[CLI-312] Inconsistent behaviour in key/value pairs (Java property style)

src/main/java/org/apache/commons/cli/DefaultParser.java

@@ -228,6 +228,9 @@ private DefaultParser(final boolean allowPartialMatching,
      */
     private void checkRequiredArgs() throws ParseException {
         if (currentOption != null && currentOption.requiresArg()) {
+            if (isJavaProperty(currentOption.getKey()) && currentOption.getValuesList().size() == 1) {
+                return;
+            }
             throw new MissingArgumentException(currentOption);
         }
     }

src/test/java/org/apache/commons/cli/bug/BugCLI312Test.java

@@ -0,0 +1,106 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.cli.bug;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.Properties;
+
+import org.apache.commons.cli.CommandLine;
+import org.apache.commons.cli.CommandLineParser;
+import org.apache.commons.cli.DefaultParser;
+import org.apache.commons.cli.MissingArgumentException;
+import org.apache.commons.cli.Option;
+import org.apache.commons.cli.Options;
+import org.apache.commons.cli.ParseException;
+import org.junit.Test;
+
+/**
+ * Demonstrates inconsistencies in parsing Java property-style options.
+ */
+public class BugCLI312Test {
+    @Test
+    public void testPropertyStyleOption_withGetOptionProperties() throws ParseException {
+        final Option o1 = Option.builder().option("D").longOpt("define").numberOfArgs(2).valueSeparator('=').build();
+
+        final Options options = new Options();
+        options.addOption(o1);
+
+        final CommandLineParser parser = new DefaultParser();
+
+        final CommandLine cl = parser.parse(options, "-Dv -Dw=1 -D x=2 -D y -D z=3 other".split(" "));
+        assertArrayEquals(new String[] {"v", "w", "1", "x", "2", "y", "z", "3"}, cl.getOptionValues('D'));
+
+        Properties properties = cl.getOptionProperties("D");
+        assertEquals("true", properties.getProperty("v"));
+        assertEquals("1", properties.getProperty("w"));
+        assertEquals("2", properties.getProperty("x"));
+        assertEquals("true", properties.getProperty("y"));
+        assertEquals("3", properties.getProperty("z"));
+        assertEquals(5, properties.size());
+        assertEquals("other", cl.getArgList().get(0));
+    }
+
+    @Test
+    public void testPropertyStyleOption_withGetOptions() throws ParseException {
+        final Option o1 = Option.builder().option("D").longOpt("define").numberOfArgs(2).valueSeparator('=').build();
+
+        final Options options = new Options();
+        options.addOption(o1);
+
+        final CommandLineParser parser = new DefaultParser();
+
+        final CommandLine cl = parser.parse(options, "-Dv -Dw=1 -D x=2 -D y -D z=3 other".split(" "));
+        assertArrayEquals(new String[] {"v", "w", "1", "x", "2", "y", "z", "3"}, cl.getOptionValues('D'));
+
+        int defineOptionsFound = 0;
+        for (final Option o : cl.getOptions()) {
+            if ("D".equals(o.getOpt())) {
+                defineOptionsFound++;
+
+                if (defineOptionsFound == 1) {
+                    assertArrayEquals(new String[] {"v"}, o.getValues());
+                } else if (defineOptionsFound == 2) {
+                    assertArrayEquals(new String[] {"w", "1"}, o.getValues());
+                } else if (defineOptionsFound == 3) {
+                    assertArrayEquals(new String[] {"x", "2"}, o.getValues());
+                } else if (defineOptionsFound == 4) {
+                    assertArrayEquals(new String[] {"y"}, o.getValues());
+                } else if (defineOptionsFound == 5) {
+                    assertArrayEquals(new String[] {"z", "3"}, o.getValues());
+                } else {
+                    fail("Didn't expect " + defineOptionsFound + " occurrences of -D");
+                }
+            }
+        }
+        assertEquals("other", cl.getArgList().get(0));
+    }
+
+    @Test
+    public void testNoOptionValues() {
+        final Option o1 = Option.builder("A").build();
+        final Option o2 = Option.builder().option("D").longOpt("define").numberOfArgs(2).valueSeparator('=').build();
+        Options options = new Options().addOption(o1).addOption(o2);
+
+        final CommandLineParser parser = new DefaultParser();
+
+        assertThrows(MissingArgumentException.class, () -> parser.parse(options, "-D -A".split(" ")));
+    }
+}