isEmpty 和 isBlank 请别乱用了，小心把服务器搞崩

科技 07-13 来源：程序猿阿嘴

大家好，我是程序汪，开发中经常有些小细节容易忽略，这些小细节往往容易导致代码缺陷，今天分享一波工具类的小细节

也许你两个都不知道,也许你除了isEmpty/isNotEmpty/isNotBlank/isBlank外,并不知道还有isAnyEmpty/isNoneEmpty/isAnyBlank/isNoneBlank的存在, come on ,让我们一起来探索org.apache.commons.lang3.StringUtils;这个工具类。

isEmpty系列

StringUtils.isEmpty()

是否为空. 可以看到 " " 空格是会绕过这种空格判断,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
/**
 *
 * NOTE: This method changed in Lang version 2.0.
 * It no longer trims the CharSequence.
 * That functionality is available in isBlank().
 *
 * @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

/**
 * Checks if none of the CharSequences are empty ("") or null.
 *
 *  * 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
 * 
 *
 * @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
/**
 * Checks if a CharSequence is whitespace, empty ("") or null.
 * @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
 /**
 * Checks if any one of the CharSequences are blank ("") or null and not whitespace only..
 * @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
/**
 * Checks if none of the CharSequences are blank ("") or null and whitespace only..
 * @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/IsBlankchecks if a String contains text检查字符串是否包含文本Trim/Stripremoves leading and trailing whitespace删除前导和尾随空格Equals/Comparecompares two strings null-safe比较两个字符串是否为null安全的startsWithcheck if a String starts with a prefix null-safe检查字符串是否以前缀null安全开头endsWithcheck 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/Containsnull-safe index-of checks包含空安全索引检查IndexOfAny/LastIndexOfAny/IndexOfAnyBut/LastIndexOfAnyButindex-of any of a set of Strings任意一组字符串的索引ContainsOnly/ContainsNone/ContainsAnydoes 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/Midnull-safe substring extractions字符串安全提取SubstringBefore/SubstringAfter/SubstringBetweensubstring extraction relative to other strings -相对其他字符串的字符串提取
Split/Joinsplits 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/Deleteremoves part of a String -删除字符串的一部分
Replace/OverlaySearches 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/Chopremoves the last part of a String删除字符串的最后一部分AppendIfMissingappends 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PrependIfMissingprepends 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/Repeatpads a String填充字符串UpperCase/LowerCase/SwapCase/Capitalize/Uncapitalizechanges the case of a String更改字符串的大小写CountMatchescounts 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/IsAsciiPrintablechecks the characters in a String检查字符串中的字符DefaultStringprotects against a null input String防止输入字符串为空Rotaterotate (circular shift) a String旋转（循环移位）字符串Reverse/ReverseDelimitedreverses a String -反转字符串
Abbreviateabbreviates 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Differencecompares Strings and reports on their differences比较字符串并报告其差异LevenshteinDistancethe 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