SpringMvc异常处理机制

预期异常和运行异常，前者通过捕获，后者通过规范代码开发、测试等手段减少发生概率。

系统dao层、service层、controller层出现都可通过throws Exception向上抛出，最终由SpringMvc前端控制器交由异常处理器进行异常处理。

SpringMvc项目异常处理两种方式

1、使用SpringMvc提供的简单异常处理器SimpleMappingExceptionResolver简单映射异常处理器。这种是当产生响应的异常后会跳转到响应的页面，需在spring-mvc.xml中配置。

2、实现Spring的异常处理接口HandlerExceptionResolver，自定义自己的异常处理器。

简单异常处理器SimpleMappingExceptionResolver

创建mavenWeb项目，pom文件引入springMvc依赖

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.0.5.RELEASE</version>
        </dependency>
    </dependencies>

web.xml配置前端控制器

<?xml version="1.0" encoding="UTF-8"?>
<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">
    <!--配置SpringMVC的前端控制器：
    配置一个servlet，类选择第三方org.springframework的DispatcherServlet
    配置该类，且路径为拦截所有来作为springMvc的前端控制器servlet  -->
    <servlet>
        <servlet-name>DispatcherServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param><!--该servlet的初始化参数-->
            <!--spring-mvc.xml是怎么加载的呢
            spring-mvc.xml是怎么加载的呢
            类似web.xml中的<context-param>application域的全局初始化参数。
            这里下面配置初始化参数spring-mvc.xml名称即为web.xml中该DispatcherServlet的servlet的init初始化参数来提供，
            以便org的DispatcherServlet根据这个servlet的init初始化参数去加载springMVC的配置文件，
            继而IOC出controller(特有行为)实例提供给前端控制器DispatcherServlet(共有行为)使用。
            -->
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:spring-mvc.xml</param-value>
        </init-param>
        <load-on-startup>2</load-on-startup><!--loadOnStartup=负整数或不加默认第一次访问该servlet执行时创建servlet对象并初始化
        loadOnStartup为0或正整数时，web服务器启动时创建servlet对象，数字越小，优先级越高-->
    </servlet>
    <servlet-mapping>
        <servlet-name>DispatcherServlet</servlet-name>
        <url-pattern>/</url-pattern><!-- 配置该servlet的路径为拦截所有/，虽会覆盖tomcat静态资源访问路径，但现在没有静态资源html之类，只有jsp动态页面。-->
    </servlet-mapping>
</web-app>

com.kdy.exception中MyException

public class MyException extends Exception{
}

com.kdy.service.impl中DemoServiceImpl

@Service
public class DemoServiceImpl implements DemoService {
    @Override
    public void show1() {
        System.out.println("抛出异常转换类型...");
        Object str = "zhangsan";
        Integer num =(Integer) str;
    }

    @Override
    public void show2() {
        System.out.println("抛出除零异常");
        int i = 1/0;
    }

    @Override
    public void show3() throws FileNotFoundException {
        System.out.println("文件找不到异常...");
        InputStream in = new FileInputStream("C:/xxx/xxx/xx.txt");
    }

    @Override
    public void show4() {
        System.out.println("空指针异常");
        String str = null;
        str.length();
    }

    @Override
    public void show5() throws MyException {
        System.out.println("自定义异常");
            throw new MyException();
    }
}

com.kdy.controller中DemoController

@Controller
public class DemoController {
    @Autowired
    private DemoService demoService;
    @RequestMapping("/show1")
    public String show1(){
        System.out.println("show running1...");
        demoService.show1();
        return "index";
    }
    @RequestMapping("/show2")
    public String show2(){
        System.out.println("show running2...");
        demoService.show2();
        return "index";
    }
    @RequestMapping("/show3")
    public String show3() throws FileNotFoundException {
        System.out.println("show running3...");
        demoService.show3();
        return "index";
    }
    @RequestMapping("/show4")
    public String show4(){
        System.out.println("show running4...");
        demoService.show4();
        return "index";
    }
    @RequestMapping("/show5")
    public String show5() throws MyException {
        System.out.println("show running5...");
        demoService.show5();
        return "index";
    }
}

resource下spring-mvc.xml中配置异常处理器

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
       http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
    ">

    <!--Controller的组件扫描-->
    <context:component-scan base-package="com.kdy"></context:component-scan>
    
    <!--配置内部资源视图解析器-->
    <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/jsp/"></property><!--前缀-->
        <property name="suffix" value=".jsp"></property><!--后缀-->
    </bean>
    
    <!--配置异常处理器-->
    <bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
        <!--<property name="defaultErrorView" value="error"/>--><!--默认异常视图：所有的Exception都走这个,这里由于上面写了视图解析器的前后缀，会把error拼接为/jsp/error.jsp-->
        <property name="exceptionMappings">
            <map>
                <entry key="java.lang.ClassCastException" value="error1"/>
                <entry key="java.lang." value="error1"/>
                <entry key="java.lang.ClassCastException" value="error1"/><!--类转换异常-->
                <entry key="java.lang.ArithmeticException" value="error2"/><!--除零异常-->
                <entry key="java.io.import java.io.FileNotFoundException;" value="error3"/><!--文件找不到异常-->
                <entry key="java.lang.NullPointerException" value="error4"/><!--空指针异常-->
                <entry key="com.kdy.exception.MyException" value="error5"/><!--自定义异常-->
            </map>
        </property>
    </bean>
</beans>

webapp下jsp的创建index.jsp

<h1>index.jsp~~~hello</h1>

webapp下jsp的创建error.jsp

<h1>通用的错误提示页面~</h1>

webapp下jsp的创建error1.jsp

<h1>类型转换异常~</h1>

webapp下jsp的创建error2.jsp

<h1>除零算数异常~</h1>

webapp下jsp的创建error3.jsp

<h1>文件找不到异常~</h1>

webapp下jsp的创建error4.jsp

<h1>空指针异常异常~</h1>

webapp下jsp的创建error5.jsp

<h1>自定义异常~</h1>

分别访问即可：http://localhost:8080/SpringException/show1... ...

自定义异常处理器，实现HandlerExceptionResolver接口

上面案例，pom文件加上servlet依赖

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.0.1</version>
            <scope>provided</scope>
        </dependency>

com.kdy.resolver中创建MyExceptionResolver实现HandlerExceptionResolver接口

public class MyExceptionResolver implements HandlerExceptionResolver {
    @Override
    public ModelAndView resolveException(javax.servlet.http.HttpServletRequest httpServletRequest, javax.servlet.http.HttpServletResponse httpServletResponse, Object o, Exception e) {
        ModelAndView modelAndView = new ModelAndView();
        if (e instanceof ClassCastException){
            modelAndView.addObject("info","类转换异常");
        }else if(e instanceof ArithmeticException){
            modelAndView.addObject("info","除零算数异常");
        }else if(e instanceof FileNotFoundException){
            modelAndView.addObject("info","文件找不到异常");
        }else if(e instanceof NullPointerException){
            modelAndView.addObject("info","空指针异常");
        }else if(e instanceof MyException){
            modelAndView.addObject("info","自定义异常");
        }
        modelAndView.setViewName("error");
        return modelAndView;
    }
}

resource下spring-mvc.xml中配置自定义异常处理器

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
       http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
    ">
    <!--Controller的组件扫描-->
    <context:component-scan base-package="com.kdy"></context:component-scan>

    <!--配置内部资源视图解析器-->
    <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/jsp/"></property><!--前缀-->
        <property name="suffix" value=".jsp"></property><!--后缀-->
    </bean>

    <!--配置异常处理器-->
<!--    <bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
        &lt;!&ndash;<property name="defaultErrorView" value="error"/>&ndash;&gt;&lt;!&ndash;默认异常视图：所有的Exception都走这个,这里由于上面写了视图解析器的前后缀，会把error拼接为/jsp/error.jsp&ndash;&gt;
        <property name="exceptionMappings">
            <map>
                <entry key="java.lang.ClassCastException" value="error1"/>
                <entry key="java.lang." value="error1"/>
                <entry key="java.lang.ClassCastException" value="error1"/>&lt;!&ndash;类转换异常&ndash;&gt;
                <entry key="java.lang.ArithmeticException" value="error2"/>&lt;!&ndash;除零异常&ndash;&gt;
                <entry key="java.io.import java.io.FileNotFoundException;" value="error3"/>&lt;!&ndash;文件找不到异常&ndash;&gt;
                <entry key="java.lang.NullPointerException" value="error4"/>&lt;!&ndash;空指针异常&ndash;&gt;
                <entry key="com.kdy.exception.MyException" value="error5"/>&lt;!&ndash;自定义异常&ndash;&gt;
            </map>
        </property>
    </bean>-->

    <!--自定义异常处理器-->
    <bean class="com.kdy.resolver.MyExceptionResolver"/>
</beans>

webapp的jsp中error.jsp改为

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>error</title>
</head>
<body>
error通用页面~~~~~~
异常类型为${info}
</body>
</html>