javaDateFormat的自定义pattern的格式解析规则：忽略特定的单词

自定义DateFormat

开发中最常用的日期解析类是simpleDateFormat，往往能完成大部分对日期解析、或者转成固定格式字符串的需求。但有时候对pattern的解析有更加复杂的需求，比如忽略掉pattern中的某些单词，或者按照自定义的脚本进行解析，这时候就需要自己定义规则了。

举个例子来说，希望将2020/8/29 转换成 “FY2020”来展示，如果pattern是“FYyyyy”，明显解析出来的结果并不是我们想要的。

以该需求为例，下面自定义一个日期处理类AdvanceDateFormat

package date;import java.text.*;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.util.*;public class AdvanceDateFormat extends DateFormat {public AdvanceDateFormat(String pattern, String ignoreWord) {this.fmt = createDateFormat(pattern, ignoreWord);}/*** 格式化时间* */@Overridepublic StringBuffer format(Date date, StringBuffer stringBuffer, FieldPosition fieldPosition) {Calendar cal = Calendar.getInstance();cal.setTime(date);LocalDateTime ldate = LocalDateTime.of(cal.get(Calendar.YEAR), cal.get(Calendar.MONTH) + 1,cal.get(Calendar.DAY_OF_MONTH), cal.get(Calendar.HOUR_OF_DAY), cal.get(Calendar.MINUTE),cal.get(Calendar.SECOND));return stringBuffer.append(this.fmt.format(ldate));}@Overridepublic Date parse(String s, ParsePosition parsePosition) {// do nothingreturn null;}/*** 构造DateTimeFormatter* */private DateTimeFormatter createDateFormat(String pattern, String ignoreWord) {DateTimeFormatterBuilder dateTimeFormatterBuilder = new DateTimeFormatterBuilder();while(pattern.length() > 0) { if(pattern.startsWith(ignoreWord)) { dateTimeFormatterBuilder.appendLiteral(ignoreWord);//处理需要忽略的单词pattern = pattern.replace(ignoreWord, "");}else if(pattern.indexOf(ignoreWord) > 0) {String patternStr = pattern.substring(0, pattern.indexOf(ignoreWord));dateTimeFormatterBuilder.appendPattern(patternStr);//添加patternpattern = pattern.replace(ignoreWord, "");}else {dateTimeFormatterBuilder.appendPattern(pattern);//添加patternpattern = pattern.replace(pattern, "");}}return dateTimeFormatterBuilder.toFormatter();}private DateTimeFormatter fmt;
}

测试类

import java.text.SimpleDateFormat;
import java.util.*;
import java.util.Base64.Decoder;
import java.util.Base64.Encoder;import date.AdvanceDateFormat;/*** @program: test2** @description** @author: Samur** @create: 2020-05-22 17:01**/
public class Test {public static void main(String[] args) {String pattern = "FYyyyy";Date date = new Date();SimpleDateFormat simpleDateFormat = new SimpleDateFormat(pattern);//使用simpleDateFormat 格式化时间String dateStr = simpleDateFormat.format(date);System.out.println(dateStr);System.out.println("=========================================");AdvanceDateFormat advanceDateFormat = new AdvanceDateFormat(pattern, "FY");String dateFormat = advanceDateFormat.format(date).toString();System.out.println(dateFormat);}
}


测试结果

520202020
=========================================
FY2020Process finished with exit code 0