Blocking a website from access for all browsers

Question

Greetings,

I would like to ask if there's a way to block website(s) from access on a computer(s) dynamically? I mean could this functionality be coded (on java native interface)?

Your response is highly appreciated.

Thanks, Cyril H.

Answer 1

Yes, you can code a simple HTTP proxy service with Java:

http://www.java2s.com/Code/Java/Network-Protocol/Asimpleproxyserver.htm

Alternatively, there are plenty of existing proxy solutions out there might suit your needs out of the box:

http://www.roseindia.net/opensource/freeproxyservers.php

You would then configure the software/devices that access websites (e.g., your browser) to point to that proxy, so that all HTTP communication passed through it.

Your proxy could then restrict access to whatever URL(s) you wanted to, based on whatever logic you wanted to code up.

If you wanted to get really fancy/secure and require folks to use the proxy (and not to choose to bypass it), you could do that, but that's probably more than you need to, given your question.

Answer 2

You could append entries to your hosts file using the Files class, as shown in this post: How to append text to an existing file in Java?.

This works on all platforms (yes, all of them: including Windows, Mac, Linux, Android, and more), and blocks access for all browsers, without the need for a proxy or special browser extensions (which can be deleted in most cases).

Here is some simple code to start you off. Feel free to edit it to fit your needs:

public void blockSite(String url) {
    // Note that this code only works in Java 7+,
    // refer to the above link about appending files for more info

    // Get OS name
    String OS = System.getProperty("os.name").toLowerCase();

    // Use OS name to find correct location of hosts file
    String hostsFile = "";
    if ((OS.indexOf("win") >= 0)) {
        // Doesn't work before Windows 2000
        hostsFile = "C:\\Windows\\System32\\drivers\\etc\\hosts";
    } else if ((OS.indexOf("mac") >= 0)) {
        // Doesn't work before OS X 10.2
        hostsFile = "etc/hosts";
    } else if ((OS.indexOf("nux") >= 0)) {
        hostsFile = "/etc/hosts";
    } else {
        // Handle error when platform is not Windows, Mac, or Linux
        System.err.println("Sorry, but your OS doesn't support blocking.");
        System.exit(0);
    }

    // Actually block site
    Files.write(Paths.get(hostsFile),
                ("127.0.0.1 " + url).getBytes(),
                StandardOpenOption.APPEND);
}

Imports for above method:

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

Sample usage:

blockSite("www.example.com");

Note:

This needs to be run as an administrator (Windows) or using sudo (Mac, Linux).

This might not work for some platforms, as it was only tested on Ubuntu Linux.

P.S. If you're making parental control software, you should also look into blocking programs. Not all things you would want to block are on the Internet. Here is some simple code for that:

/**
    Blocks programs.
    @param programs - The array of process names.
    @param timeout - The time between blocks, in milliseconds.
    This parameter should not be set below 100, to avoid slowdown.
    @author https://stackoverflow.com/users/5905216/h-a-sanger
*/
public void blockPrograms(int timeout, String...programs) throws IOException {
    // Get OS name
    String OS = System.getProperty("os.name").toLowerCase();

    // Identify correct blocking command for OS
    String command = "";
    if ((OS.indexOf("win") >= 0)) {
        command = "taskkill /f /im ";
    } else if ((OS.indexOf("mac") >= 0) || (OS.indexOf("nux") >= 0)) {
        command = "killall ";
    } else {
        // Handle error when platform is not Windows, Mac, or Linux
        System.err.println("Sorry, but your OS doesn't support blocking.");
        System.exit(0);
    }

    // Start blocking!
    while(true) {
        // Cycle through programs list
        for(int i = 0; i < programs.length; i++) {
            // Block program
            Runtime.getRuntime().exec(command + programs[i]);
        }
        // Timeout
        try { Thread.sleep(timeout); } catch(InterruptedException e) {}
    }
}

Imports for above code:

import java.io.IOException;

Sample usage:

blockPrograms(100, "chrome", "firefox");

Again, let me note this was only tested on Ubuntu Linux.