CommonLang3 中的 StringUtils 最全解析

public static boolean isEmpty(CharSequence cs)

常用函数之一，判断字符串是否为""或者 null

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

public static boolean isNotEmpty(CharSequence cs)

最常用函数之一，跟上面方法相对

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

public static boolean isAnyEmpty(CharSequence... css)

任意一个参数为空的话，返回 true，

如果这些参数都不为空的话返回 false。

在写一些判断条件的时候，这个方法还是很实用的。

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

public static boolean isNoneEmpty(CharSequence... css)

任意一个参数是空，返回 false

所有参数都不为空，返回 true

注意这些方法的用法

StringUtils.isNoneEmpty(null) = false
StringUtils.isNoneEmpty(null, "foo") = false
StringUtils.isNoneEmpty("", "bar") = false
StringUtils.isNoneEmpty("bob", "") = false
StringUtils.isNoneEmpty(" bob ", null) = false
StringUtils.isNoneEmpty(" ", "bar") = true
StringUtils.isNoneEmpty("foo", "bar") = true

public static boolean isBlank(CharSequence cs)

判断字符对象是不是空字符串，注意与 isEmpty 的区别

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

public static boolean isNotBlank(CharSequence cs)

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

原理同上

public static boolean isAnyBlank(CharSequence... css)

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("foo", "bar") = false

public static boolean isNoneBlank(CharSequence... css)

StringUtils.isNoneBlank(null) = false
StringUtils.isNoneBlank(null, "foo") = false
StringUtils.isNoneBlank(null, null) = false
StringUtils.isNoneBlank("", "bar") = false
StringUtils.isNoneBlank("bob", "") = false
StringUtils.isNoneBlank(" bob ", null) = false
StringUtils.isNoneBlank(" ", "bar") = false
StringUtils.isNoneBlank("foo", "bar") = true

public static String trim(String str)

移除字符串两端的空字符串，制表符 char <= 32 如：\n \t

如果为空的话，返回空

如果为""

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

变体有

public static String trimToNull(String str)

public static String trimToEmpty(String str)

不常用，跟 trim()方法类似

public static String strip(String str)

public static String strip(String str,
String stripChars)

str：被处理的字符串，可为空

stripChars： 删除的字符串，

StringUtils.strip(null, *) = null
StringUtils.strip("", *) = ""
StringUtils.strip("abc", null) = "abc"
StringUtils.strip(" abc", null) = "abc"
StringUtils.strip("abc ", null) = "abc"
StringUtils.strip(" abc ", null) = "abc"
StringUtils.strip(" abcyx", "xyz") = " abc"

public static boolean equals(CharSequence cs1,
CharSequence cs2)

字符串比对方法，是比较实用的方法之一，两个比较的字符串都能为空，不会报空指针异常。

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

public static boolean equalsIgnoreCase(CharSequence str1,
CharSequence str2)

上面方法的变体

字符串比较（忽略大小写），在验证码……等字符串比较，真是很实用。

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

public static int indexOf(CharSequence seq,
int searchChar)

indexOf 这个方法不必多说，这个方法主要处理掉了空字符串的问题，不会报空指针，有一定用处

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

public static int ordinalIndexOf(CharSequence str,
CharSequence searchStr,
int ordinal)

字符串在另外一个字符串里，出现第 Ordinal 次的位置

StringUtils.ordinalIndexOf(null, *, ) = -1
StringUtils.ordinalIndexOf(, null, *) = -1
StringUtils.ordinalIndexOf("", "", *) = 0
StringUtils.ordinalIndexOf("aabaabaa", "a", 1) = 0
StringUtils.ordinalIndexOf("aabaabaa", "a", 2) = 1
StringUtils.ordinalIndexOf("aabaabaa", "b", 1) = 2
StringUtils.ordinalIndexOf("aabaabaa", "b", 2) = 5
StringUtils.ordinalIndexOf("aabaabaa", "ab", 1) = 1
StringUtils.ordinalIndexOf("aabaabaa", "ab", 2) = 4
StringUtils.ordinalIndexOf("aabaabaa", "", 1) = 0
StringUtils.ordinalIndexOf("aabaabaa", "", 2) = 0

public static int lastIndexOf(CharSequence seq,
int searchChar)

字符串最后一次出现的位置

StringUtils.lastIndexOf(null, *) = -1
StringUtils.lastIndexOf("", *) = -1
StringUtils.lastIndexOf("aabaabaa", 'a') = 7
StringUtils.lastIndexOf("aabaabaa", 'b') = 5

public static int lastOrdinalIndexOf(CharSequence str,
CharSequence searchStr,
int ordinal)

字符串 searchStr 在 str 里面出现倒数第 ordinal 出现的位置

StringUtils.lastOrdinalIndexOf(null, *, ) = -1
StringUtils.lastOrdinalIndexOf(, null, *) = -1
StringUtils.lastOrdinalIndexOf("", "", *) = 0
StringUtils.lastOrdinalIndexOf("aabaabaa", "a", 1) = 7
StringUtils.lastOrdinalIndexOf("aabaabaa", "a", 2) = 6
StringUtils.lastOrdinalIndexOf("aabaabaa", "b", 1) = 5
StringUtils.lastOrdinalIndexOf("aabaabaa", "b", 2) = 2
StringUtils.lastOrdinalIndexOf("aabaabaa", "ab", 1) = 4
StringUtils.lastOrdinalIndexOf("aabaabaa", "ab", 2) = 1
StringUtils.lastOrdinalIndexOf("aabaabaa", "", 1) = 8
StringUtils.lastOrdinalIndexOf("aabaabaa", "", 2) = 8

public static boolean contains(CharSequence seq,
int searchChar)

字符串 seq 是否包含 searchChar

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

public static boolean containsAny(CharSequence cs,
char... searchChars)

包含后面数组中的任意对象，返回 true

StringUtils.containsAny(null, ) = false
StringUtils.containsAny("", ) = false
StringUtils.containsAny(, null) = false
StringUtils.containsAny(, []) = false
StringUtils.containsAny("zzabyycdxx",['z','a']) = true
StringUtils.containsAny("zzabyycdxx",['b','y']) = true
StringUtils.containsAny("aba", ['z']) = false

public static String substring(String str,
int start)

字符串截取

StringUtils.substring(null, *) = null
StringUtils.substring("", *) = ""
StringUtils.substring("abc", 0) = "abc"
StringUtils.substring("abc", 2) = "c"
StringUtils.substring("abc", 4) = ""
StringUtils.substring("abc", -2) = "bc"
StringUtils.substring("abc", -4) = "abc"

public static String left(String str,
int len)

public static String right(String str,
int len)

public static String mid(String str,
int pos,
int len)

这三个方法类似都是截取字符串

public static String[] split(String str,
String separatorChars)

字符串分割

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💿ef", ":") = ["ab", "cd", "ef"]

public static String join(T... elements)

字符串连接

StringUtils.join(null) = null
StringUtils.join([]) = ""
StringUtils.join([null]) = ""
StringUtils.join(["a", "b", "c"]) = "abc"
StringUtils.join([null, "", "a"]) = "a"

public static String join(Object[] array,
char separator)

特定字符串连接数组，很多情况下还是蛮实用，不用自己取拼字符串

StringUtils.join(null, *) = null
StringUtils.join([], *) = ""
StringUtils.join([null], *) = ""
StringUtils.join(["a", "b", "c"], ';') = "a;b;c"
StringUtils.join(["a", "b", "c"], null) = "abc"
StringUtils.join([null, "", "a"], ';') = ";;a"

public static String deleteWhitespace(String str)

删除空格

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

public static String removeStart(String str,
String remove)

删除以特定字符串开头的字符串，如果没有的话，就不删除。

StringUtils.removeStart(null, *) = null
StringUtils.removeStart("", ) = ""
StringUtils.removeStart(, null) = *
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"

public static String rightPad(String str,
int size,
char padChar)

生成订单号，的时候还是很实用的。右边自动补齐。

StringUtils.rightPad(null, *, *) = null
StringUtils.rightPad("", 3, 'z') = "zzz"
StringUtils.rightPad("bat", 3, 'z') = "bat"
StringUtils.rightPad("bat", 5, 'z') = "batzz"
StringUtils.rightPad("bat", 1, 'z') = "bat"
StringUtils.rightPad("bat", -1, 'z') = "bat"

public static String leftPad(String str,
int size,
char padChar)

左边自动补齐

StringUtils.leftPad(null, *, *) = null
StringUtils.leftPad("", 3, 'z') = "zzz"
StringUtils.leftPad("bat", 3, 'z') = "bat"
StringUtils.leftPad("bat", 5, 'z') = "zzbat"
StringUtils.leftPad("bat", 1, 'z') = "bat"
StringUtils.leftPad("bat", -1, 'z') = "bat"

public static String center(String str,
int size)

将字符在某特定长度下，句子

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 "

public static String capitalize(String str)

首字母大写

StringUtils.capitalize(null) = null
StringUtils.capitalize("") = ""
StringUtils.capitalize("cat") = "Cat"
StringUtils.capitalize("cAt") = "CAt"

public static String swapCase(String str)

反向大小写

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

public static boolean isAlpha(CharSequence cs)

判断字符串是否由字母组成

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

public static String defaultString(String str,
String defaultStr)

默认字符串，相当于三目运算，前面弱为空，则返回后面一个参数

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

public static String reverse(String str)

字符串翻转

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

public static String abbreviate(String str,
int maxWidth)

缩略字符串，

省略号要占三位。maxWith 小于 3 位会报错。

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

public static String abbreviate(String str,
int offset,
int maxWidth)

缩略字符串的一些高级用法

StringUtils.abbreviate(null, *, *) = null
StringUtils.abbreviate("", 0, 4) = ""
StringUtils.abbreviate("abcdefghijklmno", -1, 10) = "abcdefg..."
StringUtils.abbreviate("abcdefghijklmno", 0, 10) = "abcdefg..."
StringUtils.abbreviate("abcdefghijklmno", 1, 10) = "abcdefg..."
StringUtils.abbreviate("abcdefghijklmno", 4, 10) = "abcdefg..."
StringUtils.abbreviate("abcdefghijklmno", 5, 10) = "...fghi..."
StringUtils.abbreviate("abcdefghijklmno", 6, 10) = "...ghij..."
StringUtils.abbreviate("abcdefghijklmno", 8, 10) = "...ijklmno"
StringUtils.abbreviate("abcdefghijklmno", 10, 10) = "...ijklmno"
StringUtils.abbreviate("abcdefghijklmno", 12, 10) = "...ijklmno"
StringUtils.abbreviate("abcdefghij", 0, 3) = IllegalArgumentException
StringUtils.abbreviate("abcdefghij", 5, 6) = IllegalArgumentException

public static String wrap(String str,
char wrapWith)

包装，用后面的字符串对前面的字符串进行包装

StringUtils.wrap(null, *) = null
StringUtils.wrap("", *) = ""
StringUtils.wrap("ab", '\0') = "ab"
StringUtils.wrap("ab", 'x') = "xabx"
StringUtils.wrap("ab", ''') = "'ab'"
StringUtils.wrap(""ab"", '"') = """ab"""