关于Spring框架中StringUtils常用/易误用方法解析

Spring 框架给我们提供的StringUtils是我们判断字符串常用的方法,
但是有很多人一直非空判断很混乱,下面做一下总结

方法/步骤

StringUtils.isEmpty(null) = true
StringUtils.isEmpty("") = true
StringUtils.isEmpty(" ") = false 
//注意在 StringUtils 中空格作非空处理
StringUtils.isEmpty("   ") = false
StringUtils.isEmpty("bob") = false
StringUtils.isEmpty(" bob ") = false


 StringUtils.hasText(null) = false;  
 StringUtils.hasText("") = false;  
 StringUtils.hasText(" ") = false;  
 StringUtils.hasText("12345") = true;  
 StringUtils.hasText(" 12345 ") = true;  


 StringUtils.hasLength(null) = false;  
 StringUtils.hasLength("") = false;  
 StringUtils.hasLength(" ") = true;  
 StringUtils.hasLength("Hello") = true;  
   
  
 //是否包含空白字符  
 StringUtils.containsWhitespace(null)=false;  
 StringUtils.containsWhitespace("")=false;  
 StringUtils.containsWhitespace("a")=false;  
 StringUtils.containsWhitespace("abc")=false;  
 StringUtils.containsWhitespace("abc")=false;  
 StringUtils.containsWhitespace(" ")=true;  
 StringUtils.containsWhitespace(" a")=true;  
 StringUtils.containsWhitespace("abc ")=true;  
 StringUtils.containsWhitespace("a b")=true  
 StringUtils.containsWhitespace("a  b")  
  
 StringUtils.trimWhitespace(null)=null;  
 StringUtils.trimWhitespace("")="";  
 StringUtils.trimWhitespace(" ")="";  
 StringUtils.trimWhitespace("/t")="";  
 StringUtils.trimWhitespace(" a")="a";  
 StringUtils.trimWhitespace("a ")="a";  
 StringUtils.trimWhitespace(" a ")="a";  
 StringUtils.trimWhitespace(" a b ")="a b";  
  
 StringUtils.trimLeadingWhitespace(null)=null;  
 StringUtils.trimLeadingWhitespace("")="";  
 StringUtils.trimLeadingWhitespace(" ")="";  
 StringUtils.trimLeadingWhitespace("/t")="";  
 StringUtils.trimLeadingWhitespace(" a")="a";  
 StringUtils.trimLeadingWhitespace("a ")="a ";  
 StringUtils.trimLeadingWhitespace(" a ")="a ";  
 StringUtils.trimLeadingWhitespace(" a b ")="a b "  
 StringUtils.trimLeadingWhitespace(" a b  c ")="a b  c "  
  
 StringUtils.trimTrailingWhitespace(null)=null;  
 StringUtils.trimTrailingWhitespace(" ")="";  
 StringUtils.trimTrailingWhitespace("/t")="";  
 StringUtils.trimTrailingWhitespace("a ")="a";  
 StringUtils.trimTrailingWhitespace(" a")=" a";  
 StringUtils.trimTrailingWhitespace(" a ")=" a";  
 StringUtils.trimTrailingWhitespace(" a b ")=" a b";  
 StringUtils.trimTrailingWhitespace(" a b  c ")=" a b  c";  
  
  
 StringUtils.trimAllWhitespace("")="";  
 StringUtils.trimAllWhitespace(" ")="";  
 StringUtils.trimAllWhitespace("/t")="";  
 StringUtils.trimAllWhitespace(" a")="a";  
 StringUtils.trimAllWhitespace("a ")="a";  
 StringUtils.trimAllWhitespace(" a ")="a";  
 StringUtils.trimAllWhitespace(" a b ")="ab";  
 StringUtils.trimAllWhitespace(" a b  c "="abc";  

 // 统计一个子字符串在字符串出现的次数  
 StringUtils.countOccurrencesOf(null, null) == 0;  
 StringUtils.countOccurrencesOf("s", null) == 0;  
 StringUtils.countOccurrencesOf(null, "s") == 0;  
 StringUtils.countOccurrencesOf("erowoiueoiur", "WERWER") == 0;  
 StringUtils.countOccurrencesOf("erowoiueoiur", "x")=0;  
 StringUtils.countOccurrencesOf("erowoiueoiur", " ") == 0;  
 StringUtils.countOccurrencesOf("erowoiueoiur", "") == 0;  
 StringUtils.countOccurrencesOf("erowoiueoiur", "e") == 2;  
 StringUtils.countOccurrencesOf("erowoiueoiur", "oi") == 2;  
 StringUtils.countOccurrencesOf("erowoiueoiur", "oiu") == 2;  
 StringUtils.countOccurrencesOf("erowoiueoiur", "oiur") == 1;  
 StringUtils.countOccurrencesOf("erowoiueoiur", "r") == 2;  
  
 //字符串替换  
 String inString = "a6AazAaa77abaa";  
 String oldPattern = "aa";  
 String newPattern = "foo";  
 // Simple replace  
 String s = StringUtils.replace(inString, oldPattern, newPattern);  
 s.equals("a6AazAfoo77abfoo")=true;  
  
 // Non match: no change  
 s = StringUtils.replace(inString, "qwoeiruqopwieurpoqwieur", newPattern);  
 s.equals(inString)=true  
 s = StringUtils.replace(inString, oldPattern, null);  
 s.equals(inString)=true  
  
 // Null old pattern: should ignore  
 s = StringUtils.replace(inString, null, newPattern);  
        s.equals(inString)=true  
  
 //删除字符串  
 String inString = "The quick brown fox jumped over the lazy dog";  
 String noThe = StringUtils.delete(inString, "the");  
 noThe.equals("The quick brown fox jumped over  lazy dog")=true;  
 String nohe = StringUtils.delete(inString, "he");  
 nohe.equals("T quick brown fox jumped over t lazy dog")=true;  
 String nosp = StringUtils.delete(inString, " ");  
 nosp.equals("Thequickbrownfoxjumpedoverthelazydog")=true;  
 String killEnd = StringUtils.delete(inString, "dog");  
 killEnd.equals("The quick brown fox jumped over the lazy ")=true;  
 String mismatch = StringUtils.delete(inString, "dxxcxcxog");  
  mismatch.equals(inString)=true;  
  
 //删除任何字符  
 //源代码如下  
 //char c = inString.charAt(i);  
 //如果不存在 c 值，则返回 -1  
 //if (charsToDelete.indexOf(c) == -1) {  
 //out.append(c);  
 //}  
  
 String inString = "Able was I ere I saw Elba";  
  
 String res = StringUtils.deleteAny(inString, "I");  
        res.equals("Able was  ere  saw Elba")=true;  
 res = StringUtils.deleteAny(inString, "AeEba!");  
 res.equals("l ws I r I sw l")=true;  
 String mismatch = StringUtils.deleteAny(inString, "#@$#$^");  
 mismatch.equals(inString)=true;  
  
 //源代码如下 return (str != null ? "'" + str + "'" : null);  
 assertEquals("'myString'", StringUtils.quote("myString"));  
 assertEquals("''", StringUtils.quote(""));  
 assertNull(StringUtils.quote(null));  
 //将第一个字符改大写  
 StringUtils.capitalize(Str)  
 //将第一个个字符改小写  
 StringUtils.uncapitalize(str)  
  
 //mypath/myfile.txt" -> "myfile.txt  
 //获取字符串文件名和扩展名  
 StringUtils.getFilename("myfile").equals("myfile")=true;  
 StringUtils.getFilename("mypath/myfile".equals("myfile")=true;  
 StringUtils.getFilename("mypath/myfile".equals("myfile")=true;  
 StringUtils.getFilename("myfile.txt").equals("myfile.txt")=true;  
 StringUtils.getFilename("mypath/myfile.txt").equals("myfile.txt")=true;  
  
 // 获取字符串扩展名,以.分隔  
 StringUtils.getFilenameExtension("myfile")=null;  
 StringUtils.getFilenameExtension("myPath/myfile")=null;  
 StringUtils.getFilenameExtension("myfile.").equals("")=true;  
 StringUtils.getFilenameExtension("myPath/myfile.").equals("")=true;  
 StringUtils.StringUtils.getFilenameExtension("myfile.txt").equals("txt")=true;  
 StringUtils.getFilenameExtension("mypath/myfile.txt").equals("txt")=true;  
  
 //舍去文件名扩展名  
 StringUtils.stripFilenameExtension(null)=true;  
 StringUtils.stripFilenameExtension("").equals("")=true;  
 StringUtils.stripFilenameExtension("myfile").equals("myfile")=true;  
 StringUtils.stripFilenameExtension("mypath/myfile").equals("mypath/myfile")=true;  
 StringUtils.stripFilenameExtension("myfile.").equals("myfile")=true;  
 StringUtils.stripFilenameExtension("mypath/myfile.").equals("mypath/myfile")=true;  
 StringUtils.stripFilenameExtension("mypath/myfile.").equals("mypath/myfile")=true;  
 StringUtils.stripFilenameExtension("myfile.txt").equals("myfile")=true;  
 StringUtils.stripFilenameExtension("mypath/myfile.txt").equals("mypath/myfile")=true

结论

StringUtils.isEmpty() 方法是判断不了空格的,所以要慎重用这个方法
StringUtils.hasText() 可以使用这个方法判断是否有内容,但是使用里面值的时候注意要trim掉左右空格