Demo :: Validation input

EmailFormatRule.java

public class EmailFormatRule implements RegisterRule {

	public void validate(User user) {
		String EMAIL_PATTERN = "^[_A-Za-z0-9-\\+]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9-]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$";
		Pattern validEmailPattern = Pattern.compile(EMAIL_PATTERN);
		if( !validEmailPattern.matcher(user.getEmail()).matches() ) {
			throw new IllegalArgumentException("Email is wrong format");
		}
	}

}

NameEmptyRule.java

public class NameEmptyRule implements RegisterRule {

	public void validate(User user) {
		if (user.getName() == null || user.getName().trim().equals("")) {
			throw new IllegalArgumentException("Name should not empty");
		}
	}

}

RegisterRule.java

public interface RegisterRule {
	void validate(User user);
}

RegisterService.java

public boolean register(User user) {
		
	List<RegisterRule> registerRules = new ArrayList<RegisterRule>();
	registerRules.add(new NameEmptyRule());
	registerRules.add(new NameFormatRule());
	registerRules.add(new EmailEmptyRule());
	registerRules.add(new EmailFormatRule());
	registerRules.add(new EmailDomainRule());
	registerRules.add(new AgeAllowRule());
	for (RegisterRule registerRule : registerRules) {
		registerRule.validate(user);
	}
	
	return true;
}

RegisterService2.java

public class RegisterService {

	public boolean register(User user) {
		for (RegisterRule registerRule : RuleFactory.getRegisterRules()) {
			registerRule.validate(user);
		}
		
		return true;
	}

}

RuleFactory.java

public final class RuleFactory {
	private RuleFactory() {

	}

	public static List<RegisterRule> getRegisterRules() {
		List<RegisterRule> registerRules = new ArrayList<RegisterRule>();
		registerRules.add(new NameEmptyRule());
		registerRules.add(new NameFormatRule());
		registerRules.add(new EmailEmptyRule());
		registerRules.add(new EmailFormatRule());
		registerRules.add(new EmailDomainRule());
		registerRules.add(new AgeAllowRule());
		return registerRules;
	}

}

validate.java

public boolean register(User user) {
		if (user.getName() == null || user.getName().trim().equals("")) {
			throw new IllegalArgumentException("Name should not empty");
		}
		if (user.getEmail() == null || user.getEmail().trim().equals("")) {
			throw new IllegalArgumentException("Email should not empty");
		}

		if ( !user.getName().matches("[a-zA-Z]+")){
			throw new IllegalArgumentException("Name is wrong format");
		}
		String EMAIL_PATTERN = "^[_A-Za-z0-9-\\+]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9-]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$";
		Pattern validEmailPattern = Pattern.compile(EMAIL_PATTERN);
		if( !validEmailPattern.matcher(user.getEmail()).matches() ) {
			throw new IllegalArgumentException("Email is wrong format");
		}
		
		List<String> notAllowDomains = Arrays.asList("domain01.cc","domain02.cc", "domain03.cc");
		if(notAllowDomains.contains(user.getEmail().split("@")[1])) {
			throw new IllegalArgumentException("Domain Email is not allow");
		}
		
		if( user.getAge() < 20 ) {
			throw new IllegalArgumentException("Age should more than 20 years");
		}

		return true;
	}