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Java - How to check if a value is of type Date

I have a project requirement. There are values in a .txt as -
02/01/2017 00:00:00
Now I need to have some rules to check if this value in the data file is of type Date. How can I do that? Thanks. I am new to Java so any help much appreciated. Thanks

Try to parse it to date. If it throws ParseException then it is not a date.
String dateString = "02/01/2017 00:00:00";
DateFormat df = new SimpleDateFormat("MM/dd/yyyy hh:mm:ss");
Date date;
try {
date = df.parse(dateString);
} catch (ParseException e) {
e.printStackTrace();
}

If you just want valid days, use non-lenient parsing:
String dateString = "02/28/2017 00:00:00";
DateFormat df = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss");
df.setLenient(false);
Date date;
try {
date = df.parse(dateString);
System.out.println(date);
} catch (ParseException e) {
e.printStackTrace();
}
This will throw an exception for non-existing days like the 31st of February

Methord 1
Date dt = new Date(); //this should your Dynamic object
if (dt.getClass().equals(new Date().getClass()))
{
//if its date object
}
Methord 2
if(dt instanceof Date){
//if its date object
}

Use this to check date
String sDate1="31/12/1998 00:00:00";
try{
Date date1=new SimpleDateFormat("dd/MM/yyyy hh:mm:ss").parse(sDate1); `
}
catch(Exception e)
{
//Not a date..
}

You can use regular expressions to check the format
public boolean isDate(String s){
String pattern= "([0-9]{2})/([0-9]{2})/([0-9]{4}) ([0-9]{2}):([0-9]{2}):([0-9]{2})";
return s.matches(pattern);}

Here’s the Java 8 solution (it can be made to work in Java 6 and 7 too when you use the ThreeTen Backport).
private static final DateTimeFormatter DATE_TIME_FORMAT
= DateTimeFormatter.ofPattern("MM/dd/uuuu HH:mm:ss")
.withResolverStyle(ResolverStyle.STRICT);
public static boolean hasTypeDate(String stringFromTxt) {
try {
DATE_TIME_FORMAT.parse(stringFromTxt);
return true;
} catch (DateTimeParseException dtpe) {
return false;
}
}
Stay away from SimpleDateFormat for new code. It has had its time, it’s been outdated for a while now.
If you intended the day of month first (if 02/01/2017 means January 2nd), you need the format pattern dd/MM/uuuu HH:mm:ss instead.
If you need to know which date and time was in the .txt, use:
LocalDateTime dateTime = LocalDateTime.parse(stringFromTxt, DATE_TIME_FORMAT);
Link: ThreeTen Backport: java.time classes for Java 6 and 7.

public static boolean isValidDate(String inDate) {
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
dateFormat.setLenient(false);
try {
dateFormat.parse(inDate.trim());
} catch (ParseException pe) {
return false;
}
return true;
}
public static void main(String[] args) {
String file = "/path/to/your/file.txt";
try {
BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));
String line;
while ((line = br.readLine()) != null) {
// do something with line
}
br.close();
isValidDate(line));
//do what you want :)
}

How to find the given date is with in specified date range

Here is my code
boolean isWithinRange(String d)
{
boolean withinDate = false;
try
{
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
Date date = dateFormat.parse(d);
withinDate = !(date.before(startDate) || date.after(endDate));
}
catch (ParseException parseException)
{
}
return withinDate;
}
Inputs
2015-11-26
2015-11-26 - Copy
Both returning true but what i required is "2015-11-26" should be true and "2015-11-26 - Copy" should be false.

This is because SimpleDateFormat happily parses "2015-11-26" and ignores the " - Copy" part.
The javadoc states :
Parses text from the beginning of the given string to produce a date.
The method may not use the entire text of the given string.
To detect if the whole string has been used, instead use the parse(String source, ParsePosition pos) method. ParsePosition tells you where parsing stopped. Just compare this with the length of the original date string.

The problem here is we are passing the Date Format 'yyyy-MM-dd'. This will verify the given input upto this format.
For example,
static boolean isWithinRange(String d)
{
boolean withinDate = false;
try
{
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
Date date = dateFormat.parse(d);
withinDate = !(date.before(startDate) || date.after(endDate));
}
catch (ParseException parseException)
{
parseException.printStackTrace();
}
return withinDate;
}
The above code throw exception because we are passing Date format as 'yyyy-MM-dd hh:mm:ss'. So this will find the hour minutes and seconds

just test if size is 10 before your test:
if (d.length!10) return false;

public static void main(String[] args) {
isWithinRange("2015-12-11 - Copy");
isWithinRange("2015-12-11");
}
public static boolean isWithinRange(String d) {
boolean withinDate = false;
try {
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
String dd = d.indexOf(" ") !=-1 ? d.substring(0, d.indexOf(" ")) : d; // Find valid String
if(d.equals(dd)){
Date date = dateFormat.parse(d);
withinDate = !(date.before(startDate)) || date.after(endDate)));
}else{
withinDate =false;
}
} catch (ParseException parseException) {
}
return withinDate;
}

How to reformat a string date in Java

I tacked this problem in VB awhile back, and thought I could easily translate it to Java. The input comes in as a string in the format:
"mm/dd/yyyy"
I want to change this to the following format:
"mm/dd/yy"
where the last two year digits are shown only. I wrote this VB awhile back, which does just that:
Function DateFormat(ByVal myDate As String) As String
Dim reformat As Date
reformat = Date.Parse(myDate, Nothing)
Return Format(reformat, "MM/dd/yy").ToString()
End Function
How can I do this exact same thing in Java, so that the date is reformatted correctly and returned as the string it originally was? I have something like this but it is not working properly:
public static String DateFormat(String myDate){
SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
try{
Date formattedDate = formatter.parse(myDate);
return formattedDate.toString();
}catch(Exception e){
e.printStackTrace();
return null;
}
}
I am not sure how to make it the format I need, as I can't find anything similar to the Format() function VB has. Thanks in advance.

Try this :
public static String DateFormat(String myDate) throws ParseException {
SimpleDateFormat inFormat = new SimpleDateFormat("MM/dd/yyyy");
SimpleDateFormat outFormat = new SimpleDateFormat("MM/dd/yy");
Date parsedInDate = inFormat.parse(myDate);
return outFormat.format(parsedInDate);
}
At start, we declare two date formatters, then we create Date object from input String, and at the end we produce String in new format.

If I understand your question, you could use a pair of SimpleDateFormat(s)
private static final String formatIn = "MM/dd/yyyy";
private static final String formatOut = "MM/dd/yy";
private static final DateFormat sdfIn = new SimpleDateFormat(
formatIn);
private static final DateFormat sdfOut = new SimpleDateFormat(
formatOut);
public static String formatDateString(String dateIn)
throws ParseException {
return sdfOut.format(sdfIn.parse(dateIn));
}
public static void main(String[] args) {
try {
System.out.println(formatDateString("07/15/2014"));
} catch (ParseException e) {
e.printStackTrace();
}
}
Output is
07/15/14

SimpleDateFormat takes in a number of different formats. I believe the format you want is already built in and can be accessed like so...
Date date = new Date();
Format formatter = new SimpleDateFormat("MM/dd/yy");
String s = formatter.format(date);
System.out.println(s);

You've basically almost got it, just need to apply the new format.
public static String DateFormat(String myDate){
SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
try{
Date date = formatter.parse(myDate);
formatter.applyPattern("MM/dd/yy");
return formatter.format(date);
}catch(Exception e){
e.printStackTrace();
return null;
}
}

parsing only the Year in a DateFormat Java

I get a returned parsed JSON result with string values in the form of dates like "27-11-2012" which i parse to a date Object. my code for this is:
public Date stringToDateReport(String s){
//Log.d(TAG, "StringToDateReport here is " + s);
DateFormat format;
Date date = null;
//if(s.matches(""))
format = new SimpleDateFormat("dd-MMM-yyyy");
try {
date = (Date)format.parse(s);
} catch (ParseException e) {
e.printStackTrace();
}
return date;
}
now my issue is, a feature has been implemented that sometimes the json only returns a year object like "2012" and is giving me an "ParseException: Unparseable date" as expected. I was thinking of using regex to match the string pattern and parse from there, but not sure how to do that. Any ideas and also anyway to parse only year in a DateFormat?

I'd try:
public Date stringToDateReport(String s){
DateFormat format;
Date date = null;
format = new SimpleDateFormat("dd-MM-yyyy");
if(s.length()==4) {
format = new SimpleDateFormat("yyyy");
}
try {
date = (Date)format.parse(s);
} catch (ParseException e) {
//you should do a real logging here
e.printStackTrace();
}
return date;
}
The logic behind is to check if the string is only 4 long, then apply the different format. In this case, this easy method is sufficient, but in other methods, the use of regexes might be required.

Try this code
public Date stringToDateReport(String s){
//Log.d(TAG, "StringToDateReport here is " + s);
DateFormat format;
Date date = null;
if(s.indexOf("-") < 0){
format = new SimpleDateFormat("yyyy");
}else{
format = new SimpleDateFormat("dd-MMM-yyyy");
}
try {
date = (Date)format.parse(s);
} catch (ParseException e) {
e.printStackTrace();
}
return date;
}
Is there the possibility in have another format in the String s ? Or just these two?

public Date stringToDateReport(String strDate){
DateFormat formatnew SimpleDateFormat("dd-MM-yyyy");
Date date = null;
if(strDate.length()==4) {
format = new SimpleDateFormat("yyyy");
}
try {
date = (Date)format.parse(strDate);
} catch (ParseException e) {
//error parsing date
e.printStackTrace();
}
return date;
}
then call it like this :
String strDate = yourJson.getString("date");
Date d = stringToDateReport(strDate);

SimpleDateFormat parse(string str) doesn't throw an exception when str = 2011/12/12aaaaaaaaa?

Here is an example:
public MyDate() throws ParseException {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/d");
sdf.setLenient(false);
String t1 = "2011/12/12aaa";
System.out.println(sdf.parse(t1));
}
2011/12/12aaa is not a valid date string. However the function prints "Mon Dec 12 00:00:00 PST 2011" and ParseException isn't thrown.
Can anyone tell me how to let SimpleDateFormat treat "2011/12/12aaa" as an invalid date string and throw an exception?

The JavaDoc on parse(...) states the following:
parsing does not necessarily use all characters up to the end of the string
It seems like you can't make SimpleDateFormat throw an exception, but you can do the following:
SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/d");
sdf.setLenient(false);
ParsePosition p = new ParsePosition( 0 );
String t1 = "2011/12/12aaa";
System.out.println(sdf.parse(t1,p));
if(p.getIndex() < t1.length()) {
throw new ParseException( t1, p.getIndex() );
}
Basically, you check whether the parse consumed the entire string and if not you have invalid input.

To chack whether a date is valid
The following method returns if the date is in valid otherwise it will return false.
public boolean isValidDate(String date) {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/d");
Date testDate = null;
try {
testDate = sdf.parse(date);
}
catch (ParseException e) {
return false;
}
if (!sdf.format(testDate).equals(date)) {
return false;
}
return true;
}
Have a look on the following class which can check whether the date is valid or not
** Sample Example**
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class DateValidCheck {
public static void main(String[] args) {
if(new DateValidCheck().isValidDate("2011/12/12aaa")){
System.out.println("...date is valid");
}else{
System.out.println("...date is invalid...");
}
}
public boolean isValidDate(String date) {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/d");
Date testDate = null;
try {
testDate = sdf.parse(date);
}
catch (ParseException e) {
return false;
}
if (!sdf.format(testDate).equals(date)) {
return false;
}
return true;
}
}

Java 8 LocalDate may be used:
public static boolean isDate(String date) {
try {
LocalDate.parse(date, DateTimeFormatter.ofPattern("yyyy/MM/dd"));
return true;
} catch (DateTimeParseException e) {
return false;
}
}
If input argument is "2011/12/12aaaaaaaaa", output is false;
If input argument is "2011/12/12", output is true

After it successfully parsed the entire pattern string SimpleDateFormat stops evaluating the data it was given to parse.

Take a look on the method documentation which says: ParseException if the beginning of the specified string cannot be parsed.
Method source code with javadoc:
/**
* Parses text from the beginning of the given string to produce a date.
* The method may not use the entire text of the given string.
* <p>
* See the {#link #parse(String, ParsePosition)} method for more information
* on date parsing.
*
* #param source A <code>String</code> whose beginning should be parsed.
* #return A <code>Date</code> parsed from the string.
* #exception ParseException if the beginning of the specified string
* cannot be parsed.
*/
public Date parse(String source) throws ParseException
{
ParsePosition pos = new ParsePosition(0);
Date result = parse(source, pos);
if (pos.index == 0)
throw new ParseException("Unparseable date: \"" + source + "\"" ,
pos.errorIndex);
return result;
}

You can use the ParsePosition class or the sdf.setLenient(false) function
Docs:
http://docs.oracle.com/javase/7/docs/api/java/text/ParsePosition.html
http://docs.oracle.com/javase/7/docs/api/java/text/DateFormat.html#setLenient(boolean)

Simply setting sdf.setLenient(false) will do the trick..