如何在Java中的服务器套接字中处理不同的响应类型

Question

I have just started learning java. I have two projects that implement server socket. In server project, the server is responds based on an operation name that client send. Operations are dir - send server directory files (File[]) cd - current directory name (String)

Server.java

Socket client = serverSocket.accept();
DataInputStream in = new DataInputStream(client.getInputStream());
ObjectOutputStream out = new ObjectOutputStream(client.getOutputStream());
String operation = in.readUTF();
System.out.println("Performing opration : " + operation);
switch (operation) {
    case "dir":
        File[] lstOfFiles = folder.listFiles();
        out.writeObject(lstOfFiles);
        break;
    case "cd":
        out.writeObject(new String("Current Directory : " + currentDir));
        break;

}

Now how can I identify on the client side what is the object of type ?

Client.java

ObjectInputStream in = new ObjectInputStream(client.getInputStream());
File[] lstOfFiles = (File[]) in.readObject();
if(lstOfFiles !=null)
    System.out.println("Total : " + lstOfFiles.length);

But this is throwing exception ClassCastException. Then I tried

if ((in.readObject()).getClass() == String.class) {
   System.out.println((String)in.readObject());
}
else if (in.readObject().getClass() == Object.class) {
   File[] lstOfFiles = (File[]) in.readObject();
   if(lstOfFiles !=null)
      System.out.println("Total : " + lstOfFiles.length);
}

Then this is showing EOFException. How can I solve this? or any better approach ?

Answer 1

Every object in Java extends Object class, so your condition is unable to differ what you are trying to recognize. Also, you need to check if an object was returned from stream, right now you are just working on object that is possibly null.

Answer 2

if you use

in.readObject()

then after using this will empty the stream.So that's why it is throwing EOFException.

I have solved using this

Object response = in.readObject();
if(response.getClass() == String.class){
   // code to run
}
else {
   // code to run
}