SpringMVC框架08——统一异常处理

前言

在Spring MVC 应用的开发中，不管是对底层数据库操作，还是业务层或控制层操作，都会不可避免地遇到各种可预知的、不可预知的异常需要处理。如果每个过程都单独处理异常，那么系统的代码耦合度高，工作量大且不好统一，以后维护的工作量也很大。
在Spring MVC中提供了三种统一异常处理的方式，能够将所有类型的异常处理从各层中解耦出来，这样既保证了相关处理过程的功能单一，又实现了异常信息的统一处理和维护。

1、演示案例准备

为了验证Spring MVC 框架的3中异常处理方式，需要编写一个测试的应用，从Dao层、Service层、Controller层分别抛出不同的异常。本教程指定了3个异常，分别是：SQLException、自定义异常和未知异常，然后分别集成3种方式进行异常处理。
分别创建相应的包和类，如下图所示：

（1）创建自定义异常类MyException

代码示例：

package com.demo.exception;

public class MyException extends Exception {
    public MyException() {
    }

    public MyException(String message) {
        super(message);
    }
}

（2）创建Dao层异常类

代码示例：

package com.demo.dao;

import com.demo.exception.MyException;
import org.springframework.stereotype.Repository;
import java.sql.SQLException;

@Repository("testExceptionDao")
public class TestExceptionDao {

    public void daodb() throws SQLException {
        throw new SQLException("Dao中数据库异常");
    }

    public void daomy() throws MyException {
        throw new MyException("Dao中自定义异常");
    }

    public void daono() throws Exception {
        throw new Exception("Dao中的未知异常");
    }

}

（3）创建Service层异常类

在service包下创建TestExceptionService接口和TestExceptionServiceImpl实现类，在该接口中定义6个方法，其中有3个是调用Dao层，有3个是Service层的方法。
TestExceptionService接口代码示例：

package com.demo.service;

public interface TestExceptionService {
    public void servicedb() throws Exception;
    public void servicemy() throws Exception;
    public void serviceno() throws Exception;
    public void daodb() throws Exception;
    public void daomy() throws Exception;
    public void daono() throws Exception;
}

TestExceptionServiceImpl实现类代码示例：

package com.demo.service;

import com.demo.dao.TestExceptionDao;
import com.demo.exception.MyException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.sql.SQLException;

@Service("testExceptionService")
public class TestExceptionServiceImpl implements TestExceptionService {

    @Autowired
    private TestExceptionDao testExceptionDao;

    @Override
    public void servicedb() throws Exception {
        throw new SQLException("Service中数据库异常");
    }

    @Override
    public void servicemy() throws Exception {
        throw new MyException("Service中自定义异常");
    }

    @Override
    public void serviceno() throws Exception {
        throw new Exception("Service中未知异常");
    }

    @Override
    public void daodb() throws Exception {
        testExceptionDao.daodb();
    }

    @Override
    public void daomy() throws Exception {
        testExceptionDao.daomy();
    }

    @Override
    public void daono() throws Exception {
        testExceptionDao.daono();
    }

}

（4）创建控制器层异常类

代码示例：

package com.demo.controller;

import com.demo.exception.MyException;
import com.demo.service.TestExceptionService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

import java.sql.SQLException;

@Controller
public class TestExceptionController {
    @Autowired
    private TestExceptionService testExceptionService;

    @RequestMapping("/db")
    public void db() throws SQLException {
        throw new SQLException("控制器中数据库异常");
    }

    @RequestMapping("/my")
    public void my() throws MyException {
        throw new MyException("控制器中自定义异常");
    }

    @RequestMapping("no")
    public void no() throws Exception {
        throw new Exception("控制器中未知异常");
    }

    @RequestMapping("/servicedb")
    public void servicedb() throws Exception {
        testExceptionService.servicedb();
    }

    @RequestMapping("/servicemy")
    public void servicemy() throws Exception {
        testExceptionService.servicemy();
    }

    @RequestMapping("/serviceno")
    public void serviceno() throws Exception {
        testExceptionService.serviceno();
    }

    @RequestMapping("/daodb")
    public void daodb() throws Exception {
        testExceptionService.daodb();
    }

    @RequestMapping("/daomy")
    public void daomy() throws Exception {
        testExceptionService.daomy();
    }

    @RequestMapping("/daono")
    public void daono() throws Exception {
        testExceptionService.daono();
    }

}

（5）创建View视图层

View层共有5个JSP页面，分别是：
测试应用首页index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %>
<html>
<body>
<h1>演示案例</h1>
<p>
    <a href="${pageContext.request.contextPath}/daodb">处理dao中数据库异常</a>
</p>
<p>
    <a href="${pageContext.request.contextPath}/daomy">处理dao中自定义异常</a>
</p>
<p>
    <a href="${pageContext.request.contextPath}/daono">处理dao中未知异常</a>
</p>
<p>
    <a href="${pageContext.request.contextPath}/servicedb">处理service中数据库异常</a>
</p>
<p>
    <a href="${pageContext.request.contextPath}/servicemy">处理service中自定义异常</a>
</p>
<p>
    <a href="${pageContext.request.contextPath}/serviceno">处理service中未知异常</a>
</p>
<p>
    <a href="${pageContext.request.contextPath}/db">处理controller中数据库异常</a>
</p>
<p>
    <a href="${pageContext.request.contextPath}/my">处理controller中自定义异常</a>
</p>
<p>
    <a href="${pageContext.request.contextPath}/no">处理controller中未知异常</a>
</p>
</body>
</html>

404错误对应页面404.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>404</title>
</head>
<body>
    <h2>资源不存在</h2>
</body>
</html>

未知异常对应页面error.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" isErrorPage="true" %>
<html>
<head>
    <title>未知异常</title>
</head>
<body>
    <h1>未知错误：</h1>
    <%=exception%>
    <h2>错误内容：</h2>
    <%
        exception.printStackTrace(response.getWriter());
    %>
</body>
</html>

自定义异常对应页面my-error.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" isErrorPage="true" %>
<html>
<head>
    <title>自定义异常</title>
</head>
<body>
    <h1>自定义异常错误：</h1>
    <%=exception%>
    <h2>错误内容：</h2>
    <%
        exception.printStackTrace(response.getWriter());
    %>
</body>
</html>

SQL异常对应页面sql-error.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" isErrorPage="true" %>
<html>
<head>
    <title>数据库异常</title>
</head>
<body>
    <h1>数据库异常错误：</h1>
    <%=exception%>
    <h2>错误内容：</h2>
    <%
        exception.printStackTrace(response.getWriter());
    %>
</body>
</html>

（6）配置全局异常处理

在web.xml中配置全局异常404处理

<!--配置全局异常-->
<error-page>
  <error-code>404</error-code>
  <location>/404.jsp</location>
</error-page>

2、使用配置统一处理异常

在springmvc.xml中配置org.springframework.web.servlet.handler.SimpleMappingExceptionResolver类，并且要提前配置异常类和View的对应关系。
springmvc.xml配置代码如下：

<?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:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">

    <!--将AnnotationHandler自动扫描到IOC容器中-->
    <context:component-scan base-package="com"></context:component-scan>

    <!--配置视图解析器-->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <!--配置前缀-->
        <property name="prefix" value="/"></property>
        <!--配置后缀-->
        <property name="suffix" value=".jsp"></property>
    </bean>

    <!--配置异常相关-->
    <bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
        <!--定义默认的异常处理页面，当该异常类型注册时使用-->
        <property name="defaultErrorView" value="error"></property>
        <!--定义异常处理页面用来获取异常信息的变量名，默认名为exception-->
        <property name="exceptionAttribute" value="ex"></property>
        <!--定义需要特殊处理的异常，用类名或完全路径名作为key，异常页名作为值-->
        <property name="exceptionMappings">
            <props>
                <prop key="com.demo.exception.MyException">my-error</prop>
                <prop key="java.sql.SQLException">sql-error</prop>
                <!--在这里还可以继续扩展对不同异常类型的处理-->
            </props>
        </property>
    </bean>

</beans>

演示效果：

404演示效果：

3、使用接口统一处理异常

org.springframework.web.servlet.HandlerExceptionResolver 接口用于解析请求处理过程中所产生的异常。在exception包中创建一个HandlerExceptionResolver接口的实现类MyExceptionHandler，代码如下：

package com.demo.exception;

import org.springframework.web.servlet.HandlerExceptionResolver;
import org.springframework.web.servlet.ModelAndView;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;

public class MyExceptionHandler implements HandlerExceptionResolver {
    @Override
    public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object obj, Exception e) {
        Map<String,Object> model = new HashMap<String,Object>();
        model.put("ex",e);
        //根据不同错误转向不同页面（统一处理），即异常与View的对应关系
        if (e instanceof MyException) {
            return new ModelAndView("my-error",model);
        }else if (e instanceof SQLException) {
            return new ModelAndView("sql-error",model);
        }else {
            return new ModelAndView("error",model);
        }
    }
}

在springmvc.xml文件中配置实现类MyExceptionHandler的托管

<?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:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd">

    <!--将AnnotationHandler自动扫描到IOC容器中-->
    <context:component-scan base-package="com"></context:component-scan>

    <!--配置视图解析器-->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <!--配置前缀-->
        <property name="prefix" value="/"></property>
        <!--配置后缀-->
        <property name="suffix" value=".jsp"></property>
    </bean>

    <!--托管MyExceptionHandler-->
    <bean class="com.demo.exception.MyExceptionHandler"></bean>

</beans>

4、使用注解统一处理异常

在controller包下创建BaseController类，并在该类的方法中使用@ExceptionHandler注解声明异常处理方法，代码如下：

package com.demo.controller;

import com.demo.exception.MyException;
import org.springframework.web.bind.annotation.ExceptionHandler;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.sql.SQLException;

public abstract class BaseController {

    @ExceptionHandler
    public String exception(HttpServletRequest request, HttpServletResponse response,Exception e){
        request.setAttribute("ex",e);
        if (e instanceof MyException) {
            return "my-error";
        } else if (e instanceof SQLException) {
            return "sql-error";
        } else {
            return "error";
        }
    }
}

将所有需要异常处理的Controller都继承BaseController类，示例代码如下：

@Controller
public class TestExceptionController extends BaseController{
    //...
}