ProxyPass, ProxyReverse vs AJP

You can read the X-Forwarded-For in the request header.

From the Apache mod_proxy documentation:

When acting in a reverse-proxy mode (using the ProxyPass directive, for example), mod_proxy_http adds several request headers in order to pass information to the origin server. These headers are:

• X-Forwarded-For: The IP address of the client.
• X-Forwarded-Host: The original host requested by the client in the Host HTTP request header.
• X-Forwarded-Server: The hostname of the proxy server.

Be careful when using these headers on the origin server, since they will contain more than one (comma-separated) value if the original request already contained one of these headers. For example, you can use %{X-Forwarded-For}i in the log format string of the origin server to log the original clients IP address, but you may get more than one address if the request passes through several proxies.

In your servlet, you would have:

doGet(HttpServletRequest request, HttpServletResponse response){
  request.getHeader("X-Forwarded-For")
}