BAEL-2193 - Merge 2 java.util.Properties objects (#5571)

* BAEL-2268 - Guide to JerseyTest
-  second attempt without formatting changes

* BAEL-2268 - Guide to JerseyTest

- Add line break to end of file

* BAEL-2193 - Merge 2 java.util.Properties objects

* BAEL-2193 - Merge 2 java.util.Properties object

core-java/src/test/java/com/baeldung/properties/MergePropertiesUnitTest.java

@@ -0,0 +1,84 @@
+package com.baeldung.properties;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThat;
+
+import java.util.Map;
+import java.util.Properties;
+import java.util.Set;
+import java.util.stream.Stream;
+
+import org.junit.Test;
+
+public class MergePropertiesUnitTest {
+
+    @Test
+    public void givenTwoProperties_whenMergedUsingIteration_thenAllPropertiesInResult() {
+        Properties globalProperties = mergePropertiesByIteratingKeySet(propertiesA(), propertiesB());
+
+        testMergedProperties(globalProperties);
+    }
+
+    @Test
+    public void givenTwoProperties_whenMergedUsingPutAll_thenAllPropertiesInResult() {
+        Properties globalProperties = mergePropertiesByUsingPutAll(propertiesA(), propertiesB());
+
+        testMergedProperties(globalProperties);
+    }
+
+    @Test
+    public void givenTwoProperties_whenMergedUsingStreamAPI_thenAllPropertiesInResult() {
+        Properties globalProperties = mergePropertiesByUsingStreamApi(propertiesB(), propertiesA());
+
+        testMergedProperties(globalProperties);
+    }
+
+    private Properties mergePropertiesByIteratingKeySet(Properties... properties) {
+        Properties mergedProperties = new Properties();
+        for (Properties property : properties) {
+            Set<String> propertyNames = property.stringPropertyNames();
+            for (String name : propertyNames) {
+                String propertyValue = property.getProperty(name);
+                mergedProperties.setProperty(name, propertyValue);
+            }
+        }
+        return mergedProperties;
+    }
+
+    private Properties mergePropertiesByUsingPutAll(Properties... properties) {
+        Properties mergedProperties = new Properties();
+        for (Properties property : properties) {
+            mergedProperties.putAll(property);
+        }
+        return mergedProperties;
+    }
+
+    private Properties mergePropertiesByUsingStreamApi(Properties... properties) {
+        return Stream.of(properties)
+            .collect(Properties::new, Map::putAll, Map::putAll);
+    }
+
+    private Properties propertiesA() {
+        Properties properties = new Properties();
+        properties.setProperty("application.name", "my-app");
+        properties.setProperty("application.version", "1.0");
+        return properties;
+    }
+
+    private Properties propertiesB() {
+        Properties properties = new Properties();
+        properties.setProperty("property-1", "sample property");
+        properties.setProperty("property-2", "another sample property");
+        return properties;
+    }
+
+    private void testMergedProperties(Properties globalProperties) {
+        assertThat("There should be 4 properties", globalProperties.size(), equalTo(4));
+        assertEquals("Property should be", globalProperties.getProperty("application.name"), "my-app");
+        assertEquals("Property should be", globalProperties.getProperty("application.version"), "1.0");
+        assertEquals("Property should be", globalProperties.getProperty("property-1"), "sample property");
+        assertEquals("Property should be", globalProperties.getProperty("property-2"), "another sample property");
+    }
+
+}