We Keep Coding

ClientSocket NOT listening

Im flabbergasted.
I took code from https://docs.oracle.com/javase/tutorial/networking/sockets/examples/EchoServer.java
for the server. And
https://docs.oracle.com/javase/tutorial/networking/sockets/examples/EchoClient.java
for the Client. I made minor changes. Mostly so that there is no back and forth echoing. Rather the Server should constantly with 2 second delays send same string. But I just cant understand why the client isnt working.
It sends the Exception message:
Couldn't get I/O for the connection to 127.0.0.1
I run the server with: java 6788
and the client with: 127.0.0.1 6788
I tried other ports.
I do this in eclipse so I set the arguments in Runconfiguration before running the classes. I start the server first. I tried in terminal outside of eclipse. Nothing makes it work.
Basically, the client should connect to server and output with System.out.println() what the server in turn outputs to the client. But nothing happens.
what is wrong?
Client:
import java.io.*;
import java.net.*;
public class EchoClient {
public static void main(String[] args) throws IOException {
if (args.length != 2) {
System.err.println(
"Usage: java EchoClient <host name> <port number>");
System.exit(1);
}
String hostName = args[0];
int portNumber = Integer.parseInt(args[1]);
try (
Socket echoSocket = new Socket(hostName, portNumber);
BufferedReader in =
new BufferedReader(
new InputStreamReader(echoSocket.getInputStream()));
) {
String userInput;
while (true) {
System.out.println("recieved: " + in.readLine());
}
} catch (UnknownHostException e) {
System.err.println("Don't know about host " + hostName);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to " +
hostName);
System.exit(1);
}
}
}
Server:
import java.net.*;
import java.io.*;
public class EchoServer {
public static void main(String[] args) throws IOException {
if (args.length != 1) {
System.err.println("Usage: java EchoServer <port number>");
System.exit(1);
}
int portNumber = Integer.parseInt(args[0]);
System.out.println(args[0]);
InetAddress add = InetAddress.getLocalHost();
System.out.println(add.getHostAddress());
try (
ServerSocket serverSocket =
new ServerSocket(Integer.parseInt(args[0]));
Socket clientSocket = serverSocket.accept();
PrintWriter out =
new PrintWriter(clientSocket.getOutputStream());
) {
while (true) {
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
out.println("HELLO!");
}
} catch (IOException e) {
System.out.println("Exception caught when trying to listen on port "
+ portNumber + " or listening for a connection");
System.out.println(e.getMessage());
}
}
}

You have to send the answer to the client.
Add a out.flush();
while (true) {
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
out.println("HELLO!");
out.flush();
}

As in the comment I eventually found a solution. BufferedReader.readLine() "blocked". When reading from a file it returns a line after reading up to a newline character, if I understand it correctly.
But since it was "A steady flow" from server with no newlines, it just kept "reading" and never returned a String.
I then tried using BufferedReader.read() method, that reads character by character, and returns after each char (thus never blocking). It then prints each character as it arrives, also it listens for a newline being sent from server, and once a read character equals a newline, it then prints a newline instead. Sort of emulating the "read line" behaviour I was expecting from original question.
Reading part of client:
while(true) {
character = (char) reader.read();
if(Character.isISOControl(character)) {
System.out.println();
}
else {
System.out.printf("%c", character);
}
}
Sending Part of Server:
private String message = "HELLO\n";
...
while(true) {
try {
Thread.sleep(2000);
writer.write(message);
writer.flush();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

java - Unable to run programs utilising sockets (Unable to connect and listen failed)

I have two classes - Provider and Requester:
Provider
import java.io.*;
import java.net.*;
public class Provider {
ServerSocket providerSocket;
Socket connection = null;
ObjectOutputStream out;
ObjectInputStream in;
String message;
Provider() {
}
void run() {
try {
// 1. creating a server socket
providerSocket = new ServerSocket(2004, 10);
// 2. Wait for connection
System.out.println("Waiting for connection");
connection = providerSocket.accept();
System.out.println(
"Connection received from " + connection.getInetAddress().getHostName());
// 3. get Input and Output streams
out = new ObjectOutputStream(connection.getOutputStream());
out.flush();
in = new ObjectInputStream(connection.getInputStream());
sendMessage("Connection successful");
// 4. The two parts communicate via the input and output streams
do {
try {
sendMessage(
"Please enter the phrase you wish to echo or the word FINISHED to exit");
message = (String) in.readObject();
sendMessage(message);
} catch (ClassNotFoundException classnot) {
System.err.println("Data received in unknown format");
}
} while (!message.equals("FINISHED"));
} catch (IOException ioException) {
ioException.printStackTrace();
} finally {
// 4: Closing connection
try {
in.close();
out.close();
providerSocket.close();
} catch (IOException ioException) {
ioException.printStackTrace();
}
}
}
void sendMessage(String msg) {
try {
out.writeObject(msg);
out.flush();
System.out.println("server>" + msg);
} catch (IOException ioException) {
ioException.printStackTrace();
}
}
public static void main(String args[]) {
Provider server = new Provider();
while (true) {
server.run();
}
}
}
Requester
import java.io.*;
import java.net.*;
import java.util.Scanner;
public class Requester {
Socket requestSocket;
ObjectOutputStream out;
ObjectInputStream in;
String message;
Scanner input;
Requester() {
input = new Scanner(System.in);
}
void run() {
try {
// 1. creating a socket to connect to the server
requestSocket = new Socket("127.0.0.1", 2004);
System.out.println("Connected to localhost in port 2004");
// 2. get Input and Output streams
out = new ObjectOutputStream(requestSocket.getOutputStream());
out.flush();
in = new ObjectInputStream(requestSocket.getInputStream());
// 3: Communicating with the server
try {
message = (String) in.readObject();
System.out.println("server>" + message);
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
do {
try {
message = (String) in.readObject();
System.out.println(message);
message = input.nextLine();
sendMessage(message);
message = (String) in.readObject();
} catch (ClassNotFoundException classNot) {
System.err.println("data received in unknown format");
}
} while (!message.equals("FINISHED"));
} catch (UnknownHostException unknownHost) {
System.err.println("You are trying to connect to an unknown host!");
} catch (IOException ioException) {
ioException.printStackTrace();
} finally {
// 4: Closing connection
try {
in.close();
out.close();
requestSocket.close();
} catch (IOException ioException) {
ioException.printStackTrace();
}
}
}
void sendMessage(String msg) {
try {
out.writeObject(msg);
out.flush();
System.out.println("client>" + msg);
} catch (IOException ioException) {
ioException.printStackTrace();
}
}
public static void main(String args[]) {
Requester client = new Requester();
client.run();
}
}
The programs are basically meant to communicate with each other. The idea is that they each 'connect' with each other via sockets and the user should be able to enter something in the console window of Provider and have it echoed back onto the console of Requester. However, I am getting the following errors:
Provider
java.net.SocketException: Permission denied: listen failed
Requester
java.net.ConnectException: Connection refused: connect
(I can provide the rest of the errors if it would help in fixing the issue).
I have tried having the classes in the same project folder, in separate folders, and in different workspaces. I have also tried using Eclipse EE (Neon) and the SE (Oxygen). Recently, I have been having problems with ports and sockets (most notably with Tomcat and encountering the 'Cannot find free socket for debugger' in Eclipse). Would that have something to do with me being unable to run these programs?

Check your firewall settings. I was having similar problems when trying to use sockets. Make sure any relevant resources aren't blocked.
You might also want to run the command:
netstat -ano | findstr :2004
to check if that port is mistakenly in use already.

Socket closed before able to read from ObjectInputStream(BufferedInputStream(Socket.getInputStream))

I have written a small Client/Server Program which already worked once but after adding Threads and some real input Data to it, i always get a closed Socket before being able to read the Object (the String). The Program always Prints "Client has already closed Connection!" from Function handleConnection in the ProcessDataThread.
ClientCode:
synchronized private static void sendToServer(){
Socket clientSocket = null;
BufferedOutputStream socketOut = null;
ObjectOutputStream out = null;
try{
String xmlToSend = "<startTag>\n<someOtherTag id=\"5555\">\n12345\n</someOtherTag>\n</startTag>\n";
Log.d(TAG, "Trying to send the following to the Server:" + xmlToSend);
//TODO load these from file
clientSocket = new Socket( "10.0.2.2", 7777);
socketOut = new BufferedOutputStream(clientSocket.getOutputStream());
out = new ObjectOutputStream(socketOut);
out.writeObject(xmlToSend);
out.flush();
}catch(Exception ex){
Log.e(TAG, "Could not write File to Server.", ex);
}
finally{
try{
if(clientSocket != null){
clientSocket.close();
}
if(out != null){
out.close();
}
}catch(IOException ex){
Log.e(TAG, "Could not close Socket.");
}
}
}
ServerCode:
ReceiverThread:
public void run()
{
try {
ServerSocket server = new ServerSocket(port);
//Only block for 10 Seconds and try again
server.setSoTimeout(10000);
while(!server.isClosed() && !stopped){
//Run
Socket client = null;
try
{
client = server.accept();
System.out.println("Accepted ClientConnection from " + client.getRemoteSocketAddress());
new ProcessDataThread(client).start();
}
catch( SocketTimeoutException tx){
//nothing
}
catch ( IOException e ) {
e.printStackTrace();
}
finally {
if ( client != null )
try { client.close(); } catch ( IOException e ) { e.printStackTrace(); }
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
ProcessDataThread:
public class ProcessDataThread extends Thread {
Socket client;
public ProcessDataThread(Socket sock) {
// xmlToProcess = xmlString;
this.client = sock;
}
private String handleConnection() {
BufferedInputStream socketIn = null;
ObjectInputStream in = null;
String xmlToProcess = null;
try {
if(!client.isClosed()){
System.out.println("Trying to read from Stream;");
socketIn = new BufferedInputStream(client.getInputStream());
in = new ObjectInputStream(socketIn);
Object xmlString = in.readObject();
System.out.println("Read some Object from Stream:" + xmlString.toString());
if (xmlString instanceof String) {
xmlToProcess = (String) xmlString;
System.out.println("Received the following XML:\n" + xmlToProcess);
}
}else{
System.out.println("Client has already closed Connection!");
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (EOFException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (socketIn != null) {
socketIn.close();
}
if(client != null){
client.close();
}
} catch (IOException ioex) {
ioex.printStackTrace();
}
}
return xmlToProcess;
}
#Override
public void run() {
String xmlToProcess = handleConnection();
if (xmlToProcess == null || xmlToProcess.isEmpty()) {
// Es konnte kein String vom Client gelesen werden.
return;
}
System.out.println(xmlToProcess);
}
}
I made some changes with jboi's Suggestions. This is what i got now. The error stays the same. I don't even get to reading the Stream in the Server because client.getClosed()
is always true!
In the Client Code:
clientSocket = new Socket( "10.0.2.2", 7777);
clientSocket.setTcpNoDelay(true);
socketOut = new BufferedOutputStream(clientSocket.getOutputStream());
out = new ObjectOutputStream(socketOut);
out.writeObject(xmlToSend);
out.flush();
socketOut.flush();
//Close Output on Socket to signalize the Server that we finished writing!
clientSocket.shutdownOutput();
in = clientSocket.getInputStream();
byte[] receivedData = new byte[8192];
while(in.read(receivedData) != -1) {
//Wait for the Server to Close the Connection
}
In the Server Code
socketIn = new BufferedInputStream(client.getInputStream());
in = new ObjectInputStream(socketIn);
Object xmlString = in.readObject();
System.out.println("Read some Object from Stream:" + xmlString.toString());
if (xmlString instanceof String) {
xmlToProcess = (String) xmlString;
System.out.println("Received the following XML:\n" + xmlToProcess);
}
out = client.getOutputStream();
out.write(1);
//Signalize the Client that we have read everything
client.shutdownOutput();

It is very probable that your client has closed the socket in the finally block before the server was able to read the data.
In your clients finally block you should use socket.shutdownOutput, then read on the client all incoming data till EOF and then close the socket.
On your server you read till EOF and then send an object as kind of acknowledge, e.g. Number of bytes in the message. You also end the send with socket.shutdownOutput() as you've done at the client. This puts again an EOF at the end of the data. This EOF is received by the client and it will finally close the socket.

The issue seems to be the client and server are unable to identify each others state:
Client sending data to server, where server has closed the connection
Server sending/reading data to client , where client has closed the connection
Either are unable to coordinate with each other, solutions could be to establish a proper state machine. Some examples in Google if you search for (client and server state machine) gives mathematically definite state machine examples for your application: hope this comment helps.
Hence it's not useful to look into this problem in solution perspective and probably start using protocols in place like : telnet etc .

Ok now i'm feeling stupid.
I closed the Socket inside the Server Code myself.
After accepting a connection the following is executed inside the finally Block:
try {
client.close();
} catch (IOException e) {
e.printStackTrace();
}
The reason that there is this finally Block was because i didn't use Threads before so the ReceiverThread also did handle the Connection and therefore close the socket after using it.
I then moved the code to the new Thread and forgot to remove that finally block!

You can't use a buffered input stream and another kind of stream on the same socket. The buffered stream will steal data from the other one. Make up your mind. The ObjectInputStream will do everything you need. Just use that.
EDIT Re your edit, 'socket closed' means that you closed your socket and then continued to use it.

establishing communication between Java desktop app and Java browser applet via sockets

I'm new to network I/O programming, and I've run into a snag-- basically what I want to do is have a desktop app talk to the google maps javascript API. In order to facilitate this, I have built a java applet which will act as a bridge between the desktop app and the browser javascript app. When I run the desktop app and applet together in Eclipse they can communicate perfectly, and I am able to invoke applet functions by writing strings to a Socket bound to the same port the applet has established a ServerSocket connection with. For testing purposes in Eclipse, I send the string "sendJSAlertTest" to the socket's outputstream, then derive a Method instance using the java.lang.reflect API from the ServerSocket inputstream, and then finally invoke the resulting method in the applet. When the applet is running in a browser I write "sendJSAlert" to the socket instead since it leads to the actual invocation of javascript. The result in Eclipse using the appletviewer is that the desktop application context prints the output "awesome sendJSAlert" and the applet context prints the output from the sendJSAlertTest() method, "Hello Client, I'm a Server!". The result of passing "sendJSAlert" to the applet running in the browser is that the desktop application prints null, suggesting that for some reason the inputstream of the ServerSocket is empty, and the browser itself does nothing when it should generate a javascript alert box with the text "Hello Client, I'm a Server!". The browser I'm using is Google Chrome, and for the moment I am simply running everything on the local machine (e.g. no remote server involved yet)
Below is the relevant Java code and HTML:
SocketClient.java
import java.awt.event.*;
import java.io.*;
import java.net.*;
public class SocketClient {
Socket socket = null;
PrintWriter out = null;
BufferedReader in = null;
private InetAddress myAddress;
private String remoteFunction;
public SocketClient(){
}
public void listenSocket(int portNum){
//Create socket connection
try{
System.out.println("#Client Trying to create socket bound to port " + portNum);
socket = new Socket(<my hostname here as a string>, portNum);
System.out.println("the attached socket port is " + socket.getLocalPort());
System.out.flush();
out = new PrintWriter(socket.getOutputStream(), true);
out.println("sendJSAlertTest");
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String line = in.readLine();
System.out.println("#CLient side Text received from server: " + line);
} catch (UnknownHostException e) {
System.out.println("Unknown host: <my hostname here as a string>.eng");
System.exit(1);
} catch (IOException e) {
System.out.println("No I/O");
e.printStackTrace();
System.exit(1);
}
}
public void setRemoteFunction(String funcName){
remoteFunction = funcName;
}
public String getRemoteFunction(){
return remoteFunction;
}
}
SocketServer.java
import java.io.*;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.*;
class SocketServer {
ServerSocket server = null;
Socket client = null;
BufferedReader in = null;
PrintWriter out = null;
String line;
private NetComm hNet;
private Method serverMethod;
SocketServer(NetComm netmain){
hNet = netmain;
}
public void listenSocket(int portNum){
try{
System.out.println("#server Trying to create socket bound to port " + portNum);
server = new ServerSocket(portNum);
System.out.println("the attached socket port is " + server.getLocalPort());
} catch (IOException e) {
System.out.println("Could not listen on port " + portNum);
System.exit(-1);
}
try{
client = server.accept();
System.out.println("Connection accepted!");
} catch (IOException e) {
System.out.println("Accept failed: " + portNum);
System.exit(-1);
}
try{
in = new BufferedReader(new InputStreamReader(client.getInputStream()));
out = new PrintWriter(client.getOutputStream(), true);
} catch (IOException e) {
System.out.println("Accept failed: " + portNum);
System.exit(-1);
}
while(true){
try{
System.out.println("trying to read from inputstream...");
line = in.readLine();
System.out.println(line);
//Now that we have a method name, invoke it
try {
serverMethod = hNet.getClass().getDeclaredMethod(line,
String.class);
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
serverMethod.invoke(hNet, "Hello Client, I'm a Server!");
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//Send data back to client
out.println("awesome " + line);
} catch (IOException e) {
System.out.println("Read failed");
System.out.flush();
System.exit(-1);
}
}
}
protected void finalize(){
//Clean up
try{
in.close();
out.close();
server.close();
} catch (IOException e) {
System.out.println("Could not close.");
System.exit(-1);
}
}
public int getBoundLocalPort(){
return server.getLocalPort();
}
}
NetComm.java
import cresco.ai.att.ccm.core.CCMMain;
import cresco.ai.att.ccm.gui.DataPanel;
import java.io.*;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.URL;
import java.util.ArrayList;
import javax.servlet.*;
import javax.servlet.http.*;
import java.applet.*;
public class NetComm extends JApplet{//HttpServlet{
private CCMMain hMain;
private DataPanel dpLocal;
private SocketServer sockserver;
private Method serverMethod;
String testStr;
Integer testInt; /*integer */
Character testChar; /*character*/
//Testing this...
ServerSocket server = null;
Socket client = null;
BufferedReader in = null;
PrintWriter out = null;
String line;
#Override
public void init(){
sockserver = new SocketServer(this);
//For offline debug (should be disabled in a release to the webapp):
//initSocketServer is commented out in the release version and
//invoked in the Eclipse testbed version. In the webapp,
//initSocketServer is invoked from javascript (see below js sockPuppet())
//////initSocketServer(0);
String msg = "Hello from Java (using javascript alert)";
try {
getAppletContext().showDocument(new URL("javascript:doAlert(\"" +
msg +"\")"));
}
catch (MalformedURLException me) { }
}
public void sendJSAlertTest(String message){
System.out.println("sendJSAlert remotely invoked, with message: " +
message);
}
public void sendJSAlert(String message){
try {
getAppletContext().showDocument(new URL("javascript:doAlert(\"" +
message +"\")"));
}
catch (MalformedURLException me) { }
}
public void initSocketServer(int portNum){
sockserver.listenSocket(portNum);
}
public void finalizeSocketServer(){
sockserver.finalize();
}
public int socket2Me(int portNum){
try {
socks.add(new ServerSocket(portNum));
return 0; //socket opened successfully
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
return -1; //socket failed to open
}
}
public int getSocketServerPort(){
return sockserver.getBoundLocalPort();
}
public void showRectTest(){
try {
getAppletContext().showDocument(new
URL("javascript:overlayRect()"));
}
catch (MalformedURLException me) { }
}
public void setGUI(DataPanel d){
dpLocal = d;
}
}
MapViz.html
<html>
<head>
<title>Welcome to Geographic Midpoint Map Vizualization!</title>
<meta name="viewport"
content="width=device-width, initial-scale=1.0, user-scalable=no">
<meta charset="UTF-8">
<link href="https://google-developers.appspot.com/maps/documentation/javascript
/examples/default.css"
rel="stylesheet" type="text/css">
...google maps stuff omitted...
<script type="text/javascript">
<script type="text/javascript">
function overlayRect(){
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
ctx.fillStyle="#FF0000";
ctx.fillRect(0,0,150,75);
}
function doAlert(s){
alert(s);
}
function testJava(){
document.ccmApplet.showRectTest();
}
function sockPuppet(){
var i = parseInt(document.getElementById("args").value,10);
alert("parsing the input args... got " + i);
if(i == NaN || i == null){
i = 0;
}
alert("passed NaN OR null block, i is " + i);
//i = 6672; //because $%*& you, that's why!
document.ccmApplet.initSocketServer(i);
//document.ccmApplet.listenSocket(i);
alert("inittializing socket server...");
//queryPort();
alert("querying port...");
document.ccmApplet.finalizeSocketServer();
//document.ccmApplet.finalize();
alert("finalizing socket server...");
}
function queryPort(){
var d = document.getElementById("debug");
var s1 = "Last port opened was: ";
//var s2 = document.ccmApplet.getLastBoundPort();
var s2 = document.ccmApplet.getSocketServerPort();
var sFinal = s1.concat(s2);
d.value = sFinal;
}
</script>
</head>
<body>
<applet width="500" height="50" name="ccmApplet" archive="CCM.jar"
code="cresco.ai.att.ccm.io.NetComm" MAYSCRIPT></applet>
<p></p>
<canvas id="myCanvas" width="200" height="100"></canvas>
<div id="map_canvas"></div>
<input id="args" type="textentry" value="" />
<button height="50" width="50" onClick="sockPuppet()">Test Socket
Creation</button>
<input id="debug" type="debugthingy" value="debug area..." />
<button height="50" width="50" onClick="testJava()">Test Java Callback</button>
</body>
</html>
In the webapp, I fill in the args input with a valid port number on the local machine and press the Test Socket Connection button which invokes the sockPuppet() javascript. This should create a ServerSocket and bind it to the specified port, which I then separately connect my desktop client app to via SocketClient.listenSocket. The result from Eclipse in the desktop app context is "awesome sendJSAlertTest" and in the appletviewer context is the output "sendJSAlert remotely invoked, with message: Hello Client, I'm a Server!". The webapp, invoking sendJSAlert(), should call the javascript alert function on the same message, creating a popup box with the message "sendJSAlert remotely invoked, with message: Hello Client, I'm a Server!" but instead nothing happens in the browser (nor the Chrome java or javascript debug consoles), and the desktop app output is null instead of "awesome sendJSAlert" as expected
So the question: What might be the cause of the different results? I know the browser's security sandbox could be an issue, but I've included a permissions file which should allow communication via sockets on any localhost port:
grant {
permission java.net.SocketPermission
"localhost:1024-",
"accept, connect, listen, resolve";
};
It's certainly possible though that I have not applied the permissions properly (I used the sun policytool gui); what exactly needs to be done in the applet code (if anything) to apply the permissions? Could a security problem result in the lack of response I'm seeing? I'd expect an exception to be reported in Chrome's java debug console, but there weren't any...
any help would be much appreciated, thanks!
-CCJ
UPDATE:
Okay, some new information: I ran the applet again in Chrome with the javascript console open (could have sworn I tried this before without effect, but evidently not) and received the following console output--
"Uncaught Error: java.security.AccessControlException: access denied
("java.net.SocketPermission" "<myipaddress>:4218" "accept,resolve") MapVizApp.html:154
sockPuppet MapVizApp.html:154 onclick MapVizApp.html:179 Uncaught Error: Error
calling method on NPObject. sockPuppet onclick "
So the question now is why am I tripping this security exception? The policy file with the permissions given above is in the same working directory as the html page and the jar file containing the applet, and I added the following to my system's JRE security policy file
//Grants my NetComm applet the ability to accept, connect, and listen on unpriv. ports
grant codeBase "file:${user.home}\Desktop\dev\invention\ATT\MapViz\CCM.jar" {
permission java.net.SocketPermission
"localhost:1024-",
"accept, connect, listen, resolve";
};
I haven't yet signed the applet, but it was my understanding that if the policy files are in order an applet doesn't need to be signed... if I'm wrong on that please let me know. Anyway, does anyone have any suggestions as to why this security exception is being thrown despite the policy files having the above granted permissions? Is there a naming convention for policy files in working directories that the JRE looks for? My working directory policy file for now is just named ccmPolFile, but I'm not clear on how the JRE is supposed to locate it; is there something I need to add to the applet code to point the JRE at the intended working directory policy file? Further, shouldn't the system policy file grant that I added be enough by itself to satisfy socket permissions for my applet inside CCM.jar?
UPDATE 2:
I signed the applet and added the line policy.url.3=file:${user.home}\Desktop\dev\invention\ATT\MapViz\ccmPolFile.policy to my java.security file in ${java.home}/lib/security (via http://docs.oracle.com/javase/tutorial/security/tour2/step4.html#Approach2 this is apparently how the JRE locates policy files to load)... sadly, the result is exactly the same security exception. The only thing left that I know of is
AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
// perform the security-sensitive operation here
return null;
}
});
which should let me do almost anything since the applet is now signed. I wanted to keep signing out of the equation, but policy files aren't working for some reason. I'll be back shortly with how that works out

righto, so following my update 2 above, I change the listenSocket() method in SocketServer.java code to
public void listenSocket(int portNum){
AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
int portNum = 4444;
try{
System.out.println("#server Trying to create socket bound to port " + portNum);
server = new ServerSocket(portNum);
System.out.println("the attached socket port is " + server.getLocalPort());
} catch (IOException e) {
System.out.println("Could not listen on port " + portNum);
System.exit(-1);
}
try{
client = server.accept();
System.out.println("Connection accepted!");
} catch (IOException e) {
System.out.println("Accept failed: " + portNum);
System.exit(-1);
}
try{
in = new BufferedReader(new InputStreamReader(client.getInputStream()));
out = new PrintWriter(client.getOutputStream(), true);
} catch (IOException e) {
System.out.println("Accept failed: " + portNum);
System.exit(-1);
}
while(portNum==4444){
try{
System.out.println("trying to read from inputstream...");
line = in.readLine();
System.out.println(line);
//Now that we have a method name, invoke it
try {
serverMethod = hNet.getClass().getDeclaredMethod(line,
String.class);
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
serverMethod.invoke(hNet, "Hello from Javascript invoked by the
desktop app!");
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//Send data back to client
out.println("awesome " + line);
//System.out.println(line);
//System.out.flush();
} catch (IOException e) {
System.out.println("Read failed");
System.out.flush();
System.exit(-1);
}
}
return null;
}
});//end doPrivileged
}
obviously this is an unsafe kludge, but it does the trick-- I receive no security exception, and the desktop app prints "awesome sendJSAlert" so I know IO is working between the client and server contexts via sockets. The actual js alert function didn't fire, but I think that has something to do with the horrid infinite while loop in listenSocket() above...
Take home message: for some reason, to establish socket connections from an applet in google chrome I needed to sign the applet AND use AccessController.doPrivileged() to invoke my security sensitive code, despite having set my local policy and security files to grant my applet those permissions
googlers see refs:
http://www.coderanch.com/how-to/java/HowCanAnAppletReadFilesOnTheLocalFileSystem
http://docs.oracle.com/javase/7/docs/api/java/security/AccessController.html
http://www-personal.umich.edu/~lsiden/tutorials/signed-applet/signed-applet.html
http://docs.oracle.com/javase/tutorial/security/tour2/step4.html
UPDATE: Finally working 100% :D I changed the listenSocket() method above in SocketServer.java to this:
public void listenSocket(int portNum){
AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
int portNum = 4444;
try{
System.out.println("#server Trying to create socket bound to port " + portNum);
server = new ServerSocket(portNum);
System.out.println("the attached socket port is " + server.getLocalPort());
} catch (IOException e) {
System.out.println("Could not listen on port " + portNum);
System.exit(-1);
}
try{
client = server.accept();
System.out.println("Connection accepted!");
} catch (IOException e) {
System.out.println("Accept failed: " + portNum);
System.exit(-1);
}
try{
in = new BufferedReader(new InputStreamReader(client.getInputStream()));
out = new PrintWriter(client.getOutputStream(), true);
} catch (IOException e) {
System.out.println("Accept failed: " + portNum);
System.exit(-1);
}
try {
line = in.readLine();
System.out.println("line is " + line + " from the inputstream to the
serversocket");
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
if(line != null){
System.out.println("trying to read from non-null inputstream...");
//line = in.readLine();
System.out.println(line);
//Now that we have a method name, invoke that bitch!
try {
serverMethod = hNet.getClass().getDeclaredMethod(line, String.class);
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
serverMethod.invoke(hNet, "Hello From Javascript invoked by a desktop
app!");
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//Send data back to client
out.println("awesome " + line);
//System.out.println(line);
//System.out.flush();
}
return null;
}
});//end doPrivileged
}
The server.accept() method blocks until a connection is made anyway, so for this scenario where I only want to pass one command at a time to the serversocket inputstream a while loop didn't make sense. The change to an if allowed the program to actually continue on to the java.reflect stuff which invokes a method in the applet which invokes javascript functions directly. Since the port is still hard-coded and the applet utilizes doPrivileged(...) this is still not a great solution, but it does satisfy the use case of invoking javascript in a web browser from a desktop java application via a java applet bridge so it makes for a good springboard into more robust implementations!

Reading file from serial port in Java

i'm beginner in java technology, I have to read file from port. Frst I'll write "FLASH" to outputstream then I'll get response as a "FLASH_OK" from target device, after getting FLASH_OK as response then again i have to write name of the file which i want,but problem is its not writing file name to outputstream, below is my code. Please help me.
package writeToPort;
import java.awt.Toolkit;
import java.io.*;
import java.util.*;
import javax.comm.*;
import javax.swing.JOptionPane;
import constants.Constants;
public class Flashwriter implements SerialPortEventListener {
Enumeration portList;
CommPortIdentifier portId;
String messageString = "\r\nFLASH\r\n";
SerialPort serialPort;
OutputStream outputStream;
InputStream inputStream;
Thread readThread;
String one, two;
String test = "ONLINE";
String[] dispArray = new String[1];
int i = 0;
byte[] readBufferArray;
int numBytes;
String response;
FileOutputStream out;
final int FLASH = 1, FILENAME = 2;
int number;
File winFile;
public static void main(String[] args) throws IOException {
Flashwriter sm = new Flashwriter();
sm.FlashWriteMethod();
}
public void FlashWriteMethod() throws IOException {
portList = CommPortIdentifier.getPortIdentifiers();
winFile = new File("D:\\testing\\out.FLS");
while (portList.hasMoreElements()) {
portId = (CommPortIdentifier) portList.nextElement();
if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
if (portId.getName().equals("COM2")) {
try {
serialPort = (SerialPort) portId.open("SimpleWriteApp",
1000);
} catch (PortInUseException e) {
}
try {
inputStream = serialPort.getInputStream();
System.out.println(" Input Stream... " + inputStream);
} catch (IOException e) {
System.out.println("IO Exception");
}
try {
serialPort.addEventListener(this);
} catch (TooManyListenersException e) {
System.out.println("Tooo many Listener exception");
}
serialPort.notifyOnDataAvailable(true);
try {
outputStream = serialPort.getOutputStream();
inputStream = serialPort.getInputStream();
} catch (IOException e) {
}
try {
serialPort.setSerialPortParams(9600,
SerialPort.DATABITS_8, SerialPort.STOPBITS_1,
SerialPort.PARITY_NONE);
serialPort
.setFlowControlMode(SerialPort.FLOWCONTROL_NONE);
number = FLASH;
sendRequest(number);
} catch (UnsupportedCommOperationException e) {
}
}
}
}
}
public void serialEvent(SerialPortEvent event) {
SerialPort port = (SerialPort) event.getSource();
switch (event.getEventType()) {
case SerialPortEvent.DATA_AVAILABLE:
try {
if (inputStream.available() > 0) {
numBytes = inputStream.available();
readBufferArray = new byte[numBytes];
int readBytes = inputStream.read(readBufferArray);
one = new String(readBufferArray);
System.out.println("readBytes " + one);
}
if (one.indexOf("FLASH_") > -1 & !(one.indexOf("FLASH_F") > -1)) {
System.out.println("got message");
response = "FLASH_OK";
number = FILENAME;
sendRequest(number);
}
out = new FileOutputStream(winFile, true);
out.write(readBufferArray);
out.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
readBufferArray = null;
// break;
}
}
public void sendRequest(int num) {
switch (num) {
case FLASH:
try {
outputStream.write(messageString.getBytes());
outputStream.flush();
} catch (IOException e) {
e.printStackTrace();
}
break;
case FILENAME:
try {
outputStream.write("\r\n26-02-08.FLS\r\n".getBytes());
outputStream.flush();
} catch (IOException e) {
e.printStackTrace();
}
break;
}
}
}

Have you tested with a Serial Port Emulator software?
When I did this kind of app for college, our professor told us to build the app and test it using an emulator, since it's much cheaper and less error prone.
While searching for google you can find some softwares that do that. I don't remember exactly the one we used at that time, but it worked quite well.
I mean products like this: Eterlogic - Virtual Serial Ports Emulator, but that's just an example (and I haven't tested this software, I just googled it)

You are erroneously assuming that full messages are always going to be received. Instead, when a serial event is triggered, only part of the message may be available. For example, you may get an event and read "FLAS" and a subsequent event will give "H_OK". You need to adapt your code to something like this:
// member variables
byte [] receiveBuffer = new byte[BUFFER_LENGTH];
int receiveIndex = 0;
// Receive code
receiveIndex +=
inputStream.read(receiveBuffer, receiveIndex, BUFFER_LENGTH - receiveIndex);

Sorry I can't help you with the Java code but are you sure the data "FLASH" is
actually being sent on your serial port ? When I'm having this kind of problem I usually use an oscilloscope to look on the TX pin on the serial port and check if I can "see" the data being sent (the data burst will be brief but you will be able to see it). If you
can see it use the scope to look on the RX pin of the serial port and see if you can
see the "FLASH_OK" response actually being sent.
Nine out of ten times the problem isn't the software but a hardware issue often due to handshaking pins being incorrectly connected.
Good luck with this.