Add arrayToString util and tests

Introduce StringUtils.arrayToString(Object[], String) which joins object array elements using a delimiter: returns empty string for null/empty arrays, returns single element as-is, and otherwise joins via StringJoiner. Added necessary imports and a static ArrayUtils.length usage. Updated tests to cover normal cases and null-delimiter behavior (expecting NPE), and replaced literal empty string usages with the EMPTY_STRING constant in CharSequenceUtilsTest.

Author: mercyblitz

microsphere-java-core/src/main/java/io/microsphere/util/StringUtils.java

@@ -22,9 +22,11 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.StringJoiner;
 
 import static io.microsphere.collection.CollectionUtils.isEmpty;
 import static io.microsphere.collection.ListUtils.newArrayList;
+import static io.microsphere.util.ArrayUtils.length;
 import static io.microsphere.util.ArrayUtils.ofArray;
 import static io.microsphere.util.CharSequenceUtils.isEmpty;
 import static io.microsphere.util.CharSequenceUtils.length;
@@ -835,6 +837,41 @@ public static String uncapitalize(String str) {
     public static String[] toStringArray(@Nullable Collection<String> collection) {
         return isEmpty(collection) ? EMPTY_STRING_ARRAY : collection.toArray(EMPTY_STRING_ARRAY);
     }
+    
+    /**
+     * <p>Converts an array of Objects into a single String, with each element separated by the specified delimiter.</p>
+     *
+     * <p>A {@code null} or empty array returns an empty string. Each element is converted to a String using
+     * {@link String#valueOf(Object)}. If the array contains only one element, that element's String representation
+     * is returned without the delimiter.</p>
+     *
+     * <h3>Example Usage</h3>
+     * <pre>{@code
+     * StringUtils.arrayToString(null, ",")           = ""
+     * StringUtils.arrayToString(new Object[]{}, ",") = ""
+     * StringUtils.arrayToString(new Object[]{"a"}, ",") = "a"
+     * StringUtils.arrayToString(new Object[]{"a", "b", "c"}, ",") = "a,b,c"
+     * StringUtils.arrayToString(new Object[]{1, 2, 3}, "-") = "1-2-3"
+     * }</pre>
+     *
+     * @param values    the array of Objects to convert, may be {@code null} or empty
+     * @param delimiter the String to use as a delimiter between elements, may be {@code null} (treated as "null")
+     * @return the joined String, or an empty string if the input array is {@code null} or empty
+     */
+    public static String arrayToString(@Nullable Object[] values, String delimiter) {
+        int length = length(values);
+        if (length < 1) {
+            return EMPTY_STRING;
+        }
+        if (length == 1) {
+            return valueOf(values[0]);
+        }
+        StringJoiner sj = new StringJoiner(delimiter);
+        for (Object elem : values) {
+            sj.add(valueOf(elem));
+        }
+        return sj.toString();
+    }
 
     /**
      * Changes the first character of the given {@code String} to uppercase or lowercase,

microsphere-java-core/src/test/java/io/microsphere/util/CharSequenceUtilsTest.java

@@ -8,6 +8,7 @@
 import static io.microsphere.util.CharSequenceUtils.isNotEmpty;
 import static io.microsphere.util.CharSequenceUtils.length;
 import static io.microsphere.util.CharSequenceUtils.trimAllWhitespace;
+import static io.microsphere.util.StringUtils.EMPTY_STRING;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNull;
@@ -22,7 +23,7 @@
  */
 class CharSequenceUtilsTest {
 
-    static final String TEST_EMPTY_STRING = "";
+    static final String TEST_EMPTY_STRING = EMPTY_STRING;
 
     static final String TEST_BLANK_STRING = SPACE;
 

microsphere-java-core/src/test/java/io/microsphere/util/StringUtilsTest.java

@@ -18,6 +18,7 @@
 import static io.microsphere.util.StringUtils.EMPTY;
 import static io.microsphere.util.StringUtils.EMPTY_STRING;
 import static io.microsphere.util.StringUtils.EMPTY_STRING_ARRAY;
+import static io.microsphere.util.StringUtils.arrayToString;
 import static io.microsphere.util.StringUtils.capitalize;
 import static io.microsphere.util.StringUtils.contains;
 import static io.microsphere.util.StringUtils.containsWhitespace;
@@ -45,6 +46,7 @@
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.springframework.util.StringUtils.delimitedListToStringArray;
 
@@ -359,4 +361,16 @@ void testToStringArray() {
         assertArrayEquals(ofArray("a", "b", "c"), toStringArray(ofList("a", "b", "c")));
     }
 
+    @Test
+    void testArrayToString() {
+        assertSame(TEST_EMPTY_STRING, arrayToString(null, COMMA));
+        assertSame(TEST_EMPTY_STRING, arrayToString(EMPTY_STRING_ARRAY, COMMA));
+        assertSame("a", arrayToString(ofArray("a"), COMMA));
+        assertEquals("a,b,c", arrayToString(ofArray("a", "b", "c"), COMMA));
+        assertEquals("1-2-3", arrayToString(ofArray(1, 2, 3), "-"));
+        assertEquals("1,2,3", arrayToString(ofArray(1, 2, 3), COMMA));
+
+        assertThrows(NullPointerException.class, () -> arrayToString(ofArray(1, 2, 3), null));
+    }
+
 }