java-获取输入星期的最后日期

Question

Input      Output
Monday     05.03.2018
Tuesday    27.02.2018
Wednesday  28.02.2018
Thursday   01.03.2018
Friday     02.03.2018
Saturday   03.03.2018
Sunday     04.03.2018

在评论中，这是我在ATM上的代码：

private String getLastDateOfDayOfWeek(String day, String returnDateFormat) throws ParseException {
        int dayOfWeek = parseDayOfWeek(day, Locale.ENGLISH);

        Calendar cal = Calendar.getInstance(); // Today, now
        if (cal.get(Calendar.DAY_OF_WEEK) != dayOfWeek) {
            // ...
        }
        return new SimpleDateFormat(returnDateFormat).format(cal.getTime());
}

private static int parseDayOfWeek(String day, Locale locale)
            throws ParseException {
        SimpleDateFormat dayFormat = new SimpleDateFormat("EEEE", locale);
        Date date = dayFormat.parse(day);
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
        return dayOfWeek;
}

Atm I有两个函数：一个可以将字符串转换为日历的星期数，另一个是我正在搜索的方法。目前它只处理今天的一周中的一天正确的，应该做的工作为一周中的每隔一天的部分是缺失的（评论与...）

Answer 1

LocalDate.now().with(                                // Get today’s date, then move to another date.
    TemporalAdjusters.previousOrSame(                // An implementation of `TemporalAdjuster` interface, used for algorithms to move to another date. 
        DayOfWeek.valueOf( “Monday”.toUpperCase() )  // Get the enum Object with te corresponding hard-coded name in English such as `DayOfWeek.MONDAY`. 
    )
)

dayofweek枚举包含七个对象，一周中每天一个。

这7个物体的名字都是英文的，都是大写的。所以你可以从英语单词中得到对象。

String input = “Monday”.toUpperCase() ;
DayOfWeek dow = DayOfWeek.valueOf( input ) ;

对于英语以外的其他语言，定义一个列表并用每周中每一天的名称填充。使用从DayOfWeek::GetDisplayName生成的名称，这是一个自动本地化的方法。按照ISO8601标准，以星期一开始列表。搜索该列表以找到与您的输入匹配的内容。获取匹配的序数，1-7（而不是索引数0-6）。将该数字传递给DayOfWeek.ValueOf以获取DayOfWeek对象。在某些语言中，您需要一对这样的列表来搜索，因为可能会调用一个替代拼写来“独立”使用星期，而没有日期上下文。

package com.basilbourque.example;

import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import java.time.DayOfWeek;
import java.time.format.TextStyle;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;

// For a given name of day-of-week in some language, determine the matching `java.time.DayOfWeek` enum object.
// This class is the opposite of `DayOfWeek.getDisplayName` which generates a localized string for a given `DayOfWeek` object.
// Usage… DayOfWeekDelocalizer.of( Locale.CANADA_FRENCH ).parse( "lundi" ) → DayOfWeek.MONDAY
// Assumes `FormatStyle.FULL`, for day-of-week names without abbreviation.
// USE AT YOUR OWN RISK. Rough draft, quickly written. No serious testing.
public class DayOfWeekDelocalizer
{
    @NotNull
    private Locale locale;

    @NotNull
    private List < String > dayOfWeekNames, dayOfWeekNamesStandalone; // Some languages use an alternate spelling for a “standalone” day-of-week used without the context of a date.

    // Constructor. Private, for static factory method.
    private DayOfWeekDelocalizer ( @NotNull Locale locale )
    {
        this.locale = locale;

        // Populate the pair of arrays, each having the translated day-of-week names.
        int daysInWeek = 7; // Seven days in the week.
        this.dayOfWeekNames = new ArrayList <>( daysInWeek );
        this.dayOfWeekNamesStandalone = new ArrayList <>( daysInWeek );

        for ( int i = 1 ; i <= daysInWeek ; i++ )
        {
            this.dayOfWeekNames.add( DayOfWeek.of( i ).getDisplayName( TextStyle.FULL , this.locale ) );
            this.dayOfWeekNamesStandalone.add( DayOfWeek.of( i ).getDisplayName( TextStyle.FULL_STANDALONE , this.locale ) );
        }
//        System.out.println( this.dayOfWeekNames );
//        System.out.println( this.dayOfWeekNamesStandalone );
    }

    // Constructor. Private, for static factory method.
    // Personally, I think it unwise to default implicitly to a `Locale`. But I included this in case you disagree with me, and to follow the lead of the *java.time* classes. --Basil Bourque
    private DayOfWeekDelocalizer ( )
    {
        this( Locale.getDefault() );
    }

    // static factory method, instead of  constructors.
    // See article by Dr. Joshua Bloch. http://www.informit.com/articles/article.aspx?p=1216151
    // The `Locale` argument determines the human language and cultural norms used in de-localizing input strings.
    synchronized static public DayOfWeekDelocalizer of ( @NotNull Locale localeArg )
    {
        DayOfWeekDelocalizer x = new DayOfWeekDelocalizer( localeArg ); // This class could be optimized by caching this object.
        return x;
    }

    // Attempt to translate the name of a day-of-week to look-up a matching `DayOfWeek` enum object. 
    // Returns NULL if the passed String value is not found to be a valid name of day-of-week for the human language and cultural norms of the `Locale` specified when constructing this parent object, `DayOfWeekDelocalizer`.
    @Nullable
    public DayOfWeek parse ( @NotNull String input )
    {
        int index = this.dayOfWeekNames.indexOf( input );
        if ( - 1 == index )
        { // If no hit in the contextual names, try the standalone names.
            index = this.dayOfWeekNamesStandalone.indexOf( input );
        }
        int ordinal = ( index + 1 );
        DayOfWeek dow = ( ordinal > 0 ) ? DayOfWeek.of( ordinal ) : null;  // If we have a hit, determine the DayOfWeek. Else return null.
        return dow;
    }

    // `Object` overrides.

    @Override
    public boolean equals ( Object o )
    {
        if ( this == o ) return true;
        if ( o == null || getClass() != o.getClass() ) return false;

        DayOfWeekDelocalizer that = ( DayOfWeekDelocalizer ) o;

        return locale.equals( that.locale );
    }

    @Override
    public int hashCode ( )
    {
        return locale.hashCode();
    }

    public static void main ( String[] args )
    {
        // Quick testing.
        // DayOfWeekDelocalizer x = DayOfWeekDelocalizer.of( Locale.JAPAN );
        if ( DayOfWeekDelocalizer.of( Locale.CANADA_FRENCH ).parse( "lundi" ).equals( DayOfWeek.MONDAY ) )
        {
            System.out.println( "GOOD - Canada French 'lundi' is parsing to DayOfWeek.MONDAY." );
        } else
        {
            System.out.println( "BAD - Canada French 'lundi' is NOT parsing to DayOfWeek.MONDAY." );
        }
    }
}

接下来我们需要当前日期。

LocalDate today = LocalDate.now() ;

与隐式地依赖于JVM当前的默认时区相比，显式地声明您希望的/预期的时区更好。

ZoneId z = ZoneId.of( “Africa/Tunis” ) ;
LocalDate today = LocalDate.now( z ) ;

通过应用temporaladjuster移动到另一个日期。temporaladjusters类提供了我们需要的实现。

TemporalAdjuster ta = TemporalAdjusters.previousOrSame( dow ) ;
LocalDate ld = today.with( ta ) ;

您可以直接与数据库交换java.time对象。使用与JDBC4.2或更高版本兼容的JDBC驱动程序。不需要字符串，不需要java.sql.*类。

从哪里获取java.time类？

• Java SE 8、Java SE 9及更高版本
  • 内置。
  • 带有捆绑实现的标准Java API的一部分。
  • Java 9添加了一些小功能和修补程序。
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