Improve validation of layertools input

This commit improves the validation performed on the user
input provided to the layertools jarmode to provide more
clear error messages when the input is not correct and
reduce the chance of ambiguity.

Fixes gh-22042

spring-boot-project/spring-boot-tools/spring-boot-jarmode-layertools/src/main/java/org/springframework/boot/jarmode/layertools/Command.java

@@ -30,6 +30,7 @@ import java.util.stream.Stream;
  * A command that can be launched from the layertools jarmode.
  *
  * @author Phillip Webb
+ * @author Scott Frederick
  */
 abstract class Command {
 
@@ -192,6 +193,7 @@ abstract class Command {
 						return candidate;
 					}
 				}
+				throw new UnknownOptionException(name);
 			}
 			return null;
 		}
@@ -285,7 +287,13 @@ abstract class Command {
 		}
 
 		private String claimArg(Deque<String> args) {
-			return (this.valueDescription != null) ? args.removeFirst() : null;
+			if (this.valueDescription != null) {
+				if (args.isEmpty()) {
+					throw new MissingValueException(this.name);
+				}
+				return args.removeFirst();
+			}
+			return null;
 		}
 
 		@Override

spring-boot-project/spring-boot-tools/spring-boot-jarmode-layertools/src/main/java/org/springframework/boot/jarmode/layertools/LayerToolsJarMode.java

@@ -29,6 +29,7 @@ import org.springframework.boot.loader.jarmode.JarMode;
  * {@link JarMode} providing {@code "layertools"} support.
  *
  * @author Phillip Webb
+ * @author Scott Frederick
  * @since 2.3.0
  */
 public class LayerToolsJarMode implements JarMode {
@@ -63,22 +64,48 @@ public class LayerToolsJarMode implements JarMode {
 		}
 
 		private void run(String[] args) {
-			run(new ArrayDeque<>(Arrays.asList(args)));
+			run(dequeOf(args));
 		}
 
 		private void run(Deque<String> args) {
 			if (!args.isEmpty()) {
-				Command command = Command.find(this.commands, args.removeFirst());
+				String commandName = args.removeFirst();
+				Command command = Command.find(this.commands, commandName);
 				if (command != null) {
-					command.run(args);
+					runCommand(command, args);
 					return;
 				}
+				printError("Unknown command \"" + commandName + "\"");
 			}
 			this.help.run(args);
 		}
 
+		private void runCommand(Command command, Deque<String> args) {
+			try {
+				command.run(args);
+			}
+			catch (UnknownOptionException ex) {
+				printError("Unknown option \"" + ex.getMessage() + "\" for the " + command.getName() + " command");
+				this.help.run(dequeOf(command.getName()));
+			}
+			catch (MissingValueException ex) {
+				printError("Option \"" + ex.getMessage() + "\" for the " + command.getName()
+						+ " command requires a value");
+				this.help.run(dequeOf(command.getName()));
+			}
+		}
+
+		private void printError(String errorMessage) {
+			System.out.println("Error: " + errorMessage);
+			System.out.println();
+		}
+
+		private Deque<String> dequeOf(String... args) {
+			return new ArrayDeque<>(Arrays.asList(args));
+		}
+
 		static List<Command> getCommands(Context context) {
-			List<Command> commands = new ArrayList<Command>();
+			List<Command> commands = new ArrayList<>();
 			commands.add(new ListCommand(context));
 			commands.add(new ExtractCommand(context));
 			return Collections.unmodifiableList(commands);

spring-boot-project/spring-boot-tools/spring-boot-jarmode-layertools/src/main/java/org/springframework/boot/jarmode/layertools/MissingValueException.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2012-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://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.springframework.boot.jarmode.layertools;
+
+/**
+ * Exception thrown when a required value is not provided for an option.
+ *
+ * @author Scott Frederick
+ */
+class MissingValueException extends RuntimeException {
+
+	private final String optionName;
+
+	MissingValueException(String optionName) {
+		this.optionName = optionName;
+	}
+
+	@Override
+	public String getMessage() {
+		return "--" + this.optionName;
+	}
+
+}

spring-boot-project/spring-boot-tools/spring-boot-jarmode-layertools/src/main/java/org/springframework/boot/jarmode/layertools/UnknownOptionException.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2012-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://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.springframework.boot.jarmode.layertools;
+
+/**
+ * Exception thrown when an unrecognized option is encountered.
+ *
+ * @author Scott Frederick
+ */
+class UnknownOptionException extends RuntimeException {
+
+	private final String optionName;
+
+	UnknownOptionException(String optionName) {
+		this.optionName = optionName;
+	}
+
+	@Override
+	public String getMessage() {
+		return "--" + this.optionName;
+	}
+
+}