Unified handling of global exceptions

stay JavaEE Project development , Regardless of the underlying database operation process , Or the business layer process , Or the process of control layer , It's inevitable to encounter all kinds of predictable 、 Unexpected exceptions need to be handled . Each procedure handles the exception separately , Highly coupled code , The workload is heavy and not uniform , Maintenance work is also very heavy .

SpringMVC Support for exception handling , adopt SpringMVC Provides a global exception handling mechanism , It can decouple all types of exception handling from each processing process , It ensures that the function of the relevant processing process is relatively single , It also realizes the unified processing and maintenance of exception information .

Implementation of global exception Spring MVC There are many ways to handle exceptions 3 Ways of planting ：

1. Use Spring MVC The simple exception handler provided SimpleMappingExceptionResolver
2. Realization Spring Exception handling interface HandlerExceptionResolver Customize your own exception handler
3. Use @ExceptionHandler Annotation implements exception handling

Global exception handling method 1

The processor is abnormally simple to configure

To configure SimpleMappingExceptionResolver object

    <!--  Configure the method of unified handling of global exceptions  Bean （ Simple exception handler ） -->
    <bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver"> 
        <!--  An exception occurred while forwarding the page , Set the default error page  （error Represents a view ） -->
        <property name="defaultErrorView" value="error"></property> 
        <!--  When an exception occurs , Set the variable name of the exception  -->
        <property name="exceptionAttribute" value="ex"></property>
    </bean>

You can get exception information on the exception handling page

${
    ex}

Use custom exception

Parameter exception

/***  Custom exception ： Parameter exception  */
public class ParamsException extends RuntimeException {
    
    private Integer code = 300;
    private String msg = " Parameter exception !";

    public ParamsException() {
    
        super(" Parameter exception !");
    }

    public ParamsException(String msg) {
    
        super(msg);
        this.msg = msg;
    }

    public ParamsException(Integer code) {
    
        super(" Parameter exception !");
        this.code = code;
    }

    public ParamsException(Integer code, String msg) {
    
        super(msg);
        this.code = code;
        this.msg = msg;
    }

    public Integer getCode() {
    
        return code;
    }

    public void setCode(Integer code) {
    
        this.code = code;
    }

    public String getMsg() {
    
        return msg;
    }

    public void setMsg(String msg) {
    
        this.msg = msg;
    }
}

Business exceptions

/***  Custom exception ： Business exceptions  */
public class BusinessException extends RuntimeException {
    
    private Integer code = 400;
    private String msg = " Business exceptions !";

    public BusinessException() {
    
        super(" Business exceptions !");
    }

    public BusinessException(String msg) {
    
        super(msg);
        this.msg = msg;
    }

    public BusinessException(Integer code) {
    
        super(" Business exceptions !");
        this.code = code;
    }

    public BusinessException(Integer code, String msg) {
    
        super(msg);
        this.code = code;
        this.msg = msg;
    }

    public Integer getCode() {
    
        return code;
    }

    public void setCode(Integer code) {
    
        this.code = code;
    }

    public String getMsg() {
    
        return msg;
    }

    public void setMsg(String msg) {
    
        this.msg = msg;
    }
}

Set the mapping between custom exception and page

    <!--  Set the mapping between custom exception and page  -->
    <property name="exceptionMappings">
        <props> <!-- key： The path of the custom exception object ;  Set the view name of the specific processing page in the tag -->
            <prop key="com.xxxx.ssm.exception.BusinessException">buss_error</prop>
            <prop key="com.xxxx.ssm.exception.ParamsException">params_error</prop>
        </props>
    </property>

Use SimpleMappingExceptionResolver Do exception handling , It's easy to integrate 、 It has good expansibility 、 It has no advantages such as invasiveness to existing code , But this method can only get exception information , If something goes wrong , Not applicable to cases where data other than exception is required .

Global exception handling method 2 ( recommend )

Realization HandlerExceptionResolver Interface

/***  Unified handling of global exceptions  */
@Component
public class GlobalExceptionResolver implements HandlerExceptionResolver {
    
    @Override
    public ModelAndView resolveException(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object handler, Exception ex) {
    
        ModelAndView mv = new ModelAndView("error");
        mv.addObject("ex", " Default error message ");
        return mv;
    }
}

Custom exception handling

/***  Unified handling of global exceptions  */
@Component
public class GlobalExceptionResolver implements HandlerExceptionResolver {
    
    @Override
    public ModelAndView resolveException(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object handler, Exception ex) {
    
        ModelAndView mv = new ModelAndView("error");
        mv.addObject("ex", " Default error message ");
        //  Determine whether it is a custom exception 
        if (ex instanceof ParamsException) {
    
            mv.setViewName("params_error");
            ParamsException e = (ParamsException) ex;
            mv.addObject("ex", e.getMsg());
        }
        if (ex instanceof BusinessException) {
    

            mv.setViewName("business_error");
            BusinessException e = (BusinessException) ex;
            mv.addObject("ex", e.getMsg());
        }
        return mv;
    }
}
        

Use to implement HandlerExceptionResolver Interface exception handler for exception handling , It's easy to integrate 、 It has good expansibility 、 It has no advantages such as invasiveness to existing code , meanwhile , During exception handling, the object causing the exception can be obtained , Help to provide more detailed exception handling information .

Global exception handling method 3

Page processor inherits BaseController

public class BaseController {
    
    @ExceptionHandler
    public String exc(HttpServletRequest request, HttpServletResponse response, Exception ex) {
    
        request.setAttribute("ex", ex);
        if (ex instanceof ParamsException) {
    
            return "error_param";
        }
        if (ex instanceof BusinessException) {
    
            return "error_business";
        }
        return "error";
    }
}

Use @ExceptionHandler Annotation implements exception handling , It's easy to integrate 、 It has good expansibility （ Just need to be exception handling Controller Class inherited from BaseController that will do ）、 There is no need to attach Spring Configuration and other advantages , But this method is invasive to the existing code ( Existing code needs to be modified , Make related classes inherit from BaseController), Data other than exception cannot be obtained during exception handling .

Exception handling not caught

about Unchecked Exception for , Because code does not force capture , Often overlooked , If the runtime produces Unchecked Exception, And there is no corresponding capture and processing in the code , Then we may have to face the embarrassment of 404、500…… Wait for the server internal error prompt page .

At this time, we need a comprehensive and effective exception handling mechanism . At present, most servers also support in web.xml Pass through (Websphere/Weblogic) perhaps (Tomcat) Node configuration specific exception display page . modify web.xml file , Add the following ：

    <!--  Error page definition  -->
    <error-page>
        <exception-type>java.lang.Throwable</exception-type>
        <location>/500.jsp</location>
    </error-page>
    <error-page>
        <error-code>500</error-code>
        <location>/500.jsp</location>
    </error-page>
    <error-page>
        <error-code>404</error-code>
        <location>/404.jsp</location>
    </error-page>