Question

i am wondering if there is anyway to check if a ObjectInputStream or ObjectOutputStream is empty or not. i mean, in my program. at first time when it runs, the ObjectInputStream will use its readObject() method then because still the file empty it gives me an EOF exception( end of file) so i would like to check if it is empty or not then get rid off the exception:

And am i doing it right? for Serializing, i made the class with same name and attribute as below in both client and server.

public class KeyAdr implements Serializable{

 String adr;
 String key;


}
....

    static FileInputStream fIn=null;
    static ObjectInputStream oIn=null;
    private static KeyAdr test=new KeyAdr();

....

           fIn= new FileInputStream("d:\\someFile.ser");
           oIn = new ObjectInputStream(fIn);
           test= (KeyAdr) oIn.readObject(); 

EDIT:

 static  File serAdrKey=new File("d:\\someFile.ser");
     static    ObjectOutputStream oOut;
     static    FileOutputStream fOut;
     static  final   Pattern WebUrlPattern = Pattern.compile (WebUrlRegex);
     private static String WebUrlStr;
     static KeyAdr letsDoIt= new KeyAdr();

....

 public static void openStreams() throws IOException
        {
         fOut= new FileOutputStream(serAdrKey);
     oOut = new ObjectOutputStream(fOut);

        }


        @Override
public void    beforeWindowOpen(NavigationEvent event) 
        {

                     temp=event.getURL().toString();


  Matcher WebUrlMatcher = WebUrlPattern.matcher (temp);
    if (WebUrlMatcher.matches ())
    {
        int n = WebUrlMatcher.groupCount ();
      for (int i = 0; i <= n; ++i) {
    WebUrlStr = WebUrlMatcher.group (i);

}

                    letsDoIt.adr=WebUrlStr;    

                    try {
                    oOut.writeObject(letsDoIt);

                } catch (IOException ex) {
                    Logger.getLogger(Cobratest2.class.getName()).log(Level.SEVERE, null, ex);
                }


                   try {
                oOut.flush();


                   } catch (IOException ex) {
                Logger.getLogger(Cobratest2.class.getName()).log(Level.SEVERE, null, ex);
            }

Edit 2

fIn= new FileInputStream("d:\\someFile.ser");
PushbackInputStream input = new PushbackInputStream(fIn);
int c = input.read();
if(c != -1)
{
  input.unread(c);
  oIn = new ObjectInputStream(input);
  test = (KeyAdr) oIn.readObject();
  // ......
}

Edit 3:

the Edit2 codes gave me following exception with the stacktrace:

Exception in thread "main" java.io.EOFException
    at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2552)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1297)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:351)
        at test.Test.processClient(Test.java:117)
            at test.Test.run(Test.java:92)
            at test.Test.main(Test.java:159)

Answer 1

You may want to use the read method first to check if there is at least 1 byte.

read() is guaranteed to return -1 when the end of the stream has been reached, if the very first read() returns -1 the file must be empty

Addendum:
Using the FileInputStream you should be able to mark/reset to avoid losing the read byte.

You may however want to use java.util.File to check emptiness of the file beforehand.