Extract host name/domain name from URL string

问题:

I have a URL like http://hostname:port_no/control/login.jsp.

I have the above url stored in some String.Now, I need to extract hostname from the String.

I am doing like this in my Java code

String domain = url.substring(url.indexOf('/') + 2, url.lastIndexOf(':'));

I want to know if there is any better way to do the same.

回答1:

You can use the java.net.URI-class to extract the hostname from the string.

Here below is a method from which you can extract your hostname from a string.

public String getHostName(String url) {
    URI uri = new URI(url);
    String hostname = uri.getHost();
    // to provide faultproof result, check if not null then return only hostname, without www.
    if (hostname != null) {
        return hostname.startsWith("www.") ? hostname.substring(4) : hostname;
    }
    return hostname;
}

This above gives you the hostname, and is faultproof if your hostname does start with either hostname.com/... or www.hostname.com/..., which will return with 'hostname'.

If the given url is invalid (undefined hostname), it returns with null.

回答2:

java.net.URL aURL;
try {
    aURL = new java.net.URL("http://example.com:80/docs/");
    System.out.println("host = " + aURL.getHost()); //example.com
} catch (MalformedURLException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

回答3:

java.net.URL u = new URL("http://hostname:port_no/control/login.jsp");
System.err.println(u.getHost());

回答4:

If you want string work, then try the following code sample,

String URL= "http://hostname:port_no/control/login.jsp";
String s_URL[] = ULR.split("//");
String s1 = s_URL[1];
String s2[] = s1.split(":");
String hostname = s2[0];

回答5:

In Java:

String hostname = url.split("://")[1].split(":")[0];
String portnumber = url.split("://")[1].split(":")[1].split("/")[0];

Hope this helps.

回答6:

@KarelG's answer is the best answer, though I had specific issues with certain non-standard domains. The example issue is self contained below.

For certain "real world" input values, I had to add a check to the URI scheme to avoid mis-parsing of some addresses. This is the changed code.

import java.net.URI;
import java.net.*;

public class Domain {
    public static String getDomainName(String url) {
        try {
            URI uri = new URI(url);
            String domain = uri.getHost();
            System.out.println("domain: " + domain);
            if (uri.getScheme() != null) {
                return domain.startsWith("www.") ? domain.substring(4) : domain;
            } else {
                return uri.getSchemeSpecificPart();
            }

        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

}

Below is the test case and value that was failing.

Domain.java javac Domain.java java Domain

import java.net.URI;
import java.net.*;
import java.io.*;

public class Domain {

    public static String longname = "https://www.3dprintingmedia.network/longform/page.html";
    public static String name = "www.3dprintingmedia.network";

    public static void getDomain(String url) {
        try {
                        URI uri = new URI(url);
                        String domain = uri.getHost();
            System.out.println("protocol: " + uri.getScheme());
            System.out.println("path: " + uri.getPath());
                        System.out.println("name: " + name);
                        System.out.println("domain: " + domain);
                        System.out.println(domain.startsWith("www.") ? domain.substring(4) : domain);
        } catch (Exception e) {
                        e.printStackTrace();
        }
   }

    public static void main(String[] args) {
       System.out.println("Parsing domain: " + name); 
       getDomain(longname);
       getDomain(name);
       System.exit(0);
    }
}