Prevent double registration of commands

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

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2017 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
+ *
+ *      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.springframework.shell;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+
+/**
+ * A {@link CommandRegistry} that supports registration of new commands.
+ *
+ * <p>Makes sure that no two commands are registered with the same name.</p>
+ *
+ * @author Eric Bottard
+ */
+public class ConfigurableCommandRegistry implements CommandRegistry {
+
+	private Map<String, MethodTarget> commands = new HashMap<>();
+
+	@Override
+	public Map<String, MethodTarget> listCommands() {
+		return new TreeMap<>(commands);
+	}
+
+	public void register(String name, MethodTarget target) {
+		MethodTarget previous = commands.get(name);
+		if (previous != null) {
+			throw new IllegalArgumentException(
+				String.format("Illegal registration for command '%s': Attempt to register both '%s' and '%s'", name, target, previous));
+		}
+		commands.put(name, target);
+	}
+}

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

@@ -16,19 +16,17 @@
 
 package org.springframework.shell;
 
-import java.util.Map;
-
 /**
- * Strategy interface for discovering commands.
+ * Strategy interface for registering commands.
  *
  * @author Eric Bottard
  * @author Camilo Gonzalez
  */
-public interface MethodTargetResolver {
+public interface MethodTargetRegistrar {
 
 	/**
-	 * Return a mapping from {@literal <command keyword(s)>} to actual behavior.
+	 * Register mappings from {@literal <command keyword(s)>} to actual behavior.
 	 */
-	public Map<String, MethodTarget> resolve();
+	void register(ConfigurableCommandRegistry registry);
 
 }

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

@@ -33,8 +33,6 @@ import javax.validation.Validation;
 import javax.validation.executable.ExecutableValidator;
 
 import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.boot.ApplicationArguments;
-import org.springframework.boot.ApplicationRunner;
 import org.springframework.context.ApplicationContext;
 import org.springframework.core.MethodParameter;
 import org.springframework.util.ReflectionUtils;
@@ -80,9 +78,11 @@ public class Shell implements CommandRegistry {
 
 	@PostConstruct
 	public void gatherMethodTargets() throws Exception {
-		for (MethodTargetResolver resolver : applicationContext.getBeansOfType(MethodTargetResolver.class).values()) {
-			methodTargets.putAll(resolver.resolve());
+		ConfigurableCommandRegistry registry = new ConfigurableCommandRegistry();
+		for (MethodTargetRegistrar resolver : applicationContext.getBeansOfType(MethodTargetRegistrar.class).values()) {
+			resolver.register(registry);
 		}
+		methodTargets = registry.listCommands();
 	}
 
 	/**

spring-shell-core/src/test/java/org/springframework/shell/ConfigurableCommandRegistryTest.java

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2017 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
+ *
+ *      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.springframework.shell;
+
+import static org.hamcrest.collection.IsMapContaining.hasEntry;
+import static org.hamcrest.collection.IsMapContaining.hasKey;
+import static org.junit.Assert.*;
+
+import org.hamcrest.collection.IsMapContaining;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+/**
+ * Unit tests for {@link ConfigurableCommandRegistry}.
+ *
+ * @author Eric Bottard
+ */
+public class ConfigurableCommandRegistryTest {
+
+	@Rule
+	public ExpectedException thrown= ExpectedException.none();
+
+	@Test
+	public void testRegistration() {
+		ConfigurableCommandRegistry registry = new ConfigurableCommandRegistry();
+		registry.register("foo", MethodTarget.of("toString", this, "some command"));
+
+		assertThat(registry.listCommands(), hasKey("foo"));
+	}
+
+	@Test
+	public void testDoubleRegistration() {
+		ConfigurableCommandRegistry registry = new ConfigurableCommandRegistry();
+		registry.register("foo", MethodTarget.of("toString", this, "some command"));
+
+		thrown.expect(IllegalArgumentException.class);
+		thrown.expectMessage("foo");
+		thrown.expectMessage("toString");
+		thrown.expectMessage("hashCode");
+
+		registry.register("foo", MethodTarget.of("hashCode", this, "some command"));
+	}
+
+}