09-SpringMVC03

今日知识

1. SpringMVC自定义异常处理
2. SpringMVC的interceptor（过滤器）

SpringMVC自定义异常处理

1.web.xml正常写

<servlet>
    <servlet-name>DispatcherServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <!--<load-on-startup>1</load-on-startup>-->
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:application.xml</param-value>
    </init-param>
</servlet>
<servlet-mapping>
    <servlet-name>DispatcherServlet</servlet-name>
    <url-pattern>/</url-pattern>
</servlet-mapping>

2. application.xml写法

<context:component-scan base-package="com.rqy"/>
<mvc:annotation-driven/>
<!--配置springmvc视图解析器-->
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix" value="/WEB-INF/views/"/>
    <property name="suffix" value=".jsp"/>
</bean>

3. Controller处理层

@Controller
public class HelloController  {
@RequestMapping("hello")
public String hello(int type) throws Exception {
    if (type==1){
    throw  new MyException("你的用户名过长");//自定义异常
    }else if (type==2){
        throw new FileSizeException();
    }else if (type>2){
        throw new UnknownParamException();
    }
    return "hello" ;
}
}

4. 自定义异常MyException-->其他异常也类似

public class MyException extends Exception {
public MyException(String  message){
    super(message);
    }
}

5. 注册自定义异常处理器（会自动拦截异常）

* 避免直接在页面显示异常信息，我们自定义异常处理器，抛出对应的异常时将转发到不同的页面上。
* 案例：
* @Component
public class CustomExceptionResolver implements HandlerExceptionResolver {
@Override
public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object o, Exception e) {
    ModelAndView modelAndView = new ModelAndView();
    System.out.println(o);
    if (e instanceof MyException) {
        MyException myException = (MyException) e;
        modelAndView.addObject("content", myException.getMessage());
        modelAndView.setViewName("customException");
    } else if (e instanceof FileSizeException) {

        modelAndView.setViewName("fileException");
    } else if (e instanceof UnknownParamException) {
        modelAndView.setViewName("paramException");

    }
    return modelAndView;
}
}
* 其中customException，fileException，paramException对应的jsp页面
* 例如：页面打印出： 自定义的异常 ${content}，即可。

SpringMVC的interceptor（过滤器）

1. 原理：就是过滤器

2. ctrl+o:直接可以调出实现接口的方法

3. implements HandlerInterceptor

* public class MySecondInterceptor implements HandlerInterceptor {
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    System.out.println("preHandle2");
    return true;
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
    System.out.println("postHandle2");
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
    System.out.println("afterCompletion2");
}
}

4. 如果一个为false的话，下面的全部流程都不进行

5. xml配置

*     <mvc:interceptors>
    <!--全部请求都通过interceptor-->
    <!--/**-->
    <bean class="com.rqy.interceptor.MyFirstInterceptor"/>
    <bean class="com.rqy.interceptor.MySecondInterceptor"/>
    <!--<ref bean="interceptor3"/>-->
    <!--interc拦截部分请求-->
    <!--user/query
    user/add
    user/register-->
    <mvc:interceptor>
        <!--localhost/user/a yes-->
        <mvc:mapping path="/user/**"/>
        <bean class="com.rqy.interceptor.MyThirdInterceptor"/>
    </mvc:interceptor>
</mvc:interceptors>

6. 结论：preHandle全为true才会执行到requestMapping和postHandle

7. 案例（用户未登录拦截到login.jsp）

* public class MyFirstInterceptor implements HandlerInterceptor {
    //当返回值为false时不能够进入RequestMapping对应的方法
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("preHandle1");
        String username = request.getParameter("username");
        if (username==null|| "".equals(username)){
            return true;//如果没有参数提交，继续验证下面方法postHandle，看看用户是否登录了
        }else {
            request.getSession().setAttribute("username",username);
            return true;  //username不为空，意味用户登录操作，不进行拦截
        }
    }
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        String username = (String) request.getSession().getAttribute("username");
        if (username==null|| "".equals(username)){
            modelAndView.setViewName("login");//用户未登录返回login界面
        }else {
            modelAndView.addObject("username",username);
            modelAndView.setViewName("hello");
        }
        System.out.println("postHandle1");
    }
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("afterCompletion1");
    }
}