java异常在实际开发中的应

梦里梦外; 2022-07-31 15:19 246阅读 0赞

异常是java的一大特色，用好了受益匪浅！不瞎扯了，开始写用法，这里控制层用的spring mvc！

思考问题，我们如何做才能使得service层彻底处理所有业务逻辑从而基本实现service和controller层的完全解耦？

所有做过开发的都知道，struts2在处理服务器验证的时候一般会把验证逻辑放在action，这样做没有什么不好，但是如果放在service是否更好，还有其他一些特殊的逻辑要放在service层，有时候特别不方便！现在，我讲讲我所使用的异常转换问题，相信各位大神轻松理解，在自己实际项目中也可以用到！

以service层处理参数验证问题为例：

1.定义parameter异常来封装无需和数据库交互的参数错误信息：

public class ParameterException extends Exception {
    
    	private static final long serialVersionUID = 1L;
    	
    	private Map<String, String> fields = new HashMap<String, String>();
    	
    	public Map<String, String> getFields() {
    		return fields;
    	}
    
    	public void setFields(Map<String, String> fields) {
    		this.fields = fields;
    	}
    	
    	public void addFields(String key, String value) {
            fields.put(key, value);
        }
    
        public boolean isEmpty() {
            return fields.isEmpty();
        }
    
    	public ParameterException() {
    		super();
    		// TODO Auto-generated constructor stub
    	}
    
    	public ParameterException(String message, String flag) {
    		super(message);
    	}
    	
    	
    }

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2.定义ServiceException来封装需要和数据库交互的参数错误信息，如密码不正确

public class ServiceException extends Exception {
        private static final long serialVersionUID = 1L;
    
        private int code = 0;
        private String message = null;
    
        public ServiceException(int code, String message) {
            this.message = message;
            this.code = code;
        }
    
        public ServiceException() {
    
        }
    
        @Override
        public String getMessage() {
            return message;
        }
    
        public void setMessage(String message) {
            this.message = message;
        }
    
        public int getCode() {
            return code;
        }
    
        public void setCode(int code) {
            this.code = code;
        }
    
    }

3.Service层以login为例，验证用户名，密码信息:

@Override
    	public User login(String userNumber, String password)
    			throws ParameterException, ServiceException {//这里抛出具体的异常
    		User user = null;
    		password = DigestUtils.md5Hex(password);
    		ParameterException parameterException = new ParameterException();
    		if (StringUtil.isEmpty(userNumber) || StringUtil.isEmpty(password)) {
    			parameterException.addFields("loginMessage", "用户名或密码为空");
    			throw parameterException;
    		}
    		user = userDao.getUserByUserNumber(userNumber);
    		if (user == null) {
    			throw new ServiceException(10000, "用户不存在");
    		} else if (!password.equals(user.getPassword())
    				&& !userNumber.equals(user.getUserName())) {
    			throw new ServiceException(10001, "密码不正确");
    		}
    		return user;
    	}

4.controller层处理异常，返回信息到页面:

@RequestMapping(value = "/login", method = RequestMethod.POST)
    	public ModelAndView login(String userNumber, String password, HttpSession session) {
    		ModelAndView mav = null;	
    		User user = null;
    		try {
    			user = userService.login(userNumber, password);
    		} catch (ParameterException parameterException) {//这里进行catch操作，出现异常则返回信息到页面
    			Map<String, String> fields = parameterException.getFields();
    			mav = new ModelAndView("login");
    			mav.addObject("fields", fields);
    			return mav;
    		} catch (ServiceException serviceException) {
    			mav = new ModelAndView("login");
    			mav.addObject("loginMessage", serviceException.getMessage());
    			return mav;
    		}
    		user.setPassword(null);
    		session.setAttribute("user", user);
    		Role role = null;
    		if(user != null) {
    			role = userService.getRoleByUserId(user.getId());
    			session.setAttribute("roleName", role.getRoleName());
    			if("系统管理员".equals(role.getRoleName())) {
    				mav = new ModelAndView(new RedirectView("list", true));
    			}
    			if("学生".equals(role.getRoleName())) {
    				 mav = new ModelAndView(new RedirectView("/student/list", true));
    			}
    			if("老师".equals(role.getRoleName())) {
    				mav = new ModelAndView(new RedirectView("/teacher/list", true));
    			}
    		}
    		return mav;
    	}

5.页面拿到错误信息并展示:

<form action="${pageContext.request.contextPath }/user/login" method="post" id="login">
    	<div class="loginTop">
    		<div class="sysNameStyle">
    			<div class="sysNameLocate"></div>
    		</div>
    	</div>
    	<div class="loginBottom">
    		<div class="userName">
    			<div class="labelStyle">
    				学号:
    			</div>
    			<div class="inputStyle">
    				<input type="text" name="userNumber" id="userNumber" class="inputWidth"/>
    			</div>
    			<div class="errorMessage">
    				${loginMessage }${fields['loginMessage'] }
    			</div>
    		</div>
    		
    		<div class="passWord">
    			<div class="labelStyle">
    				密码:
    			</div>
    			<div class="inputStyle">
    				<input type="password" name="password" id="passWord" class="inputWidth"/>
    			</div>
    		</div>
    		
    		<div class="submit">
    			<div class="resetLocate">
    				<input type="reset" value="取消" class="submitStyle"/>
    			</div>
    			<div class="submitLocate">
    				<input type="submit" value="登陆" class="submitStyle"/>
    			</div>
    		</div>
    	</div>
    </form>