Parsing Dates Without a Year in Java: Fixing the Common Error

Incorrect Example

This example tries to parse a date string that lacks a year using a simple pattern "dd MMM".

package com.fun

import com.fun.frame.SourceCode
import java.time.LocalDate
import java.time.format.DateTimeFormatter

class TSSS extends SourceCode {
    public static void main(String[] args) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd MMM", Locale.CHINA);
        String date = "02 12";
        LocalDate localDate = LocalDate.parse(date, formatter);
        System.out.println(localDate);
        System.out.println(formatter.format(localDate));
    }
}

Output

INFO-> 当前用户：fv，IP：192.168.0.100，工作目录：/Users/fv/Documents/workspace/fun/,系统编码格式:UTF-8,系统Mac OS X版本:10.15.3
Exception in thread "main" java.time.format.DateTimeParseException: Text '02 12' could not be parsed at index 3
	at java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:1947)
	at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1849)
	at java.time.LocalDate.parse(LocalDate.java:400)
	... (stack trace truncated)
Process finished with exit code 1

Correct Solution

The pattern "dd MMM" alone is insufficient; we need DateTimeFormatterBuilder to provide a default year for parsing.

package com.fun

import com.fun.frame.SourceCode
import java.time.LocalDate
import java.time.format.DateTimeFormatter
import java.time.format.DateTimeFormatterBuilder
import java.time.temporal.ChronoField

class TSSS extends SourceCode {
    public static void main(String[] args) {
        DateTimeFormatter formatter = new DateTimeFormatterBuilder()
                .appendPattern("dd MM")
                .parseDefaulting(ChronoField.YEAR, 2020)
                .toFormatter(Locale.CHINA);
        String date = "02 11";
        LocalDate localDate = LocalDate.parse(date, formatter);
        System.out.println(localDate);
        System.out.println(formatter.format(localDate));
    }
}

Correct Output

INFO-> 当前用户：fv，IP：192.168.0.100，工作目录：/Users/fv/Documents/workspace/fun/,系统编码格式:UTF-8,系统Mac OS X版本:10.15.3
2020-11-02
02 11
Process finished with exit code 0