字符串操作之 ==> apache.commons.lang3.StringUtils

一、常用方法

1、判斷是否為空串

• isBlank(final CharSequence cs)：判斷是否為空字符串；
• isEmpty(final CharSequence cs)：判斷是否為空字符串；
• isNotBlank(final CharSequence cs)：判斷不是空字符串；
• isNotEmpty(final CharSequence cs)：判斷不是空字符串；
• 說明：isBlank和isEmpty的區別在於在於空格字符串的判斷不同，isEmpty認為空格字符不是空字符串

StringUtils.isBlank(null);      = true
StringUtils.isBlank("");        = true
StringUtils.isBlank(" ");       = true
StringUtils.isBlank("hello");   = false
StringUtils.isBlank(" hello "); = false
---------------------------------------
StringUtils.isEmpty(null);      = true
StringUtils.isEmpty("");        = true
StringUtils.isEmpty(" ");       = false
StringUtils.isEmpty("hello");   = false
StringUtils.isEmpty(" hello "); = false
------------------------------------------
StringUtils.isNotBlank(null);      = false
StringUtils.isNotBlank("");        = false
StringUtils.isNotBlank(" ");       = false
StringUtils.isNotBlank("hello");   = true
StringUtils.isNotBlank(" hello "); = true
------------------------------------------
StringUtils.isNotEmpty(null);      = false
StringUtils.isNotEmpty("");        = false
StringUtils.isNotEmpty(" ");       = true
StringUtils.isNotEmpty("hello");   = true
StringUtils.isNotEmpty(" hello "); = true

2、去除字符串前后空格及換行符

• trim(final String str):去除字符串前后空格，同時不改變原字符串；
• trimToNull(final String str)：去除字符串前后空格，如果去除后是空字符串就轉為null；
• trimToEmpty(final String str)：去除字符串前后空格，如果去除后是空字符串就轉為空字符串(null轉為""）;
• strip(final String str)：這個也可以去除字符串的前后空格，不改變原字符串；
• stripToNull(String str)：同trimToNull(final String str)類似；
• stripToEmpty(final String str)：同trimToEmpty(final String str)類似；
• String[] stripAll(final String... strs)：對數組中的所有字符串進行去除空格；

StringUtils.trim(" hello ");      = "hello"
StringUtils.trim("\n hello \n");  = "hello"
StringUtils.trimToNull(null);     = null
StringUtils.trimToNull("    \n"); = null
StringUtils.trimToEmpty(null);    = ""
StringUtils.trimToEmpty("\n  \n");= ""
--------------------------------------------
StringUtils.strip(" hello ");     = "hello"
StringUtils.strip("\n hello \n"); = "hello"
StringUtils.stripToNull(null);    = null
StringUtils.stripToNull("     "); = null
StringUtils.stripToEmpty(null);   = ""
StringUtils.stripToEmpty("     ");= ""
--------------------------------------------
StringUtils.stripAll(" \n abc", null, "\n aab \n"); = [abc, null, aab]

3、字符串剝離

• strip(String str, final String stripChars)：從str的前后剝離stripChars字符串；
• stripStart(final String str, final String stripChars)：從開始的地方剝離指定字符串；
• stripEnd(final String str, final String stripChars)：從結束的地方剝離字符串；
• String[] stripAll(final String[] strs, final String stripChars)：對數組中的每個字符串進行字符串剝離；

StringUtils.strip("abcde", "de");        = "abc"
StringUtils.strip("abcde", "ed");        = "abc"
StringUtils.stripStart("deabced", "ed"); = "abced"
StringUtils.stripStart("deabced", "de"); = "abced"
StringUtils.stripEnd("  abcyx", "xyz");  = "  abc"
StringUtils.stripEnd("120.00", ".0");    = "12"
StringUtils.stripAll(new String[]{"aab", "abc", "aba"}, "ab"); = ["","c",""]

4、字符串截取

• truncate(final String str, final int maxWidth)：截取字符串的前maxWidth個字符；
• 如果str的長度小於maxWidth就直接返回str；
• 如果maxWidth小於0則拋出IllegalArgumentException異常；
• truncate(final String str, final int offset, final int maxWidth)：截取指定區域的字符串；

StringUtils.truncate(null, 0);  = null
StringUtils.truncate(null, 2);  = null
StringUtils.truncate("", 4);    = ""
StringUtils.truncate("abcdefg", 4); = "abcd"
StringUtils.truncate(null, 0, 0);   = null
StringUtils.truncate(null, 2, 4);   = null
StringUtils.truncate("", 0, 10);    = ""
StringUtils.truncate("", 2, 10);    = ""
StringUtils.truncate("abcdefghij", 0, 3); = "abc"
StringUtils.truncate("abcdefghij", 5, 6); = "fghij"
StringUtils.truncate("abcdefghijklmno", -1, 10); = java.lang.IllegalArgumentException: offset cannot be negative
StringUtils.truncate("abcdefghijklmno", Integer.MIN_VALUE, 10); = java.lang.IllegalArgumentException: offset cannot be negative
StringUtils.truncate("abcdefghijklmno", 0, Integer.MAX_VALUE);  = "abcdefghijklmno"

5、字符串比較

• equals(final CharSequence cs1, final CharSequence cs2):判斷兩個字符串是否相等；
• equalsIgnoreCase(final CharSequence str1, final CharSequence str2)：判斷兩個字符串在忽略大小寫下是否相等；
• compare(final String str1, final String str2)：比較兩個字符串的大小；
• compareIgnoreCase(final String str1, final String str2)：忽略大小寫下比較兩個字符串的大小；
• equalsAny(final CharSequence string, final CharSequence... searchStrings):比較多字符串中是否存在相同的字符串；
• equalsAnyIgnoreCase(final CharSequence string, final CharSequence...searchStrings)：忽略大小寫是否存在相同字符； 

StringUtils.equals("abc", null);  = false
StringUtils.equals("abc", "abc"); = true
StringUtils.equals("abc", "ABC"); = false
StringUtils.equalsIgnoreCase("abc", "ABC"); = true
--------------------------------------------------
StringUtils.compare("abc", "abc");          = 0
StringUtils.compare("a", "b");              = -1
StringUtils.compare("b", "a");              = 1
StringUtils.compare("a", "B");              = 31
StringUtils.compare("ab", "abc");           = -1
StringUtils.compareIgnoreCase("a", "B");    = -1
StringUtils.compareIgnoreCase("A", "b");    = -1
StringUtils.compareIgnoreCase("ab", "ABC"); = -1
--------------------------------------------------
StringUtils.equalsAny("abc", "abc", "def"); = true
StringUtils.equalsAny("abc", "ABC", "DEF"); = false
StringUtils.equalsAnyIgnoreCase("abc", "abc", "def"); = true
StringUtils.equalsAnyIgnoreCase("abc", "ABC", "DEF"); = true

6、字符串查找

• indexOf(final CharSequence seq, final int searchChar)：查找指定字符在字符串中首次出現的位置的索引值；
• indexOf(final CharSequence seq, final int searchChar, final int startPos)：從指定位置final int startPos開始查找；
• indexOfIgnoreCase(final CharSequence str, final CharSequence searchStr)：忽略大小寫的查找字符串首次出現位置
• indexOfIgnoreCase(final CharSequence str, final CharSequence searchStr, int startPos)：同`indexOf類似；
• lastIndexOf(final CharSequence seq, final int searchChar)：從尾部開始查找；
• lastIndexOf(final CharSequence seq, final int searchChar, final int startPos)：同理從尾部開始查找指定位置前的字符；

StringUtils.indexOf("aabaabaa", 'b');    = 2
StringUtils.indexOf("aabaabaa", "");     = 0
StringUtils.indexOf("aabaabaa", "b", 3); = 5
StringUtils.indexOfIgnoreCase("aabaabaa", "B");    = 2
StringUtils.indexOfIgnoreCase("aabaabaa", "B", 3); = 5
StringUtils.ordinalIndexOf("abababab", "abab", 3); = 4
StringUtils.lastIndexOf("aabaabaa", 'b');    = 5
StringUtils.lastIndexOf("aabaabaa", 'b', 4); = 0

7、是否包含字符串

• contains(final CharSequence seq, final int searchChar：是否包含指定字符串；
• containsIgnoreCase(final CharSequence str, final CharSequence searchStr：忽略大小寫下檢查是否包含指定字符串
• containsWhitespace(final CharSequence seq)：是否包含空白字符串；
• containsAny(final CharSequence cs, final char... searchChars)：判斷字符竄是否包含后面多個中的任意一個；
• containsOnly(final CharSequence cs, final char... valid)：判斷前面的字符是否全部是后面的字符組成的；
• containsNone(final CharSequence cs, final char... searchChars)：判斷前面字符是否不含其后字符的任意一個字符;

StringUtils.contains("abc", "a");  = true
StringUtils.contains("abc", 'z');  = false
StringUtils.containsIgnoreCase("abc", "A");      = true
StringUtils.containsIgnoreCase("abc", "Z");      = false
StringUtils.containsWhitespace("abc");           = false
StringUtils.containsWhitespace("a  bc");         = true
StringUtils.containsAny("zzabyycdxx", 'a', 'f'); = true
StringUtils.containsAny("zzabyycdxx", 'b', 'y'); = true
StringUtils.containsAny("zzabyycdxx", 'z', 'y'); = true
StringUtils.containsAny("aba", 'z');             = false
StringUtils.containsOnly("abab", 'a', 'b', 'c'); = true
StringUtils.containsOnly("ab1", "abc");          = false
StringUtils.containsOnly("abz", 'a', 'b', 'c');  = false
StringUtils.containsNone("abab", "ab");          = false
StringUtils.containsNone("ab1", 'x', 'y', 'z');  = true
StringUtils.containsNone("abz", "xyz");          = false

8、截取字符串

• substring(final String str, int start)：指定開始為止截取字符串；
• String substring(final String str, int start, int end):指定開始和結束為止截取字符串；
• left(final String str, final int len)：得到一個字符串最左邊的len個字符；
• right(final String str, final int len)：得到一個字符串最右邊的len個字符；
• mid(final String str, int pos, final int len)：得到中間的指定區域的字符，是左包含；
• substringBefore(final String str, final String separator)：得到一個字符串中第一個分割符之前的字符串；
• substringAfter(final String str, final String separator)：同理，得到一個字符串第一個分割符之后的字符串；

StringUtils.substring("abc", 2);        = "c"
StringUtils.substring("abc", 4);        = ""
StringUtils.substring("abc", -2);       = "bc"
StringUtils.substring("abc", -4);       = "abc"
StringUtils.substring("abc", 2, 2);     = ""
StringUtils.substring("abc", -2, -1);   = "b"
StringUtils.substring("abc", -4, 2);    = "ab"
StringUtils.left("abc", 2);     = "ab"
StringUtils.left("abc", 4);     = "abc"
StringUtils.right("abc", 2);    = "bc"
StringUtils.right("abc", 4);    = "abc"
StringUtils.mid("abc", 2, 4);   = "c"
StringUtils.mid("abc", 4, 2);   = ""
StringUtils.mid("abc", -2, 2);  = "ab"
StringUtils.substringBefore("abcba", "b"); = "a"
StringUtils.substringBefore("abc", "c");   = "ab"
StringUtils.substringBefore("abc", "d");   = "abc"
StringUtils.substringAfter("abcba", "b");  = "cba"
StringUtils.substringAfter("abc", "c");    = ""
StringUtils.substringAfter("abc", "d");    = ""

9、字符串分割

• String[] split(final String str)：按照空格分割字符串，返回數組；
• String[] split(final String str, final char separatorChar)：指定分割符分割字符串；
• String[] split(final String str, final String separatorChars, final int max)：指定分割符，指定最大分割的數組大小;
• String[] splitByCharacterTypeCamelCase(final String str)：根據字符串類型分割字符串；

StringUtils.split("abc  def");    = ["abc","def"]
StringUtils.split(" abc ");       = ["abc"]
StringUtils.split("a,,b,c", ','); = ["a","b","c"]
StringUtils.split("a:b:c", '.');  = ["a:b:c"]
StringUtils.split("a b c", ' ');  = ["a","b","c"]
StringUtils.split("ab:cd:ef", ":", 3); = ["ab","cd","ef"]
StringUtils.split("ab:cd:ef", ":", 2); = ["ab","cd:ef"]
StringUtils.split("ab:cd:ef", ":", 1); = ["ab:cd:ef"]
StringUtils.splitByCharacterTypeCamelCase("number5");   = ["number","5"]
StringUtils.splitByCharacterTypeCamelCase("fooBar");    = ["foo","Bar"]
StringUtils.splitByCharacterTypeCamelCase("foo200Bar"); = ["foo","200","Bar"]
StringUtils.splitByCharacterTypeCamelCase("ASFRules");  = ["ASF","Rules"]

10、字符串拼接

• join(final T... elements)；普通的連接字符串
• join(final Object[] array, final char separator)：指定連接符，連接字符串；

StringUtils.join("a", "b", "c");  = "abc"
StringUtils.join(null, "", "a");  = "a"
StringUtils.join(new String[]{"a", "b", "c"}, ';');  = "a;b;c"
StringUtils.join(new String[]{"a", "b", "c"}, null); = "abc"
StringUtils.join(new String[]{null, "", "a"}, ';');  = ";;a"

11、刪除和替換字符串

• removeStart(final String str, final String remove)：刪除字符串中的指定的前綴字符串；
• removeStartIgnoreCase(final String str, final String remove)：同removeStart類似，只是忽略的大小寫；
• removeEnd(final String str, final String remove)：同removeStart相反；
• deleteWhitespace(final String str)：刪除字符串中的空格；
• remove(final String str, final String remove)：從字符串中移除指定字符串；
• removeAll(final String text, final String regex)：移除符合正則表達式的所有字符串；
• replaceOnce(final String text, final String searchString, final String replacement)：將字符串中指定字符替換一個；
• replaceAll(final String text, final String regex, final String replacement)：將字符串中指定字符替換所有； 

StringUtils.removeStart("www.domain.com", "www.");   = "domain.com"
StringUtils.removeStart("domain.com", "www.");       = "domain.com"
StringUtils.removeStart("www.domain.com", "domain"); = "www.domain.com"
StringUtils.removeStart("abc", "");                  = "abc"
StringUtils.deleteWhitespace("abc");                 = "abc"
StringUtils.deleteWhitespace("   ab  c  ");          = "abc"
StringUtils.removeEnd("www.domain.com", ".com.");    = "www.domain.com"
StringUtils.removeEnd("www.domain.com", ".com");     = "www.domain"
StringUtils.removeEnd("www.domain.com", "domain");   = "www.domain.com"
StringUtils.remove("queued", "ue");        = "qd"
StringUtils.remove("queued", "zz");        = "queued"
StringUtils.replaceOnce("aba", "a", null); = "aba"
StringUtils.replaceOnce("aba", "a", "");   = "ba"
StringUtils.replaceOnce("aba", "a", "z");  = "zba"
StringUtils.replaceAll("aba", "a", "z");  = "zbz"

12、生成重復字符串

• repeat(final String str, final int repeat)：生成指定重復次數的重復字符串；

StringUtils.repeat("a", 3);  = "aaa"
StringUtils.repeat("ab", 2); = "abab"
StringUtils.repeat("a", -2); = ""

13、字符串出現次數

• countMatches(final CharSequence str, final CharSequence sub)：獲取指定字符串在原字符串中出現的次數；

StringUtils.countMatches("abba", "a");  = 2
StringUtils.countMatches("abba", "ab"); = 1

二、其他方法

1、判斷是否是空格

• isWhitespace(final CharSequence cs) 

StringUtils.isWhitespace("");    = true
StringUtils.isWhitespace("  ");  = true
StringUtils.isWhitespace("abc"); = false

2、判斷字符串是否由空格或者數字組成

• isNumericSpace(final CharSequence cs)

StringUtils.isNumericSpace("12 3");  = true
StringUtils.isNumericSpace("12.3");  = false

3、判斷是否全是小寫/大寫

• isAllLowerCase(final CharSequence cs)
• isAllUpperCase(final CharSequence cs) 

StringUtils.isAllLowerCase("abc");  = true
StringUtils.isAllLowerCase("abC");  = false
StringUtils.isAllUpperCase("ABC");  = true
StringUtils.isAllUpperCase("aBC");  = false

4、判斷字符串是否以什么開頭/結尾

• startsWith(final CharSequence str, final CharSequence prefix)
• endsWith(final CharSequence str, final CharSequence suffix)

StringUtils.startsWith("abcdef", null);  = false
StringUtils.startsWith("abcdef", "abc"); = true
StringUtils.startsWith("ABCDEF", "abc"); = false
StringUtils.endsWith("ABCDEF", "def");   = false
StringUtils.endsWith("ABCDEF", "cde");   = false
StringUtils.endsWith("ABCDEF", "DEF");   = true

5、字符串反轉

• reverse(final String str)

StringUtils.reverse("bat"); = "tab"