BAEL-7382 Add code for calculating weekdays between two dates

core-java-modules/core-java-date-operations-4/README.md

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+## Core Date Operations (Part 4)
+This module contains articles about date operations in Java.
+
+### Relevant Articles:
+
+

core-java-modules/core-java-date-operations-4/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-date-operations-4</artifactId>
+    <name>core-java-date-operations-4</name>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>11</source>
+                    <target>11</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>joda-time</groupId>
+            <artifactId>joda-time</artifactId>
+            <version>${joda-time.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <joda-time.version>2.12.5</joda-time.version>
+    </properties>
+
+</project>

core-java-modules/core-java-date-operations-4/src/main/java/com/baeldung/calculateweekdays/CalculateWeekdays.java

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+package com.baeldung.calculateweekdays;
+
+import java.time.DayOfWeek;
+import java.time.LocalDate;
+import java.time.temporal.ChronoUnit;
+import java.time.temporal.TemporalAdjusters;
+import java.util.Arrays;
+
+public class CalculateWeekdays {
+
+    public long getWorkingDaysWithStream(LocalDate start, LocalDate end){
+        return start.datesUntil(end)
+          .map(LocalDate::getDayOfWeek)
+          .filter(day -> !Arrays.asList(DayOfWeek.SATURDAY, DayOfWeek.SUNDAY).contains(day))
+          .count();
+    }
+
+    public long getWorkingDaysWithoutStream(LocalDate start, LocalDate end) {
+        boolean startOnWeekend = false;
+
+        // If starting at the weekend, move to following Monday
+        if(start.getDayOfWeek().getValue() > 5){
+            start = start.with(TemporalAdjusters.next(DayOfWeek.MONDAY));
+            startOnWeekend = true;
+        }
+        boolean endOnWeekend = false;
+        // If ending at the weekend, move to previous Friday
+        if(end.getDayOfWeek().getValue() > 5){
+            end = end.with(TemporalAdjusters.previous(DayOfWeek.FRIDAY));
+            endOnWeekend = true;
+        }
+        // Cover case where starting on Saturday and ending following Sunday
+        if(start.isAfter(end)){
+            return 0;
+        }
+        // Get total weeks
+        long weeks = ChronoUnit.WEEKS.between(start, end);
+
+        long addValue = startOnWeekend || endOnWeekend ? 1 : 0;
+
+        // Add on days that did not make up a full week
+        return ( weeks * 5 ) + ( end.getDayOfWeek().getValue() - start.getDayOfWeek().getValue() ) + addValue;
+    }
+
+
+}

core-java-modules/core-java-date-operations-4/src/test/java/com/baeldung/calculateweekdays/CalculateWeekdaysUnitTest.java

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+package com.baeldung.calculateweekdays;
+
+import static junit.framework.TestCase.assertEquals;
+
+import java.time.LocalDate;
+
+import org.junit.Test;
+
+public class CalculateWeekdaysUnitTest {
+
+    // Start Saturday end following Sunday (answer is 0)
+    LocalDate startTomorrow = LocalDate.of(2023, 12, 2);
+    LocalDate endTomorrow = LocalDate.of(2023, 12, 3);
+
+    // Three week gap with midweek start and finish (answer is 17)
+    LocalDate startThreeWeeks = LocalDate.of(2023, 11, 28);
+    LocalDate endThreeWeeks = LocalDate.of(2023, 12, 21);
+
+    // Three week gap with midweek start and weekend finish (answer is 17)
+    LocalDate startThreeWeeks2 = LocalDate.of(2023, 11, 6);
+    LocalDate endThreeWeeks2 = LocalDate.of(2023, 12, 30);
+
+    // Week gap start and end on weekend (answer is 40)
+    LocalDate startThreeWeeksWeekend = LocalDate.of(2023, 12, 2);
+    LocalDate endThreeWeeksWeekend = LocalDate.of(2023, 12, 9);
+
+    @Test
+    public void givenTwoDaysOnSameWeekend_whenUsingStreams_calculateWeekdays(){
+        CalculateWeekdays c = new CalculateWeekdays();
+        long result = c.getWorkingDaysWithStream(startTomorrow, endTomorrow);
+        assertEquals(0, result);
+    }
+
+    @Test
+    public void givenTwoDaysOnSameWeekend_whenUsingMaths_calculateWeekdays(){
+        CalculateWeekdays c = new CalculateWeekdays();
+        long result = c.getWorkingDaysWithoutStream(startTomorrow, endTomorrow);
+        assertEquals(0, result);
+    }
+
+    @Test
+    public void givenAThreeWeekGapMidweekDates_whenUsingStreams_calculateWeekdays(){
+        CalculateWeekdays c = new CalculateWeekdays();
+        long result = c.getWorkingDaysWithStream(startThreeWeeks, endThreeWeeks);
+        assertEquals(17, result);
+    }
+
+    @Test
+    public void givenAThreeWeekGapMidweekDates_whenUsingMaths_calculateWeekdays(){
+        CalculateWeekdays c = new CalculateWeekdays();
+        long result = c.getWorkingDaysWithoutStream(startThreeWeeks, endThreeWeeks);
+        assertEquals(17, result);
+    }
+
+    @Test
+    public void givenThreeWeekGapMidweekAndWeekendDates_whenUsingStreams_calculateWeekdays(){
+        CalculateWeekdays c = new CalculateWeekdays();
+        long result = c.getWorkingDaysWithStream(startThreeWeeksWeekend, endThreeWeeksWeekend);
+        assertEquals(5, result);
+    }
+
+    @Test
+    public void givenThreeWeekGapMidweekAndWeekendDates_whenUsingMaths_calculateWeekdays(){
+        CalculateWeekdays c = new CalculateWeekdays();
+        long result = c.getWorkingDaysWithoutStream(startThreeWeeksWeekend, endThreeWeeksWeekend);
+        assertEquals(5, result);
+    }
+
+    @Test
+    public void givenThreeWeekGapWeekendDates_whenUsingStreams_calculateWeekdays(){
+        CalculateWeekdays c = new CalculateWeekdays();
+        long result = c.getWorkingDaysWithStream(startThreeWeeks2, endThreeWeeks2);
+        assertEquals(40, result);
+    }
+
+    @Test
+    public void givenThreeWeekGapWeekendDates_whenUsingMaths_calculateWeekdays(){
+        CalculateWeekdays c = new CalculateWeekdays();
+        long result = c.getWorkingDaysWithoutStream(startThreeWeeks2, endThreeWeeks2);
+        assertEquals(40, result);
+    }
+
+}