하이버네이트 validator 설치 

class MyValidatorFactory

public class MyValidatorFactory {

	//유효성 체크
	public static Validator createValidaor(){
		ValidatorFactory factory =Validation.buildDefaultValidatorFactory();
		return factory.getValidator();
	}
	
}

class CreateUserServlet

package com.slipp.user;

import java.io.IOException;
import java.util.Iterator;
import java.util.Set;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.validation.ConstraintViolation;
import javax.validation.Validator;

import com.slipp.db.Database;
import com.slipp.support.MyValidatorFactory;

@WebServlet("/users/save")
public class CreateUserServlet extends HttpServlet {

	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
			
		String userId=request.getParameter("userId");	
		String password=request.getParameter("password");
		String name=request.getParameter("name");
		String email=request.getParameter("email");
	
		User user=new User(userId, password, name, email);
		Validator validator=MyValidatorFactory.createValidaor();  
		Set<ConstraintViolation<User>> constraintViolations=validator.validate(user);
		if(constraintViolations.size() >0){
			String errorMessage=constraintViolations.iterator().next().getMessage();
			forwordJSP(request, response, errorMessage);
			return;
		}else {
			
		}
		
		Iterator<ConstraintViolation<User>> iterator =constraintViolations.iterator();
		while(iterator.hasNext()){
			ConstraintViolation<User> each=iterator.next();	
		}	
		//Database.addUser(user);
		UserDAO dao =new UserDAO();
		dao.insert(user);	
		response.sendRedirect("/");
		
	}
	
	private void forwordJSP(HttpServletRequest request, HttpServletResponse response,
			String errorMessage) throws ServletException, IOException{
		request.setAttribute("errorMessage", errorMessage);
		RequestDispatcher rd=request.getRequestDispatcher("/login.jsp");
		rd.forward(request, response);
	}
	

}

form.jsp

				<form class="form-horizontal" action="/users/save" method="post">
					<c:if test="${not empty errorMessage }">
						<div class="control-group">
							<label class="controls">${errorMessage }</label>
						</div>
					</c:if>
					<div class="control-group">
						<label class="control-label" for="userId">사용자 아이디</label>
						<div class="controls">
							<input type="text" name="userId" value="" />
						</div>
					</div>