Creo ExpReg para meterle las expresiones regulares

src/main/java/com/carpooling/carpoolingaoraha/entidades/Usuario.java

 package com.carpooling.carpoolingaoraha.entidades;
 
+import com.carpooling.carpoolingaoraha.utils.ExprReg;
 import jakarta.persistence.*;
 import org.antlr.v4.runtime.misc.NotNull;
 import org.intellij.lang.annotations.Pattern;
@@ -33,7 +34,7 @@ public class Usuario {
     @Id
     @NotNull
     @Size(min=9, max=9)
-    @Pattern(regexp=Expr.Reg.DNI)
+    @Pattern(regexp = ExprReg.DNI)
     private String DNI;
 
     @Size(min=9, max=9)

src/main/java/com/carpooling/carpoolingaoraha/utils/ExprReg.java

+package com.carpooling.carpoolingaoraha.utils;
+
+public class ExprReg {
+    public ExprReg(){}
+        public static final String DNI = "";
+
+}