验证字符串为空或 null 的最佳方法

Question

i am sure this must have been asked before in different ways - as isEmptyOrNull is so common yet people implement it differently. but i have below curious query in terms of best available approach which is good for memory and performance both.

1) Below does not account for all spaces like in case of empty XML tag

return inputString==null || inputString.length()==0;

2) Below one takes care but trim can eat some performance + memory

return inputString==null || inputString.trim().length()==0;

3) Combining one and two can save some performance + memory (As Chris suggested in comments)

return inputString==null || inputString.trim().length()==0 || inputString.trim().length()==0;

4) Converted to pattern matcher (invoked only when string is non zero length)

private static final Pattern p = Pattern.compile("\\s+");

return inputString==null || inputString.length()==0 || p.matcher(inputString).matches();

5) Using libraries like - Apache Commons ( StringUtils.isBlank/isEmpty ) or Spring ( StringUtils.isEmpty ) or Guava ( Strings.isNullOrEmpty ) or any other option?

Answer 1

Useful method from Apache Commons:

 org.apache.commons.lang.StringUtils.isBlank(String str)

https://commons.apache.org/proper/commons-lang/javadocs/api-2.6/org/apache/commons/lang/StringUtils.html#isBlank(java.lang.String)

Answer 2

To detect if a string is null or empty, you can use the following without including any external dependencies on your project and still keeping your code simple/clean:

if(myString==null || myString.isEmpty()){
    //do something
}

or if blank spaces need to be detected as well:

if(myString==null || myString.trim().isEmpty()){
    //do something
}

you could easily wrap these into utility methods to be more concise since these are very common checks to make:

public final class StringUtils{

    private StringUtils() { }   

    public static bool isNullOrEmpty(string s){
        if(s==null || s.isEmpty()){
            return true;
        }
        return false;
    }

    public static bool isNullOrWhiteSpace(string s){
        if(s==null || s.trim().isEmpty()){
            return true;
        }
        return false;
    }
}

and then call these methods via:

if(StringUtils.isNullOrEmpty(myString)){...}

and

if(StringUtils.isNullOrWhiteSpace(myString)){...}

Answer 3

Just to show java 8's stance to remove null values.

String s = Optional.ofNullable(myString).orElse("");
if (s.trim().isEmpty()) {
    ...
}

Makes sense if you can use Optional<String> .

Answer 4

This one from Google Guava could check out "null and empty String" in the same time.

Strings.isNullOrEmpty("Your string.");

Add a dependency with Maven

<dependency>
  <groupId>com.google.guava</groupId>
  <artifactId>guava</artifactId>
  <version>20.0</version>
</dependency>

with Gradle

dependencies {
  compile 'com.google.guava:guava:20.0'
}

Answer 5

Haven't seen any fully-native solutions, so here's one:

return str == null || str.chars().allMatch(Character::isWhitespace);

Basically, use the native Character.isWhitespace() function. From there, you can achieve different levels of optimization, depending on how much it matters (I can assure you that in 99.99999% of use cases, no further optimization is necessary):

return str == null || str.length() == 0 || str.chars().allMatch(Character::isWhitespace);

Or, to be really optimal (but hecka ugly):

int len;
if (str == null || (len = str.length()) == 0) return true;
for (int i = 0; i < len; i++) {
  if (!Character.isWhitespace(str.charAt(i))) return false;
}
return true;

One thing I like to do:

Optional<String> notBlank(String s) {
  return s == null || s.chars().allMatch(Character::isWhitepace))
    ? Optional.empty()
    : Optional.of(s);
}

...

notBlank(myStr).orElse("some default")

Answer 6

Apache Commons Lang 有StringUtils.isEmpty(String str)方法，如果参数为空或为空则返回 true

Answer 7

springframework library Check whether the given String is empty.

f(StringUtils.isEmpty(str)) {
    //.... String is blank or null
}

Answer 8

Optional.ofNullable(label)
.map(String::trim)
.map(string -> !label.isEmpty)
.orElse(false)

OR

TextUtils.isNotBlank(label);

the last solution will check if not null and trimm the str at the same time

Answer 9

In most of the cases, StringUtils.isBlank(str) from apache commons library would solve it. But if there is case, where input string being checked has null value within quotes, it fails to check such cases.

Take an example where I have an input object which was converted into string using String.valueOf(obj) API. In case obj reference is null, String.valueOf returns "null" instead of null.

When you attempt to use, StringUtils.isBlank("null") , API fails miserably, you may have to check for such use cases as well to make sure your validation is proper.

Answer 10

With the openJDK 11 you can use the internal validation to check if the String is null or just white spaces

import jdk.internal.joptsimple.internal.Strings;
...

String targetString;
if (Strings.isNullOrEmpty(tragetString)) {}

Answer 11

Simply and clearly:

if (str == null || str.trim().length() == 0) {
    // str is empty
}

Answer 12

You can make use of Optional and Apache commons Stringutils library

Optional.ofNullable(StringUtils.noEmpty(string1)).orElse(string2);

here it will check if the string1 is not null and not empty else it will return string2

Answer 13

If you have to test more than one string in the same validation, you can do something like this:

import java.util.Optional;
import java.util.function.Predicate;
import java.util.stream.Stream;

public class StringHelper {

  public static Boolean hasBlank(String ... strings) {

    Predicate<String> isBlank = s -> s == null || s.trim().isEmpty();

    return Optional
      .ofNullable(strings)
      .map(Stream::of)
      .map(stream -> stream.anyMatch(isBlank))
      .orElse(false);
  }

}

So, you can use this like StringHelper.hasBlank("Hello", null, "", " ") or StringHelper.hasBlank("Hello") in a generic form.

Answer 14

We can make use of below

Optional.ofNullable(result).filter(res -> StringUtils.isNotEmpty(res))
            .ifPresent( s-> val.set(s));