Introduce ResultHandlerService

- Replace main use of ResultHandler with ResultHandlerService which is
  a framework type of impl for handlers found from conversion service.
  This handles types better and easier to handle with bean cycles, etc.
- Removed IterableResultHandler to think about these use cases later
  when further refactoring is done.
- TypeHierarchyResultHandler is removed and better functionality now
  via ResultHandlerService.
- Relates #336

Author: jvalkeal

spring-shell-autoconfigure/src/main/java/org/springframework/shell/boot/SpringShellAutoConfiguration.java

@@ -17,6 +17,7 @@
 package org.springframework.shell.boot;
 
 import java.util.Collection;
+import java.util.Set;
 
 import javax.validation.Validation;
 import javax.validation.Validator;
@@ -33,8 +34,9 @@
 import org.springframework.core.convert.converter.GenericConverter;
 import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.shell.ResultHandler;
+import org.springframework.shell.ResultHandlerService;
 import org.springframework.shell.Shell;
-import org.springframework.shell.result.IterableResultHandler;
+import org.springframework.shell.result.GenericResultHandlerService;
 import org.springframework.shell.result.ResultHandlerConfig;
 
 /**
@@ -71,8 +73,16 @@ public Validator validator() {
 	}
 
 	@Bean
-	public Shell shell(@Qualifier("main") ResultHandler resultHandler, @Qualifier("iterableResultHandler") IterableResultHandler iterableResultHandler) {
-		iterableResultHandler.setDelegate(resultHandler);
-		return new Shell(resultHandler);
+	public ResultHandlerService resultHandlerService(Set<ResultHandler<?>> resultHandlers) {
+		GenericResultHandlerService service = new GenericResultHandlerService();
+		for (ResultHandler<?> resultHandler : resultHandlers) {
+			service.addResultHandler(resultHandler);
+		}
+		return service;
+	}
+
+	@Bean
+	public Shell shell(ResultHandlerService resultHandlerService) {
+		return new Shell(resultHandlerService);
 	}
 }

spring-shell-core/src/main/java/org/springframework/shell/ResultHandlerService.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2021 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;
+
+import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.lang.Nullable;
+
+/**
+ * A service interface for result handling.
+ *
+ * @author Janne Valkealahti
+ */
+public interface ResultHandlerService {
+
+	/**
+	 * Handle result.
+	 *
+	 * @param result the result
+	 */
+	void handle(@Nullable Object result);
+
+	/**
+	 * Handle result to the specified {@ resultType}.
+	 *
+	 * @param result the result
+	 * @param resultType the result type
+	 */
+	void handle(@Nullable Object result, @Nullable TypeDescriptor resultType);
+}

spring-shell-core/src/main/java/org/springframework/shell/Shell.java

@@ -55,10 +55,11 @@
  * </p>
  *
  * @author Eric Bottard
+ * @author Janne Valkealahti
  */
 public class Shell {
 
-	private final ResultHandler resultHandler;
+	private final ResultHandlerService resultHandlerService;
 
 	/**
 	 * Marker object returned to signify that there was no input to turn into a command
@@ -84,8 +85,8 @@ public class Shell {
 	 */
 	protected static final Object UNRESOLVED = new Object();
 
-	public Shell(ResultHandler resultHandler) {
-		this.resultHandler = resultHandler;
+	public Shell(ResultHandlerService resultHandlerService) {
+		this.resultHandlerService = resultHandlerService;
 	}
 
 	@Autowired(required = false)
@@ -125,7 +126,7 @@ public void run(InputProvider inputProvider) throws IOException {
 				if (e instanceof ExitRequest) { // Handles ExitRequest thrown from hitting CTRL-C
 					break;
 				}
-				resultHandler.handleResult(e);
+				resultHandlerService.handle(e);
 				continue;
 			}
 			if (input == null) {
@@ -134,7 +135,7 @@ public void run(InputProvider inputProvider) throws IOException {
 
 			result = evaluate(input);
 			if (result != NO_INPUT && !(result instanceof ExitRequest)) {
-				resultHandler.handleResult(result);
+				resultHandlerService.handle(result);
 			}
 		}
 	}

spring-shell-core/src/main/java/org/springframework/shell/result/GenericResultHandler.java

@@ -0,0 +1,14 @@
+package org.springframework.shell.result;
+
+import java.util.Set;
+
+import org.springframework.core.convert.TypeDescriptor;
+
+public interface GenericResultHandler {
+
+    Set<Class<?>> getHandlerTypes();
+
+    void handle(Object result, TypeDescriptor resultType);
+
+    boolean matches(TypeDescriptor resultType);
+}