Java date format verification several instance programs

This article will introduce you to a date format verification example. This is a date verification program written by another student. I hope this method will be helpful to you.

Requirement: because the system has many date formats, the input of the date verification function is a date string and a format string. The format string is defined in Java format (reference address ).
At the beginning, I thought it was very simple. I wrote the following code directly.

The Code is as follows:	Copy code
Public static boolean isDate (String dttm, String format ){ Boolean retValue = false; If (dttm! = Null ){ SimpleDateFormat formatter = new SimpleDateFormat (format ); Try { Formatter. parse (dttm ); RetValue = true; } Catch (ParseException e ){ } } Return retValue; }

After writing it, I tested it and found that the date 2012/12/43 also returned True, so I checked the data and set the conversion without carrying formatter. setLenient (false); then I used it, and the code is

The Code is as follows:	Copy code
Public static boolean isDate (String dttm, String format ){ Boolean retValue = false; If (dttm! = Null ){ SimpleDateFormat formatter = new SimpleDateFormat (format ); Formatter. setLenient (false ); Try { Formatter. parse (dttm ); RetValue = true; } Catch (ParseException e ){ } } Return retValue; }

Here, I thought everything would be fine. However, tests later showed that only the first part of the date will be converted when there is a separator. For example, 2012/12/43ABCD will return True. After thinking about it, I thought it would be converted to the date type, then to the string type, and then compare whether the two are equal, but I immediately rejected this scheme because the customer requested a non-strict date format, for example, if the format is yyyy/MM/dd, enter 2012/1/2 to pass the verification. Then I thought about it. I thought we should first use a regular expression for verification and then verify whether it is a date type. The Code is as follows:

The Code is as follows:

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Public static boolean isDate (String dttm, String format ){ Boolean retValue = false; If (dttm = null | dttm. isEmpty () | format = null | format. isEmpty ()){ Return retValue; } String regFormat = format; RegFormat = regFormat. replaceAll ("(^ ') | (' $ )",""); RegFormat = regFormat. replaceAll ("'([^'])", "$1 "); RegFormat = regFormat. replace ("''","'"); RegFormat = regFormat. replace ("\","\\"); RegFormat = regFormat. replaceAll ("[MdHmsS] +", "\ d + "); RegFormat = regFormat. replaceAll ("[y] +", "\ d {1, 4 }"); If (! Dttm. matches ("^" + regFormat + "$ ")){ Return false; } SimpleDateFormat formatter = new SimpleDateFormat (format ); Formatter. setLenient (false ); Try { Formatter. parse (dttm ); RetValue = true; } Catch (ParseException e ){ } Return retValue; }

The above Code only corresponds to yMdHmsS. Although it is enough for the system at that time, it still does not feel very good. I think there should be a general method. Check the Java API and find that the parse method also has a parameter method. After understanding how to use it, change the code to the following:

The Code is as follows:

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Private static boolean isDate (String dttm, String format ){ If (dttm = null | dttm. isEmpty () | format = null | format. isEmpty ()){ Return false; } DateFormat formatter = new SimpleDateFormat (format ); Formatter. setLenient (false ); ParsePosition pos = new ParsePosition (0 ); Date date = formatter. parse (dttm, pos ); If (date = null | pos. getErrorIndex ()> 0 ){ Return false; } If (pos. getIndex ()! = Dttm. length ()){ Return false; } Return true; }

I thought it would be fine, but two bugs were found in subsequent tests. One is that when the input date does not have a year (the year is not input by default), the default value is 1970. In this case, if the year is a leap year, the verification fails on the 9th. The other is that the date size of Java is different from that of Oracle. Oracle seems to support up to 2/29, while Java can support more than 20 thousand years. So the code is changed to the following:

The Code is as follows:

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Private static boolean isDate (String dttm, String format ){ If (dttm = null | dttm. isEmpty () | format = null | format. isEmpty ()){ Return false; } If (format. replaceAll ("'. +? '"," "). IndexOf (" y ") <0 ){ Format + = "/yyyy "; DateFormat formatter = new SimpleDateFormat ("/yyyy "); Dttm + = formatter. format (new Date ()); } DateFormat formatter = new SimpleDateFormat (format ); Formatter. setLenient (false ); ParsePosition pos = new ParsePosition (0 ); Date date = formatter. parse (dttm, pos ); If (date = null | pos. getErrorIndex ()> 0 ){ Return false; } If (pos. getIndex ()! = Dttm. length ()){ Return false; } If (formatter. getCalendar (). get (Calendar. YEAR)> 9999 ){ Return false; } Return true; }