拦截器和异常处理器

拦截器和异常处理器

拦截器

拦截器(Interceptor)，主要完成请求参数的解析、将页面表单参数赋给值栈中相应属性、执行功能检验、程序异常调试等工作。

准备

创建模块

如下为完整的项目结构

web.xml

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
  
  <filter>
    <filter-name>CharacterEncodingFilterfilter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilterfilter-class>
    <init-param>
      <param-name>encodingparam-name>
      <param-value>UTF-8param-value>
    init-param>
    <init-param>
      <param-name>forceResponseEncodingparam-name>
      <param-value>trueparam-value>
    init-param>
  filter>
  <filter-mapping>
    <filter-name>CharacterEncodingFilterfilter-name>
    <url-pattern>/*url-pattern>
  filter-mapping>
  
  <filter>
    <filter-name>HiddenHttpMethodFilterfilter-name>
    <filter-class>org.springframework.web.filter.HiddenHttpMethodFilterfilter-class>
  filter>
  <filter-mapping>
    <filter-name>HiddenHttpMethodFilterfilter-name>
    <url-pattern>/*url-pattern>
  filter-mapping>
  
  <servlet>
    <servlet-name>DispatcherServletservlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServletservlet-class>
    <init-param>
      <param-name>contextConfigLocationparam-name>
      <param-value>classpath:springMVC.xmlparam-value>
    init-param>
    
    <load-on-startup>1load-on-startup>
  servlet>
  <servlet-mapping>
    <servlet-name>DispatcherServletservlet-name>
    <url-pattern>/url-pattern>
  servlet-mapping>
web-app>

SpringMVC.xml

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    
    <context:component-scan base-package="com.louis">context:component-scan>
    
    <bean id="viewResolver" class="org.thymeleaf.spring5.view.ThymeleafViewResolver">
        <property name="order" value="1"/>
        <property name="characterEncoding" value="UTF-8"/>
        <property name="templateEngine">
            <bean class="org.thymeleaf.spring5.SpringTemplateEngine">
                <property name="templateResolver">
                    <bean class="org.thymeleaf.spring5.templateresolver.SpringResourceTemplateResolver">
                        <property name="prefix" value="/WEB-INF/templates/"/>
                        <property name="suffix" value=".html"/>
                        <property name="templateMode" value="HTML5"/>
                        <property name="characterEncoding" value="UTF-8"/>
                    bean>
                property>
            bean>
        property>
    bean>
beans>

创建拦截器类FirstInterceptor

package com.louis.interceptors;

import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * @author XRY
 * @date 2023年07月04日18:35
 */
@Component
public class FirstInterceptor implements HandlerInterceptor {
    @Override
    //控制器方法执行之前执行
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("FirstInterceptor----->preHandle");
        return HandlerInterceptor.super.preHandle(request, response, handler);
    }

    @Override
    //控制器方法执行之后执行
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("FirstInterceptor----->postHandle");
        HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);
    }

    @Override
    //在视图渲染之后执行
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("FirstInterceptor----->afterCompletion");
        HandlerInterceptor.super.afterCompletion(request, response, handler, ex);
    }
}

1、拦截器的配置

SpringMVC中的拦截器用于拦截控制器方法的执行，它需要实现HandlerInterceptor或继承HandlerInterceptorAdapter类(过时)并且必须在SpringMVC的配置文件中进行配置。

法一

<mvc:interceptors>
    <bean class="com.louis.interceptors.FirstInterceptor">bean>
mvc:interceptors>

法二

<mvc:interceptors>
    <ref bean="firstInterceptor">ref>
mvc:interceptors>

法三

<mvc:interceptors>
    <mvc:interceptor>
        
        <mvc:mapping path="/**"/>
        
        <mvc:exclude-mapping path="/"/>
        <ref bean="firstInterceptor">ref>
    mvc:interceptor>
mvc:interceptors>

2、拦截器的三个抽象方法

preHandle:控制器方法执行之前执行preHandle(),其boolean类型的返回值表示是否拦截或放行，返回true为放行，即调用控制器方法，返回false表示拦截，即不调用控制器方法。

postHandle:控制器方法执行之后执行postHandle()

afterComplation:处理完视图和模型数据，渲染视图完毕之后执行afterComplation()

3、多个拦截器的执行顺序

①若多个拦截器的preHandle()都返回true
此时多个拦截器的执行顺序和拦截器在SpringMVC的配置文件的配置顺序有关，preHandle()会按照配置的顺序执行，而postHandle()和afterHandle()会按照配置的反顺序执行。

②若某个拦截器的preHandle返回了false
preHandle()返回false和它之前的拦截器的preHandle()都会执行，postHandle()都不执行，返回false拦截器之前的拦截器的afterComplation()会执行。

实例

创建两个拦截器FirstInterceptor和SecondInterceptor它们的内容除了输出语句都相同

SecondInterceptor

package com.louis.interceptors;

import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * @author XRY
 * @date 2023年07月04日18:35
 */
@Component
public class SecondInterceptor implements HandlerInterceptor {
    @Override
    //控制器方法执行之前执行
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("SecondInterceptor----->preHandle2");
        return false;
    }

    @Override
    //控制器方法执行之后执行
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("SecondInterceptor----->postHandle2");
        HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);
    }

    @Override
    //在视图渲染之后执行
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("SecondInterceptor----->afterCompletion2");
        HandlerInterceptor.super.afterCompletion(request, response, handler, ex);
    }
}

SpringMVC.xml

<mvc:interceptors>
    <ref bean="firstInterceptor">ref>
    <ref bean="secondInterceptor">ref>
mvc:interceptors>

结果

所有拦截器的preHandle返回都会true

FirstInterceptor----->preHandle
SecondInterceptor----->preHandle2
SecondInterceptor----->postHandle2
FirstInterceptor----->postHandle
SecondInterceptor----->afterCompletion2
FirstInterceptor----->afterCompletion

设置SecondeInterceptor的preHandle为false

FirstInterceptor----->preHandle
SecondInterceptor----->preHandle2
FirstInterceptor----->afterCompletion

---

异常处理器

分类

1、基于配置的异常处理

SpringMVC提供了一个处理控制器方法执行过程中所出现的异常的接口：HandlerExceptionResolver,它的实现类有：DefaultHandlerExceptionResolver和SimpleMappingExceptionResolver
SimpleMappingExceptionResolver为自定义异常处理器，使用方式如下：

在SpringMVC.xml中进行配置

<bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
    <property name="exceptionMappings">
        <props>
            
            <prop key="java.lang.ArithmeticException">errorprop>
        props>
    property>
    
    <property name="exceptionAttribute" value="exception">property>
bean>

创建异常跳转视图error

DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8" xmlns:th="http://www.thymeleaf.org">
    <title>Titletitle>
head>
<body>
出错了！！

<p th:text="${exception}">p>
body>
html>

index.html

<a th:href="@{/testExceptionHandler}">测试异常处理a>

控制器

@RequestMapping("/testExceptionHandler")
public String testExceptionHandler(){
    System.out.println(1/0);
    return "success";
}

测试

2、基于注解的异常处理

异常类

@ControllerAdvice
public class ExceptionAnnotation {
    @ExceptionHandler(value = {ArithmeticException.class, NullPointerException.class})
    /*参数用来显示异常信息*/
    public String testExcept(Exception exception, Model model){
        model.addAttribute("exception", exception);
        return "error";
    }
}

测试