我已经阅读了很多关于服务层和 Controller 之间差异的理论，但我对如何在实践中实现这一点有一些疑问。 Service layer and controller: who takes care of what?的一个答案说:

I try to restrict controllers to doing work related to validating http parameters, deciding what service method to call with what parameters, what to put in the httpsession or request, what view to redirect or forward to, or similar web-related stuff.

来自http://www.bennadel.com/blog/2379-a-better-understanding-of-mvc-model-view-controller-thanks-to-steven-neiland.htm :

Red Flags: My Controller architecture might be going bad if:

The Controller makes too many requests to the Service layer. The Controller makes a number of requests to the Service layer that don't return data. The Controller makes requests to the Service layer without passing in arguments.

目前我正在用 Spring MVC 开发一个 web 应用程序，我有这样的方法来保存更改的用户的电子邮件:

/**
     * <p>If no errors exist, current password is right and new email is unique,
     * updates user's email and redirects to {@link #profile(Principal)}
     */
    @RequestMapping(value = "/saveEmail",method = RequestMethod.POST)
    public ModelAndView saveEmail(
            @Valid @ModelAttribute("changeEmailBean") ChangeEmailBean changeEmailBean,
            BindingResult changeEmailResult,
            Principal user,
            HttpServletRequest request){

        if(changeEmailResult.hasErrors()){
            ModelAndView model = new ModelAndView("/client/editEmail");
            return model;
        }
        final String oldEmail = user.getName();
        Client client = (Client) clientService.getUserByEmail(oldEmail);
        if(!clientService.isPasswordRight(changeEmailBean.getCurrentPassword(), 
                                          client.getPassword())){
            ModelAndView model = new ModelAndView("/client/editEmail");
            model.addObject("wrongPassword","Password doesn't match to real");
            return model;
        }
        final String newEmail = changeEmailBean.getNewEmail();
        if(clientService.isEmailChanged(oldEmail, newEmail)){
            if(clientService.isEmailUnique(newEmail)){
                clientService.editUserEmail(oldEmail, newEmail);
                refreshUsername(newEmail);
                ModelAndView profile = new ModelAndView("redirect:/client/profile");
                return profile;
            }else{
                ModelAndView model = new ModelAndView("/client/editEmail");
                model.addObject("email", oldEmail);
                model.addObject("emailExists","Such email is registered in system already");
                return model;
            }
        }
        ModelAndView profile = new ModelAndView("redirect:/client/profile");
        return profile;
    }

您可以看到我对服务层有很多请求，并且我从 Controller 进行重定向——这是业务逻辑。请展示此方法的更好版本。

还有一个例子。我有这个方法，它返回用户的个人资料:

/**
     * Returns {@link ModelAndView} client's profile
     * @param user - principal, from whom we get {@code Client}
     * @throws UnsupportedEncodingException
     */
    @RequestMapping(value = "/profile", method = RequestMethod.GET)
    public ModelAndView profile(Principal user) throws UnsupportedEncodingException{
        Client clientFromDB = (Client)clientService.getUserByEmail(user.getName());
        ModelAndView model = new ModelAndView("/client/profile");
        model.addObject("client", clientFromDB);
        if(clientFromDB.getAvatar() != null){
            model.addObject("image", convertAvaForRendering(clientFromDB.getAvatar()));
        }
        return model;
    }

方法convertAvaForRendering(clientFromDB.getAvatar())放在这个controller的super class里，是这个方法放对了，还是一定要放在service层？？

请帮忙，这对我来说真的很重要。

最佳答案

Spring Controller 通常与 Spring API(具有 Model、ModelAndView...)或 Servlet API( HttpServletRequest, HttpServletResponse...)。方法可以返回解析为模板名称 (JSP...) 的 String 结果。 Controller 肯定偏向于 Web GUI，对 Web 技术有很强的依赖性。

服务应该在设计时考虑到业务逻辑，而不是对客户端的假设。我们可以远程服务，将其公开为 Web 服务，实现 Web 前端或 Swing 客户端。 服务 不应该 不依赖于 Spring MVC、Servlet API 等。这样，如果您需要重新定位您的应用程序，您可以重用大部分业务逻辑。

至于从 Controller 层对服务层调用过多的注意事项，主要是性能问题，恕我直言，这是不同的。如果对服务层的每次调用都查询数据库，您可能会遇到性能问题。如果服务层和 Controller 层不在同一个 JVM 中运行，您也可能会遇到性能问题。这是设计应用程序的另一个非常重要的方面，但它表明您应该对服务调用进行外观处理，以便为 Controller 层提供更粗粒度的操作。

关于java - service层和controller在实践中的区别，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/38677889/