<param-name>noLoginPaths</param-name>  引數名可自取

 <filter>
        <filter-name>LoginFilter</filter-name>
        <filter-class>com.imooc.filter.LoginFilter</filter-class>
        <init-param>
            <param-name>noLoginPaths</param-name>
            <param-value>login.jsp;fail.jsp;LoginServlet</param-value>
        </init-param>
        <init-param>
            <param-name>charset</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>LoginFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
 

StringnoLoginPaths=config.getInitParameter("noLoginPaths");  

然後通過判斷使用者請求的url 是否符合 noLoginPaths 中設定的不過濾選項，如果如何，就呼叫do.filter放行

關鍵程式碼 

if(noLoginPaths!=null){
			String[] strArray = noLoginPaths.split(";");
			for (int i = 0; i < strArray.length; i++) {
				
				if(strArray[i]==null || "".equals(strArray[i]))continue;
				
				if(request.getRequestURI().indexOf(strArray[i])!=-1 ){
					arg2.doFilter(arg0, arg1);
					return;
				}
			}
			
		}
 

完整程式碼

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;
import javax.servlet.http.HttpSession;

public class LoginFilter implements Filter {

	private FilterConfig config;
	
	@Override
	public void destroy() {

	}

	@Override
	public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2) throws IOException, ServletException {

		HttpServletRequest request = (HttpServletRequest) arg0;
		HttpServletResponse response = (HttpServletResponse) arg1;
		HttpSession session = request.getSession();
		
		String noLoginPaths = config.getInitParameter("noLoginPaths");
		
		String charset = config.getInitParameter("charset");
		if(charset==null){
			charset = "UTF-8";
		}
		request.setCharacterEncoding(charset);
		
		if(noLoginPaths!=null){
			String[] strArray = noLoginPaths.split(";");
			for (int i = 0; i < strArray.length; i++) {
				
				if(strArray[i]==null || "".equals(strArray[i]))continue;
				
				if(request.getRequestURI().indexOf(strArray[i])!=-1 ){
					arg2.doFilter(arg0, arg1);
					return;
				}
			}
			
		}
		
		
		
		
		if(session.getAttribute("username")!=null){
			arg2.doFilter(arg0, arg1);
		}else{
			response.sendRedirect("login.jsp");
		}
		
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		config = arg0;
	}

}