Java 不同的SimpleDataFormat解析

我想检查一个日期是否与我定义的模式匹配。请看下面我的代码

date = null

List<String> formatStrings = Arrays.asList("yyyy-MM-dd", "dd.MM.yyyy", "yyyyMMdd", "yyyy/MM/dd", "dd/MM/yyyy");

        for (String formatStr: formatStrings) {
            try {
                dateType = new Date(new SimpleDateFormat(formatStr).parse(myCol).getTime());

            } catch (ParseException e) {}
        }
        return date;

我还编写了一个单元测试来测试我的函数是否工作，但它只有在变量有模式时才工作：yyyy-MM-dd，所以是列表中的第一个模式。如果我有任何其他模式，它会显示一个例外

你能帮帮我吗？我写错了哪一行？

避免遗留日期时间类 您正在使用可怕的日期时间类，这些类在几年前被JSR310定义的业界领先的现代java.time类所取代

java.time 切换到使用LocalDate和DateTimeFormatter

DateTimeFormatter预定义了两种预期格式，每种格式都是标准格式的变体。对于其他三种格式，我们定义了一种格式化模式

package work.basil.example;

import java.time.LocalDate;
import java.time.Month;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeParseException;
import java.util.List;
import java.util.Objects;

public class Demo
{
    public static void main ( String[] args )
    {
        Demo app = new Demo ();
        app.demo ();
    }

    private void demo ( )
    {
        // ("yyyy-MM-dd", "dd.MM.yyyy", "yyyyMMdd", "yyyy/MM/dd", "dd/MM/yyyy"
        final List < DateTimeFormatter > formatterList = List.of (
                DateTimeFormatter.ISO_LOCAL_DATE ,
                DateTimeFormatter.ofPattern ( "dd.MM.uuuu" ) ,
                DateTimeFormatter.BASIC_ISO_DATE ,
                DateTimeFormatter.ofPattern ( "uuuu/M/dd" ) ,
                DateTimeFormatter.ofPattern ( "dd/MM/uuuu" )
        );

        final List < String > inputs = List.of ( "2020-01-23" , "23.01.2020" , "20200123" , "2020/01/23" , "23/01/2020" );

        for ( String input : inputs )
        {
            LocalDate localDate = null;
            for ( DateTimeFormatter formatter : formatterList )
            {
                try
                {
                    localDate = LocalDate.parse ( input , formatter );
                    if ( ! localDate.equals ( LocalDate.of ( 2020 , Month.JANUARY , 23 ) ) )
                    {
                        throw new IllegalStateException ( "Oops! Unexpected result. " + input + " ➙ " + localDate );
                    }
                    System.out.println ( input + " ➙ " + localDate );
                    break; // Bail out of this inner FOR loop, as we have successfully parsed this input.
                } catch ( DateTimeParseException e )
                {
                    // Swallow exception, as we expect most to fail.
                }
            }
            Objects.requireNonNull ( localDate , "Oops, unexpected input: " + input );
        }
    }
}

看这个

2020-01-23➙ 2020-01-23

23.01.2020➙ 2020-01-23

20200123➙ 2020-01-23

2020/01/23➙ 2020-01-23

2020年1月23日➙ 2020-01-23

---

你有什么例外？也许抓住并忽略那个？不，它只是检查我的var是否有第一个模式，但没有其他模式。。。如果它没有第一个，它直接进入例外日期是一个日期。它不能匹配或不匹配模式。日期的字符串表示形式可能与模式匹配。我认为这是正则表达式应用程序的一种tak；在try块内部-否则，即使第一个模式成功，您也会尝试所有模式。仅供参考，您使用的是几年前被JSR 310中定义的java.time类所取代的糟糕的日期时间类。请参阅DateTimeFormatter和DateTimeFormatterBuilder。

package work.basil.example;

import java.time.LocalDate;
import java.time.Month;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeParseException;
import java.util.List;
import java.util.Objects;

public class Demo
{
    public static void main ( String[] args )
    {
        Demo app = new Demo ();
        app.demo ();
    }

    private void demo ( )
    {
        // ("yyyy-MM-dd", "dd.MM.yyyy", "yyyyMMdd", "yyyy/MM/dd", "dd/MM/yyyy"
        final List < DateTimeFormatter > formatterList = List.of (
                DateTimeFormatter.ISO_LOCAL_DATE ,
                DateTimeFormatter.ofPattern ( "dd.MM.uuuu" ) ,
                DateTimeFormatter.BASIC_ISO_DATE ,
                DateTimeFormatter.ofPattern ( "uuuu/M/dd" ) ,
                DateTimeFormatter.ofPattern ( "dd/MM/uuuu" )
        );

        final List < String > inputs = List.of ( "2020-01-23" , "23.01.2020" , "20200123" , "2020/01/23" , "23/01/2020" );

        for ( String input : inputs )
        {
            LocalDate localDate = null;
            for ( DateTimeFormatter formatter : formatterList )
            {
                try
                {
                    localDate = LocalDate.parse ( input , formatter );
                    if ( ! localDate.equals ( LocalDate.of ( 2020 , Month.JANUARY , 23 ) ) )
                    {
                        throw new IllegalStateException ( "Oops! Unexpected result. " + input + " ➙ " + localDate );
                    }
                    System.out.println ( input + " ➙ " + localDate );
                    break; // Bail out of this inner FOR loop, as we have successfully parsed this input.
                } catch ( DateTimeParseException e )
                {
                    // Swallow exception, as we expect most to fail.
                }
            }
            Objects.requireNonNull ( localDate , "Oops, unexpected input: " + input );
        }
    }
}