I have a code example for you for redirecting a user to the login page.
Note that I have a POJO loginInfo that has four properties: orgId, username, password, url
These are set up before this code.
To get the orgId
Code:

    GetUserInfoResult userInfo = salesforceService.getUserInfo();
    loginInfo.setOrgId(userInfo.getOrganizationId());

For us on our test server, the loginInfo.url is https://tapp0.salesforce.com/sserv/login.jsp

Username and Password are the self service user's user name and password.  Your application needs to know these in order to log the user in.  You can get the username from salesforce using the contact info, but you will either have to pick a password, set it, and save it in a way available to your application or have the user enter their password.

Then you can redirect the user to the url returned in the following snippet (this code logs the user in then redirects them to the self service site home page) (NB this will only work if the ip address for your self service users is allowed to change - this is set up through customizing your account)

Code:

        String dataToPost = "orgId=" + loginInfo.getOrgId() + "&un=" + loginInfo.getUsername() + "&pw=" + loginInfo.getPassword();
        byte[] byteArray = dataToPost.getBytes("UTF-8");
        
        // log the user in
        HttpURLConnection connection = null;
        OutputStream requestStream = null;
        InputStream responseStream = null;
        BufferedReader rd = null;
        StringBuffer responseBuf = new StringBuffer();
        String redirectUrl = null;
        
        try {
            URL url = new URL(loginInfo.getUrl());
            connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("POST");
            connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            connection.setDoOutput(true);
            connection.connect();
            requestStream = connection.getOutputStream();
            requestStream.write(byteArray);
            requestStream.flush();
            responseStream = connection.getInputStream();
            rd = new BufferedReader(new InputStreamReader(connection.getInputStream(), "UTF-8"));
            
            String line = "";
            while ((line = rd.readLine()) != null) {
                responseBuf.append(line);
            }
            
            // extract redirect url from response
            int beginIndexUrl = responseBuf.indexOf("<meta http-equiv=\"Refresh\" content=\"0; URL=") + 43;
            if (beginIndexUrl > 43) {
                int endIndexUrl = responseBuf.indexOf("\"", beginIndexUrl);
                redirectUrl = url.getProtocol() + "://" + url.getHost() + URLDecoder.decode(responseBuf.substring(beginIndexUrl, endIndexUrl), "UTF-8");
            }
            
        } finally {
            
            if (connection != null) {
                try {
                    connection.disconnect();
                } catch (Exception e) {
                    // do nothing
                }
            }
            
            if (requestStream != null) {
                try {
                    requestStream.close();
                } catch (Exception e) {
                    // do nothing
                }
            }
            
            if (responseStream != null) {
                try {
                    responseStream.close();
                } catch (Exception e) {
                    // do nothing
                }
            }
            
            if (rd != null) {
                try {
                    rd.close();
                } catch (Exception e) {
                    // do nothing
                }
            }
        }
        
        return redirectUrl;

Thanks you!
It work.
But I have one another question.
How could I now if a SelfServiceUser password have been reset ?

Clettebou

Hi,  I tried using the code given below to login to SelfService portal, but was unable to connect.The response I received did not contain the '<meta' tag for refresh but the 'refresh' is added as a header. After the first successful request to login I am not able to reach the actual home page. The refresh url is exactly same as my initial url. Can somebody pls help me ?