blocks|key|3033624|text|我能想到的最短的解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3033625|if+(string.trim().length()+>+0)+...|code-block|syntax|javascript|3033626|这只检查(非)空格。如果您想要检查特定的字符类，则需要使用功能强大的match()和正则表达式，例如：|offset|length|style|CODE|3033627|if+(string.matches(".*\\w.*"))+...|3033628|...which检查至少一个(ASCII)字母数字字符。|3033629|entityMap^0|0|0|Y|7|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@$I|V|J|W|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Shortest solution I can think of:

<pre><code>if (string.trim().length() &gt; 0) ...
</code></pre>

This only checks for (non) white space. If you want to check for particular character classes, you need to use the mighty <code>match()</code> with a regexp such as:

<pre><code>if (string.matches(".*\\w.*")) ...
</code></pre>

...which checks for at least one (ASCII) alphanumeric character.

blocks|key|305414|text|StringUtils.isBlank(CharSequence)|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|305415|https://commons.apache.org/proper/commons-lang/javadocs/api-release/org/apache/commons/lang3/StringUtils.html#isBlank-java.lang.CharSequence-|unstyled|offset|length|305416|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|3X|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|Q|8|@]|9|@$G|R|H|S|1|T]]|A|$]]|$1|I|3|-4|5|F|7|U|8|@]|9|@]|A|$]]]|J|$K|$5|L|M|N|A|$O|E]]]]

<pre><code>StringUtils.isBlank(CharSequence)
</code></pre>

<a href="https://commons.apache.org/proper/commons-lang/javadocs/api-release/org/apache/commons/lang3/StringUtils.html#isBlank-java.lang.CharSequence-" rel="nofollow noreferrer">https://commons.apache.org/proper/commons-lang/javadocs/api-release/org/apache/commons/lang3/StringUtils.html#isBlank-java.lang.CharSequence-</a>

blocks|key|305425|text|trim方法应该非常适合您。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|305426|http://download.oracle.com/docs/cd/E17476_01/javase/1.4.2/docs/api/java/lang/String.html#trim()|offset|length|305427|305428|返回字符串的副本，省略了前导空格和尾随空格。如果此String对象表示空字符序列，或者此String对象表示的字符序列的第一个和最后一个字符的代码都大于'\u0020‘(空格字符)，则返回对此String对象的引用。|blockquote|305429|305430|否则，如果字符串中没有代码大于'\u0020‘的字符，则创建并返回一个表示空字符串的新字符串对象。|305431|否则，设k是代码大于'\u0020‘的字符串的第一个字符的索引，m是代码大于'\u0020’的字符串的最后一个字符的索引。将创建一个新的String对象，表示该字符串的子字符串，该子字符串以索引k处的字符开始，以索引m处的字符结束-即this.substring(k，m%2B1)的结果。|305432|此方法可用于从字符串的开头和结尾修剪空格；实际上，它还修剪所有ASCII控制字符。|305433|返回:删除了前导空格和尾随空格的此字符串的副本，如果此字符串没有前导或尾随空格或尾随空格，则返回此字符串。|305434|305435|您可以裁剪然后与空字符串进行比较，或者可能检查长度是否为0。|305436|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|2N|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@]|9|@$D|14|E|15|1|16]]|A|$]]|$1|F|3|-4|5|6|7|17|8|@]|9|@]|A|$]]|$1|G|3|H|5|I|7|18|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|19|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1A|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|1B|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1C|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1D|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|T|3|U|5|6|7|1F|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|W|$X|$5|Y|Z|10|A|$11|C]]]]

The trim method should work great for you.

<a href="http://download.oracle.com/docs/cd/E17476_01/javase/1.4.2/docs/api/java/lang/String.html#trim()" rel="nofollow noreferrer">http://download.oracle.com/docs/cd/E17476_01/javase/1.4.2/docs/api/java/lang/String.html#trim()</a>

<blockquote>
 Returns a copy of the string, with
 leading and trailing whitespace
 omitted. If this String object
 represents an empty character
 sequence, or the first and last
 characters of character sequence
 represented by this String object both
 have codes greater than '\u0020' (the
 space character), then a reference to
 this String object is returned.
 
 Otherwise, if there is no character
 with a code greater than '\u0020' in
 the string, then a new String object
 representing an empty string is
 created and returned.
 
 Otherwise, let k be the index of the
 first character in the string whose
 code is greater than '\u0020', and let
 m be the index of the last character
 in the string whose code is greater
 than '\u0020'. A new String object is
 created, representing the substring of
 this string that begins with the
 character at index k and ends with the
 character at index m-that is, the
 result of this.substring(k, m+1).
 
 This method may be used to trim
 whitespace from the beginning and end
 of a string; in fact, it trims all
 ASCII control characters as well.
 
 Returns: A copy of this string with
 leading and trailing white space
 removed, or this string if it has no
 leading or trailing white space.leading or trailing white space.
</blockquote>

You could trim and then compare to an empty string or possibly check the length for 0.

blocks|key|3033684|text|我会使用Apache+Commons+Lang库。它有一个名为StringUtils的类，对于所有类型的字符串操作都很有用。要检查字符串是否全部为空格，可以使用以下命令：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3033685|StringUtils.isBlank(<your+string>)|code-block|syntax|javascript|3033686|下面是参考：StringUtils.isBlank|offset|length|3033687|entityMap|0|LINK|mutability|MUTABLE|url|https://commons.apache.org/proper/commons-lang/javadocs/api-release/org/apache/commons/lang3/StringUtils.html#isBlank-java.lang.CharSequence-^0|0|0|6|J|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

I would use the Apache Commons Lang library. It has a class called StringUtils that is useful for all sorts of String operations. For checking if a String is not all whitespaces, you can use the following:

<pre><code>StringUtils.isBlank(&lt;your string&gt;)
</code></pre>

Here is the reference: <a href="https://commons.apache.org/proper/commons-lang/javadocs/api-release/org/apache/commons/lang3/StringUtils.html#isBlank-java.lang.CharSequence-" rel="noreferrer">StringUtils.isBlank</a>

blocks|key|3247902|text|这个答案更侧重于旁注“即至少有一个字母数字字符”。除此之外，它不会给其他(更早的)解决方案增加太多东西，除了在字符串为null的情况下，它不会对NPE造成伤害。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3247903|如果(1)+s为null或(2)+s为空或(3)+s仅包含白字符，我们需要false。|3247904|public+static+boolean+containsNonWhitespaceChar(String+s)+{
++return+!((s+==+null)+%7C%7C+"".equals(s.trim()));
}|code-block|syntax|javascript|3247905|entityMap^0|1N|4|0|8|4|11|5|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|X|8|@]|D|@]|E|$]]]|N|$]]

This answer focusses more on the sidenote "i.e. has at least one alphanumeric character". Besides that, it doesn't add too much to the other (earlier) solution, except that it doesn't hurt you with NPE in case the String is <code>null</code>. 

We want <code>false</code> if (1) s is <code>null</code> or (2) s is empty or (3) s only contains whitechars.

<pre><code>public static boolean containsNonWhitespaceChar(String s) {
 return !((s == null) || "".equals(s.trim()));
}
</code></pre>

blocks|key|303432|text|替代方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|303433|boolean+isWhiteSpaces(+String+s+)+{
++++return+s+!=+null+&&+s.matches("\\s%2B");
+}|code-block|syntax|javascript|303434|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Alternative: 

<pre><code>boolean isWhiteSpaces( String s ) {
 return s != null &amp;&amp; s.matches("\\s+");
 }
</code></pre>

blocks|key|303445|text|比Carl+Smotricz提到的略短一些：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|303446|!string.trim().isEmpty();|code-block|syntax|javascript|303447|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Slightly shorter than what was mentioned by Carl Smotricz:

<pre><code>!string.trim().isEmpty();
</code></pre>

blocks|key|3247963|text|if(target.matches("\\S"))+
++++//+then+string+contains+at+least+one+non-whitespace+character|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3247964|注意使用反斜杠cap-S，意思是“非空格字符”|unstyled|3247965|我敢打赌这是最简单的(也许也是最快的？)解决方案。|3247966|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>if(target.matches("\\S")) 
 // then string contains at least one non-whitespace character
</code></pre>

Note use of back-slash cap-S, meaning "non-whitespace char"

I'd wager this is the simplest (and perhaps the fastest?) solution.

blocks|key|3033933|text|如果您只检查空格而不关心null，那么您可以使用org.apache.commons.lang.StringUtils.isWhitespace(String字符串，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3033934|StringUtils.isWhitespace(String+str);|offset|length|style|CODE|3033935|(检查字符串是否仅包含空格。)|3033936|如果您还想检查null(包括空格)，那么|3033937|StringUtils.isBlank(String+str);|code-block|syntax|javascript|3033938|entityMap^0|0|0|11|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@$D|U|E|V|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|W|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|X|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|Y|8|@]|9|@]|A|$O|P]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

If you are only checking for whitespace and don't care about null then you can use org.apache.commons.lang.StringUtils.isWhitespace(String str), 

<code>StringUtils.isWhitespace(String str);</code>

(Checks if the String contains only whitespace.)

If you also want to check for null(including whitespace) then

<pre><code>StringUtils.isBlank(String str);
</code></pre>

blocks|key|3033960|text|trim()和其他提到的正则表达式并不适用于所有类型的空格|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3033961|即:+Unicode字符‘行分隔符’http://www.fileformat.info/info/unicode/char/2028/index.htm|offset|length|3033962|Java函数Character.isWhitespace()涵盖了所有情况。|3033963|这就是为什么应该使用前面提到的solution+StringUtils.isWhitespace(+String+)+/or+StringUtils.isBlank(String)的原因。|style|BOLD|3033964|entityMap|0|LINK|mutability|MUTABLE|url|http://www.fileformat.info/info/unicode/char/2028/index.htm^0|0|I|1N|0|0|0|O|Y|1N|V|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@]|9|@$D|V|E|W|1|X]]|A|$]]|$1|F|3|G|5|6|7|Y|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|Z|8|@$D|10|E|11|J|K]|$D|12|E|13|J|K]]|9|@]|A|$]]|$1|L|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|M|$N|$5|O|P|Q|A|$R|S]]]]

trim() and other mentioned regular expression do not work for all types of whitespaces

i.e: Unicode Character 'LINE SEPARATOR' <a href="http://www.fileformat.info/info/unicode/char/2028/index.htm" rel="nofollow noreferrer">http://www.fileformat.info/info/unicode/char/2028/index.htm</a>

Java functions Character.isWhitespace() covers all situations.

That is why already mentioned solution
StringUtils.isWhitespace( String ) /or StringUtils.isBlank(String)
should be used.

blocks|key|3033995|text|如果您使用的是Java11或更高版本，新的isBlank字符串方法将派上用场：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|3033996|!s.isBlank();|code-block|syntax|javascript|3033997|如果您使用的是Java8、9或10，则可以构建一个简单的流来检查字符串是否仅为空格：|3033998|!s.chars().allMatch(Character::isWhitespace));|3033999|除了不需要任何第三方库(如Apache+Commons+Lang+)外，这些解决方案还具有处理任何空白字符的优势，而不是许多其他答案中建议的trim-based解决方案所建议的纯'+'空格。有关所有支持的空白类型的详尽列表，请参阅Javadocs。请注意，在这两种情况下，空字符串也包含在内。|3034000|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/javase/8/docs/api/java/lang/Character.html#isWhitespace-int-^0|7|6|L|7|0|0|7|A|0|0|1Y|4|2H|3|37|8|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|D]]|E|@]|F|$]]|$1|G|3|H|5|I|7|14|8|@]|E|@]|F|$J|K]]|$1|L|3|M|5|6|7|15|8|@$9|16|A|17|B|C]]|E|@]|F|$]]|$1|N|3|O|5|I|7|18|8|@]|E|@]|F|$J|K]]|$1|P|3|Q|5|6|7|19|8|@$9|1A|A|1B|B|D]|$9|1C|A|1D|B|D]]|E|@$9|1E|A|1F|1|1G]]|F|$]]|$1|R|3|-4|5|6|7|1H|8|@]|E|@]|F|$]]]|S|$T|$5|U|V|W|F|$X|Y]]]]

If you are using Java 11 or more recent, the new <code>isBlank</code> string method will come in handy:
<pre><code>!s.isBlank();
</code></pre>
If you are using Java 8, 9 or 10, you could build a simple stream to check that a string is not whitespace only:
<pre><code>!s.chars().allMatch(Character::isWhitespace));
</code></pre>
In addition to not requiring any third-party libraries such as Apache Commons Lang, these solutions have the advantage of handling any white space character, and not just plain <code>' '</code> spaces as would a <code>trim</code>-based solution suggested in many other answers. You can refer to the <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Character.html#isWhitespace-int-" rel="nofollow noreferrer">Javadocs</a> for an exhaustive list of all supported white space types. Note that empty strings are also covered in both cases.

blocks|key|303560|text|使用Java-11%2B，您可以使用Java来检查给定的字符串是否全部由空格组成--+String.isBlank|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|303561|String+str1+=+"++++";
System.out.println(str1.isBlank());+//+made+up+of+all+whitespaces,+prints+true

String+str2+=+"++++a";
System.out.println(str2.isBlank());+//+prints+false|code-block|syntax|javascript|303562|相同的javadoc是：|303563|/**
+*+Returns+{@code+true}+if+the+string+is+empty+or+contains+only
+*+{@link+Character#isWhitespace(int)+white+space}+codepoints,
+*+otherwise+{@code+false}.
+*
+*+@return+{@code+true}+if+the+string+is+empty+or+contains+only
+*+++++++++{@link+Character#isWhitespace(int)+white+space}+codepoints,
+*+++++++++otherwise+{@code+false}
+*
+*+@since+11
+*/
public+boolean+isBlank()|303564|entityMap^0|15|E|15|E|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|D]]|E|@]|F|$]]|$1|G|3|H|5|I|7|W|8|@]|E|@]|F|$J|K]]|$1|L|3|M|5|6|7|X|8|@]|E|@]|F|$]]|$1|N|3|O|5|I|7|Y|8|@]|E|@]|F|$J|K]]|$1|P|3|-4|5|6|7|Z|8|@]|E|@]|F|$]]]|Q|$]]

With Java-11+, you can make use of the <code>String.isBlank</code> API to check if the given string is not all made up of whitespace - 

<pre><code>String str1 = " ";
System.out.println(str1.isBlank()); // made up of all whitespaces, prints true

String str2 = " a";
System.out.println(str2.isBlank()); // prints false
</code></pre>

The javadoc for the same is :

<pre><code>/**
 * Returns {@code true} if the string is empty or contains only
 * {@link Character#isWhitespace(int) white space} codepoints,
 * otherwise {@code false}.
 *
 * @return {@code true} if the string is empty or contains only
 * {@link Character#isWhitespace(int) white space} codepoints,
 * otherwise {@code false}
 *
 * @since 11
 */
public boolean isBlank()
</code></pre>

blocks|key|3034091|text|StringUtils.isEmptyOrWhitespaceOnly(<your+string>)|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3034092|将检查：-是否为null+-是否仅为空格-是否为空字符串"“|unstyled|3034093|https://www.programcreek.com/java-api-examples/?class=com.mysql.jdbc.StringUtils&method=isEmptyOrWhitespaceOnly|offset|length|3034094|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|33|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|S|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|T|8|@]|9|@$I|U|J|V|1|W]]|A|$]]|$1|K|3|-4|5|F|7|X|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|H]]]]

<pre><code>StringUtils.isEmptyOrWhitespaceOnly(&lt;your string&gt;)
</code></pre>

will check :
 - is it null
 - is it only space
 - is it empty string ""

<a href="https://www.programcreek.com/java-api-examples/?class=com.mysql.jdbc.StringUtils&amp;method=isEmptyOrWhitespaceOnly" rel="nofollow noreferrer">https://www.programcreek.com/java-api-examples/?class=com.mysql.jdbc.StringUtils&amp;method=isEmptyOrWhitespaceOnly</a>

blocks|key|305623|text|只是在openjdk+13，Windows+10上的性能比较。对于每个文本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|305624|"abcd"
"++++"
"+\r\n\t"
"+ab+"
"+\n\n\r\t+++\n\r\t\t\t+++\r\n\r\n\r\t+\t\t\t\r\n\n"
"lorem+ipsum+dolor+sit+amet++consectetur+adipisici+elit"
"1234657891234567891324569871234567891326987132654798"|code-block|syntax|javascript|305625|已执行以下测试之一：|305626|//+trim+%2B+empty
input.trim().isEmpty()

//+simple+match
input.matches("\\S")

//+match+with+precompiled+pattern
final+Pattern+PATTERN+=+Pattern.compile("\\S");
PATTERN.matcher(input).matches()

//+java+11's+isBlank
input.isBlank()|305627|每次10.000.000次。|305628|结果：|305629|METHOD++++min+++max+++note
trim:++++++18+++313+++much+slower+if+text+not+trimmed
match:+++1799++2010+++
pattern:++571+++662+++
isBlank:+++60+++338+++faster+the+earlier+hits+the+first+non-whitespace+character|305630|令人惊讶的是，trim%2Bempty是最快的。即使它需要构造修剪后的文本。比查找单个非空格字符的简单for循环更快……|305631|编辑：文本越长，数字差异越大。修剪长文本要比简单的循环花费更长的时间。但是，正则表达式仍然是最慢的解决方案。|offset|length|style|BOLD|305632|entityMap^0|0|0|0|0|0|0|0|0|0|3|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|17|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|18|8|@$U|19|V|1A|W|X]]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|Z|$]]

Just an performance comparement on openjdk 13, Windows 10. For each of theese texts:

<pre><code>"abcd"
" "
" \r\n\t"
" ab "
" \n\n\r\t \n\r\t\t\t \r\n\r\n\r\t \t\t\t\r\n\n"
"lorem ipsum dolor sit amet consectetur adipisici elit"
"1234657891234567891324569871234567891326987132654798"
</code></pre>

executed one of following tests:

<pre><code>// trim + empty
input.trim().isEmpty()

// simple match
input.matches("\\S")

// match with precompiled pattern
final Pattern PATTERN = Pattern.compile("\\S");
PATTERN.matcher(input).matches()

// java 11's isBlank
input.isBlank()
</code></pre>

each 10.000.000 times.

The results:

<pre><code>METHOD min max note
trim: 18 313 much slower if text not trimmed
match: 1799 2010 
pattern: 571 662 
isBlank: 60 338 faster the earlier hits the first non-whitespace character
</code></pre>

Quite surprisingly the trim+empty is the fastest. Even if it needs to construct the trimmed text. Still faster then simple for-loop looking for one single non-whitespaced character...

EDIT:
The longer text, the more numbers differs. Trim of long text takes longer time than just simple loop. However, the regexs are still the slowest solution.

blocks|key|300567|text|虽然就我个人而言，我更喜欢!str.isBlank()，正如其他人已经建议的(或str+->+!str.isBlank()作为谓词)，上面提到的str.trim()方法的一个更现代、更有效的版本是使用str.strip()+-将nulls视为“空白”：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|BOLD|entityRanges|data|300568|if+(str+!=+null+&&+str.strip().length()+>+0)+{...}|code-block|syntax|javascript|300569|例如作为谓词，用于流，例如在单元测试中：|300570|@Test
public+void+anyNonEmptyStrippedTest()+{
++++String[]+strings+=+null;
++++Predicate<String>+isNonEmptyStripped+=+str+->+str+!=+null+&&+str.strip().length()+>+0;
++++assertTrue(Optional.ofNullable(strings).map(arr+->+Stream.of(arr).noneMatch(isNonEmptyStripped)).orElse(true));
++++strings+=+new+String[]+{+null,+"",+"+",+"\\n",+"\\t",+"\\r"+};
++++assertTrue(Optional.ofNullable(strings).map(arr+->+Stream.of(arr).anyMatch(isNonEmptyStripped)).orElse(true));
++++strings+=+new+String[]+{+null,+"",+"+",+"\\n",+"\\t",+"\\r",+"test"+};
}|300571|entityMap^0|D|E|14|L|20|A|2S|B|36|5|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]|$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|D]]|E|@]|F|$]]|$1|G|3|H|5|I|7|12|8|@]|E|@]|F|$J|K]]|$1|L|3|M|5|6|7|13|8|@]|E|@]|F|$]]|$1|N|3|O|5|I|7|14|8|@]|E|@]|F|$J|K]]|$1|P|3|-4|5|6|7|15|8|@]|E|@]|F|$]]]|Q|$]]

While personally I would be preferring <code>!str.isBlank()</code>, as others already suggested (or <code>str -&gt; !str.isBlank()</code> as a Predicate), a more modern and efficient version of the <code>str.trim()</code> approach mentioned above, would be using <code>str.strip()</code> - considering nulls as &quot;whitespace&quot;:
<pre><code>if (str != null &amp;&amp; str.strip().length() &gt; 0) {...}
</code></pre>
For example as Predicate, for use with streams, e. g. in a unit test:
<pre><code>@Test
public void anyNonEmptyStrippedTest() {
 String[] strings = null;
 Predicate&lt;String&gt; isNonEmptyStripped = str -&gt; str != null &amp;&amp; str.strip().length() &gt; 0;
 assertTrue(Optional.ofNullable(strings).map(arr -&gt; Stream.of(arr).noneMatch(isNonEmptyStripped)).orElse(true));
 strings = new String[] { null, &quot;&quot;, &quot; &quot;, &quot;\\n&quot;, &quot;\\t&quot;, &quot;\\r&quot; };
 assertTrue(Optional.ofNullable(strings).map(arr -&gt; Stream.of(arr).anyMatch(isNonEmptyStripped)).orElse(true));
 strings = new String[] { null, &quot;&quot;, &quot; &quot;, &quot;\\n&quot;, &quot;\\t&quot;, &quot;\\r&quot;, &quot;test&quot; };
}
</code></pre>

blocks|key|3248325|text|public+static+boolean+isStringBlank(final+CharSequence+cs)+{
++++++++int+strLen;
++++++++if+(cs+==+null+%7C%7C+(strLen+=+cs.length())+==+0)+{
++++++++++++return+true;
++++++++}
++++++++for+(int+i+=+0;+i+<+strLen;+i%2B%2B)+{
++++++++++++if+(!Character.isWhitespace(cs.charAt(i)))+{
++++++++++++++++return+false;
++++++++++++}
++++++++}
++++++++return+true;
++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3248326|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>public static boolean isStringBlank(final CharSequence cs) {
 int strLen;
 if (cs == null || (strLen = cs.length()) == 0) {
 return true;
 }
 for (int i = 0; i &lt; strLen; i++) {
 if (!Character.isWhitespace(cs.charAt(i))) {
 return false;
 }
 }
 return true;
 }
</code></pre>

I want to check that Java String or character array is not just made up of whitespaces, using Java?

This is a very similar question except it's Javascript: 
<a href="https://stackoverflow.com/questions/2031085/check-if-string-contains-characters-whitespaces-not-only-whitespaces"><a href="https://stackoverflow.com/questions/2031085/check-if-string-contains-characters-whitespaces-not-only-whitespaces">How can I check if string contains characters &amp; whitespace, not just whitespace?</a></a>

EDIT: I removed the bit about alphanumeric characters, so it makes more sense.

How do I check that a Java String is not all whitespaces?

单元测试

Windows

Java

我想使用Java检查Java字符串或字符数组是否不仅仅由空格组成？这是一个非常相似的问题，除了它是Javascript：编辑：我去掉了关于字母数字字符的部分，所以它更有意义。

问如何检查Java字符串是否全部为空格？
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