sending a 2d array jquery post to java servlet

You can use exactly the same technique as the example you link to. This is because it uses JSON to serialise the data, so it can send entire JS data structures in one go. So, taking the example, but rebuilding it for a 2d array and tweaking it to send actual JSON:

var obj=[ [1.1, 1.2], [2.1, 2.2], [3.1, 3.2] ];
$.ajax({
        url:"myUrl",
        type:"POST",
        dataType:'json',
        success:function(data){
            // codes....
        },
        data:JSON.stringify(obj),
        contentType: 'application/json'
    });

Then this will send a string to your server, like:

"[[1.1,1.2],[2.1,2.2],[3.1,3.2]]"

Your Java servlet will then have to deserialise this and use it however you want. In this example, the JSON will be sent as RAW post data; if you want to get it via the request object, you can do something like:

var obj=[ [1.1, 1.2], [2.1, 2.2], [3.1, 3.2] ];
$.ajax({
        url:"myUrl",
        type:"POST",
        dataType:'json',
        success:function(data){
            // codes....
        },
        data: {json: JSON.stringify(obj)}
    });

Then you should be able to get the JSON string from:

request.getParameterValues("json");