@code true} if the String is non-{@code null} and has content after being trimmed.
090     */
091    public static boolean isNotBlank(final String s) {
092        return !isBlank(s);
093    }
094
095    /**
096     * <p>
097     * Checks if a CharSequence is not empty ("") and not null.
098     * </p>
099     *
100     * <pre>
101     * Strings.isNotEmpty(null)      = false
102     * Strings.isNotEmpty("")        = false
103     * Strings.isNotEmpty(" ")       = true
104     * Strings.isNotEmpty("bob")     = true
105     * Strings.isNotEmpty("  bob  ") = true
106     * </pre>
107     *
108     * <p>
109     * Copied from Apache Commons Lang org.apache.commons.lang3.StringUtils.isNotEmpty(CharSequence)
110     * </p>
111     *
112     * @param cs the CharSequence to check, may be null
113     * @return {@code true} if the CharSequence is not empty and not null
114     */
115    public static boolean isNotEmpty(final CharSequence cs) {
116        return !isEmpty(cs);
117    }
118
119    /**
120     * Returns a quoted string.
121     * 
122     * @param str a String
123     * @return {@code 'str'}
124     */
125    public static String quote(final String str) {
126        return Chars.QUOTE + str + Chars.QUOTE;
127    }
128
129    /**
130     * <p>
131     * Removes control characters (char &lt;= 32) from both ends of this String returning {@code null} if the String is
132     * empty ("") after the trim or if it is {@code null}.
133     *
134     * <p>
135     * The String is trimmed using {@link String#trim()}. Trim removes start and end characters &lt;= 32.
136     * </p>
137     *
138     * <pre>
139     * Strings.trimToNull(null)          = null
140     * Strings.trimToNull("")            = null
141     * Strings.trimToNull("     ")       = null
142     * Strings.trimToNull("abc")         = "abc"
143     * Strings.trimToNull("    abc    ") = "abc"
144     * </pre>
145     *
146     * <p>
147     * Copied from Apache Commons Lang org.apache.commons.lang3.StringUtils.trimToNull(String)
148     * </p>
149     *
150     * @param str the String to be trimmed, may be null
151     * @return the trimmed String, {@code null} if only chars &lt;= 32, empty or null String input
152     */
153    public static String trimToNull(final String str) {
154        final String ts = str == null ? null : str.trim();
155        return isEmpty(ts) ? null : ts;
156    }
157}