Your request is wrong. If you use a POST request, then the parameters client, apikey, apiver and pver should be part of the URL.
The request body should only consist of the URLs to check (plus the number of URLS on the first line).
So it could look like this:
String baseURL="https://sb-ssl.google.com/safebrowsing/api/lookup";
String arguments = "";
arguments + =URLEncoder.encode("client", "UTF-8") + "=" + URLEncoder.encode("myapp", "UTF-8") + "&";
arguments + =URLEncoder.encode("apikey", "UTF-8") + "=" + URLEncoder.encode("12341234", "UTF-8") + "&";
arguments + =URLEncoder.encode("appver", "UTF-8") + "=" + URLEncoder.encode("1.5.2", "UTF-8") + "&";
arguments + =URLEncoder.encode("pver", "UTF-8") + "=" + URLEncoder.encode("3.0", "UTF-8");
// Construct the url object representing cgi script
URL url = new URL(baseURL + "?" + arguments);
// Get a URLConnection object, to write to POST method
URLConnection connect = url.openConnection();
// Specify connection settings
connect.setDoInput(true);
connect.setDoOutput(true);
// Get an output stream for writing
OutputStream output = connect.getOutputStream();
PrintStream pout = new PrintStream (output);
pout.print("2");
pout.println();
pout.print("http://www.google.com");
pout.println();
pout.print("http://www.facebook.com");
pout.close();