异常处理

当servlet出现异常时，servlet容器使用exception-type元素来找到与抛出的异常类型相匹配的配置

public class ExceptionHandler extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Throwable throwable = (Throwable) req.getAttribute("javax.servlet.error.exception");
        Integer code = (Integer) req.getAttribute("javax.servlet.error.status_code");
        String message = (String) req.getAttribute("javax.servlet.error.message");
        System.out.println("=========");
        System.out.println(throwable);
        System.out.println("=========");
        System.out.println(code);
        System.out.println("=========");
        System.out.println(message);
    }
}

<!-- 配置异常处理的servlet -->
<servlet>
    <servlet-name>ExceptionHandler</servlet-name>
    <servlet-class>com.zhanghe.study.servlet.ExceptionHandler</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>ExceptionHandler</servlet-name>
    <url-pattern>/ExceptionHandler</url-pattern>
</servlet-mapping>
<!-- 配置哪些错误码会调用该异常处理类 -->
<error-page>
    <error-code>404</error-code>
    <location>/ExceptionHandler</location>
</error-page>
<!-- 配置哪些异常类型会调用该异常处理类 -->
<error-page>
    <exception-type>java.lang.ArithmeticException</exception-type>
    <location>/ExceptionHandler</location>
</error-page>

如果出现异常，会在请求域中设置相应的属性

可以使用request.getAttribute(“”)取出

javax.servlet.error.status_code //错误码，Integer类型
javax.servlet.error.exception_type  // 异常类型，Class类型
javax.servlet.error.message    //异常信息,String类型
javax.servlet.error.request_uri  //出现异常的uri地址，String类型
javax.servlet.error.exception  //异常，Throwable类型
javax.servlet.error.servlet_name  //servlet名称，String类型