在java中读取和写入日期/日历到txt文件

Question

How can I read and write a Date/Calendar to a txt file. I want to store the map of Date,String key value pair to a text file and be able to restore it back into a map. What I did right now is just looping through all of the map and write Date.tostring() + “," + string to the txt file but I don't know how to restore Date.tostring() to a Date, by the way, is there any possibility I only want year/month/date/hour/minutes but no time zone in my Date.tostring() and still restore it back into a Date object?

Answer 1

You can save the time to txt file with the format you see in time variable below and then parse it using the rest of the code.

String time = "Jul 24 2012 05:19:34";
DateFormat df = new SimpleDateFormat("MMM dd yyyy HH:mm:ss");
Date date = df.parse(time);

Answer 2

You can use this method which creates a folder with a random name and then insert a date to a txt file there:

 try {
        Random rand = new Random();
        DateFormat df = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");
        Date today = Calendar.getInstance().getTime();
        String reportDate = df.format(today);
        String dateToPrintToFile = reportDate;
        File folder = new File("<your Folder>/" + rand);
        File file = new File("<your Folder>/" + rand + "/testDate.txt");
        if (!file.exists()) {
            file.createNewFile();
        }
        FileWriter fw = new FileWriter(file.getAbsoluteFile());
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write(dateToPrintToFile);
        bw.close();
    } catch (Exception e) {
        e.printStackTrace();
    }

Answer 3

you can use SimpleDateFormat for formating date

SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd/HH/mm");
String line = sdf.format(date) + "," + text;

restore

String[] l = line.split(",");
Date d = sdf.parse(l[0]);
String text = l[1];

Answer 4

If you don't want to deal with parsing complex human-readable date strings, the Date.getTime() function

Returns the number of milliseconds since January 1, 1970, 00:00:00 GMTrepresented by this Date object.

In other words you can get this long value and write that to file (as a string) instead of a human-readable date string. Then read the long (as a string) back in from the text file and instantiate with

String[] l = line.split(","); //Split the line by commas
long value = Long.ParseLong(l[0]); //Parse the string before the comma to a long
Date readDate = new Date(value); //Instantiate a Date using the long