isEmpty 和 isBlank 的用法区别，至少一半的人答不上来...-isblank和isempty的区别

isEmpty系列

StringUtils.isEmpty()

是否为空. 可以看到 " " 空格是会绕过这种空判断,因为是一个空格,并不是严格的空值,会导致 isEmpty(" ")=false

StringUtils.isEmpty(null) = true
StringUtils.isEmpty("") = true
StringUtils.isEmpty(" ") = false
StringUtils.isEmpty("bob") = false
StringUtils.isEmpty(" bob ") = false
/**
*
* <p>NOTE: This method changed in Lang version 2.0.
* It no longer trims the CharSequence.
* That functionality is available in isBlank().</p>
*
* @param cs  the CharSequence to check, may be null
* @return {@code true} if the CharSequence is empty or null
* @since 3.0 Changed signature from isEmpty(String) to isEmpty(CharSequence)
*/
public static boolean isEmpty(final CharSequence cs) {
   return cs == null || cs.length() == 0;
}

StringUtils.isNotEmpty()

相当于不为空 , = !isEmpty()。

public static boolean isNotEmpty(final CharSequence cs) {
       return !isEmpty(cs);
   }

StringUtils.isAnyEmpty()

是否有一个为空,只有一个为空,就为true

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
/**
* @param css  the CharSequences to check, may be null or empty
* @return {@code true} if any of the CharSequences are empty or null
* @since 3.2
*/
public static boolean isAnyEmpty(final CharSequence... css) {
 if (ArrayUtils.isEmpty(css)) {
   return true;
 }
 for (final CharSequence cs : css){
   if (isEmpty(cs)) {
     return true;
   }
 }
 return false;
}

StringUtils.isNoneEmpty()

相当于!isAnyEmpty(css) , 必须所有的值都不为空才返回true

/**
* <p>Checks if none of the CharSequences are empty ("") or null.</p>
*
* <pre>
* 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
* </pre>
*
* @param css  the CharSequences to check, may be null or empty
* @return {@code true} if none of the CharSequences are empty or null
* @since 3.2
*/
public static boolean isNoneEmpty(final CharSequence... css) {

isBank系列

StringUtils.isBlank()

是否为真空值(空格或者空值)

StringUtils.isBlank(null) = true
StringUtils.isBlank("") = true
StringUtils.isBlank(" ") = true
StringUtils.isBlank("bob") = false
StringUtils.isBlank(" bob ") = false
/**
* <p>Checks if a CharSequence is whitespace, empty ("") or null.</p>
* @param cs  the CharSequence to check, may be null
* @return {@code true} if the CharSequence is null, empty or whitespace
* @since 2.0
* @since 3.0 Changed signature from isBlank(String) to isBlank(CharSequence)
*/
public static boolean isBlank(final CharSequence cs) {
   int strLen;
   if (cs == null || (strLen = cs.length()) == 0) {
       return true;
   }
   for (int i = 0; i < strLen; i++) {
       if (Character.isWhitespace(cs.charAt(i)) == false) {
           return false;
       }
   }
   return true;
}

StringUtils.isNotBlank()

是否真的不为空,不是空格或者空值 ,相当于!isBlank();

public static boolean isNotBlank(final CharSequence cs) {
       return !isBlank(cs);
   }

StringUtils.isAnyBlank()

是否包含任何真空值(包含空格或空值)

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
/**
* <p>Checks if any one of the CharSequences are blank ("") or null and not whitespace only..</p>
* @param css  the CharSequences to check, may be null or empty
* @return {@code true} if any of the CharSequences are blank or null or whitespace only
* @since 3.2
*/
public static boolean isAnyBlank(final CharSequence... css) {
 if (ArrayUtils.isEmpty(css)) {
   return true;
 }
 for (final CharSequence cs : css){
   if (isBlank(cs)) {
     return true;
   }
 }
 return false;
}

StringUtils.isNoneBlank()

是否全部都不包含空值或空格。

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
/**
* <p>Checks if none of the CharSequences are blank ("") or null and whitespace only..</p>
* @param css  the CharSequences to check, may be null or empty
* @return {@code true} if none of the CharSequences are blank or null or whitespace only
* @since 3.2
*/
public static boolean isNoneBlank(final CharSequence... css) {
 return !isAnyBlank(css);
}

StringUtils的其他方法。

可以参考官方的文档,里面有详细的描述,有些方法还是很好用的。

https://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/StringUtils.html

方法名	英文解释	中文解释
IsEmpty/IsBlank	checks if a String contains text	检查字符串是否包含文本
Trim/Strip	removes leading and trailing whitespace	删除前导和尾随空格
Equals/Compare	compares two strings null-safe	比较两个字符串是否为null安全的
startsWith	check if a String starts with a prefix null-safe	检查字符串是否以前缀null安全开头
endsWith	check if a String ends with a suffix null-safe	检查字符串是否以后缀null安全结尾
IndexOf/LastIndexOf/Contains	null-safe index-of checks	包含空安全索引检查
IndexOfAny/LastIndexOfAny/IndexOfAnyBut/LastIndexOfAnyBut	index-of any of a set of Strings	任意一组字符串的索引
ContainsOnly/ContainsNone/ContainsAny	does String contains only/none/any of these characters	字符串是否仅包含/无/这些字符中的任何一个
Substring/Left/Right/Mid	null-safe substring extractions	字符串安全提取
SubstringBefore/SubstringAfter/SubstringBetween	substring extraction relative to other strings -相对其他字符串的字符串提取
Split/Join	splits a String into an array of substrings and vice versa	将字符串拆分为子字符串数组，反之亦然
Remove/Delete	removes part of a String -删除字符串的一部分
Replace/Overlay	Searches a String and replaces one String with another	搜索字符串，然后用另一个字符串替换
Chomp/Chop	removes the last part of a String	删除字符串的最后一部分
AppendIfMissing	appends a suffix to the end of the String if not present	如果不存在后缀，则在字符串的末尾附加一个后缀
PrependIfMissing	prepends a prefix to the start of the String if not present	如果不存在前缀，则在字符串的开头添加前缀
LeftPad/RightPad/Center/Repeat	pads a String	填充字符串
UpperCase/LowerCase/SwapCase/Capitalize/Uncapitalize	changes the case of a String	更改字符串的大小写
CountMatches	counts the number of occurrences of one String in another	计算一个字符串在另一个字符串中出现的次数
IsAlpha/IsNumeric/IsWhitespace/IsAsciiPrintable	checks the characters in a String	检查字符串中的字符
DefaultString	protects against a null input String	防止输入字符串为空
Rotate	rotate (circular shift) a String	旋转（循环移位）字符串
Reverse/ReverseDelimited	reverses a String -反转字符串
Abbreviate	abbreviates a string using ellipsis or another given String	使用省略号或另一个给定的String缩写一个字符串
Difference	compares Strings and reports on their differences	比较字符串并报告其差异
LevenshteinDistance	the number of changes needed to change one String into another	将一个String转换为另一个String所需的更改次数