如何将Date对象转换为字符串/ long并通过客户端/服务器发送

Question

Hi i'm having a little trouble with sending a Date object from a Client to a Server so that i can compare them. So basically what i'm trying to do is: 1)Send the Date object 2)Compare their times 3)Set the time to both machines with the average time from both

So far i have done this:

Server:

public class Server implements Runnable{
    private int port;
    private String name;
    private Date mydate = new Date();
    private Date date;
    public Server(int port, String name){
        this.port=port;
        this.name=name;
    }
    public synchronized void run(){
        while(true){
        try{

            method();

        }
        catch(Exception e){
            return;
        }

        }
    }

    public synchronized void method() throws Exception{
        long dates;
        long average=0;
        String[] values = new String[10];

        DateFormat df = new SimpleDateFormat("EEE MMM dd kk:mm:ss zzz yyyy");
      ServerSocket server = new ServerSocket(port);

      Socket s=server.accept();

      InputStream in= s.getInputStream();
      OutputStream out = s.getOutputStream();

      PrintWriter w = new PrintWriter(out);
      Scanner r = new Scanner(in);
      for(int i=0; i<10; i++){
      String msg = r.next();
      values[i] = msg;

    }
      for(int j=0; j<values.length; j++){
          dates = Long.parseLong(values[j]);
          date = new Date(dates);
          average = average + date.getTime();
      }
      average = (average - mydate.getTime())/2;
      mydate.setTime(average);
      System.out.println(name+": "+mydate.toString());
}
}

Client:

public class Client implements Runnable{
    private int port;
    private int id;
    Date time = new Date();
    Date time2 = new Date();
    public Client(int port,int id){
        this.port=port;
        this.id = id;
    }

    public synchronized void run(){

        try{
            Thread.sleep(5000);

            method();

        }
        catch(Exception e){
            return;
        }

    }

    public synchronized void method() throws Exception{
        DateFormat df = new SimpleDateFormat("EEE MMM dd kk:mm:ss zzz yyyy");
        Random ran = new Random(500);
        int d = ran.nextInt(500)+500;
        time.setTime(time.getTime()+d);
        String datestr;
        Socket s = new Socket("localhost", port);

        InputStream in= s.getInputStream();
        OutputStream out = s.getOutputStream();

        PrintWriter w = new PrintWriter(out);
        Scanner r = new Scanner(in);
        for(int i=0; i<10; i++){
        time.setTime(time.getTime()+d);
        datestr = df.format(time);
        w.println(datestr);
        w.flush();
        }


    }
}

But the result i get is 'nothing' just white space. The program compiles fine with now errors and i kind of know where the problem is but i just can't figure out how to parse the values correctly so that they can be read properly. Please help me :S

Answer 1

In your client you send the date as a string formated by SimpleDateFormat resulting in something like: "Sat Mai 04 22:27:24 PST 2013"

On the server side you take this string an tries to parse it as a long so that you can use it future in the Date(long date) constructor.

The new Date(long date) expect date to be unixtime. Unixtime is what you get when you call date.getTime(). Unixtime is milliseconds sins 01.01.1970 00:00:00:0000.

I would expect server to throw som kind of parse exception.

You have to deside if you want to use SimpleDateFormat to format transmittion side and the use SimpleDateFormat parse on the reciving side. Or send the unixtime.

I would've recommend sending the unixtime. You convert from Date object by:

Long unixtime =  date.getTime() 

And back:

Date date = new Date(unixtime)

or serverside you dont need the date object at all, you only use it to call getTime() witch in turn gives back unixtime.

Server:

public class Server implements Runnable{
    private int port;
    private String name;
    private Date mydate = new Date();
    private Date date;
    public Server(int port, String name){
        this.port=port;
        this.name=name;
    }
    public synchronized void run(){
        while(true){
        try{

            method();

        }
        catch(Exception e){
            return;
        }

        }
    }

    public synchronized void method() throws Exception{
        long unixtime;
        long average=0;
        String[] values = new String[10];

        ServerSocket server = new ServerSocket(port);

      Socket s=server.accept();

      InputStream in= s.getInputStream();
      OutputStream out = s.getOutputStream();

      PrintWriter w = new PrintWriter(out);
      Scanner r = new Scanner(in);
      for(int i=0; i<10; i++){
      String msg = r.next();
      values[i] = msg;

    }
      for(int j=0; j<values.length; j++){
          unixtime= Long.parseLong(values[j]);
          average = average + unixtime;
      }
      average = (average - mydate.getTime())/2;
      mydate.setTime(average);
      System.out.println(name+": "+mydate.toString());
}
}

Client:

public class Client implements Runnable{
    private int port;
    private int id;
    Date time = new Date();
    Date time2 = new Date();
    public Client(int port,int id){
        this.port=port;
        this.id = id;
    }

    public synchronized void run(){

        try{
            Thread.sleep(5000);

            method();

        }
        catch(Exception e){
            return;
        }

    }

    public synchronized void method() throws Exception{
        Random ran = new Random(500);
        int d = ran.nextInt(500)+500;
        time.setTime(time.getTime()+d);
        Socket s = new Socket("localhost", port);

        InputStream in= s.getInputStream();
        OutputStream out = s.getOutputStream();

        PrintWriter w = new PrintWriter(out);
        Scanner r = new Scanner(in);
        for(int i=0; i<10; i++){
        time.setTime(time.getTime()+d);
        w.println(time.getTime());
        w.flush();
        }


    }
}