jsp获取ip地址

Question

whats the best way of preventing someone from voting twice? How do i get the users ip address? What if they are on a large network? will everyone on that network show the same ip? thanks

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UPDATE: request.getRemoteAddr() and request.getRemoteHost() return the Server names, not the client's host name and ip. Anyone else got any bright ideas?

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Ok, so lets forget about the voting twice thing. Im just trying to get the users ip address? i tried request.getRemoteAddr() and request.getRemoteHost() and think im getting the servers address. I have access to two separate networks and am getting the same IP address :(

Answer 1

In your JSP, use request.getRemoteAddr() . This returns the IP address of the agent that sent the request as a String.

Also, request.getRemoteHost() will attempt to get the fully qualified host name. If it can't resolve the name however, the IP address will be returned as in getRemoteAddr() .

Answer 2

To get the IP of a client behind a router/firewall you can use request.getHeader("X-FORWARDED-FOR") .

The X-Forwarded-For (XFF) HTTP header is a de facto standard for identifying the originating IP address of a client connecting to a web server through an HTTP proxy or load balancer. http://en.wikipedia.org/wiki/X-Forwarded-For

Keep in mind though, that this value can be changed by the proxies between you and the client. Though it should be the correct IP.

Answer 3

If users are behind NAT router or proxy server , you will see them with the same IP address. Therefore, it is not the best way of allowing users to vote once.

An alternative would be to use cookies , but again, it is possible to erase the cookie and vote again.

Answer 4

AFAIK the ONLY way of preventing a second vote is by authenticating. Obviously this is not always possible, so you have to mitigate the possibility of a single user casting a ton of votes.

• Throttle the voting by source IP. Use the getRemoteAddr() to allow, say... a vote per hour?... per minute? ... it will depend on how much voting you expect. Adjust the number according to experience.
• Plant a cookie on the response for every voting poll, which expires after the ballot closes.
• Make it harder to forge requests by checking and validating headers like Referer and User-Agent .

Answer 5

在JSP页面中，只需使用以下表达式： ${pageContext.request.remoteAddr}

Answer 6

You can get the IP address with request.getRemoteAddr(). If the network is using a NAT router, all users will get the same address though