如何将字符串输入转换为毫秒到Date

Question

I have a java method which needs to convert a Date from one input String format to another. The input and output formats must retain all millisecond detail, as this is for a process tracking solution where timestamps will often be just milliseconds apart.

The SimpleDateFormat seems to be losing all millisecond data, and just returning random numbers for the seconds and milliseconds.

input date String: "05/23/2013 12:32:13.45133" input date format: "MM/dd/yyyy HH:mm:ss.SSSSS" output date format: "yyyyMMddHHmmssSSS"

Given the above input date and format, my resulting Date String is: 20130523123258133. This is obviously completely off from the input seconds.

The input format may vary, but the output format must always be the same.

Below is the current method:

private long dateSequencer(String inputDt, String inputFormat) {
    long result = 0;
    try {
        // Convert input date into yyyyMMddHHmmssSSS format for sequencing
        SimpleDateFormat dtFrmt = new SimpleDateFormat(inputFormat);
        Date dt = new Date();
        dt = dtFrmt.parse(inputDt);
        // input String converted to Date, now reformat to Long
        dtFrmt = new SimpleDateFormat("yyyyMMddHHmmssSSS");
        String reFrmt = dtFrmt.format(dt);
        result = Long.parseLong(reFrmt);
    } catch (Exception ex) {
        System.out.println("++++ Exception converting dateSequencer: " + ex.toString());
    }
    System.out.print("+++ABM dateSeq: [inputDt=" + inputDt + "] [inputFormat=" + inputFormat + "] [result=" + result +"]");
    return result;
}

Log file entry from runtime:

+++ABM dateSeq: [inputDt=05/23/2013 12:32:13.45133] [inputFormat=MM/dd/yyyy HH:mm:ss.SSSSS] [result=20130523123258133]

Since the input format may change, I cannot manually parse the input String to rely on a specific pattern. This is why I am allowing the pattern to be passed, and using a SimpleDateFormat to convert to Date, then back to String.

How can I do this, reliably? Is there a more efficient way to convert a given input Date string, to a standard format?

Thanks!

Answer 1

If you can assume that in every case month, day, minute, second have 2 digits, year has 4 digits and milliseconds have 3 digits and just the pattern differs, you can simply do the following:

public static long convert(String inputDt, String inputFormat) {
    int dd = inputFormat.indexOf("dd");
    int MM = inputFormat.indexOf("MM");
    int yyyy = inputFormat.indexOf("yyyy");
    int HH = inputFormat.indexOf("HH");
    int mm = inputFormat.indexOf("mm");
    int ss = inputFormat.indexOf("ss");
    int SSS = inputFormat.indexOf("SSS");
    return Long.valueOf(inputDt.substring(yyyy,yyyy+4) + inputDt.substring(MM, MM+2) + inputDt.substring(dd, dd+2) + inputDt.substring(HH, HH+2)
            + inputDt.substring(mm, mm+2) + inputDt.substring(ss, ss+2) + inputDt.substring(SSS,SSS+3));        
}

convert("05/23/2013 12:32:13.133", "MM/dd/yyyy HH:mm:ss.SSS") yields 20130523123213133

Answer 2

Your input date String: "05/23/2013 12:32:13.45133" contains 5 digits for milliseconds. And It's not possible... There must be 3 digits. So 45133 milliseconds is equals to 45 seconds and 133 millis. Your input date string is the date "05/23/2013 12:32:58.133"

Answer 3

java.time

The modern approach uses the java.time classes that years ago supplanted the troubled old classes such as Date & Calendar & SimpleDateFormat . No need to ever touch those terrible legacy classes again.

Define a formatting pattern to suit your input with the DateTimeFormatter class.

String input = "05/23/2013 12:32:13.45133"
DateTimeFormatter formatterInput = DateTimeFormatter.ofPattern( "MM/dd/uuuu HH:mm:ss.SSSSS" );
LocalDateTime ldt = LocalDateTime.parse( input , formatterInput );

DateTimeFormatter formatterOutput = DateTimeFormatter.ofPattern( "uuuuMMddHHmmssSSS" );
String output = ldt.format( formatterOutput );

System.out.println( ldt );
System.out.println( output );

ISO 8601

By the way, your desired output format happens to be close to the standard ISO 8601 format. The “basic” versions in the standard minimize the use of delimiters: YYYY-MM-DDTHH:MM:SS.S versus YYYYMMDDTHHMMSS.S as you have done.

I suggest you make a practice of using the standard format rather than inventing your own. To comply, add the T between the date portion and the time portion.

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date , Calendar , & SimpleDateFormat .

The Joda-Time project, now in maintenance mode , advises migration to the java.time classes.

To learn more, see the Oracle Tutorial . And search Stack Overflow for many examples and explanations. Specification is JSR 310 .

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes.

Where to obtain the java.time classes?

• Java SE 8 , Java SE 9 , Java SE 10 , Java SE 11 , and later - Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP… .

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval , YearWeek , YearQuarter , and more .