EE filter 问题 - 黑马程序员技术交流社区

package com.itheima.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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public abstract class AbstractFilter implements Filter {
private FilterConfig filterConfig;
public void init(FilterConfig filterConfig) throws ServletException {
this.filterConfig = filterConfig;
init();
}
public void init()throws ServletException{
}
public FilterConfig getFilterConfig() {
return filterConfig;
}
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request;
HttpServletResponse response;
try{
request = (HttpServletRequest)req;----------------？？？？？？？？？
response = (HttpServletResponse)resp;？？？？？？？？？？？？？？？？？？
}catch(Exception e){
throw new RuntimeException("non-http request or response");
}
doFilter(request, response, chain);
}
public abstract void doFilter(HttpServletRequest request, HttpServletResponse response,
FilterChain chain) throws IOException, ServletException;
public void destroy() {
}
}
有问号那两行，为什么强转。

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