commons-lang3工具类学习（三）

六、ObjectUtils

Object工具类

allNotNull(Object... values) 检查所有元素是否为空,返回一个boolean

如果有一个元素为空返回false，所有元素不为空或元素为empty返回true

ObjectUtils.allNotNull(*)             = true
ObjectUtils.allNotNull(*, *)          = true
ObjectUtils.allNotNull(null)          = false
ObjectUtils.allNotNull(null, null)    = false
ObjectUtils.allNotNull(null, *)       = false
ObjectUtils.allNotNull(*, null)       = false
ObjectUtils.allNotNull(*, *, null, *) = false

anyNotNull(Object... values) 检查元素是否为空,返回一个boolean

如果有一个元素不为空返回true

ObjectUtils.anyNotNull(*)                = true
ObjectUtils.anyNotNull(*, null)          = true
ObjectUtils.anyNotNull(null, *)          = true
ObjectUtils.anyNotNull(null, null, *, *) = true
ObjectUtils.anyNotNull(null)             = false
ObjectUtils.anyNotNull(null, null)       = false

clone(T obj) 拷贝一个对象并返回

compare(T c1, T c2) 比较两个对象,返回一个int值

defaultIfNull(T object, T defaultValue) 如果对象为空返回一个默认值

firstNonNull(T... values) 返回数组中第一个不为空的值

notEqual(Object object1, Object object2) 判断两个对象不相等，返回一个boolean

七、RandomUtils

随机工具类

nextBoolean() 返回一个随机boolean值

nextBytes(int count) 返回一个指定大小的随机byte数组

nextDouble() 返回一个随机double值

nextDouble(double startInclusive, double endInclusive) 返回一个指定范围的随机double值

nextFloat() 返回一个随机float值

nextFloat(float startInclusive, float endInclusive) 返回一个指定范围的随机float值

nextInt() 返回一个随机int值

nextInt(int startInclusive, int endExclusive) 返回一个指定范围的随机int值

nextLong() 返回一个随机long值

nextLong(long startInclusive, long endExclusive) 返回一个指定范围的随机long值

八、SystemUtils

操作系统工具类

FILE_ENCODING 返回系统编码

IS_JAVA_1_1、...、IS_JAVA_1_8、IS_JAVA_10、IS_JAVA_9 判断java版本,返回一个boolean

IS_OS_LINUX 判断系统是否是linux,返回一个boolean

IS_OS_MAC 判断系统是否是mac,返回一个boolean

IS_OS_WINDOWS、IS_OS_WINDOWS_10、 IS_OS_WINDOWS_2000、IS_OS_WINDOWS_2003、IS_OS_WINDOWS_2008、IS_OS_WINDOWS_7、 IS_OS_WINDOWS_8、 IS_OS_WINDOWS_95、 IS_OS_WINDOWS_98、 IS_OS_WINDOWS_XP 判断系统是否是windows,返回一个boolean

JAVA_CLASS_PATH 返回系统CLASS_PATH值

JAVA_CLASS_VERSION 返回系统java版本

JAVA_HOME 返回系统java home

JAVA_RUNTIME_VERSION 返回java运行版本

JAVA_VERSION 返回java版本

OS_NAME 返回系统名

OS_VERSION 返回系统版本

USER_COUNTRY 返回用户国家编号

USER_DIR 返回项目文件夹

USER_HOME 返回系统用户主文件夹

USER_LANGUAGE 返回系统用户语言

USER_NAME 返回系统用户名

九、StringUtils

字符串工具类

abbreviate(String str, int maxWidth) 返回一个指定长度加省略号的字符串，maxWidth必须大于3

StringUtils.abbreviate(null, *)      = null
StringUtils.abbreviate("", 4)        = ""
StringUtils.abbreviate("abcdefg", 6) = "abc..."
StringUtils.abbreviate("abcdefg", 7) = "abcdefg"
StringUtils.abbreviate("abcdefg", 8) = "abcdefg"
StringUtils.abbreviate("abcdefg", 4) = "a..."
StringUtils.abbreviate("abcdefg", 3) = IllegalArgumentException

abbreviate(String str, int offset, int maxWidth) 返回一个指定长度加省略号的字符串，maxWidth必须大于3

abbreviate(String str, String abbrevMarker, int maxWidth) 返回一个自定义省略号的指定长度字符串，maxWidth必须大于3

StringUtils.abbreviate(null, "...", *)      = null
StringUtils.abbreviate("abcdefg", null, *)  = "abcdefg"
StringUtils.abbreviate("", "...", 4)        = ""
StringUtils.abbreviate("abcdefg", ".", 5)   = "abcd."
StringUtils.abbreviate("abcdefg", ".", 7)   = "abcdefg"
StringUtils.abbreviate("abcdefg", ".", 8)   = "abcdefg"
StringUtils.abbreviate("abcdefg", "..", 4)  = "ab.."
StringUtils.abbreviate("abcdefg", "..", 3)  = "a.."
StringUtils.abbreviate("abcdefg", "..", 2)  = IllegalArgumentException
StringUtils.abbreviate("abcdefg", "...", 3) = IllegalArgumentException

abbreviateMiddle(String str, String abbrevMarker, int maxWidth) 将字符串缩短到指定长度（length），字符串的中间部分用替换字符串（middle）显示

StringUtils.abbreviateMiddle("abc", null, 0)      = "abc"
StringUtils.abbreviateMiddle("abc", ".", 0)      = "abc"
StringUtils.abbreviateMiddle("abc", ".", 3)      = "abc"
StringUtils.abbreviateMiddle("abcdef", ".", 4)     = "ab.f"

appendIfMissing(String str, CharSequence suffix, CharSequence... suffixes) 如果str不是以任何suffixes结尾，将字符串suffix拼接到字符串str后面

StringUtils.appendIfMissing(null, null) = null
StringUtils.appendIfMissing("abc", null) = "abc"
StringUtils.appendIfMissing("", "xyz") = "xyz"
StringUtils.appendIfMissing("abc", "xyz") = "abcxyz"
StringUtils.appendIfMissing("abcxyz", "xyz") = "abcxyz"
StringUtils.appendIfMissing("abcXYZ", "xyz") = "abcXYZxyz"

appendIfMissingIgnoreCase(String str, CharSequence suffix, CharSequence... suffixes) 同上 不区分大小写

capitalize(String str) 将字符串第一个字符大写并返回

center(String str, int size) 用空格字符填充使字符串str位于长度为size的大字符串中间

StringUtils.center(null, *)   = null
StringUtils.center("", 4)     = "    "
StringUtils.center("ab", -1)  = "ab"
StringUtils.center("ab", 4)   = " ab "
StringUtils.center("abcd", 2) = "abcd"
StringUtils.center("a", 4)    = " a  "

center(String str, int size, char padChar) 用指定字符填充使字符串str位于长度为size的大字符串中间

chomp(String str) 删除字符串末尾的一个换行符,返回一个新的字符串（换行符"n", "r", or "rn"）

StringUtils.chomp(null)          = null
StringUtils.chomp("")            = ""
StringUtils.chomp("abc \r")      = "abc "
StringUtils.chomp("abc\n")       = "abc"
StringUtils.chomp("abc\r\n")     = "abc"
StringUtils.chomp("abc\r\n\r\n") = "abc\r\n"
StringUtils.chomp("abc\n\r")     = "abc\n"
StringUtils.chomp("abc\n\rabc")  = "abc\n\rabc"
StringUtils.chomp("\r")          = ""
StringUtils.chomp("\n")          = ""
StringUtils.chomp("\r\n")        = ""

chop(String str) 删除字符串末尾的一个字符，返回一个新的字符串

StringUtils.chop(null)          = null
StringUtils.chop("")            = ""
StringUtils.chop("abc \r")      = "abc "
StringUtils.chop("abc\n")       = "abc"
StringUtils.chop("abc\r\n")     = "abc"
StringUtils.chop("abc")         = "ab"
StringUtils.chop("abc\nabc")    = "abc\nab"
StringUtils.chop("a")           = ""
StringUtils.chop("\r")          = ""
StringUtils.chop("\n")          = ""
StringUtils.chop("\r\n")        = ""

compare(String str1, String str2) 比较两个字符串，返回一个int值

str1等于str2（或都为空）返回0
str1小于str2返回小于0
str1大于str2返回大于0

StringUtils.compare(null, null)   = 0
StringUtils.compare(null , "a")   < 0
StringUtils.compare("a", null)    > 0
StringUtils.compare("abc", "abc") = 0
StringUtils.compare("a", "b")     < 0
StringUtils.compare("b", "a")     > 0
StringUtils.compare("a", "B")     > 0
StringUtils.compare("ab", "abc")  < 0

contains(CharSequence seq, CharSequence searchSeq) 检查字符串中是否包含指定字符，返回boolean

StringUtils.contains(null, *)     = false
StringUtils.contains(*, null)     = false
StringUtils.contains("", "")      = true
StringUtils.contains("abc", "")   = true
StringUtils.contains("abc", "a")  = true
StringUtils.contains("abc", "z")  = false

containsAny(CharSequence cs, CharSequence... searchCharSequences) 检查字符串中是否包含任一字符，返回boolean

StringUtils.containsAny(null, *)            = false
StringUtils.containsAny("", *)              = false
StringUtils.containsAny(*, null)            = false
StringUtils.containsAny(*, [])              = false
StringUtils.containsAny("abcd", "ab", null) = true
StringUtils.containsAny("abcd", "ab", "cd") = true
StringUtils.containsAny("abc", "d", "abc")  = true

containsNone(CharSequence cs, String invalidChars) 检查字符串不包含指定字符，返回boolean

StringUtils.containsNone(null, *)       = true
StringUtils.containsNone(*, null)       = true
StringUtils.containsNone("", *)         = true
StringUtils.containsNone("ab", "")      = true
StringUtils.containsNone("abab", "xyz") = true
StringUtils.containsNone("ab1", "xyz")  = true
StringUtils.containsNone("abz", "xyz")  = false

containsOnly(CharSequence cs, String validChars) 检查字符串只包含特定的字符，返回boolean

StringUtils.containsOnly(null, *)       = false
StringUtils.containsOnly(*, null)       = false
StringUtils.containsOnly("", *)         = true
StringUtils.containsOnly("ab", "")      = false
StringUtils.containsOnly("abab", "abc") = true
StringUtils.containsOnly("ab1", "abc")  = false
StringUtils.containsOnly("abz", "abc")  = false

containsWhitespace(CharSequence seq) 检查字符串中是否包含空格字符，返回boolean

countMatches(CharSequence str, CharSequence sub) 检查字符串中出现指定字符的次数，返回一个int值

StringUtils.countMatches(null, *)       = 0
StringUtils.countMatches("", *)         = 0
StringUtils.countMatches("abba", null)  = 0
StringUtils.countMatches("abba", "")    = 0
StringUtils.countMatches("abba", "a")   = 2
StringUtils.countMatches("abba", "ab")  = 1
StringUtils.countMatches("abba", "xxx") = 0

defaultIfBlank(T str, T defaultStr) 如果字符串为null、空（""），或全是空格，将返回指定字符串，否则返回原值

StringUtils.defaultIfBlank(null, "NULL")  = "NULL"
StringUtils.defaultIfBlank("", "NULL")    = "NULL"
StringUtils.defaultIfBlank(" ", "NULL")   = "NULL"
StringUtils.defaultIfBlank("bat", "NULL") = "bat"
StringUtils.defaultIfBlank("", null)      = null

defaultIfEmpty(T str, T defaultStr) 如果字符串为null、空（""），将返回指定字符串，否则返回原值

StringUtils.defaultIfEmpty(null, "NULL")  = "NULL"
StringUtils.defaultIfEmpty("", "NULL")    = "NULL"
StringUtils.defaultIfEmpty(" ", "NULL")   = " "
StringUtils.defaultIfEmpty("bat", "NULL") = "bat"
StringUtils.defaultIfEmpty("", null)      = null

defaultString(String str) 如果字符串为null，将返回空的字符串（""），否则返回原值

StringUtils.defaultString(null)  = ""
StringUtils.defaultString("")    = ""
StringUtils.defaultString("bat") = "bat"

defaultString(String str, String defaultStr) 如果字符串为null，将返回指定字符，否则返回原值

StringUtils.defaultString(null, "NULL")  = "NULL"
StringUtils.defaultString("", "NULL")    = ""
StringUtils.defaultString("bat", "NULL") = "bat"

deleteWhitespace(String str) 删除字符串中的空格字符，并返回新的字符串

StringUtils.deleteWhitespace(null)         = null
StringUtils.deleteWhitespace("")           = ""
StringUtils.deleteWhitespace("abc")        = "abc"
StringUtils.deleteWhitespace("   ab  c  ") = "abc"

difference(String str1, String str2) 比较两个字符串差异，并返回差异的字符，返回第二个字符串的剩余部分，这意味着“ABC”和“AB”之间的区别是空字符串而不是“C”。

StringUtils.difference(null, null) = null
StringUtils.difference("", "") = ""
StringUtils.difference("", "abc") = "abc"
StringUtils.difference("abc", "") = ""
StringUtils.difference("abc", "abc") = ""
StringUtils.difference("abc", "ab") = ""
StringUtils.difference("ab", "abxyz") = "xyz"
StringUtils.difference("abcde", "abxyz") = "xyz"
StringUtils.difference("abcde", "xyz") = "xyz"

endsWith(CharSequence str, CharSequence suffix) 检查字符串是否以指定字符结尾，返回一个boolean

StringUtils.endsWith(null, null)      = true
StringUtils.endsWith(null, "def")     = false
StringUtils.endsWith("abcdef", null)  = false
StringUtils.endsWith("abcdef", "def") = true
StringUtils.endsWith("ABCDEF", "def") = false
StringUtils.endsWith("ABCDEF", "cde") = false
StringUtils.endsWith("ABCDEF", "")    = true

endsWithAny(CharSequence sequence, CharSequence... searchStrings) 检查字符串是否以指定字符数组结尾，返回一个boolean

StringUtils.endsWithAny(null, null)      = false
StringUtils.endsWithAny(null, new String[] {"abc"})  = false
StringUtils.endsWithAny("abcxyz", null)     = false
StringUtils.endsWithAny("abcxyz", new String[] {""}) = true
StringUtils.endsWithAny("abcxyz", new String[] {"xyz"}) = true
StringUtils.endsWithAny("abcxyz", new String[] {null, "xyz", "abc"}) = true
StringUtils.endsWithAny("abcXYZ", "def", "XYZ") = true
StringUtils.endsWithAny("abcXYZ", "def", "xyz") = false

endsWithIgnoreCase(CharSequence str, CharSequence suffix) 检查字符串是否以指定字符（不区分大小写）结尾，返回一个boolean

StringUtils.endsWithIgnoreCase(null, null)      = true
StringUtils.endsWithIgnoreCase(null, "def")     = false
StringUtils.endsWithIgnoreCase("abcdef", null)  = false
StringUtils.endsWithIgnoreCase("abcdef", "def") = true
StringUtils.endsWithIgnoreCase("ABCDEF", "def") = true
StringUtils.endsWithIgnoreCase("ABCDEF", "cde") = false

equals(CharSequence cs1, CharSequence cs2) 比较两个字符串是否相等，返回一个boolean

StringUtils.equals(null, null)   = true
StringUtils.equals(null, "abc")  = false
StringUtils.equals("abc", null)  = false
StringUtils.equals("abc", "abc") = true
StringUtils.equals("abc", "ABC") = false

equalsAnyIgnoreCase(CharSequence string, CharSequence... searchStrings) 比较两个字符串是否相等（不区分大小写），返回一个boolean

StringUtils.equalsIgnoreCase(null, null)   = true
StringUtils.equalsIgnoreCase(null, "abc")  = false
StringUtils.equalsIgnoreCase("abc", null)  = false
StringUtils.equalsIgnoreCase("abc", "abc") = true
StringUtils.equalsIgnoreCase("abc", "ABC") = true

equalsAny(CharSequence string, CharSequence... searchStrings) 比较字符串是否与指定字符串数组中某一值相等，返回一个boolean

StringUtils.equalsAny(null, (CharSequence[]) null) = false
StringUtils.equalsAny(null, null, null)    = true
StringUtils.equalsAny(null, "abc", "def")  = false
StringUtils.equalsAny("abc", null, "def")  = false
StringUtils.equalsAny("abc", "abc", "def") = true
StringUtils.equalsAny("abc", "ABC", "DEF") = false

equalsAnyIgnoreCase(CharSequence string, CharSequence... searchStrings) 比较字符串是否与指定字符串数组中某一值相等（不区分大小写），返回一个boolean

StringUtils.equalsAnyIgnoreCase(null, (CharSequence[]) null) = false
StringUtils.equalsAnyIgnoreCase(null, null, null)    = true
StringUtils.equalsAnyIgnoreCase(null, "abc", "def")  = false
StringUtils.equalsAnyIgnoreCase("abc", null, "def")  = false
StringUtils.equalsAnyIgnoreCase("abc", "abc", "def") = true
StringUtils.equalsAnyIgnoreCase("abc", "ABC", "DEF") = true

getCommonPrefix(String... strs) 获取字符串数组元素公共字符，返回string

StringUtils.getCommonPrefix(null) = ""
StringUtils.getCommonPrefix(new String[] {}) = ""
StringUtils.getCommonPrefix(new String[] {"abc"}) = "abc"
StringUtils.getCommonPrefix(new String[] {null, null}) = ""
StringUtils.getCommonPrefix(new String[] {"", ""}) = ""
StringUtils.getCommonPrefix(new String[] {"", null}) = ""
StringUtils.getCommonPrefix(new String[] {"abc", null, null}) = ""
StringUtils.getCommonPrefix(new String[] {null, null, "abc"}) = ""
StringUtils.getCommonPrefix(new String[] {"", "abc"}) = ""
StringUtils.getCommonPrefix(new String[] {"abc", ""}) = ""
StringUtils.getCommonPrefix(new String[] {"abc", "abc"}) = "abc"
StringUtils.getCommonPrefix(new String[] {"abc", "a"}) = "a"
StringUtils.getCommonPrefix(new String[] {"ab", "abxyz"}) = "ab"
StringUtils.getCommonPrefix(new String[] {"abcde", "abxyz"}) = "ab"
StringUtils.getCommonPrefix(new String[] {"abcde", "xyz"}) = ""
StringUtils.getCommonPrefix(new String[] {"xyz", "abcde"}) = ""
StringUtils.getCommonPrefix(new String[] {"i am a machine", "i am a robot"}) = "i am a "

indexOf(CharSequence seq, CharSequence searchSeq) 检查指定字符在字符串中出现的位置，返回一个int值

StringUtils.indexOf(null, *)          = -1
StringUtils.indexOf(*, null)          = -1
StringUtils.indexOf("", "")           = 0
StringUtils.indexOf("", *)            = -1 (except when * = "")
StringUtils.indexOf("aabaabaa", "a")  = 0
StringUtils.indexOf("aabaabaa", "b")  = 2
StringUtils.indexOf("aabaabaa", "ab") = 1
StringUtils.indexOf("aabaabaa", "")   = 0

indexOfIgnoreCase(CharSequence seq, CharSequence searchSeq) 检查指定字符在字符串中出现的位置（不区分大小写），返回一个int值

isAllBlank(CharSequence... css) 检查数组所有字符是否为null、empty、或全是空格字符，返回一个boolean

StringUtils.isAllBlank(null)             = true
StringUtils.isAllBlank(null, "foo")      = false
StringUtils.isAllBlank(null, null)       = true
StringUtils.isAllBlank("", "bar")        = false
StringUtils.isAllBlank("bob", "")        = false
StringUtils.isAllBlank("  bob  ", null)  = false
StringUtils.isAllBlank(" ", "bar")       = false
StringUtils.isAllBlank("foo", "bar")     = false
StringUtils.isAllBlank(new String[] {})  = true

isAllEmpty(CharSequence... css) 检查数组所有字符是否为null、empty，返回一个boolean

StringUtils.isAllEmpty(null)             = true
StringUtils.isAllEmpty(null, "")         = true
StringUtils.isAllEmpty(new String[] {})  = true
StringUtils.isAllEmpty(null, "foo")      = false
StringUtils.isAllEmpty("", "bar")        = false
StringUtils.isAllEmpty("bob", "")        = false
StringUtils.isAllEmpty("  bob  ", null)  = false
StringUtils.isAllEmpty(" ", "bar")       = false
StringUtils.isAllEmpty("foo", "bar")     = false

isAllLowerCase(CharSequence cs) 检查字符串中所有字符是否是小写，返回一个boolean

isAllUpperCase(CharSequence cs) 检查字符串中所有字符是否是大写，返回一个boolean

isAnyBlank(CharSequence... css) 检查数组中字符串是否有一个为null、empty或全是空格字符，返回一个boolean

StringUtils.isAnyBlank(null)             = true
StringUtils.isAnyBlank(null, "foo")      = true
StringUtils.isAnyBlank(null, null)       = true
StringUtils.isAnyBlank("", "bar")        = true
StringUtils.isAnyBlank("bob", "")        = true
StringUtils.isAnyBlank("  bob  ", null)  = true
StringUtils.isAnyBlank(" ", "bar")       = true
StringUtils.isAnyBlank(new String[] {})  = false
StringUtils.isAnyBlank(new String[]{""}) = true
StringUtils.isAnyBlank("foo", "bar")     = false

isAnyEmpty(CharSequence... css) 检查数组中字符串是否有一个为null、empty，返回一个boolean

StringUtils.isAnyEmpty(null)             = true
StringUtils.isAnyEmpty(null, "foo")      = true
StringUtils.isAnyEmpty("", "bar")        = true
StringUtils.isAnyEmpty("bob", "")        = true
StringUtils.isAnyEmpty("  bob  ", null)  = true
StringUtils.isAnyEmpty(" ", "bar")       = false
StringUtils.isAnyEmpty("foo", "bar")     = false
StringUtils.isAnyEmpty(new String[]{})   = false
StringUtils.isAnyEmpty(new String[]{""}) = true

isBlank(CharSequence cs) 检查字符串是否为null、empty或空格字符，返回一个boolean

StringUtils.isBlank(null)      = true
StringUtils.isBlank("")        = true
StringUtils.isBlank(" ")       = true
StringUtils.isBlank("bob")     = false
StringUtils.isBlank("  bob  ") = false

isEmpty(CharSequence cs) 检查字符串是否为null、empty，返回一个boolean

StringUtils.isEmpty(null)      = true
StringUtils.isEmpty("")        = true
StringUtils.isEmpty(" ")       = false
StringUtils.isEmpty("bob")     = false
StringUtils.isEmpty("  bob  ") = false

isNotBlank(CharSequence cs) 检查字符串是否不为null、empty或空格字符，返回一个boolean

isNotEmpty(CharSequence cs) 检查字符串是否不为null、empty，返回一个boolean

isNumeric(CharSequence cs) 检查字符串是否是数字，返回一个boolean

StringUtils.isNumeric(null)   = false
StringUtils.isNumeric("")     = false
StringUtils.isNumeric("  ")   = false
StringUtils.isNumeric("123")  = true
StringUtils.isNumeric("१२३")  = true
StringUtils.isNumeric("12 3") = false
StringUtils.isNumeric("ab2c") = false
StringUtils.isNumeric("12-3") = false
StringUtils.isNumeric("12.3") = false
StringUtils.isNumeric("-123") = false
StringUtils.isNumeric("+123") = false

isWhitespace(CharSequence cs) 检查字符串是否是空格字符，返回一个boolean

StringUtils.isWhitespace(null)   = false
StringUtils.isWhitespace("")     = true
StringUtils.isWhitespace("  ")   = true
StringUtils.isWhitespace("abc")  = false
StringUtils.isWhitespace("ab2c") = false
StringUtils.isWhitespace("ab-c") = false

join(byte[] array, char separator) 将字节数组转换成string，以指定字符分隔

StringUtils.join(null, *)               = null
StringUtils.join([], *)                 = ""
StringUtils.join([null], *)             = ""
StringUtils.join([1, 2, 3], ';')  = "1;2;3"
StringUtils.join([1, 2, 3], null) = "123"

char、double、float、int、long、short、object、T同理

joinWith(String separator, Object... objects) 将多个元素已指定字符分隔拼接成String

StringUtils.joinWith(",", {"a", "b"})        = "a,b"
StringUtils.joinWith(",", {"a", "b",""})     = "a,b,"
StringUtils.joinWith(",", {"a", null, "b"})  = "a,,b"
StringUtils.joinWith(null, {"a", "b"})       = "ab"

lastIndexOf(CharSequence seq, CharSequence searchSeq) 获取指定字符在字符串中的最后一个索引位置

StringUtils.lastIndexOf(null, *)          = -1
StringUtils.lastIndexOf(*, null)          = -1
StringUtils.lastIndexOf("", "")           = 0
StringUtils.lastIndexOf("aabaabaa", "a")  = 7
StringUtils.lastIndexOf("aabaabaa", "b")  = 5
StringUtils.lastIndexOf("aabaabaa", "ab") = 4
StringUtils.lastIndexOf("aabaabaa", "")   = 8

left(String str, int len) 返回从左边开始指定大小的字符串

StringUtils.left(null, *)    = null
StringUtils.left(*, -ve)     = ""
StringUtils.left("", *)      = ""
StringUtils.left("abc", 0)   = ""
StringUtils.left("abc", 2)   = "ab"
StringUtils.left("abc", 4)   = "abc"

right(String str, int len) 同上相反

length(CharSequence cs) 获取字符串大小，返回一个int

lowerCase(String str) 将字符串转换为小写，返回一个string

StringUtils.lowerCase(null)  = null
StringUtils.lowerCase("")    = ""
StringUtils.lowerCase("aBc") = "abc"

upperCase(String str) 同上相反

mid(String str, int pos, int len) 获取字符串指定位置区间的字符，返回一个string

StringUtils.mid(null, *, *)    = null
StringUtils.mid(*, *, -ve)     = ""
StringUtils.mid("", 0, *)      = ""
StringUtils.mid("abc", 0, 2)   = "ab"
StringUtils.mid("abc", 0, 4)   = "abc"
StringUtils.mid("abc", 2, 4)   = "c"
StringUtils.mid("abc", 4, 2)   = ""
StringUtils.mid("abc", -2, 2)  = "ab"

overlay(String str, String overlay, int start, int end) 在字符串位置区间插入指定字符，返回一个string

StringUtils.overlay(null, *, *, *)            = null
StringUtils.overlay("", "abc", 0, 0)          = "abc"
StringUtils.overlay("abcdef", null, 2, 4)     = "abef"
StringUtils.overlay("abcdef", "", 2, 4)       = "abef"
StringUtils.overlay("abcdef", "", 4, 2)       = "abef"
StringUtils.overlay("abcdef", "zzzz", 2, 4)   = "abzzzzef"
StringUtils.overlay("abcdef", "zzzz", 4, 2)   = "abzzzzef"
StringUtils.overlay("abcdef", "zzzz", -1, 4)  = "zzzzef"
StringUtils.overlay("abcdef", "zzzz", 2, 8)   = "abzzzz"
StringUtils.overlay("abcdef", "zzzz", -2, -3) = "zzzzabcdef"
StringUtils.overlay("abcdef", "zzzz", 8, 10)  = "abcdefzzzz"

prependIfMissing(String str, CharSequence prefix, CharSequence... prefixes) 在字符串最左边插入指定字符，如果已存在，将不插入，返回一个string

StringUtils.prependIfMissing(null, null) = null
StringUtils.prependIfMissing("abc", null) = "abc"
StringUtils.prependIfMissing("", "xyz") = "xyz"
StringUtils.prependIfMissing("abc", "xyz") = "xyzabc"
StringUtils.prependIfMissing("xyzabc", "xyz") = "xyzabc"
StringUtils.prependIfMissing("XYZabc", "xyz") = "xyzXYZabc"

prependIfMissingIgnoreCase(String str, CharSequence prefix, CharSequence... prefixes) 同上，只是不区分大小写

remove(String str, char remove) 删除字符串中指定字符，返回一个string

StringUtils.remove(null, *)       = null
StringUtils.remove("", *)         = ""
StringUtils.remove("queued", 'u') = "qeed"
StringUtils.remove("queued", 'z') = "queued"

removeIgnoreCase(String str, String remove) 同上，只是不区分大小写

removeAll(String text, String regex) 根据匹配规则删除所有字符，返回一个string

StringUtils.removeAll(null, *)      = null
StringUtils.removeAll("any", null)  = "any"
StringUtils.removeAll("any", "")    = "any"
StringUtils.removeAll("any", ".*")  = ""
StringUtils.removeAll("any", ".+")  = ""
StringUtils.removeAll("abc", ".?")  = ""
StringUtils.removeAll("A<__>\n<__>B", "<.*>")      = "A\nB"
StringUtils.removeAll("A<__>\n<__>B", "(?s)<.*>")  = "AB"
StringUtils.removeAll("ABCabc123abc", "[a-z]")     = "ABC123"

removeEnd(String str, String remove) 删除字符串结尾指定字符，返回一个string

StringUtils.removeEnd(null, *)      = null
StringUtils.removeEnd("", *)        = ""
StringUtils.removeEnd(*, null)      = *
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.removeEnd("abc", "")    = "abc"

removeStart(String str, String remove) 同上相反

removeEndIgnoreCase(String str, String remove) 同上，只是不区分大小写

removeFirst(String text, String regex) 根据匹配规则删除第一次出现的字符，返回一个string

StringUtils.removeFirst(null, *)      = null
StringUtils.removeFirst("any", null)  = "any"
StringUtils.removeFirst("any", "")    = "any"
StringUtils.removeFirst("any", ".*")  = ""
StringUtils.removeFirst("any", ".+")  = ""
StringUtils.removeFirst("abc", ".?")  = "bc"
StringUtils.removeFirst("A<__>\n<__>B", "<.*>")      = "A\n<__>B"
StringUtils.removeFirst("A<__>\n<__>B", "(?s)<.*>")  = "AB"
StringUtils.removeFirst("ABCabc123", "[a-z]")          = "ABCbc123"
StringUtils.removeFirst("ABCabc123abc", "[a-z]+")      = "ABC123abc"

repeat(String str, int repeat) 将字符重复指定次数拼接成新的字符串，返回一个string

StringUtils.repeat(null, 2) = null
StringUtils.repeat("", 0)   = ""
StringUtils.repeat("", 2)   = ""
StringUtils.repeat("a", 3)  = "aaa"
StringUtils.repeat("ab", 2) = "abab"
StringUtils.repeat("a", -2) = ""

replace(String text, String searchString, String replacement) 用replacement替换字符串中的所有searchString，返回一个string

StringUtils.replace(null, *, *)        = null
StringUtils.replace("", *, *)          = ""
StringUtils.replace("any", null, *)    = "any"
StringUtils.replace("any", *, null)    = "any"
StringUtils.replace("any", "", *)      = "any"
StringUtils.replace("aba", "a", null)  = "aba"
StringUtils.replace("aba", "a", "")    = "b"
StringUtils.replace("aba", "a", "z")   = "zbz"

reverse(String str) 将字符串反转，返回一个string

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

reverseDelimited(String str, char separatorChar) 将字符串指定分隔符出的字符反转

 StringUtils.reverseDelimited(null, *)      = null
 StringUtils.reverseDelimited("", *)        = ""
 StringUtils.reverseDelimited("a.b.c", 'x') = "a.b.c"
 StringUtils.reverseDelimited("a.b.c", ".") = "c.b.a"

split(String str, String separatorChars) 将字符串以指定字符分隔，返回数组

StringUtils.split(null, *)         = null
StringUtils.split("", *)           = []
StringUtils.split("abc def", null) = ["abc", "def"]
StringUtils.split("abc def", " ")  = ["abc", "def"]
StringUtils.split("abc  def", " ") = ["abc", "def"]
StringUtils.split("ab:cd:ef", ":") = ["ab", "cd", "ef"]

substring(String str, int start) 将字符串从指定位置区间截取，返回string

swapCase(String str) 将字符串大小写互转，返回一个string

StringUtils.swapCase(null)                 = null
StringUtils.swapCase("")                   = ""
StringUtils.swapCase("The dog has a BONE") = "tHE DOG HAS A bone"

toEncodedString(byte[] bytes, Charset charset) 将字符串转为指定编码格式，返回一个string

trim(String str) 去除字符串空格

trimToEmpty(String str) 去除字符串空格，null转为empty，返回一个string

StringUtils.trimToEmpty(null)          = ""
StringUtils.trimToEmpty("")            = ""
StringUtils.trimToEmpty("     ")       = ""
StringUtils.trimToEmpty("abc")         = "abc"
StringUtils.trimToEmpty("    abc    ") = "abc"