Servlet 中使用 RequestDispatcher 来集中处理异常-优快云博客

[b]Servlet 中使用 RequestDispatcher 来集中处理异常[/b]

利用Servlet 的 RequestDispatcher 方法，可以将不同的异常封装在请求中，发给一个 Servlet 来统一处理，可以有效的避免代码重复，提高管理效率。

举例如下：

测试环境：JDK1.6.0_21 Tomcat6.0.29

第一步：创建一个产生异常的Servlet(DemoServlet)

package cn.test;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DemoServlet extends HttpServlet {

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		try{
			int a=100;
			int b=0;
			int c=a/b;

		}catch(ArithmeticException ae){
			request.setAttribute("servletException",ae);
			request.setAttribute("servletExceptionUrl", request.getRequestURI());
			RequestDispatcher rd = request.getRequestDispatcher("ExceptionHandlerServlet");
			rd.forward(request, response);
		}
	}
}

第二步：建立一个处理异常的Servlet(ExceptionHandlerServlet)

package cn.test;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ExceptionHandlerServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
    		throws ServletException, IOException {

    	response.setContentType("text/html;charset=GB2312");
		PrintWriter out = response.getWriter();

		out.println("<html><head><title>系统错误</title></head>");
		out.println("<body>");
		String uri = (String) request.getAttribute("servletExceptionUrl");
		Object msg = request.getAttribute("servletException");
		out.println("<p>错误位置：" + uri + "</p>");
		out.println("<p>错误信息：[" + msg + "]</p>");
		out.println("</body></html>");
		out.close();	
    }
}

web.xml的配置信息:

 <servlet>
    <description></description>
    <display-name>DemoServlet</display-name>
    <servlet-name>DemoServlet</servlet-name>
    <servlet-class>cn.test.DemoServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>DemoServlet</servlet-name>
    <url-pattern>/Demo</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>ExceptionHandlerServlet</display-name>
    <servlet-name>ExceptionHandlerServlet</servlet-name>
    <servlet-class>cn.test.ExceptionHandlerServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ExceptionHandlerServlet</servlet-name>
    <url-pattern>/ExceptionHandlerServlet</url-pattern>
  </servlet-mapping>

网页显示如下信息：

[img]http://dl.iteye.com/upload/picture/pic/72864/aa604aa9-e858-341f-a639-7f7042282888.jpg[/img]

我们可以对这个Servlet进行统一的包装，使他成为一个中央错误页。还有一个好处就是报错是自定义的页面而不是Tomcat默认的页面，没有容器的相关信息。