Persistent connection
I am trying to establish a permanent connection between a MIDLet in J2ME and a J2SE Servlet.
I have tried different possibilities whitout success. The first thing I have tried is setting the Connection property to Keep-alive. I have also tried increasing the content-length property in the server by two (I have read in an article that sometimes there are some problems between a MIDlet and a Servlet because of the content-length).
If I try to write just one time there is no problem, but when writting for a second time I receive an Exception in the MIDlet as follows:
java.io.IOException: connection already open
at com.sun.midp.io.j2me.http.Protocol.setRequestProperty(+18)
at com.sun.midp.io.j2me.http.Protocol.flush(+30)
at com.sun.midp.io.BaseOutputStream.flush(+11)
at java.io.DataOutputStream.flush(+7)
at Pru.commandAction(+104)
at javax.microedition.lcdui.Display$DisplayAccessor.commandAction(+152)
at com.sun.kvem.midp.lcdui.EmulEventHandler$EventLoop.run(+459)
I am not sure if the MIDP specification does not support persistent connectios between MIDlets and servlets. I would appreciate if you could help me with it or if you have an example of communications using persistent connecitions between MIDlets and Servlets. The versions I am using are:
J2ME Wireless Toolkit 1.0.4_01
Apache Tomcat 4.0.3 (servlet engine)
Implementation of the Servlet 2.3
Looking forward to hearing from you
William
I enclose a file with the midlet and servlet, and the different ways I have used to read and write.
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import javax.microedition.io.*;
import java.io.*;
public class Pru extends MIDlet implements CommandListener{
private Display _display;
private Command _send = new Command("Send", Command.OK,2);
private Form _form;
HttpConnection conn = null;
DataOutputStream dout = null;
InputStream din = null;
public Pru(){
}
public void startApp() throws MIDletStateChangeException{
try{
conn = (HttpConnection)Connector.open("http://xxx/servlet/Prueba"); //Conexion abierta
}
catch(IOException e){
}
_display=Display.getDisplay(this);
_form=new Form("Registration");
_form.addCommand(_send);
_form.setCommandListener(this);
_display.setCurrent(_form);
}
public void pauseApp(){
}
public void destroyApp(boolean unconditional){
_form=null;
notifyDestroyed();
try{
dout.close();
din.close();
conn.close();
}
catch(IOException e){
}
}
public void commandAction(Command c, Displayable s){
System.out.println("Entro en command, dout vale: " + dout + "\n");
if(c == _send){
String cadena = new String("Holapp");
String leido = new String();
try{
dout = conn.openDataOutputStream();
if(dout == null){
conn.setRequestMethod(HttpConnection.POST);
/********I have tried to set different properties each time but without a satisfactory solution********************/
/*
conn.setRequestProperty( "User-Agent", "Profile/MIDP-1.0 Configuration/CLDC-1.0" );
conn.setRequestProperty( "Content-Language", "en-US" );
conn.setRequestProperty( "Accept", "application/octet-stream" );
conn.setRequestProperty( "Content-Accept", "application/octet-stream" );
conn.setRequestProperty("Protocol", "HTTP/1.1");
conn.setRequestProperty("Connection", "Keep-Alive");
conn.setRequestProperty("Host", "la.it.uc3m.es");
conn.setRequestProperty("URL", "http://la.it.uc3m.es/examples/servlet/Prueba");
conn.setRequestProperty("Content-Type", "");
conn.setRequestProperty( "Content-Length","4");
*/
}
// else{
//try{
//conn.setRequestMethod(HttpConnection.POST);
/*
System.out.println( " Content-Accept es : " + conn.getRequestProperty("Content-Accept") + "\n");
System.out.println( "Content-Length es : " + conn.getRequestProperty("Content-Length") + "\n");
System.out.println( " User es : " + conn.getRequestProperty("User-Agent") + "\n");
System.out.println( "Language es : " + conn.getRequestProperty("Content-Language") + "\n");
System.out.println( "Protocolo es : " + conn.getProtocol() + "\n");
System.out.println( "el metodo es : " + conn.getRequestMethod() + "\n");
*/
/*}catch(IOException e){
System.out.println("El error es :" + e.getMessage());
e.printStackTrace();
}*/
// }
byte[] datos = cadena.getBytes();
// conn.setRequestProperty( "Content-Length",String.valueOf(cadena.length()));
dout.write(datos);
dout.flush();
System.out.println( "la longitud es : " + conn.getHeaderField("Content-Length") + "\n");
if(din == null){
din = conn.openInputStream();
}
StringBuffer sb = new StringBuffer("");
int cad = 0;
long len = conn.getLength();
for (int ccnt=0; ccnt < len; ccnt++){
cad = din.read();
sb.append((char)cad);
}
//******************* ANOTHER WAY TO READ***************************
/*StringBuffer sb = new StringBuffer("");
int ch = 0;
while ((ch = din.read()) != -1) {
sb.append((char)ch);
}
*/
System.out.println("Leido: " + sb.toString() + "\n");
System.out.println(" el codigo de respuesta " +conn.getResponseMessage()+"\n");
//I try to read again in order to check the state of the conexion (close, keep-alive)
dout.write(datos);
dout.flush();
}
catch(IOException e){
System.out.println("Excepcion capturada: " + e.getMessage() + "\n");
e.printStackTrace();
}
}//if
}//commandAction
}
/************************************************************************************
SERVLET
*********************************************************************************/
import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class Prueba extends HttpServlet{
int contador=0;
public void init(ServletConfig configuracion) throws ServletException{
super.init(configuracion);
int resultado=-1;
System.out.println("Servlet Pru arrancado...\n");
System.out.println("SE ha visitado..."+contador+"\n");
}
public void doPost(HttpServletRequest request,HttpServletResponse response) throws IOException, ServletException {
String text = new String();
System.out.println("1 Estoy en post ...\n");
contador++;
System.out.println("SE ha visitado..."+contador+"\n");
try{
InputStream din = request.getInputStream();
int lon=request.getContentLength()+2;
String s="";
System.out.println("despues din null el tama駉 recibido es "+lon+"\n");
for (int cont=0;cont<long ;cont++ ){
text = text + (char)din.read();
}
System.out.println( " El metodo es : " + request.getMethod() + "\n");
System.out.println( "URL es : " + request.getRequestURL() + "\n");
System.out.println( " User es : " + request.getHeader("User-Agent") + "\n");
System.out.println( "Language es : " + request.getHeader("Content-Language") + "\n");
System.out.println( " Accept es : " + request.getHeader("Accept") + "\n");
System.out.println( "Content-Accept es : " + request.getHeader("Content-Accept") + "\n");
System.out.println( "Content-Length es : " + request.getHeader("Content-Length") + "\n");
System.out.println( "la conexion es : " + request.getHeader("Connection") + "\n");
System.out.println( "Protocolo es : " + request.getProtocol() + "\n");
//**********************ANOTHER WAY TO READ***********************************
/* if(lon >2 ){
System.out.println("he entrado en el if \n");
BufferedReader reader=request.getReader();
char[] buffer=new char[lon];
System.out.println(" he llamado a la funcion getReader");
int i =reader.read(buffer,0,buffer.length);
System.out.println(" reader.read");
s=new String(buffer);
s=s.substring(0,s.length()-2);
System.out.println(" los datos leidos son :"+ s);
}
*/
//******************* ANOTHER WAY TO READ***************************
/*StringBuffer sb = new StringBuffer("");
int ch = 0;
while ((ch = din.read()) != -1) {
sb.append((char)ch);
}
*/
System.out.println("Hemos leido: " + text + "\n");
String cadena="echo"+text;
System.out.println("Mando: " + cadena + "\n");
// response.setContentType("application/octet-stream");
//response.setStatus(response.SC_OK);
response.setContentLength(cadena.length());
OutputStream dout = response.getOutputStream();
byte[] datos = cadena.getBytes();
dout.write(datos);
System.out.println("Salido de post\n");
}
catch(IOException e){
System.out.println("Excepcion en servlet: " + e.getMessage() + "\n");
}
}
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException{
doPost(request,response);
}
