How to write regex to identify different date patterns of a String in android?

Question

I receive different date patterns in APIs. Is there any way to identify the date pattern of the string received in an API so that I can format them without throwing any date exceptions?

Answer 1

Use this String extension function to identify the date pattern of the String.

/**
 * Created By Sweta 
 *  *  Method to check Input Date Pattern Before before Formatting
 * @param outputPattern This parameter takes the output DATE Pattern as String
 *  Checks four patterns: "dd/mm/yyyy", "mm/dd/yyyy hh:MM:ss", "dd MMM yyyy", "yyyy-MM-dd",
 *  "yyyy-MM-dd'T'HH:mm:ss", "dd-MMM-yyyy", "MM/dd/yyyy hh:mm:ss a", "dd-mm-yyyy hh:mm:ss",
 *  "dd-mm-yyyy hh:mm:ss a", "mm/dd/yyyy hh:mm:ss", "mm/dd/yyyy"
 */
@Suppress("NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS")
fun String.checkInputDatePatternBefore(outputPattern: String): String {

    //"dd/mm/yyyy"
    val regex1 = "^(3[01]|[12][0-9]|0[1-9]|[1-9])/(1[0-2]|0[1-9]|[1-9])/[0-9]{4}$".toRegex()
    
    //"mm/dd/yyyy hh:MM:ss"
    val regex2 =
        "^(1[0-2]|0[1-9]|[1-9])/(3[01]|[12][0-9]|0[1-9]|[1-9])/[0-9]{4} [0-9][0-9]:([0]?[0-5] 
    [0-9]|[0-9]):([0-5][0-9])$"
            .toRegex()

    //"dd MMM yyyy"
    val regex3 = "(3[01]|[12][0-9]|0[1-9]|[1-9])[\\s][a-zA-Z]{3}[\\s][0-9]{4}$".toRegex()
   
    //"yyyy-MM-dd"
    val regex4 =
        "([0-9]{4})[\\-](1[0-2]|0[1-9]|[1-9])[\\-](3[01]|[12][0-9]|0[1-9]|[1-9])$".toRegex()
    //"yyyy-MM-dd'T'HH:mm:ss"
   
   val regex5 =
        "([0-9]{4})[\\-](1[0-2]|0[1-9]|[1-9])[\\-](3[01]|[12][0-9]|0[1-9])[T][0-9][0-9]:([0]? 
   [0-5][0-9]|[0-9]):([0-5][0-9])$".toRegex()

    //"dd-MMM-yyyy"
    val regex6 = "(3[01]|[12][0-9]|0[1-9]|[1-9])[\\-][a-zA-Z]{3}[\\-][0-9]{4}$".toRegex()

    //"MM/dd/yyyy hh:mm:ss a"
    val regex7 =
        "^((1[0-2]|0[1-9]|[1-9])/3[01]|[12][0-9]|0[1-9]|[1-9])/[0-9]{4}[\\s][0-9][0-9]:([0]? 
   [0-5][0-9]|[0-9]):([0-5][0-9])[\\s][a-zA-Z]{2}$"
            .toRegex()

    //28-02-2022 12:12:24
    //"dd-mm-yyyy hh:mm:ss"
    val regex8 =
        "(3[01]|[12][0-9]|0[1-9]|[1-9])[\\-](1[0-2]|0[1-9]|[1-9])[\\-][0-9]{4}[\\s][0-9][0-9]: 
  ([0]?[0-5][0-9]|[0-9]):([0-5][0-9])$".toRegex()
  
   //"dd-mm-yyyy hh:mm:ss a"
    val regex9 =
        "(3[01]|[12][0-9]|0[1-9]|[1-9])[\\-](1[0-2]|0[1-9]|[1-9])[\\-][0-9]{4}[\\s][0-9][0-9]: 
   ([0]?[0-5][0-9]|[0-9]):([0-5][0-9])[\\s][a-zA-Z]{2}$".toRegex()
  
   //"mm/dd/yyyy hh:mm:ss"
    val regex10 =
        "(1[0-2]|0[1-9]|[1-9])[/](3[01]|[12][0-9]|0[1-9]|[1-9])[/][0-9]{4}[\\s][0-9][0-9]: 
   ([0]?[0-5][0-9]|[0-9]):([0-5][0-9])$"
            .toRegex()
   
   //"mm/dd/yyyy"
    val regex11 =
        "(1[0-2]|0[1-9]|[1-9])[/](3[01]|[12][0-9]|0[1-9]|[1-9])[/][0-9]{4}$"
            .toRegex()


    val bool1: Boolean = regex1.matches(this)
    val bool2: Boolean = regex2.matches(this)
    val bool3: Boolean = regex3.matches(this)
    val bool4: Boolean = regex4.matches(this)
    val bool5: Boolean = regex5.matches(this)
    val bool6: Boolean = regex6.matches(this)
    val bool7: Boolean = regex7.matches(this)
    val bool8: Boolean = regex8.matches(this)
    val bool9: Boolean = regex9.matches(this)
    val bool10: Boolean = regex10.matches(this)
    val bool11: Boolean = regex11.matches(this)

    when {
        bool1 -> {
            Log.d(TAG, "Pattern dd/mm/yyyy")
            return "Pattern dd/mm/yyyy"
        }
        bool2 -> {
            Log.d(TAG, "Pattern mm/dd/yyyy hh:MM:ss")
            return "Pattern mm/dd/yyyy hh:MM:ss"
        }
        bool3 -> {
            Log.d(TAG, "Pattern dd MMM yyyy")
            return "Pattern dd MMM yyyy"
        }
        bool4 -> {
            Log.d(TAG, "Pattern yyyy-MM-dd")
            return "Pattern yyyy-MM-dd"
        }
        bool5 -> {
            Log.d(TAG, "Pattern yyyy-MM-dd'T'HH:mm:ss")
            return "Pattern yyyy-MM-dd'T'HH:mm:ss"
        }
        bool6 -> {
            Log.d(TAG, "Pattern dd-MMM-yyyy")
            return "Pattern dd-MMM-yyyy"
        }
        bool7 -> {
            Log.d(TAG, "Pattern MM/dd/yyyy hh:mm:ss a")
            return "Pattern MM/dd/yyyy hh:mm:ss a"
        }
        bool8 -> {
            Log.d(TAG, "Pattern dd-mm-yyyy hh:mm:ss")
            return "Pattern dd-mm-yyyy hh:mm:ss"
        }
        bool9 -> {
            Log.d(TAG, "Pattern dd-mm-yyyy hh:mm:ss AM/PM")
            return "Pattern dd-mm-yyyy hh:mm:ss AM/PM"
        }
        bool10 -> {
            Log.d(TAG, "Pattern mm/dd/yyyy hh:mm:ss")
            return "Pattern mm/dd/yyyy hh:mm:ss"
        }
        bool11 -> {
            Log.d(TAG, "Pattern mm/dd/yyyy")
            return "Pattern mm/dd/yyyy"
        }
        else -> {
            Log.d(TAG, "Date pattern not recognized!")
            Log.d(TAG, this)
            return "Date pattern not recognized!"
        }
    }
}