Question: the length of mobile number varies from country to country. Tired regular expresssion but (Ex:India allows 10 digits, which is not validating UAE which ranges from 7 to 9 digits)

Answer: 
you can try using Google's phone number library. It contains the `isValidNumber`function which provides "full validation of a phone number for a region using length and prefix information".
<https://github.com/googlei18n/libphonenumber>
Add this dependency to your pom.xml

```xml
<!-- https://mvnrepository.com/artifact/com.googlecode.libphonenumber/libphonenumber -->
<dependency>
    <groupId>com.googlecode.libphonenumber</groupId>
    <artifactId>libphonenumber</artifactId>
    <version>8.4.3</version>
</dependency>

```