Question

我正在开发一个涉及几个servlet和一些jsp页面的小型MVC项目。在项目的早期，我添加了这个ErrorHandler-servlet：

package org.ics.ejb.lab;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/ErrorHandler")
public class ErrorHandler extends HttpServlet {
	private static final long serialVersionUID = 1L;
       

    public ErrorHandler() {
        super();
    }
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		processError(request, response);
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		processError(request, response);
	}
	
	private void processError(HttpServletRequest request, HttpServletResponse response) throws IOException {

		        Throwable throwable = (Throwable) request
		                .getAttribute("javax.servlet.error.exception");
		        Integer statusCode = (Integer) request
		                .getAttribute("javax.servlet.error.status_code");
		        String servletName = (String) request
		                .getAttribute("javax.servlet.error.servlet_name");
		        if (servletName == null) {
		            servletName = "Unknown";
		        }
		        String requestUri = (String) request
		                .getAttribute("javax.servlet.error.request_uri");
		        if (requestUri == null) {
		            requestUri = "Unknown";
		        }
		        
		          response.setContentType("text/html");
		      
		          PrintWriter out = response.getWriter();
		          out.write("<html><head><title>Exception/Error Details</title></head><body>");
		          if(statusCode != 500){
		              out.write("<h3>Error Details</h3>");
		              out.write("<strong>Status Code</strong>:"+statusCode+"<br>");
		              out.write("<strong>Requested URI</strong>:"+requestUri);
		          }else{
		              out.write("<h3>Exception Details</h3>");
		              out.write("<ul><li>Servlet Name:"+servletName+"</li>");
		              out.write("<li>Exception Name:"+throwable.getClass().getName()+"</li>");
		              out.write("<li>Requested URI:"+requestUri+"</li>");
		              out.write("<li>Exception Message:"+throwable.getMessage()+"</li>");
		              out.write("</ul>");
		          }
		          
		          out.write("<p>Show Mats Svensson this error message. Then go back and try again.</p>");
		         //out.write("<a href="index.html">Go back</a>");
		          out.write("<br><br>");
		          out.write("</body></html>");
		    }
}

然后我将其添加到动态Web项目的web.xml文件中：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>EmpClientProject</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
  </welcome-file-list>
    <error-page>
    <exception-type>java.lang.Throwable</exception-type>
    <location>/ErrorHandler</location>
  </error-page>
  	<servlet>
  	<servlet-name>JUnitEETestServlet</servlet-name>
 	 <servlet-class>org.junitee.servlet.JUnitEEServlet</servlet-class>
  </servlet>
  <servlet-mapping>
  <servlet-name>JUnitEETestServlet</servlet-name>
<url-pattern>/TestServlet/*</url-pattern>
</servlet-mapping>
</web-app>

它很早就开始了，但是当我添加更多内容，html页面，图像等时，ErrorHandler-servlet突然停止工作，我还没有弄清楚为什么。我想不出任何原因。

这是代表nullreferenceexception的代码，假设员工在数据库中不存在。用于捕获这个但不再存在的servlet：

package org.ics.ejb.lab;

import java.io.IOException;

import javax.ejb.EJB;
import javax.servlet.RequestDispatcher;
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 example.ejb.ics.Department;
import example.ejb.ics.Employee;
import examples.facade.ics.FacadeLocal;

@WebServlet("/EmpServlet")
public class EmpServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	
	@EJB
	FacadeLocal facade;
    public EmpServlet() {
        super();
    }

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		System.out.print("Error: Does not exist in database, try again");
	}
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String url = null;
		String operation = request.getParameter("operation");
		 
				if(operation.equals("showemployee")) {		
					String socialsn = request.getParameter("socialsn");
					Long pnr = Long.parseLong(socialsn);
					Employee e = facade.findBySocialSN(pnr);
					request.setAttribute("employee", e);
					url="/ShowEmployee.jsp";
				} else if(operation.equals("searchemployee")){
					url="/SearchEmployee.jsp";
				} else if(operation.equals("updatedept")){
					String depnr = request.getParameter("newdeptid");	
					int intdepnr = Integer.parseInt(depnr);
					Department d = facade.findByDeptId(intdepnr);				
					String socialsn = request.getParameter("employeeSN");
					Long pnr = Long.parseLong(socialsn);
					Employee e = facade.findBySocialSN(pnr);

					e.setDepartment(d);
				
					Employee updatedEmployee = facade.updateEmployee(e);
					request.setAttribute("employee", updatedEmployee);
					request.setAttribute("department", d);
					url="/ShowEmployee.jsp";
				}
				else{
					url="/SearchEmployee.jsp";
				}
				
			RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(url);
			dispatcher.forward(request, response);
	}
}

错误处理servlet停止工作，我不知道为什么:(

0 个答案: