java url 本地文件是否存在,使用URL检查远程服务器上是否存在文件

How can I check in Java if a file exists on a remote server (served by HTTP), having its URL? I don't want to download the file, just check its existence.

解决方案

import java.net.*;

import java.io.*;

public static boolean exists(String URLName){

try {

HttpURLConnection.setFollowRedirects(false);

// note : you may also need

// HttpURLConnection.setInstanceFollowRedirects(false)

HttpURLConnection con =

(HttpURLConnection) new URL(URLName).openConnection();

con.setRequestMethod("HEAD");

return (con.getResponseCode() == HttpURLConnection.HTTP_OK);

}

catch (Exception e) {

e.printStackTrace();

return false;

}

}

If the connection to a URL (made with HttpURLConnection) returns with HTTP status code 200 then the file exists.

EDIT: Note that since we only care it exists or not there is no need to request the entire document. We can just request the header using the HTTP HEAD request method to check if it exists.