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How to parse a yyyy-MM-dd HH:mm:ss to Date?

I'm trying to parse a date with the format "" to Date.
DateFormat sdf = new SimpleDateFormat("dd/MM/yyyy HH:mm:ss");
Date date = sdf.parse(dateStr);
String = sdf.format(date);
An example of the dateStr is "2020-04-14 16:34:40.0117372".
I get an error when trying to parse the string, but I don't know why.
The error I'm getting is the following:
java.text.ParseException: Unparseable date: "2020-04-14 16:34:40.0117372"
Why can't I parse this date? How can I do it?

You are using "dd/MM/yyyy" for date format, but you should be using "yyyy-MM-dd" (inverse order, and dashes instead of slashes)
Also I suggest you use modern java.time packages and do something like this:
String str = "2020-04-14 16:34:40.0117372";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSSSSSS");
LocalDateTime dateTime = LocalDateTime.parse(str, formatter);
Edit: Having 7 digits for milliseconds is correct, first digits for milliseconds and the rest for nanoseconds. strange. Usually you want 3 digits because 1000 milliseconds is a second. You likely have nanoseconds, which should be dealt with by this method.

Unable to parse this date

I am getting dates in this format 14-MAY-13 01.17.16.250000 PM and
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("dd-MMM-yy hh:mm:ss aaa");
simpleDateFormat.parse("14-MAY-13 01.17.16.250000 PM")
Gives me this exception
java.text.ParseException: Unparseable date: "14-MAY-13 01.17.16.250000 PM" ..What should be format of simpledateformat?

Try
new SimpleDateFormat("dd-MMM-yy hh.mm.ss.SSSSSS aaa");

The format must be corrected (see the javadoc for more information). You should also set the Locale to the SimpleDateFormat to be sure the month will be parsed with the correct language.
new SimpleDateFormat("dd-MMM-yy hh.mm.ss.SSSSSS aaa", Locale.US);
If you don't give the Locale, SimpleDateFormat will use the default locale of your system which can be not the locale of the given string input.

You need to use the SSSSSS for milliseconds and replace : with . to match this part 01.17.16.250000.
SimpleDateFormat simpleDateFormat =
new SimpleDateFormat("dd-MMM-yy hh.mm.ss.SSSSSS aaa");

In your Formatstring you expect hh:mm:ss but in your input string your have hh.mm.ss and you also didn't include the miliseconds.
So the format string should be dd-MMM-yy hh.mm.ss.SSSSSS aaa

Simple date format and date formate should be same, try this
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("dd-MMM-yy hh:mm:ss:SSSSSS aaa");
Date d = simpleDateFormat.parse("14-MAY-13 01:17:16:250000 PM");

the exception with parsing a date YYYY-MM-DD HH:mm:ss

I try to parse a date in the format YYYY-MM-DD HH:mm:ss
String now = "2012-11-02 12:02:00";
DateFormat formatter;
formatter = new SimpleDateFormat("EEE MMM dd HH:mm:ss z yyyy");
Date date_temp = (Date) formatter.parse(now.toString());
System.out.println("output: " + date_temp);
It gives me following exception
java.text.ParseException: Unparseable date: "2012-11-02 12:02:00"

Well yes, you've created a formatted with one format ("EEE MMM dd HH:mm:ss z yyyy") and then given it a string in a completely different format to parse. Why did you think that would work? Try this:
// Locale specified to avoid any cultural differences. You may also
// want to specify the time zone.
DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss",
Locale.US);
Date date = formatter.parse(now);
Note that the parsed Date does not know anything about formatting - the result of calling toString() (as you're doing implicitly here) is always just the default format, in the JRE default time zone. If you want to print it out with a particular format, use SimpleDateFormat again.
Also note that I've combined declaration and initialization for the variable. Prefer that over declaring a variable in one line and giving it an initial value later.

Of course your date string is not in the format you are using in SimpleDateFormat. So it won't be able to parse it into a date object.
Try using this: -
DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

Java - Date constructor accepts a Date String, But deprecated. Tried alternatives, but no luck

String temp_date="07/28/2011 11:06:37 AM";
Date date = new Date(temp_date); //Depricated
SimpleDateFormat sdf = new SimpleDateFormat("MMM-dd-yyyy hh:mm:ss");
String comp_date= sdf.format(date);
System.out.println(comp_date);
This works, But If I use something like this
String temp_date="07/28/2011 11:06:37 AM";
try{
SimpleDateFormat sdf = new SimpleDateFormat("MMM-dd-yyyy hh:mm:ss");
Date comp_date= sdf.parse(temp_date);
System.out.println(comp_date);
}catch(Exception e){
System.out.println(e);
}
This exception is thrown:
java.text.ParseException: Unparseable date: "07/28/2011 11:06:37 AM"

Your parsing pattern is wrong. It does not match the date string representation. The MMM denotes a 3-letter localized month abbreviation, while you have 2-digit month number in your actual date, you need MM. You've also slashes / as date/month/year separator and not -. For the AM/PM marker you also need an a afterwards so that the right hh can be parsed.
This should work:
SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy hh:mm:ss a");
For an explanation of those patterns, read the SimpleDateFormat javadoc.
I believe that your concrete functional requirement is to convert the given date string as specified by the pattern MM/dd/yyyy hh:mm:ss a into another date string format, as specified by the pattern MMM-dd-yyyy hh:mm:ss. In that case, you should then have two SimpleDateFormat instances, one which parses the string in the given pattern to a Date and another which formats the parsed Date to the given pattern. This should do what you want:
String inputDate = "07/28/2011 11:06:37 AM";
Date date = new SimpleDateFormat("MM/dd/yyyy hh:mm:ss a").parse(inputDate);
String outputDate = new SimpleDateFormat("MMM-dd-yyyy HH:mm:ss").format(date);
System.out.println(outputDate); // Jul-28-2011 11:06:37
Note that I changed hh in output to be HH because it would otherwise end up in 1-12 hour representation without an AM/PM marker. The HH represents it as 0-23 hour.

The format you gave the SimpleDateFormat uses - between the month, date, and year. Your string uses slashes.

At first look, it looks as if your format string is wrong.
MMM -- You specified this for the month, but you aren't passing a 3 char month.
Try MM and see if that helps.
Take a look at this for some additional date format information:
http://www.java2s.com/Tutorial/Java/0040__Data-Type/SimpleDateFormat.htm

Date format in Java

Few questions:
How can I print now (The current Date/Time) in the format below.
How can I convert a string date, into a date object if I know the format, same format as below.
Example:
2011-05-04 19:12:46 -0500
Format:
YYYY-MM-DD HH:MM:SS [+|-]hh[mm]

Try:
Date yourDate = new Date(...);
SimpleDateFormat myDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss Z");
System.out.print(myDateFormat.format(yourDate);
The link to SimpleDateFormat Javadoc is here.

Check out SimpleDateFormat: http://download.oracle.com/javase/6/docs/api/java/text/SimpleDateFormat.html
SimpleDateFormat.format() and SimpleDateFormat.parse()