Add @ConditionalOnProperty annotation

Add @ConditionalOnProperty which enables conditional bean creation when
all required properties are defined in the Environment.

Fixes gh-812

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/ConditionalOnProperty.java

+/*
+ * Copyright 2012-2014 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.boot.autoconfigure.condition;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.context.annotation.Conditional;
+import org.springframework.core.env.Environment;
+
+/**
+ * {@link Conditional} that only matches when the specified properties are defined in
+ * {@link Environment}
+ * 
+ * @author Maciej Walkowiak
+ * @since 1.1.0
+ */
+@Conditional(OnPropertyCondition.class)
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.TYPE, ElementType.METHOD })
+public @interface ConditionalOnProperty {
+
+	/**
+	 * One or more properties that must be present.
+	 * @return the property names
+	 */
+	String[] value();
+
+}

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/OnPropertyCondition.java

+/*
+ * Copyright 2012-2014 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.boot.autoconfigure.condition;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.springframework.context.annotation.Condition;
+import org.springframework.context.annotation.ConditionContext;
+import org.springframework.core.type.AnnotatedTypeMetadata;
+import org.springframework.util.StringUtils;
+
+/**
+ * {@link Condition} that checks if properties are defined in environment.
+ * 
+ * @author Maciej Walkowiak
+ * @see ConditionalOnProperty
+ * @since 1.1.0
+ */
+class OnPropertyCondition extends SpringBootCondition {
+
+	@Override
+	public ConditionOutcome getMatchOutcome(ConditionContext context,
+			AnnotatedTypeMetadata metadata) {
+
+		String[] onProperties = (String[]) metadata.getAnnotationAttributes(
+				ConditionalOnProperty.class.getName()).get("value");
+
+		List<String> missingProperties = new ArrayList<String>();
+
+		for (String property : onProperties) {
+			if (!context.getEnvironment().containsProperty(property)) {
+				missingProperties.add(property);
+			}
+		}
+
+		if (missingProperties.isEmpty()) {
+			return ConditionOutcome.match();
+		}
+
+		return ConditionOutcome
+				.noMatch("@ConditionalOnProperty missing required properties: "
+						+ StringUtils.arrayToCommaDelimitedString(missingProperties
+								.toArray()) + " not found");
+	}
+
+}

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/ConditionalOnPropertyTests.java

+/*
+ * Copyright 2012-2014 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.boot.autoconfigure.condition;
+
+import org.junit.Test;
+import org.springframework.boot.test.EnvironmentTestUtils;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Tests for {@link ConditionalOnProperty}.
+ * 
+ * @author Maciej Walkowiak
+ */
+public class ConditionalOnPropertyTests {
+
+	private AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+
+	@Test
+	public void testBeanIsCreatedWhenAllPropertiesAreDefined() {
+		EnvironmentTestUtils.addEnvironment(this.context.getEnvironment(),
+				"property1=value1", "property2=value2");
+		setupContext();
+		assertTrue(this.context.containsBean("foo"));
+		assertEquals("foo", this.context.getBean("foo"));
+	}
+
+	@Test
+	public void testBeanIsNotCreatedWhenNotAllPropertiesAreDefined() {
+		EnvironmentTestUtils.addEnvironment(this.context.getEnvironment(),
+				"property1=value1");
+		setupContext();
+		assertFalse(this.context.containsBean("foo"));
+	}
+
+	private void setupContext() {
+		this.context.register(MultiplePropertiesRequiredConfiguration.class);
+		this.context.refresh();
+	}
+
+	@Configuration
+	@ConditionalOnProperty({ "property1", "property2" })
+	protected static class MultiplePropertiesRequiredConfiguration {
+
+		@Bean
+		public String foo() {
+			return "foo";
+		}
+
+	}
+
+}