XMLHttpRequest java javascript

Question

I try to communicate between javascript and java. My script javascript send a message to java and java send a response.

javascript part:

    var xmlhttp = new XMLHttpRequest();
    xmlhttp.onreadystatechange=function()
      {
      if (xmlhttp.readyState==4)
        {
        alert(xmlhttp.responseText);
        }
      }
    var s = "LIGNE \n 2 \n il fait beau \nEND\n";
    xmlhttp.open("POST","http://localhost:6020",true);
    xmlhttp.send(s);

java part:

    try {
        serverSocket = new ServerSocket(6020);
    } catch (IOException e) {
        System.err.println("Could not listen on port: 6020.");
        System.exit(-1);
    }
    serverSocket.accept()
    BufferedReader br = new BufferedReader(
                new InputStreamReader(socket.getInputStream()));
    BufferedWriter bw =  new BufferedWriter(
                new OutputStreamWriter(socket.getOutputStream()));
    String ligne = "";
    while(!(ligne = plec.readLine()).equals("END")){
        System.out.println(ligne);
    }
    bw.write("Il fait beau\n");
    bw.flush();
    bw.close();
    plec.close();
    socket.close();

output java :

POST / HTTP/1.1
Host: localhost:6020
User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:13.0) Gecko/20100101 Firefox/13.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: fr,fr-fr;q=0.8,en-us;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: keep-alive
Referer: http://localhost:8080/test.html
Content-Length: 30
Content-Type: text/plain; charset=UTF-8
Origin: http://localhost:8080
Pragma: no-cache
Cache-Control: no-cache

LIGNE 
 2 
 il fait beau

So, I receive correctly the message send by javascript but the alert his always empty. How to response at this message? I try a lot of possiblity but they don't work. And I don't want to use the servlet, it's to heavy to do that.

Thanks.

Edit:

I did this :

bw.write("HTTP/1.1 200 OK\r\n"+
        "Content-Type: text/html; charset=utf-8\r\n"+
        "Content-Length: 13\r\n\r\n" +
        "il fait beau\n");

and this:

String data = "il fait beau \n";

StringBuilder builder = new StringBuilder();

builder.append("HTTP/1.1 200 OK\r\n");
builder.append("Content-Type: text/html; charset=utf-8\r\n");
builder.append("Content-Length:" + data.length() + "\r\n\r\n");
builder.append(data);
bw.write(builder.toString());

But the alert remain empty. Maybe it's a problem in the javascript.

Update the output java : section of your question to show what happens when you send the new request. — Anirudh Ramanathan
– Anirudh Ramanathan, Commented Jul 17, 2012 at 12:26
Try opening http://localhost:6020 in your browser, to debug this. You should see the text displayed in the browser, if your response is correct. You can also debug the response, using LiveHttpHeaders addon in firefox Also, note the edit to my answer. Change the content-type to text/plain. — Anirudh Ramanathan
– Anirudh Ramanathan, Commented Jul 17, 2012 at 12:32
@DarkXphenomenon I just open the localhost:6020 in a browser and "il fait beau" appeared. — AnthonyMaia
– AnthonyMaia, Commented Jul 17, 2012 at 12:38

Anirudh Ramanathan · Accepted Answer · 2012-07-17 12:30:48Z

3

The javascript needs to see a full HTTP response. Merely sending back characters to it, makes it discard the reply as it is an invalid HTTP response.

In your java code, send back something like this

HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
Content-Length: <length of data>

---data here---

Reference

Something like:

StringBuilder builder = new StringBuilder();
builder.append("HTTP/1.1 200 OK\r\n");
builder.append("Content-Type: text/plain; charset=utf-8\r\n");
builder.append("Content-Length:" + data.length() + "\r\n\r\n);
builder.append(data);
bw.write(builder.toString());

edited Jul 17, 2012 at 12:30

answered Jul 17, 2012 at 12:03

Anirudh Ramanathan

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4 Comments

AnthonyMaia Over a year ago

How do I build a complete HTTP response?

1' OR 1 -- Over a year ago

You need to add at least HTTP/1.1 200 OK because only then, readyState==4 in JavaScript and a Content-Length for your response. (Or you send a chunked response but I guess this is too complicated in your case.)

AnthonyMaia Over a year ago

@Birk what's a chunked response?

1' OR 1 -- Over a year ago

If you send Content-Length you have to know the length of your response before. If you do not know before, you can make use of Content-Transfer-Encoding: chunked (en.wikipedia.org/wiki/Chunked_transfer_encoding)

1' OR 1 -- · Accepted Answer · 2012-07-17 12:40:41Z

2

Try:

bw.write("HTTP/1.1 200 OK\r\n"+
            "Content-Type: text/html; charset=utf-8\r\n"+
            "Content-Length: 13\r\n\r\n" +
            "il fait beau\n");

HTTP-Headers are separated by \r\n (CRLF). Headers and body is spearated by \r\n\r\n.

Note that you set the length to 13 because you also have to count the \n at the end of your string.

EDIT: It does not work because of the cross-domain-policy. http://localhost:6020 is not the same port as the website which executes your JavaScript and so the xmlhttprequest might not be delivered.

edited Jul 17, 2012 at 12:40

answered Jul 17, 2012 at 12:14

1' OR 1 --

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6 Comments

AnthonyMaia Over a year ago

Thanks, but always nothing in the alert.

1' OR 1 -- Over a year ago

Sorry, I have currently Content-Length: 13\r\n\r\n+ in my code. Remove the +. This is a typing mistake. I have changed it in my example. Then it should work.

AnthonyMaia Over a year ago

It's not the problem, I remove it but always nothing.

Anirudh Ramanathan Over a year ago

+1 :D That didn't occur to me! @AnthonyMaia, is the site from which you are executing the XMLHttp request also on localhost?

1' OR 1 -- Over a year ago

Also if it was, it cannot be the same port because already his Java-program is using it. I also cannot find another reason why it should not work. But I first didn't think of it either^^

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