从Java中的文本文件读取时间

Question

I am trying to write some codes in java to read a text file, but when it read a time in (hh:mm) formate as example below:

6:30 14:30

and there is my java code to convert the string to Data formate

DateFormat formatter = new SimpleDateFormat("hh:mm");
strLine = br.readLine();
strLine = strLine.trim();
tokens2 = strLine.split(" ");
System.out.println((Date)formatter.parse(tokens2[0]));

the output will be:

Thu Jan 01 06:30:00 AST 1970

it will give in long formate Date , While I want just take timezone(06:30). what should I do ? Any advice.

edit: the problem solved by Joda time by this code:

LocalTime.parse(tokens2[0]);

it is just take time

Answer 1

Firstly, your time pattern is wrong - you should be using HH:mm as you're using a 24-hour clock in your examples.

Secondly, you're parsing a Date . A Date is just an instant in time: it doesn't know about the time zone, calendar, whether you're interested in just the time, just the date etc.

Thirdly, you're seeing that output because you're basically just calling Date.toString() .

There's no type in Java to represent just "a time of day" (which isn't at all the same as a time zone, by the way). You could format a Date to just include the time part, but if you want to do that, I'd strongly recommend using a time zone of UTC to avoid any possible DST problems.

A better solution would be to use Joda Time which has a LocalTime type - ideal for your situation. You can parse that ( DateTimeFormatter.parseLocalTime ) and then work with it appropriately, formatting it (again to just a time) whenever you want.

Answer 2

I assume you want to read and parse 6:30 and output it as 06:30 , right?

Well, a first step would be to use the formatter, to output the date again:

System.out.println(formatter.format((Date)formatter.parse(tokens2[0])));

Btw, your format would not be able to correctly format 14:30 since h means the hour in am/pm, eg 1-12. Your format should be HH:mm instead, otherwise you'd get the output 02:30 instead of 14:30 .

Answer 3

You can use a SimpledateFormatter in two ways.

1. to parse a String and create a Date
2. to create a String aout of a Date

You want both in your example. First you want to parse a String and create a Date (even if you are only interestet in the time part). In the second step you want to create a String out of this Date and print it to System.out.

Date date=formatter.parse(tokens2[0]);     //use the 'formatter' to parse the String
Sytem.out.println(formatter.format(date)); //use the 'formatter' to define the format of the output.

Answer 4

Using java.time

The other answers are correct but now outdated.

The java.time.LocalTime class represents a time-of-day without a date and without a time zone. The class can directly parse a string in standard ISO 8601 format using 24-hour clock: HH:MM or HH:MM:SS

LocalTime lt = LocalTime.parse( "14:30" );
String output = lt.toString();  // 14:30

Formatting

Use a DateTimeFormatter if you want other formats. Even localize automatically.

DateTimeFormatter f = DateTimeFormatter.ofLocalizedDateTime( FormatStyle.FULL );
f = f.withLocale( Locale.CANADA_FRENCH ); // Cultural norms & human language
String output = lt.format( f );

About java.time

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

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

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

Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport and further adapted to Android in 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.