由于项目需要,需要内外网都能同时访问，原本的不能符合要求，只能着手修改，以下是 修改步骤。我用的是cas-client-core-3.3.3.jar的客户端版本
1.获得cas-client-core-3.3.3.jar的源码。
2.新增工具类CustomConfigUtil,我把工具类放在org.jasig.cas.client.util下。

package org.jasig.cas.client.util;
 
import java.util.HashMap;
import java.util.Map;
 
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
 
public class CustomConfigUtil {
     
    /**
     * @Description 获取属性文件中的属性信息
     * @return
     */
    public static Map<String, String> getCustomConfig(
            final ServletContext servletContext,
            final HttpServletRequest request) {
        Map<String, String> map = new HashMap<String, String>();
        Map<String, String> map2 = HttpConnectionUtil.getServiceUrlMap();
        //读取配置文件
        Map<String, String> segmentMap = PropertiesUtil.readProperties(CustomConfigUtil.class.getResource("/").getPath() + "segment.properties");
        boolean falg = false;
        for (String key : segmentMap.keySet()) {
            //判断是否属于某个网段
            falg =  HttpConnectionUtil.ipIsValid(segmentMap.get(key), request.getRemoteAddr());
            if(falg){
                break;
            }
        }
        // 判断请求是从外网访问还是从内网访问
        if (falg) {
            //client客户端地址
            map.put("client", map2.get("cas.inClient"));
            //cas服务器地址
            map.put("casServerTicketUrl", map2.get("cas.inCasServer"));
            //cas服务器地址
            map.put("casServerTicket", map2.get("cas.inCasServerTicket"));
        } else {
            //client客户端地址
            map.put("client", map2.get("cas.outClient"));
            //cas服务器地址
            map.put("casServerTicketUrl", map2.get("cas.outCasServer"));
            //cas服务器地址
            boolean flag =  HttpConnectionUtil.isConnection(map2.get("cas.outCasServerTicket"));
            if(flag){
                map.put("casServerTicket", map2.get("cas.outCasServerTicket"));
            }else{
                map.put("casServerTicket", map2.get("cas.inCasServerTicket"));
            }
        }
        return map;
    }
}

3.新增工具类HttpConnectionUtil 代码如下

package org.jasig.cas.client.util;
 
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Map;
 
public class HttpConnectionUtil {
 
    /**
     * 测试网络是否能连接通畅
     *
     * @param serviceURL
     * @return
     */
    public static boolean isConnection(String serviceURL) {
        try {
            URL url = new URL(serviceURL);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(2000);// 2秒则超时
            conn.setReadTimeout(2000);
            int state = conn.getResponseCode();
            if (state == 200) {
                return true;
            }
        } catch (Exception e) {
            return false;
        }
        return false;
    }
 
    public static boolean ipIsValid(String ipSection, String ip) { 
        if (ipSection == null)
            throw new NullPointerException("IP段不能为空！"); 
        if (ip == null)
            throw new NullPointerException("IP不能为空！"); 
        ipSection = ipSection.trim();
        ip = ip.trim();
        final String REGX_IP = "((25[0-5]|2[0-4]\\d|1\\d{2}|[1-9]\\d|\\d)\\.){3}(25[0-5]|2[0-4]\\d|1\\d{2}|[1-9]\\d|\\d)"; 
        final String REGX_IPB = REGX_IP + "\\-" + REGX_IP; 
        if (!ipSection.matches(REGX_IPB) || !ip.matches(REGX_IP)) 
            return false; 
        int idx = ipSection.indexOf('-'); 
        String[] sips = ipSection.substring(0, idx).split("\\."); 
        String[] sipe = ipSection.substring(idx + 1).split("\\."); 
        String[] sipt = ip.split("\\."); 
        long ips = 0L, ipe = 0L, ipt = 0L; 
        for (int i = 0; i < 4; ++i) { 
            ips = ips << 8 | Integer.parseInt(sips[i]); 
            ipe = ipe << 8 | Integer.parseInt(sipe[i]); 
            ipt = ipt << 8 | Integer.parseInt(sipt[i]); 
        } 
        if (ips > ipe) { 
            long t = ips; 
            ips = ipe; 
            ipe = t; 
        } 
        return ips <= ipt && ipt <= ipe; 
    }
 
    public static void main(String[] args) {
        if (ipIsValid("127.0.0.1-127.0.0.1", "127.0.0.1")) {
            System.out.println("ip属于该网段");
        } else{
            System.out.println("ip不属于该网段");
        }
    }
      
      
     /**
     * 获取配置文件信息
     *
     * @return
     */
     public static Map<String, String> getServiceUrlMap() {
         return PropertiesUtil.readProperties(HttpConnectionUtil.class
                 .getResource("/").getPath() + "cas-service.properties");
     }
 
 
}

4.新增工具类：PropertiesUtil：

package org.jasig.cas.client.util;
 
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;
 
public class PropertiesUtil {
 
    public static Map<String, String> readProperties(String path) {
         
        Map<String, String> map = new HashMap<String, String>();
        try {
            Properties props = new Properties();
//          System.out.println(path);
            props.load(new FileInputStream(path));
            Enumeration<?> enum1 = props.propertyNames();
            while(enum1.hasMoreElements()) {
              String strKey = (String) enum1.nextElement();
              String strValue = props.getProperty(strKey);
              map.put(strKey, strValue);
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return map;
    }
}

5.所属的两个配置文件
cas-service.properties文件：

#cas服务端的内网和外网
cas.inCasServer=http://10.206.20.52:8982/cas
cas.outCasServer=http://218.6.169.98:18982/cas

#客户端的内网和外网
cas.inClient=http://10.206.20.52:8982/tickets
cas.outClient=http://218.6.169.98:18982/tickets

#服务端的内网和外网
cas.inCasServerTicket=http://10.206.20.52:8982/cas
cas.outCasServerTicket=http://218.6.169.98:18982/cas

segment.properties文件：

#网段
segment_1 =10.0.0.0-10.255.255.255
segment_2 =172.16.0.0-172.31.255.255
segment_3 =192.168.0.0-192.168.255.255
segment_4 =172.10.0.0-172.31.255.255

6.做好以上工作开始修改源码,首先修改AuthenticationFilte ,添加静态属性
public static final String CONST_CAS_GATEWAY = "const_cas_gateway";
然后找到方法：doFilter 方法内容修改为：

public final void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
    throws IOException, ServletException
  {
    HttpServletRequest request = (HttpServletRequest)servletRequest;
    HttpServletResponse response = (HttpServletResponse)servletResponse;
    HttpSession session = request.getSession(false);
    String ticket = request.getParameter(getArtifactParameterName());
    Assertion assertion = session != null ? 
      (Assertion)session.getAttribute("_const_cas_assertion_") : null;
    boolean wasGatewayed = (session != null) && 
      (session.getAttribute("_const_cas_gateway_") != null);
    
    String isToLogout = request.getParameter("isToLogout");
    if ((CommonUtils.isBlank(ticket)) && (assertion == null) && (!wasGatewayed) && 
      (!"1".equals(isToLogout)))
    {
      this.logger.debug("noticket and no assertion found");
      if (this.gateway)
      {
        this.logger.debug("settinggateway attribute in session");
        request.getSession(true).setAttribute("_const_cas_gateway_", "yes");
      }
　　　　//修改部分
      String serviceUrl = constructServiceUrl(request, response, 
        "auth");
      
      Map<String, String> config = CustomConfigUtil.getCustomConfig(
        request.getServletContext(), request);
      this.casServerLoginUrl = ((String)config.get("casServerTicketUrl")).toString();
      setCasServerLoginUrl(((String)config.get("casServerTicketUrl")).toString());
      String urlToRedirectTo = CommonUtils.constructRedirectUrl(
        this.casServerLoginUrl, getServiceParameterName(), 
        serviceUrl, this.renew, this.gateway);
      if (this.logger.isDebugEnabled()) {
        this.logger.debug("redirectingto \"" + urlToRedirectTo + "\"");
      }
      response.sendRedirect(urlToRedirectTo);
      return;
    }
    if (session != null)
    {
      this.logger.debug("removinggateway attribute from session");
      session.setAttribute("_const_cas_gateway_", null);
    }
    filterChain.doFilter(request, response);
  }

7.修改后constructServiceUrl报错 因为之前该方法只有两个参数 现在修改为3个 找到改方法的类AbstractCasFilter
源码在113行那样constructServiceUrl重载该方法：

protected final String constructServiceUrl(final HttpServletRequest request, final HttpServletResponse response,final String type) {
        //从配置文件中取出cas服务器的登陆地址
      Map<String,String> config = CustomConfigUtil.getCustomConfig(request.getServletContext(),request);
      if("auth".equals(type)){
          this.serverName = config.get("client").toString();
          this.service = config.get("client").toString();
      }else if("validation".equals(type)){
          this.serverName = config.get("casServerTicket").toString();
          this.service = config.get("client").toString();
}

注意 该方法调用的地方还有几个 需要全部都修改为重载的方法 可以先不忙重载, 先在原方法修改 看到源码报错的地方修改后在做调整，其他地方调整后传人参数为：“validation”
很多地方写的不是很好，配置文件那些有的都直接到里面固定了，有些还需要优化 不过总体来说 是可以实现了内网和外网的通用访问。

具体项目和说明示例可下载：
http://pan.baidu.com/s/1sklXCK1