Messaging all players via a seversided mod

I want to send a message to all players like the tellraw command, but without using any commands

I want a Message like this:

'<misterx>: Hello World'

to be shown to every player as if the player misterx sent this message. 

each message sender instance is it's own object 

public class virtual_user {
    static ArrayList users = new ArrayList<String>();
    private String username;
    public virtual_user(String name)
    {   
        String original = name;
        int adder = 0;
        while(users.contains(name)) 
        {
            adder++;
            name = original + adder;
        }
        this.username = name;
        users.add(name);
    }
    public void delete ()
    {
        int index = users.indexOf(this.username);
        if(index != -1)
        users.remove(index);
    }
    public void sendMessage(String message)
    {
        //send message to all players using this players name etc.
    }


}

this is what i got so far 

now i need the content of sendmessage, but i don't know how to send any messages to a client from a server sided viewpoint