Checking if a URL exists or not

问题:

I need to check whether a URL exists or not. I want to write a servlet for this i.e. to check whether a URL exists or not. If the URL entered does not exist, then it should return some message.

回答1:

Better solution for HTTP :

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 you are looking for any other URL try this code

  public static boolean exists(String URLName){
      boolean result = false;
      try {
          url = new URL("ftp://ftp1.freebsd.org/pub/FreeBSD/");
          //url = new URL("ftp://ftp1.freebsd.org/pub/FreeBSD123/");//this will fail

          input = url.openStream();

           System.out.println("SUCCESS");
           result = true;

            } catch (Exception ex) {
               Logger.getLogger(NewClass.class.getName()).log(Level.SEVERE, null, ex);
            }
         return result;
  }

Source :http://www.rgagnon.com/javadetails/java-0059.html

回答2:

You could try HTTP's HEAD method to see if the server returns a status code of 200 on a particular URL and act accordingly.

See http://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol and scroll down to the Request Methods.

回答3:

You can make a connection, get the input stream back, and check for null.

回答4:

I used this bash script for check urls, but need put all files in a file "urls.csv"

#!/bin/bash

###############################################
# mailto: [e-mail]
# checkurls
# https://github.com/ggerman/checkurls/
# require curl
###############################################

url() {
  cat urls.csv | 
  replace  | 
  show
}

replace() {
  tr ',' ' '
}

show() {
  awk '{print $1}'
}

url | \
while read CMD; do
  echo $CMD
  curl -Is $CMD | head -n 1
done