Support optional command line arguments with empty values

Spring Framework provides two implementations of the
CommandLinePropertySource API: SimpleCommandLinePropertySource and
JOptCommandLinePropertySource.

Prior to this commit, JOptCommandLinePropertySource supported empty
values for optional arguments; whereas, SimpleCommandLinePropertySource
did not.

This commit modifies the implementation of SimpleCommandLinePropertySource
to allow empty values for optional arguments.

Closes gh-24464

spring-core/src/test/java/org/springframework/core/env/JOptCommandLinePropertySourceTests.java

@@ -28,6 +28,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Unit tests for {@link JOptCommandLinePropertySource}.
  *
  * @author Chris Beams
+ * @author Sam Brannen
  * @since 3.1
  */
 class JOptCommandLinePropertySourceTests {
@@ -53,6 +54,17 @@ class JOptCommandLinePropertySourceTests {
 		assertThat(ps.getProperty("foo")).isEqualTo("");
 	}
 
+	@Test // gh-24464
+	void withOptionalArg_andArgIsEmpty() {
+		OptionParser parser = new OptionParser();
+		parser.accepts("foo").withOptionalArg();
+		OptionSet options = parser.parse("--foo=");
+
+		PropertySource<?> ps = new JOptCommandLinePropertySource(options);
+		assertThat(ps.containsProperty("foo")).isTrue();
+		assertThat(ps.getProperty("foo")).isEqualTo("");
+	}
+
 	@Test
 	void withNoArg() {
 		OptionParser parser = new OptionParser();
@@ -74,7 +86,7 @@ class JOptCommandLinePropertySourceTests {
 		OptionSet options = parser.parse("--foo=bar,baz,biz");
 
 		CommandLinePropertySource<?> ps = new JOptCommandLinePropertySource(options);
-		assertThat(ps.getOptionValues("foo")).isEqualTo(Arrays.asList("bar","baz","biz"));
+		assertThat(ps.getOptionValues("foo")).containsExactly("bar", "baz", "biz");
 		assertThat(ps.getProperty("foo")).isEqualTo("bar,baz,biz");
 	}
 
@@ -85,7 +97,7 @@ class JOptCommandLinePropertySourceTests {
 		OptionSet options = parser.parse("--foo=bar", "--foo=baz", "--foo=biz");
 
 		CommandLinePropertySource<?> ps = new JOptCommandLinePropertySource(options);
-		assertThat(ps.getOptionValues("foo")).isEqualTo(Arrays.asList("bar","baz","biz"));
+		assertThat(ps.getOptionValues("foo")).containsExactly("bar", "baz", "biz");
 		assertThat(ps.getProperty("foo")).isEqualTo("bar,baz,biz");
 	}
 
@@ -123,7 +135,7 @@ class JOptCommandLinePropertySourceTests {
 
 		assertThat(ps.containsProperty("nonOptionArgs")).isFalse();
 		assertThat(ps.getProperty("nonOptionArgs")).isNull();
-		assertThat(ps.getPropertyNames().length).isEqualTo(2);
+		assertThat(ps.getPropertyNames()).hasSize(2);
 	}
 
 	@Test

spring-core/src/test/java/org/springframework/core/env/SimpleCommandLineArgsParserTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,17 +25,24 @@ import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 
-class SimpleCommandLineParserTests {
+/**
+ * Unit tests for {@link SimpleCommandLineArgsParser}.
+ *
+ * @author Chris Beams
+ * @author Sam Brannen
+ */
+class SimpleCommandLineArgsParserTests {
+
+	private final SimpleCommandLineArgsParser parser = new SimpleCommandLineArgsParser();
+
 
 	@Test
 	void withNoOptions() {
-		SimpleCommandLineArgsParser parser = new SimpleCommandLineArgsParser();
 		assertThat(parser.parse().getOptionValues("foo")).isNull();
 	}
 
 	@Test
 	void withSingleOptionAndNoValue() {
-		SimpleCommandLineArgsParser parser = new SimpleCommandLineArgsParser();
 		CommandLineArgs args = parser.parse("--o1");
 		assertThat(args.containsOption("o1")).isTrue();
 		assertThat(args.getOptionValues("o1")).isEqualTo(Collections.EMPTY_LIST);
@@ -43,63 +50,52 @@ class SimpleCommandLineParserTests {
 
 	@Test
 	void withSingleOptionAndValue() {
-		SimpleCommandLineArgsParser parser = new SimpleCommandLineArgsParser();
 		CommandLineArgs args = parser.parse("--o1=v1");
 		assertThat(args.containsOption("o1")).isTrue();
-		assertThat(args.getOptionValues("o1").get(0)).isEqualTo("v1");
+		assertThat(args.getOptionValues("o1")).containsExactly("v1");
 	}
 
 	@Test
 	void withMixOfOptionsHavingValueAndOptionsHavingNoValue() {
-		SimpleCommandLineArgsParser parser = new SimpleCommandLineArgsParser();
 		CommandLineArgs args = parser.parse("--o1=v1", "--o2");
 		assertThat(args.containsOption("o1")).isTrue();
 		assertThat(args.containsOption("o2")).isTrue();
 		assertThat(args.containsOption("o3")).isFalse();
-		assertThat(args.getOptionValues("o1").get(0)).isEqualTo("v1");
+		assertThat(args.getOptionValues("o1")).containsExactly("v1");
 		assertThat(args.getOptionValues("o2")).isEqualTo(Collections.EMPTY_LIST);
 		assertThat(args.getOptionValues("o3")).isNull();
 	}
 
 	@Test
 	void withEmptyOptionText() {
-		SimpleCommandLineArgsParser parser = new SimpleCommandLineArgsParser();
-		assertThatIllegalArgumentException().isThrownBy(() ->
-				parser.parse("--"));
+		assertThatIllegalArgumentException().isThrownBy(() -> parser.parse("--"));
 	}
 
 	@Test
 	void withEmptyOptionName() {
-		SimpleCommandLineArgsParser parser = new SimpleCommandLineArgsParser();
-		assertThatIllegalArgumentException().isThrownBy(() ->
-				parser.parse("--=v1"));
+		assertThatIllegalArgumentException().isThrownBy(() -> parser.parse("--=v1"));
 	}
 
 	@Test
 	void withEmptyOptionValue() {
-		SimpleCommandLineArgsParser parser = new SimpleCommandLineArgsParser();
-		assertThatIllegalArgumentException().isThrownBy(() ->
-				parser.parse("--o1="));
+		CommandLineArgs args = parser.parse("--o1=");
+		assertThat(args.containsOption("o1")).isTrue();
+		assertThat(args.getOptionValues("o1")).containsExactly("");
 	}
 
 	@Test
 	void withEmptyOptionNameAndEmptyOptionValue() {
-		SimpleCommandLineArgsParser parser = new SimpleCommandLineArgsParser();
-		assertThatIllegalArgumentException().isThrownBy(() ->
-				parser.parse("--="));
+		assertThatIllegalArgumentException().isThrownBy(() -> parser.parse("--="));
 	}
 
 	@Test
 	void withNonOptionArguments() {
-		SimpleCommandLineArgsParser parser = new SimpleCommandLineArgsParser();
 		CommandLineArgs args = parser.parse("--o1=v1", "noa1", "--o2=v2", "noa2");
-		assertThat(args.getOptionValues("o1").get(0)).isEqualTo("v1");
-		assertThat(args.getOptionValues("o2").get(0)).isEqualTo("v2");
+		assertThat(args.getOptionValues("o1")).containsExactly("v1");
+		assertThat(args.getOptionValues("o2")).containsExactly("v2");
 
 		List<String> nonOptions = args.getNonOptionArgs();
-		assertThat(nonOptions.get(0)).isEqualTo("noa1");
-		assertThat(nonOptions.get(1)).isEqualTo("noa2");
-		assertThat(nonOptions.size()).isEqualTo(2);
+		assertThat(nonOptions).containsExactly("noa1", "noa2");
 	}
 
 	@Test

spring-core/src/test/java/org/springframework/core/env/SimpleCommandLinePropertySourceTests.java

@@ -26,6 +26,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * Unit tests for {@link SimpleCommandLinePropertySource}.
  *
  * @author Chris Beams
+ * @author Sam Brannen
  * @since 3.1
  */
 class SimpleCommandLinePropertySourceTests {
@@ -60,6 +61,14 @@ class SimpleCommandLinePropertySourceTests {
 		assertThat(ps.getProperty("o3")).isNull();
 	}
 
+	@Test // gh-24464
+	void withOptionalArg_andArgIsEmpty() {
+		EnumerablePropertySource<?> ps = new SimpleCommandLinePropertySource("--foo=");
+
+		assertThat(ps.containsProperty("foo")).isTrue();
+		assertThat(ps.getProperty("foo")).isEqualTo("");
+	}
+
 	@Test
 	void withDefaultNonOptionArgsNameAndNoNonOptionArgsPresent() {
 		EnumerablePropertySource<?> ps = new SimpleCommandLinePropertySource("--o1=v1", "--o2");
@@ -70,7 +79,7 @@ class SimpleCommandLinePropertySourceTests {
 
 		assertThat(ps.containsProperty("nonOptionArgs")).isFalse();
 		assertThat(ps.getProperty("nonOptionArgs")).isNull();
-		assertThat(ps.getPropertyNames().length).isEqualTo(2);
+		assertThat(ps.getPropertyNames()).hasSize(2);
 	}
 
 	@Test