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
