Best way to verify string is empty or null

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)

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>.

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)){...}

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'
}