Implement more flexible error handling

- Add exception handling around new interface CommandExceptionResolver
  which allows to define a chain of resolvers to process errors before
  exception is bubbled up to result handlers.
- Will be foundation to add more sophisticated error handling features
  compared to what spring itself have for rest layer.
- Resolver returns CommandHandlingResult holder which further can be
  used to make a choice what to print into console and if spesific exit
  code should be used in non-interactive mode.
- Exception handling can be defined globally and per command giving
  a change for user to customise i.e. error thrown by parser.
- CommandParserExceptionResolver replaces CommandParserExceptionsExceptionResultHandler
  and provides more meaninful message for missing options.
- Fixes #503

spring-shell-samples/src/main/java/org/springframework/shell/samples/e2e/ErrorHandlingCommands.java

@@ -0,0 +1,91 @@
+/*
+ * Copyright 2022 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.shell.samples.e2e;
+
+import org.springframework.boot.ExitCodeGenerator;
+import org.springframework.context.annotation.Bean;
+import org.springframework.shell.command.CommandRegistration;
+import org.springframework.shell.command.CommandExceptionResolver;
+import org.springframework.shell.command.CommandHandlingResult;
+import org.springframework.shell.standard.ShellComponent;
+
+/**
+ * Commands used for e2e test.
+ *
+ * @author Janne Valkealahti
+ */
+@ShellComponent
+public class ErrorHandlingCommands extends BaseE2ECommands {
+
+	@Bean
+	public CommandRegistration testErrorHandlingRegistration() {
+		return CommandRegistration.builder()
+			.command(REG, "error-handling")
+			.group(GROUP)
+			.withOption()
+				.longNames("arg1")
+				.required()
+				.and()
+			.withErrorHandling()
+				.resolver(new CustomExceptionResolver())
+				.and()
+			.withTarget()
+				.function(ctx -> {
+					String arg1 = ctx.getOptionValue("arg1");
+					if ("throw1".equals(arg1)) {
+						throw new CustomException1();
+					}
+					if ("throw2".equals(arg1)) {
+						throw new CustomException2(11);
+					}
+					if ("throw3".equals(arg1)) {
+						throw new RuntimeException();
+					}
+					return "Hello " + arg1;
+				})
+				.and()
+			.build();
+	}
+
+	private static class CustomException1 extends RuntimeException {
+	}
+
+	private static class CustomException2 extends RuntimeException implements ExitCodeGenerator {
+
+		private int code;
+
+		CustomException2(int code) {
+			this.code = code;
+		}
+
+		@Override
+		public int getExitCode() {
+			return code;
+		}
+	}
+
+
+	private static class CustomExceptionResolver implements CommandExceptionResolver {
+
+		@Override
+		public CommandHandlingResult resolve(Exception e) {
+			if (e instanceof CustomException1) {
+				return CommandHandlingResult.of("Hi, handled exception\n", 42);
+			}
+			return null;
+		}
+	}
+}

spring-shell-samples/src/main/java/org/springframework/shell/samples/e2e/RequiredValueCommands.java

@@ -31,7 +31,7 @@ public class RequiredValueCommands extends BaseE2ECommands {
 
 	@ShellMethod(key = LEGACY_ANNO + "required-value", group = GROUP)
 	public String testRequiredValueAnnotation(
-		@ShellOption String arg1
+		@ShellOption(help = "Desc arg1") String arg1
 	) {
 		return "Hello " + arg1;
 	}
@@ -43,6 +43,7 @@ public class RequiredValueCommands extends BaseE2ECommands {
 			.group(GROUP)
 			.withOption()
 				.longNames("arg1")
+				.description("Desc arg1")
 				.required()
 				.and()
 			.withTarget()

spring-shell-samples/src/main/java/org/springframework/shell/samples/e2e/ValidatedValueCommands.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2022 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.shell.samples.e2e;
+
+import jakarta.validation.constraints.Min;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.shell.command.CommandRegistration;
+import org.springframework.shell.standard.ShellComponent;
+import org.springframework.shell.standard.ShellMethod;
+import org.springframework.shell.standard.ShellOption;
+
+/**
+ * Commands used for e2e test.
+ *
+ * @author Janne Valkealahti
+ */
+@ShellComponent
+public class ValidatedValueCommands extends BaseE2ECommands {
+
+	@ShellMethod(key = LEGACY_ANNO + "validated-value", group = GROUP)
+	public String testValidatedValueAnnotation(
+		@ShellOption @Min(value = 1) Integer arg1,
+		@ShellOption @Min(value = 1) Integer arg2
+	) {
+		return "Hello " + arg1;
+	}
+
+	@Bean
+	public CommandRegistration testValidatedValueRegistration() {
+		return CommandRegistration.builder()
+			.command(REG, "validated-value")
+			.group(GROUP)
+			.withOption()
+				.longNames("arg1")
+				.type(Integer.class)
+				.required()
+				.and()
+			.withOption()
+				.longNames("arg2")
+				.type(Integer.class)
+				.required()
+				.and()
+			.withTarget()
+				.function(ctx -> {
+					Integer arg1 = ctx.getOptionValue("arg1");
+					return "Hello " + arg1;
+				})
+				.and()
+			.build();
+	}
+
+}