Here we can learn two ways to validate file name extensions in the system using regular expressions:
– Regex matcher method
– String matches method
In these examples, file extensions ‘.txt’ or ‘.xml’ will return ‘true’.
Regular expression used is: .+\\.(?i)(txt|xml)$.
where
.+ – matches one or more of any character
\. – followed by a dot
(?i) – ignores case sensitive check
(txt/xml) – file extensions ‘.txt’ or ‘.xml’
$ – end of line
Example 1 – Regex matcher method
class RegExTest
{
public static void main( String args[] )
{
String[] fileNames = { “file.txt”, “file.xml”, “file-name.txt”, “file_name.txt”, “file.name.txt”,
“file name.txt”, “file.abc”, “file.tmp”, “filetxt.abc”, “file.txt.abc”, “xml”, “.xml”, };
Pattern pattern = Pattern.compile( “.+\\.(?i)(txt|xml)$” );
Arrays.stream( fileNames ).forEach( fileName ->
{
Matcher matcher = pattern.matcher( fileName );
System.out.println( fileName + ” – ” + matcher.matches() );
} );
}
}
Example 2 – String “matches” method
import java.util.Arrays;
class RegExTest
{
public static void main( String args[] )
{
String[] fileNames = { “file.txt”, “file.xml”, “file-name.txt”, “file_name.txt”, “file.name.txt”,
“file name.txt”, “file.abc”, “file.tmp”, “filetxt.abc”, “file.txt.abc”, “xml”, “.xml”, };
Arrays.stream(fileNames).forEach( fileName ->
{
System.out.println( fileName + ” – ” + fileName.matches( “.+\\.(?i)(txt|xml)$” ) );
} );
}
Output in both cases
file.txt – true
file.xml – true
file-name.txt – true
file_name.txt – true
file.name.txt – true
file name.txt – true
file.abc – false
file.tmp – false
filetxt.abc – false
file.txt.abc – false
xml – false
.xml – false