10月24日<java web 中Filter的使用>

案例：使用Filter验证用户登录安全控制

<filter>
    <filter-name>SessionFilter</filter-name>
    <filter-class>com.action.login.SessionFilter</filter-class>
    <init-param>
        <param-name>logonStrings</param-name><!-- 对登录页面不进行过滤 -->
        <param-value>/project/index.jsp;login.do</param-value>
    </init-param>
    <init-param>
        <param-name>includeStrings</param-name><!-- 只对指定过滤参数后缀进行过滤 -->
        <param-value>.do;.jsp</param-value>
    </init-param>
    <init-param>
        <param-name>redirectPath</param-name><!-- 未通过跳转到登录界面 -->
        <param-value>/index.jsp</param-value>
    </init-param>
    <init-param>
        <param-name>disabletestfilter</param-name><!-- Y:过滤无效 -->
        <param-value>N</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>SessionFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

package com.action.login;

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.HttpServletResponseWrapper;

/**
 *    判断用户是否登录,未登录则退出系统
 */
public class SessionFilter implements Filter {
    
    public FilterConfig config;
    
    public void destroy() {
        this.config = null;
    }
    
    public static boolean isContains(String container, String[] regx) {
        boolean result = false;

        for (int i = 0; i < regx.length; i++) {
            if (container.indexOf(regx[i]) != -1) {
                return true;
            }
        }
        return result;
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest hrequest = (HttpServletRequest)request;
        HttpServletResponseWrapper wrapper = new HttpServletResponseWrapper((HttpServletResponse) response);
        
        String logonStrings = config.getInitParameter("logonStrings");        // 登录登陆页面
        String includeStrings = config.getInitParameter("includeStrings");    // 过滤资源后缀参数
        String redirectPath = hrequest.getContextPath() + config.getInitParameter("redirectPath");// 没有登陆转向页面
        String disabletestfilter = config.getInitParameter("disabletestfilter");// 过滤器是否有效
        
        if (disabletestfilter.toUpperCase().equals("Y")) {    // 过滤无效
            chain.doFilter(request, response);
            return;
        }
        String[] logonList = logonStrings.split(";");
        String[] includeList = includeStrings.split(";");
        
        if (!this.isContains(hrequest.getRequestURI(), includeList)) {// 只对指定过滤参数后缀进行过滤
            chain.doFilter(request, response);
            return;
        }
        
        if (this.isContains(hrequest.getRequestURI(), logonList)) {// 对登录页面不进行过滤
            chain.doFilter(request, response);
            return;
        }
        
        String user = ( String ) hrequest.getSession().getAttribute("useronly");//判断用户是否登录
        if (user == null) {
            wrapper.sendRedirect(redirectPath);
            return;
        }else {
            chain.doFilter(request, response);
            return;
        }
    }

    public void init(FilterConfig filterConfig) throws ServletException {
        config = filterConfig;
    }
}

 几点说明：1.request.getContextPath()得到的是web应用的路径，（e.g   /MyTest）;所以在实际应用中常常用这种方法先得到这个web应用的路径。这样方便进行移植

              2.这里面对响应的处理利用了装饰者模式，也就是在HttpServletResponse外面加了一层外衣。底层的实现还是委托给了被包装的HttpServletResponse 对象上。在这个例子中其实没有必要这样包装一下。以为仅仅进行了一个转向。但是如果要在过滤器中对响应进行一番处理的情况下。这个包装就必不可少，否则响应就会直接返回容器，而不是沿着chains层层弹栈再回到浏览器。比如要对响应的内容进行压缩，这时就如上做一个包装。就可以达到先返回过滤器再回到容器的操作。具体的实现代码看《head first servlet&jsp》p690-p694