今天上午10：00开始，空间换IP，中断访问数小时。我在域名控制面板中更改了dns记录，把域名指向新的IP后，大概1个多小时吧，新的域名解析就生效了。原来听说域名解析要6个小时以上才会生效，现在生效时间这么快，是现在的技术更新了，还是只是局部用户访问有效呢（比如外国用户访问时就并没有生效，也就是说全球的IP解析生效不同步）？我就不得而知了。网络方面的知识还是太少了。
空间恢复访问后，基本上是正常。但是我发现本站生成静态文件的部分不能工作了。下面这段代码执行出错：
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
...
URL url = new URL(str);
URLConnection connection = url.openConnection();
connection.connect();
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报错为：
java.net.ConnectException: Connection timed out: connect
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后来，连这个状态都达在到了，报错为：
java.net.UnknownHostException: java.learndiary.com
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上网查了资料，感觉下面这个论坛的问题跟我碰到的有点相像：
http://forum.java.sun.com/thread.jspa?threadID=450114&messageID=2043150
其中最后那位朋友的回复启发了我如下：
ckelley114
Posts:1
Registered: 4/5/06
java.net.ConnectException: Connection timed out
Apr 5, 2006 7:55 AM (reply 3 of 3)
Click to email this message
This is a remote site connection to the internet with a DSL modem and a Cisco pix fire wall. When they get this message they can still use the internet, but can not use the current application. The server is a Windows 2000. To release them they have to cycle the power to the DSL modem and Cisco pix. Can you tell me what is causing this problem?
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我连猜带蒙看他的大意是:远程站点通过一个DSL modem和一个Cisco pix防火墙连接到因特网。通过因特网访问能够工作，但是当前的应用访问不能工作，会得到上面的出错信息。是windows2000服务器。解决这个问题必须使访问通过DSL modem和Cisco pix防火墙...
还有另一个地方的答案也与防火墙有关：
转自：（http://www.iexp.com/support/forums/message.cfm?message_ID=260）
Support Forums
Forums
CFX_RawSocket
java.net.ConnectException: Connection timed out: connect. Java exception occurred in call to method
Subject: RE: RE: RE: java.net.ConnectException: Connection timed out: connect. Java exception occurred in call to method
Date: 03/18/2004 10:01 AM
Author: Dominic <oad74@yahoo.com >
Reply to this message
Just want to appreciate the answer given to this problem. I had the same problem
connectiong to a server behind a firewall and changing
IP address to the machine name works.
bravo!
Dominic
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>Hi,
>
>
I guess you might be trying to connect to the
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server which is behind a firewall. Generally the
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IP address of the server will be different behind
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firewall and outside the firewall. So instead of
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using the IP address if you use the fully qualified
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host name of the server while connecting, then it
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will connect without this exception.
>
>
Murali.
>
>
>
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>------------
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>
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>If I implement the tag in Coldfusion and I try to call it it comes back with the error: java.net.ConnectException: Connection timed out: connect. Java exception occurred in call to method. I think this is due to the fact that my server is behind a firewall so uit can't get to the url provided. How can I define a proxy server to connect the URL provided?
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的确，通过我的手工输入调用访问上面的代码能够工作。就是空间里的程序本身不能访问。
我试着把域名改为其它的辅助域名（www.learndiary.com或www.123go.org.cn，都是用301重定向到主域名java.learndiary.com的）就一切正常了。
又是一个糊里糊涂的出现问题，糊里糊涂的解决问题的例子。
这叫知其然不知其所以然。没办法，我没有能力去掌握所有的知识和细节。只要解决问题就OK了。