i have 2 java applications connected to each other via LAN (wifi network)
the first one ServerApp.java
public class ServerApp {
public static void zzz(){
System.out.println("hi");
}
public static void main(String[] args) {
try {
ServerSocket ss=new ServerSocket(6666);
Socket s=ss.accept();
DataInputStream dis = new DataInputStream(s.getInputStream());
String str =(String)dis.readUTF();
System.out.print("message : "+str);
ss.close();
} catch (IOException e) {
System.out.println(e);
}
}
}
the second one ClientApp.java
public class ClientApp {
public static void main(String[] args) {
try {
Scanner in = new Scanner(System.in);
System.out.print("send message to the server ?[y/n]:");
String inputString=in.next();
if ("y".equals(inputString)) {
Socket s= new Socket("192.168.20.125", 6666);
DataOutputStream dout=new DataOutputStream(s.getOutputStream());
dout.writeUTF("hellow server\n");
dout.writeUTF("zzz");
dout.flush();
dout.close();
s.close();
} else if ("n".equals(inputString)) {
System.out.println("exit");
} else {
System.out.println("error: you should enter a valid value");
}
} catch (IOException e) {
System.out.println(e);
}
}
}
what happens is, the client app send a message to the server app via LAN using the server IP address - the server app have a method call zzz() so all I want is how do I make the client app call this method ( if possible )
thanks
#MichalLonski how to I make the "obj" indicate to the ServerApp
As it is static method you have to point ServerApp.class, like below:
public class ServerApp {
public static void zzz() {
System.out.println("hi");
}
public static void main(String[] args) throws Exception {
String methodName = "zzz";
java.lang.reflect.Method method = ServerApp.class.getMethod(methodName);
method.invoke(ServerApp.class);
}
}
You can change it to use not static, but instance methods. In order to do that you have to create an instance of ServerApp class, like this:
public class ServerApp {
public void foo() {
System.out.println("Hello there from non static method!");
}
public static void main(String[] args) throws Exception {
String methodName = "foo";
ServerApp app = new ServerApp();
java.lang.reflect.Method method = app.getClass().getMethod(methodName);
method.invoke(app);
}
}
Edit:
If you want to specify also the class of which method you want to call, you can do it this way:
package com.example;
class Foo {
public static void bar() {
System.out.println("Hello there.");
}
}
public class ServerApp {
public static void main(String[] args) throws Exception {
//read the class and method name from the socket
String className = "com.example.Foo";
String methodName = "bar";
Class<?> clazz = Class.forName(className);
clazz.getMethod(methodName).invoke(clazz);
}
}
Related
I want to send an object having OS Name to a server. This OS Name output should be of PC sending object but it displays OS Name of PC running server..
Here is my code :
//Client : it can send data i.e. object to server
class Client
{
private Socket socket = null;
private ObjectOutputStream outputStream = null;
public Client(String con){
System.out.println("conn value: "+con);
java.util.Timer t = new java.util.Timer();
try{
socket = new Socket(con, 27051);
t.scheduleAtFixedRate(new TimerTask() {
#Override
public void run() {
try {
outputStream = new ObjectOutputStream(socket.getOutputStream());
SI sysinfo=new SI();
outputStream.writeObject(sysinfo);
System.out.println("Sent Data: "+sysinfo.otherInfo());
} catch (Exception se) {
t.cancel();
}
}
}, 0, 1);
}
catch(Exception em)
{
}
}
}
//Server class: should receive data from client
class Server extends SwingWorker<Void,Void>{
Socket csocket=null;
protected Void doInBackground() throws Exception {
final ServerSocket ssock = new ServerSocket(27051);
System.out.println("Server Listening..!!");
while (true) {
try{
Socket sock = ssock.accept();
new Thread(new Server(sock)).start();
}
catch(Exception e){
System.out.println("unabke to create socket");
}
}
}
Server() throws Exception{
doInBackground();
}
Server(Socket csocket) {
this.csocket=csocket;
Thread t1=new Thread(r1);
t1.start();
}
Runnable r1=new Runnable()
{
public void run() {
try {
System.out.println("Run initated");
while(true)
{
if(csocket.isClosed())
{
break;
}
else{
System.out.println(csocket);
ObjectInputStream inStream = new
ObjectInputStream(csocket.getInputStream());
SI sysinfo= (SI) inStream.readObject();
System.out.println("Received: "+sysinfo.otherInfo());
System.out.println(ObjectStreamClass.lookup(sysinfo.getClass()).getSerialVersion
UID());
}
}
}
catch (Exception e) {
System.out.println("Exception"+ e.getMessage());
}
}
};
}
//class undergoing serialization
public class SI implements Serializable
{
private static final long serialVersionUID = 1L;
String otherInfo()
{
OperatingSystemMXBean bean = (com.sun.management.OperatingSystemMXBean) ManagementFactory
.getOperatingSystemMXBean();
String os_name=bean.getName();
return os_name;
}
}
//class A: It has main function and it executes first and user decides whether he/she want to be in server mode or in client mode. As user cannot be in 2 modes simultaneously..
class A
{
public static void main(String[] args) throws Exception
{
System.out.println("Enter 0 for Server 1 for Client Mode");
Scanner s=new Scanner(System.in);
int i=s.nextInt();
if(i==0)
{
Server ser=new Server();
ser.execute();
}
else if(i==1)
{
System.out.println("Enter IP");
String conn=s.next();
Client c=new Client(conn);
}
else
System.out.println("Invalid Selection exit..");
}
}
As I wrote in my comment you must transfer the data, not the function. Some sample code below...
First, change your SI class as follows:
public class SI implements Serializable {
private static final long serialVersionUID = 1L;
private String osName;
public void setOsName(String osName) { this.osName = osName; }
public void getOsName() { return this.osName; }
}
Second, modify your client to first determine the OS and the build the SI object...
...
OperatingSystemMXBean bean = (com.sun.management.OperatingSystemMXBean) ManagementFactory
.getOperatingSystemMXBean();
String osName=bean.getName();
SI sysinfo = new SI();
sysinfo.setOsName(osName);
...
outputStream.writeObject(sysinfo);
...
Third, modify your server accordingly.
I'm trying to tie my PrintStream object to the console's output and error streams so that whatever I write there will also be written to my log file.
public static void tieOutputStreams(String fileName) {
try {
File output = new File(fileName);
FileWriter writer = new FileWriter(output);
writer.close();
outputStream = new TiedOutputStream(output);
}
catch (Exception e) {
e.printStackTrace();
}
System.setErr(outputStream);
System.setOut(outputStream);
}
Once I'm done writing, I could reset it back to the way things were.
public static void resetOutputStreams() {
outputStream.close();
System.setErr(System.err);
System.setOut(System.out);
}
TiedOutputStream class looks like this:
public class TiedOutputStream extends PrintStream {
public TiedOutputStream(File logFile) throws FileNotFoundException {
super(logFile);
}
#Override
public void print(Object obj) {
super.print(obj);
System.out.print(obj);
}
#Override
public PrintStream printf(String format, Object... args) {
super.printf(format, args);
System.out.printf(format, args);
return this;
}
#Override
public void println(Object args) {
super.println(args);
System.out.println(args);
}
}
And my main method:
public static void main(String[] args) {
try {
TieOutputStreams.tieOutputStreams("./sample.log");
System.out.println("Output console");
System.err.println("Error console");
float num = 1.123456f;
System.out.printf("A float: %.6f", num);
} catch (Exception e) {
e.printStackTrace();
}
finally {
TieOutputStreams.resetOutputStreams();
}
}
I want these statements to be printed on both my log file and the System consoles (out / err). For reasons I don't know, this isn't working. I appreciate all the answers and comments. Thanks in advance!
I know there is Log4j. But I want to do this anyway.
This doesn't work mainly because you didn't save the original System.out and because you didn't override println(String obj) When you call System.out.println("Output console"); you won't hit in the method you override because that one expects and object and there is a more specific method in PrintStream that expects a String argument
This seems to work:
public class TiedOutputStream extends PrintStream {
private final PrintStream sout;
private final PrintStream serr;
public TiedOutputStream(File logFile) throws FileNotFoundException {
super(logFile);
sout = System.out;//save standard output
serr = System.err;
}
#Override
public void print(Object obj) {
super.print(obj);
sout.print(obj);
}
#Override
public void println(String obj) {
super.println(obj);
sout.println(obj);
}
#Override
public PrintStream printf(String format, Object... args) {
super.printf(format, args);
sout.printf(format, args);
return this;
}
#Override
public void println(Object args) {
super.println(args);
sout.println(args);
}
}
Not sure why tieOutputStreams created that FileWriter
public static void tieOutputStreams(String fileName) {
try {
File output = new File(fileName);
outputStream = new TiedOutputStream(output);
System.setErr(outputStream);
System.setOut(outputStream);
} catch (Exception e) {
e.printStackTrace();
}
}
main method remains the same. You should update resetOutputStreams to restore to original out and err. I would override all print* method from PrintStream if I would use this.
I have a server that contains an ArrayList in " ServerInfo " and when I try to take from ClientRMI an element of the ArrayList(in ServerInfo) for example adf.getSGM ( 0 ).incrementCount( ) ;
"count" does not increase it's as if every time I call it instantiates a new class SGM
in a few words I want to interact from ClientRMI with ArrayList that is on ServerInfo (SORRY FOR ENGLISH)
Hear are the classes :
SERVER
public class ServerRMI {
public static void main(String[] args) {
Registry registry = null;
String name = "ServerInfo";
try {
System.out.println("Init RMI");
ServerInfoInterface sir = ServerInfo.getInstance();
ServerInfoInterface stub = (ServerInfoInterface) UnicastRemoteObject.exportObject(sir, 0);
registry = LocateRegistry.createRegistry(9000);
registry.bind(name, stub);
System.out.println("RMI OK");
System.out.println("Init SGM...");
for(int i=0;i<3;i++){
ServerInfo.getInstance().addSGM(new SGM());
}
System.out.println("Init SGM OK");
} catch (Exception e) {
System.out.println("RMI Error"+e.toString());
registry = null;
}
}
}
public class ServerInfo implements ServerInfoInterface{
private ArrayList<SGM> sgmHandler = new ArrayList<SGM>();
// Singleton pattern
private static ServerInfo instance;
// Singleton pattern
public static ServerInfo getInstance() {
if (instance == null){
System.out.println("ServerInfo new instance");
instance = new ServerInfo();
}
return instance;
}
#Override
public synchronized void addSGM(SGM sgm) throws RemoteException {
sgmHandler.add(sgm);
}
#Override
public synchronized SGM getSGM(int i) throws RemoteException {
return sgmHandler.get(i);
}
}
public interface ServerInfoInterface extends Remote{
public void addSGM(SGM sgm) throws RemoteException;
public SGM getSGM(int i) throws RemoteException;
}
public class SGM implements Serializable{
/**
*
*/
private static final long serialVersionUID = -4756606091542270097L;
private int count=0;
public void incrementCount(){
count++;
}
public void decrementCount(){
count--;
}
public int getCount(){
return count;
}
}
CLIENT
public class ClientRMI {
private ServerInfoInterface sgmInterface;
public void startServer() {
String name = "ServerInfo";
Registry registry;
try {
registry = LocateRegistry.getRegistry(9000);
try {
sgmInterface = (ServerInfoInterface) registry.lookup(name);
sgmInterface.getSGM(0).incrementCount();
System.out.println(sgmInterface.getSGM(0).getCount()); // always 0
} catch (AccessException e) {
System.out.println("RIM AccessException"+ e.toString());
} catch (RemoteException e) {
System.out.println("RIM RemoteException"+ e.toString());
} catch (NotBoundException e) {
System.out.println("RIM NotBoundException"+ e.toString());
}
} catch (RemoteException e) {
System.out.println("RIM RemoteException registry"+ e.toString());
}
}
}
You're creating an SGM at the server, passing it via Serialization to the client, incrementing its count at the client, and then expecting that count to be magically increased at the server.
It can't work.
You will have to make SGM a remote object, with its own remote interface, or else provide a remote method in the original remote interface to increment the count of a GSM, specified by index.
I have the following code:
class ClassDetails {
private String current_class;
public ClassDetails(String current_class) {
this.current_class = current_class;
}
public void getClassDetails() throws ClassNotFoundException {
try {
Class theClass = Class.forName(current_class);
String name = theClass.getName() ;
System.out.println(name);
} catch (ClassNotFoundException e) {
System.out.println(e.getMessage());
}
}
}
class MMain {
public static void main(String[] args) {
ClassDetails C = new ClassDetails(args[0]);
C.getClassDetails();
}
}
And I have this error in main:
Unhandled exception type ClassNotFoundException
How can I solve this?
Your main method calls the getClassDetails() method, which throws that exception, as the signature shows:
public void getClassDetails() throws ClassNotFoundException
And you aren't catching it, or throwing it in the method, so your code will not compile. So you must either do:
public static void main(String[] args) throws ClassNotFoundException {
ClassDetails C = new ClassDetails(args[0]);
C.getClassDetails();
}
Or:
public static void main(String[] args) {
ClassDetails C = new ClassDetails(args[0]);
try
{
C.getClassDetails();
}
catch(ClassNotFoundException ex)
{
//Add exception handling here
}
}
I'm building an application in Java which requires a Hashtable to be accessed from instances of two classes and both extend threads. I have declared the Hashtable in one of the two classes. I always get null when i try to access the Hashtable contents from one of the classes. The other class is able to access the contents without any problem. I thought this was a problem of concurrency control. Since these are threads of different classes we cannot use synchronized methods. Is there a way to make the Hashtable accessible from threads of both the classes?
Here are the some parts of the code of my application
This is the class which stores the HashMap:
public class DataStore {
public Map ChatWindows ;
public DataStore()
{
ChatWindows = new ConcurrentHashMap();
}
public synchronized void putWindow(String with,ChatWindow t)
{
ChatWindows.put(with,t);
notifyAll();
}
public synchronized ChatWindow getWindow(String with)
{
notifyAll();
return (ChatWindow)ChatWindows.get(with);
}
public synchronized void ChatWindowOpen(chatClient cc,String with,String msg)
{
// chatWith = with;
ChatWindow t;
System.out.println(with);
t = getWindow(with);
if(t == null)
{
t = new ChatWindow(cc,with,msg);
// th = new Thread(t);
putWindow(with, t);
// th.start();
}
else
{
t.setVisible(true);
}
}
}
Two classes which access 'ChatWindows' HashMap
public class chatClient extends javax.swing.JFrame implements
Runnable,ListSelectionListener,MouseListener,WindowListener{
static String LoginName,chatWith,msgToChatWindow;
Thread listThread=null,th,chatListen;
static Socket soc;
static DataOutputStream dout,dout1;
static DataInputStream din,din1;
DefaultListModel listModel;
ChatWindow t;
public DataStore ds;
/** Creates new form chatClient */
public chatClient(Login l,DataStore ds) {
listModel = new DefaultListModel();
initComponents();
clientList.addListSelectionListener(this);
clientList.addMouseListener(this);
addWindowListener(this);
this.LoginName=l.loginName;
soc = l.soc2;
din = l.din2;
dout = l.dout2;
dout1 = l.dout1;
din1 = l.din1;
super.setTitle(LoginName);
listThread = new Thread(this);
listThread.start();
this.ds = ds;
}
.
.
.
.
public void mouseClicked(MouseEvent e)
{
chatWith = (String)clientList.getSelectedValue();
ds.ChatWindowOpen(this,chatWith,"");
}
This class has run() method too, but that doesn't use the HashMap. This class is able to access the 'ChatWindows' properly.'ChatListenThread' class is not able to access the contents of HashMap properly.
public class ChatListenThread implements Runnable{
DataOutputStream dout1;
DataInputStream din1;
public static chatClient cc;
public static ChatWindow t;
public DataStore ds;
public ChatListenThread(Login l,DataStore ds)
{
din1 = l.din1;
dout1= l.dout1;
this.ds = ds;
}
.
.
.
.
public void run(){
while(true)
{
try{
String msgFromServer=new String();
msgFromServer = din1.readUTF();
StringTokenizer st=new StringTokenizer(msgFromServer);
String msgFrom=st.nextToken();
String MsgType=st.nextToken();
String msg = "";
while(st.hasMoreTokens())
{
msg=msg+" " +st.nextToken();
}
ds.ChatWindowOpen(cc,msgFrom,msg);
}
catch(IOException e)
{
System.out.println("Read failed");
}
}
}
}
It's possible. Take a look at Sharing data safely between two threads.
Okey, I couldn't use your code because I don't understand, what I did see was that you want something like this:
Create a empty JFrame with a JTabbedPane and start a thread that connects to a Socket
When input comes on the socket, create a ChatPanel (~JTextArea) and add it to one of the tabs
Add the ChatPanel to a Map that handles the messages from "from"
Pass the message to the newly created ChatPanel
So I did that and I'm posting the code below! Hope that you can use it!
If you like to test this, first start the TestChatServer (code below) and then the ChatSupervisor.
This is the code for the client
public class ChatSupervisor extends JFrame implements Runnable {
JTabbedPane tabs = new JTabbedPane();
Map<String, ChatPanel> chats = new ConcurrentHashMap<String, ChatPanel>();
public ChatSupervisor() {
super("Test Chat");
add(tabs, BorderLayout.CENTER);
new Thread(this).start();
}
public void run() {
Socket sock = null;
try {
sock = new Socket("localhost", 32134);
Scanner s = new Scanner(sock.getInputStream());
while (true) {
String from = s.next();
String type = s.next();
String message = s.nextLine();
getChat(from).incomingMessage(type, message);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
if (sock != null) try { sock.close(); } catch (IOException e) {}
}
}
public ChatPanel getChat(String from) {
if (!chats.containsKey(from))
chats.put(from, new ChatPanel(from));
return chats.get(from);
}
public static void main(String[] args) {
ChatSupervisor cs = new ChatSupervisor();
cs.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
cs.setSize(400, 300);
cs.setVisible(true);
}
class ChatPanel extends JTextArea {
public ChatPanel(final String from) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
tabs.addTab(from, ChatPanel.this);
}
});
}
public void incomingMessage(final String type, final String message) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
append("[" + type + "]" + message);
append("\n");
}
});
}
}
}
This is the code for the test server:
public class TestChatServer {
public static void main(String[] args) throws Exception {
Socket s = new ServerSocket(32134).accept();
System.out.println("connected");
PrintWriter p = new PrintWriter(s.getOutputStream());
while (true) {
p.println("hello info Hello World!");
p.flush();
Thread.sleep(1000);
for (int i = 0; i < 10; i++) {
p.println("test" + i + " warn Testing for testing " + i);
p.flush();
Thread.sleep(100);
}
}
}
}