怎样用java servelet处理异常 - 问答

在Java Servlet中处理异常的最佳实践是使用全局异常处理器。这样可以确保所有未捕获的异常都能得到适当的处理，并提供有用的错误信息给用户。以下是使用全局异常处理器处理异常的步骤：

创建一个自定义的异常类（可选）：如果你需要创建一个特定的异常类来处理Servlet中的异常，可以创建一个新的Java类，继承自Exception类或其他适当的异常类。
创建一个全局异常处理器类，实现javax.servlet.http.HttpServlet类，并重写doGet()和doPost()方法。在这些方法中，使用try-catch语句捕获异常，并处理它们。

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/globalExceptionHandler")
public class GlobalExceptionHandlerServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        handleException(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        handleException(request, response);
    }

    private void handleException(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");

        if (statusCode == null) {
            statusCode = HttpServletResponse.SC_INTERNAL_SERVER_ERROR;
        }

        response.setContentType("text/html;charset=UTF-8");
        response.setStatus(statusCode);

        request.setAttribute("errorMessage", "An error occurred while processing your request.");
        request.getRequestDispatcher("/errorPage.jsp").forward(request, response);
    }
}

在web.xml中配置全局异常处理器Servlet：

<servlet>
    <servlet-name>GlobalExceptionHandlerServlet</servlet-name>
    <servlet-class>com.example.GlobalExceptionHandlerServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>GlobalExceptionHandlerServlet</servlet-name>
    <url-pattern>/globalExceptionHandler</url-pattern>
</servlet-mapping>

或者在Spring Boot应用中，使用@ControllerAdvice和@ExceptionHandler注解创建一个全局异常处理类：

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.servlet.ModelAndView;

@ControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(Exception.class)
    public ResponseEntity<Object> handleException(Exception ex) {
        ModelAndView modelAndView = new ModelAndView("errorPage");
        modelAndView.addObject("errorMessage", "An error occurred while processing your request.");
        return new ResponseEntity<>(modelAndView, HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

在应用中抛出异常：

当你的Servlet或其他组件遇到异常时，将异常对象设置到请求属性中，如下所示：

try {
    // Your code that might throw an exception
} catch (Exception ex) {
    request.setAttribute("javax.servlet.error.status_code", HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
    throw ex;
}

这样，当异常发生时，全局异常处理器将捕获它，并返回适当的错误页面给用户。

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