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How can I reformat date and time?

How can I convert 24 hours time format into 12 hours format? I know this question has been asked many times, but my problem is different. My current time is:
Tue Nov 07 18:44:47 GMT+05:00 2017
I just want 6:44 pm from my date time. I tried this:
private void convertTime(String time)
{
try {
final SimpleDateFormat sdf = new SimpleDateFormat("H:mm");
final Date dateObj = sdf.parse(time);
System.out.println(dateObj);
System.out.println(new SimpleDateFormat("K:mm a").format(dateObj));
} catch (final ParseException e) {
e.printStackTrace();
}
}

final SimpleDateFormat sdf = new SimpleDateFormat("hh:mm");
Using hh will give you 12 hours format and HH 24 hour format. More details on documentation.
Edit:
Your initial format must be the following in order to parse your date string to a Date object:
final SimpleDateFormat sdf = new SimpleDateFormat("EEE MMM d HH:mm:ss 'GMT'Z yyyy");
final Date dateObj = sdf.parse(time);
After that you can format time to your needs.

From SimpleDateFormat documentation:
"h:mm a": 12:08 PM
So the format you need for:
I just want 6:44 pm from my date time
is:
final SimpleDateFormat sdf1 = new SimpleDateFormat("EEE MMM d HH:mm:ss z yyyy");
Date date = sdf1.parse(time);
final SimpleDateFormat sdf = new SimpleDateFormat("h:mm a");
String newDateString = sdf.format(date);

try {
final SimpleDateFormat sdf = new SimpleDateFormat("hh:mm");
final Date dateObj = sdf.parse(time);
System.out.println(dateObj);
System.out.println(new SimpleDateFormat("K:mm a").format(dateObj));
} catch (final ParseException e) {
e.printStackTrace();
}

Parse yyyy-MM-DD String to Date yyyy-MM-DD in Android?

String startDateStr = "2017-02-03"
DateFormat formatter = new SimpleDateFormat("yyyy-MM-DD",Locale.US);
Date date = (Date)formatter.parse(startDateStr);
2017-02-03 date is parsed to Tue Jan 03 00:00:00 GMT+05:45 2017
Did I
miss something?
Update
I needed a string to be converted to a date object
while maintaining the same format.
The reason for this is I want to make use of public boolean after(Date when) method

This will work ^_^
DateFormat inputFormat = new SimpleDateFormat("yyyy-MM-dd");
DateFormat outputFormat = new SimpleDateFormat("dd MMM yyyy");
String startDateStr ="2017-02-03";
Date date = null;
try {
date = inputFormat.parse(startDateStr);
String startDateStrNewFormat = outputFormat.format(date);
} catch (ParseException e) {
e.printStackTrace();
}
Little explanation of your output :
D is Day in year (1-365)
d is day in month (1-31)
Check the document

Use SimpleDateFormat type for fomatter. You are creating DateFormat object but using SimpleDateFormat.
String startDateStr = "2017-02-03"
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd",Locale.US);
Date date = (Date)formatter.parse(startDateStr);

Yes you missed something. You used DD instead of dd in your yyyy-MM-DD format string. Here is how you do it:
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
String formattedDate = sdf.format(new Date());

Parse String Date time in java

I have a date time (which is a string) in the following format: 2/19/2015 5:25:35 p.m, and I wanted to turn it in the following Date Format: Thu Feb 19 5:25:35 p.m. CET 2015 I tried the following code:
String sDatePrecedenteExecution = "19/02/2015 17:30:29";
SimpleDateFormat format = new SimpleDateFormat ("ddd d mmm yyyy HH: mm: ss");
Date date = format.parse (sDatePrecedenteExecution)
but I got the following error:
java.text.ParseException: unparseable Date: "2/19/2015 5:30:29 p.m."
Has java.text.DateFormat.parse (DateFormat.java:337)

You are currently using the "output" format to read your incoming date string (2/19/2015 5:25:35 p.m), which is why you see the error.
You need to specify a second format for parsing your incoming date string, and use that format to parse instead. It should look like this:
SimpleDateFormat inFormat = new SimpleDateFormat ("dd/MM/yyyy HH:mm:ss")
Date date = inFormat.parse(sDatePrecedenteExecution)
Note that you also have a bug in your output format - m means minutes, and you want MMM, which is months. Have a look at the docs.

Your SimpleDateFormat doesn't match the format which you are entering. They should reflect the same.
Try this code
String parseDate = ""19/02/2015 17:30:29";
SimpleDateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");
Date parsedDate = dateFormat.parse(parseDate);

You need to change your code something like...
String sDatePrecedenteExecution = "19/02/2015 17:30:29";
SimpleDateFormat format = new SimpleDateFormat ("dd/mm/yyyy HH:mm:ss");
try {
Date date = format.parse (sDatePrecedenteExecution);
System.out.println(date);
format = new SimpleDateFormat ("ddd d mmm yyyy HH: mm: ss");
String str = format.format(date);
System.out.println(str);
} catch (ParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

Try this pattern:
SimpleDateFormat format = new SimpleDateFormat ("dd mm yyyy HH:mm:ss");
You went wrong when you made: "ddd d mmm yyyy HH: mm: ss"

Use this pattern "dd/M/yyyy HH:mm:ss" instead & read the documentation
SimpleDateFormat format = new SimpleDateFormat ("dd/M/yyyy HH:mm:ss");
String sDatePrecedenteExecution = "19/02/2015 17:30:29";
try{date =format.parse (sDatePrecedenteExecution);
}catch(Exception ex){//deal with it here}
System.out.println(date.toString()); //Thu Feb 19 17:30:29 UTC 2015

Trouble parsing Java Date Object?

I am receiving a Java Date formatted like so: "Sun Sep 14 02:00:00 PDT 2014" into a yyyy-MM-dd format but I can't seem to parse it. What I tried is the following:
String time = "Sun Sep 14 02:00:00 PDT 2014";
SimpleDateFormat f = new SimpleDateFormat("yyyy-MM-dd");
Date contractEffectiveDateFormat = f.parse(time);
System.out.println("Date: " + contractEffectiveDateFormat);
However, I get an error saying that this date is unparsable. I'm not sure how to go about parsing this date because if I try to parse the date using the following:
DateFormat df = new SimpleDateFormat("EEE MMM dd kk:mm:ss z yyyy");
which is how to actually parse the date correctly into a Date object,
the string would turn into a Date object, but I can't seem to do anything with it from there. I want to turn it in so that it looks like 2014-09-14. Any ideas on how to do so? Thanks!

Use two DateFormat(s) one for input and for output,
String time = "Sun Sep 14 02:00:00 PDT 2014";
DateFormat out = new SimpleDateFormat("yyyy-MM-dd");
DateFormat in = new SimpleDateFormat("EEE MMM dd kk:mm:ss z yyyy");
try {
Date effectiveDate = in.parse(time);
System.out.println("Date: " + out.format(effectiveDate));
} catch (ParseException e) {
e.printStackTrace();
}
Output is the requested
Date: 2014-09-14

Your incoming string is this String time = "Sun Sep 14 02:00:00 PDT 2014";
which means the SimpleDateFormat pattern should match the incoming String pattern so you need to use SimpleDateFormat like this
DateFormat inFormat=new SimpleDateFormat("EEE MMM dd kk:mm:ss z yyyy",Locale.ENGLISH);
Then when you called parse() on inFormat it will give you Date Object which doesnot have particular format associated with it. So in order to format the Date again you need to create SimpleDateFormat object specifying the format you want which is this
DateFormat outFormat = new SimpleDateFormat("yyyy-MM-dd", Locale.ENGLISH);
Ultimately bind all together
One more thing always specify the Locale
String time = "Sun Sep 14 02:00:00 PDT 2014";
DateFormat outFormat = new SimpleDateFormat("yyyy-MM-dd", Locale.ENGLISH);
// good practice to specify the locale
DateFormat inFormat=new SimpleDateFormat("EEE MMM dd kk:mm:ss z yyyy",Locale.ENGLISH);
try {
Date parsedDate = inFormat.parse(time);
System.out.println("Required Formatted Date: " + outFormat.format(effectiveDate));
} catch (ParseException e) {
e.printStackTrace();
}

Simply add another SimpleDateFormat that'll allow you to present the Date object the way you want:
public static void main(String[] args) throws ParseException {
String time = "Sun Sep 14 02:00:00 PDT 2014";
DateFormat df = new SimpleDateFormat("EEE MMM dd kk:mm:ss z yyyy");
Date contractEffectiveDateFormat = df.parse(time);
System.out.println("Date: " + contractEffectiveDateFormat);
SimpleDateFormat f = new SimpleDateFormat("yyyy-MM-dd");
System.out.println(f.format(contractEffectiveDateFormat)); // prints 2014-09-14
}

Getting the month and day from a TimeStamp

I have a String timeStamp in this format "Wed, 29 Jan 2014 20:14:15 GMT". I want to be able to compare this date with another date that is in this format 01/25/1999. I have tried simpledateformatter but with no success.
String a = connection.getHeaderField("Last-Modified"); //Returns Wed, 29 Jan 2014 20:14:15 GMT
Date lastModDate = new Date(file.lastModified()); //returns 01/25/1999
This is the simpleDateFormatter I tried implementing
SimpleDateFormat formatter;
Date dateIn = null;
formatter = new SimpleDateFormat("EEE MMM dd HH:mm:ss z yyyy", Locale.US);
try{
dateIn = (Date)formatter.parse(a);
}catch(ParseException e){
e.printStackTrace();
}
Log.d(TAG, "The server date is formated to : " + dateIn);
The dateIn is always null.
I want the to be able to do something like this
SimpleDateFormat sdf = new SimpleDateFormat("dd/mm/yyyy");
Date strDate = sdf.parse(valid_until);
if (new Date().after(strDate)) {
}

Use the following code...you will get the problem right.
Calendar calender = Calendar.getInstance();
SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
String timeStamp = formatter.format(calender.getTime());
Date strDate = formatter.parse(timeStamp);
String currentTimeStamp = formatter.format(new Date());
Date currentTime = formatter.parse(currentTimeStamp);
if (currentTime.after(strDate)) {
}

Don't know what you tried but this should work:
String a = connection.getHeaderField("Last-Modified");
Date date = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.ENGLISH).parse(a);
This can help http://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html

The reason is that you are using the wrong date format for your formatter. If the date you receive looks like
"Wed, 29 Jan 2014 20:14:15 GMT"
Then you should use the following format
formatter = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.US);

You should use the Calendar class and its subclass GregorianCalendar. For exampe, to get the month of your date:
Calendar cal = new GregorianCalendar();
cal.setTime(date);
cal.get(Calendar.MONTH);