hibernate - 在Spring MVC中，在何处捕获数据库异常

Question

我正在上面(http://viralpatel.net/blogs/spring3-mvc-hibernate-maven-tutorial-eclipse-example/)建议的结构中使用。我尝试添加重复的条目，这导致以下异常:

SEVERE: Servlet.service() for servlet [appServlet] in context with path [/cct] threw exception [Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException: Duplicate entry 'a@b.com' for key 'PRIMARY'; SQL [n/a]; constraint [null]; nested exception is org.hibernate.exception.ConstraintViolationException: Duplicate entry 'a@b.com' for key 'PRIMARY'] with root cause
com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry 'a@b.com' for key 'PRIMARY'
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
    at << removed for readability>> org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
    at com.sun.proxy.$Proxy26.addUser(Unknown Source)
    at com.bilitutor.cct.control.HomeController.signup(HomeController.java:56)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    << removed for readability>> 

我有以下问题:

为什么异常是由 Controller (userService.addUser(user)中的com.bilitutor.cct.control.HomeController)而不是DAO(sessionFactory.getCurrentSession().save(user);)捕获，然后冒泡到 Controller ？

我知道我收到了org.springframework.dao.DataIntegrityViolationException，因为我使用的是@Repository批注，它可能会进行异常转换(如果我错了，请更正我)。在那种情况下，当我捕获到异常时，如何找到该异常的错误代码？

作为最佳实践，捕获异常的最佳位置是哪一层(DAO，服务或 Controller )？

相关类(class):

Controller :

package com.bilitutor.cct.control;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.dao.DataIntegrityViolationException;
import org.springframework.web.bind.annotation.ModelAttribute;

import com.bilitutor.cct.bean.*;
import com.bilitutor.cct.service.*;

/**
 * Handles requests for the application home page.
 */
@Controller
public class HomeController {

    @Autowired
    UserService userService;

    @ModelAttribute("user")
    public User getUserObect() {
      return new User();
    }

    private static final Logger logger = LoggerFactory.getLogger(HomeController.class);

    /**
     * Landing page. Just return the login.jsp
     */
    @RequestMapping(value = "/", method = RequestMethod.GET)
    public String home(Model model) {
        logger.info("home() called");
        return "login";
    }

    /**
     * Login. Either forward to the user's homepage or return back the error
     */
    @RequestMapping(value = "/login", method = RequestMethod.GET)
    public String login(Model model) {
        logger.info("login() called");
        return "login";
    }

    /**
     * New User signup. If user already exists, send back the error, or send an email and forward to the email validation page
     */
    @RequestMapping(value = "/signup", method = RequestMethod.POST)
    public String signup(@ModelAttribute("user")User user, BindingResult result) {
        logger.info("signup() : email="+user.getEmail()+" pass="+user.getPassword()+" accessCode="+user.getAccessCode());
        userService.addUser(user);
        return "login";
    }

}

服务:

package com.bilitutor.cct.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import com.bilitutor.cct.dao.UserDAO;
import com.bilitutor.cct.bean.User;

@Service
public class UserServiceImpl implements UserService {

    @Autowired
    private UserDAO userDAO;

    @Transactional
    public void addUser(User user) {
        userDAO.addUser(user);
    }

    @Transactional
    public void removeUser(String email) {
        userDAO.removeUser(email);
    }

}

道:

package com.bilitutor.cct.dao;

import com.bilitutor.cct.bean.User;

import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

@Repository
public class UserDAOImpl implements UserDAO {

    @Autowired
    private SessionFactory sessionFactory;

    public void setSessionFactory(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
    }

    public void addUser(User user) {
        sessionFactory.getCurrentSession().save(user);
    }

    public void removeUser(String email) {
        User user = (User) sessionFactory.getCurrentSession().load(User.class, email);
        if (user!=null) {
            sessionFactory.getCurrentSession().delete(user);
        }

    }
}

Answer 1

服务层发生异常。你可以看到它的踪影
at com.sun.proxy.$Proxy26.addUser(Unknown Source)

@Transactional
public void addUser(User user) {
    userDAO.addUser(user);
}

如先前的回答所述，您的事务边界位于服务层，因此在那里发生异常。

我建议从服务方法中捕获/抛出适当的业务异常(已检查的异常)。服务方法结合了您的业务逻辑，因此，如果发生任何错误，应通过服务方法引发的异常将其正确地传达给外部世界。例如:WeakPasswordException，UserNameExistsException等

关于 org.springframework.dao.DataIntegrityViolationException尝试调用 getCause()查看包装的异常