Filter的细节三学习笔记

当需要过滤include请求的资源时，可以设置dispatcher为INCLUDE过滤方式
d)当需要过滤error请求的资源时，可以设置dispatcher为ERROR过滤方式
注意：一定在要web.xml文件声明错误代码或类型
`<error-page>
<error-code>500</error-code>
<location>/sys_500.jsp</location>
</error-page>

<filter-mapping>
<filter-name>MappingFilter</filter-name>
<url-pattern>/*</url-pattern>

<dispatcher>ERROR</dispatcher>

</filter-mapping>
`

e)对于过滤Servlet资源时，即可使用url-pattern，又可以使用servlet-name
f)一个Filter可以过滤1个或N个资源

</filter>
<filter-mapping>
<filter-name>MappingFilter</filter-name>
<url-pattern>/FromServlet</url-pattern>
<dispatcher>REQUEST</dispatcher>
<dispatcher>FORWARD</dispatcher>
<dispatcher>INCLUDE</dispatcher>
<dispatcher>ERROR</dispatcher>
</filter-mapping>
<filter-mapping>
<filter-name>MappingFilter</filter-name>
<url-pattern>/ToServlet</url-pattern>
<dispatcher>REQUEST</dispatcher>
</filter-mapping>
<filter>`

import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;public class MappingFilter implements Filter {    public void destroy() {    }    public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {        System.out.println("MappingFilter::doFilter():A");        chain.doFilter(request,response);        System.out.println("MappingFilter::doFilter():B");        System.out.println("模拟正在写日志Log4J");    }    public void init(FilterConfig filterConfig) throws ServletException {    }}//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 ToServlet extends HttpServlet {    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {        System.out.println("ToServlet::doGet()");        //int i = 10 / 0;    }}//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 FromServlet extends HttpServlet {    public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {        System.out.println("FromServlet::doGet()");        request.getRequestDispatcher("/ToServlet").forward(request,response);        //request.getRequestDispatcher("/ToServlet").include(request,response);    }}