Avoid package cycle between beans.factory.annotation and b.f.support

See gh-2060

Author: jhoeller

spring-beans/src/main/java/org/springframework/beans/factory/annotation/ParameterResolutionDelegate.java

@@ -0,0 +1,171 @@
+/*
+ * Copyright 2002-2019 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.beans.factory.annotation;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.AnnotatedElement;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Executable;
+import java.lang.reflect.Parameter;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
+import org.springframework.beans.factory.config.DependencyDescriptor;
+import org.springframework.core.MethodParameter;
+import org.springframework.core.annotation.AnnotatedElementUtils;
+import org.springframework.core.annotation.SynthesizingMethodParameter;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
+
+/**
+ * Public delegate for resolving autowirable parameters on externally managed
+ * constructors and methods.
+ *
+ * @author Sam Brannen
+ * @author Juergen Hoeller
+ * @since 5.2
+ * @see #isAutowirable
+ * @see #resolveDependency
+ */
+public final class ParameterResolutionDelegate {
+
+	private static final AnnotatedElement EMPTY_ANNOTATED_ELEMENT = new AnnotatedElement() {
+		@Override
+		@Nullable
+		public <T extends Annotation> T getAnnotation(Class<T> annotationClass) {
+			return null;
+		}
+		@Override
+		public Annotation[] getAnnotations() {
+			return new Annotation[0];
+		}
+		@Override
+		public Annotation[] getDeclaredAnnotations() {
+			return new Annotation[0];
+		}
+	};
+
+
+	private ParameterResolutionDelegate() {
+	}
+
+
+	/**
+	 * Determine if the supplied {@link Parameter} can <em>potentially</em> be
+	 * autowired from an {@link AutowireCapableBeanFactory}.
+	 * <p>Returns {@code true} if the supplied parameter is annotated or
+	 * meta-annotated with {@link Autowired @Autowired},
+	 * {@link Qualifier @Qualifier}, or {@link Value @Value}.
+	 * <p>Note that {@link #resolveDependency} may still be able to resolve the
+	 * dependency for the supplied parameter even if this method returns {@code false}.
+	 * @param parameter the parameter whose dependency should be autowired
+	 * (must not be {@code null})
+	 * @param parameterIndex the index of the parameter in the constructor or method
+	 * that declares the parameter
+	 * @see #resolveDependency
+	 */
+	public static boolean isAutowirable(Parameter parameter, int parameterIndex) {
+		Assert.notNull(parameter, "Parameter must not be null");
+		AnnotatedElement annotatedParameter = getEffectiveAnnotatedParameter(parameter, parameterIndex);
+		return (AnnotatedElementUtils.hasAnnotation(annotatedParameter, Autowired.class) ||
+				AnnotatedElementUtils.hasAnnotation(annotatedParameter, Qualifier.class) ||
+				AnnotatedElementUtils.hasAnnotation(annotatedParameter, Value.class));
+	}
+
+	/**
+	 * Resolve the dependency for the supplied {@link Parameter} from the
+	 * supplied {@link AutowireCapableBeanFactory}.
+	 * <p>Provides comprehensive autowiring support for individual method parameters
+	 * on par with Spring's dependency injection facilities for autowired fields and
+	 * methods, including support for {@link Autowired @Autowired},
+	 * {@link Qualifier @Qualifier}, and {@link Value @Value} with support for property
+	 * placeholders and SpEL expressions in {@code @Value} declarations.
+	 * <p>The dependency is required unless the parameter is annotated or meta-annotated
+	 * with {@link Autowired @Autowired} with the {@link Autowired#required required}
+	 * flag set to {@code false}.
+	 * <p>If an explicit <em>qualifier</em> is not declared, the name of the parameter
+	 * will be used as the qualifier for resolving ambiguities.
+	 * @param parameter the parameter whose dependency should be resolved (must not be
+	 * {@code null})
+	 * @param parameterIndex the index of the parameter in the constructor or method
+	 * that declares the parameter
+	 * @param containingClass the concrete class that contains the parameter; this may
+	 * differ from the class that declares the parameter in that it may be a subclass
+	 * thereof, potentially substituting type variables (must not be {@code null})
+	 * @param beanFactory the {@code AutowireCapableBeanFactory} from which to resolve
+	 * the dependency (must not be {@code null})
+	 * @return the resolved object, or {@code null} if none found
+	 * @throws BeansException if dependency resolution failed
+	 * @see #isAutowirable
+	 * @see Autowired#required
+	 * @see SynthesizingMethodParameter#forExecutable(Executable, int)
+	 * @see AutowireCapableBeanFactory#resolveDependency(DependencyDescriptor, String)
+	 */
+	@Nullable
+	public static Object resolveDependency(
+			Parameter parameter, int parameterIndex, Class<?> containingClass, AutowireCapableBeanFactory beanFactory)
+			throws BeansException {
+
+		Assert.notNull(parameter, "Parameter must not be null");
+		Assert.notNull(containingClass, "Containing class must not be null");
+		Assert.notNull(beanFactory, "AutowireCapableBeanFactory must not be null");
+
+		AnnotatedElement annotatedParameter = getEffectiveAnnotatedParameter(parameter, parameterIndex);
+		Autowired autowired = AnnotatedElementUtils.findMergedAnnotation(annotatedParameter, Autowired.class);
+		boolean required = (autowired == null || autowired.required());
+
+		MethodParameter methodParameter = SynthesizingMethodParameter.forExecutable(
+				parameter.getDeclaringExecutable(), parameterIndex);
+		DependencyDescriptor descriptor = new DependencyDescriptor(methodParameter, required);
+		descriptor.setContainingClass(containingClass);
+		return beanFactory.resolveDependency(descriptor, null);
+	}
+
+	/**
+	 * Due to a bug in {@code javac} on JDK versions prior to JDK 9, looking up
+	 * annotations directly on a {@link Parameter} will fail for inner class
+	 * constructors.
+	 * <h4>Bug in javac in JDK &lt; 9</h4>
+	 * <p>The parameter annotations array in the compiled byte code excludes an entry
+	 * for the implicit <em>enclosing instance</em> parameter for an inner class
+	 * constructor.
+	 * <h4>Workaround</h4>
+	 * <p>This method provides a workaround for this off-by-one error by allowing the
+	 * caller to access annotations on the preceding {@link Parameter} object (i.e.,
+	 * {@code index - 1}). If the supplied {@code index} is zero, this method returns
+	 * an empty {@code AnnotatedElement}.
+	 * <h4>WARNING</h4>
+	 * <p>The {@code AnnotatedElement} returned by this method should never be cast and
+	 * treated as a {@code Parameter} since the metadata (e.g., {@link Parameter#getName()},
+	 * {@link Parameter#getType()}, etc.) will not match those for the declared parameter
+	 * at the given index in an inner class constructor.
+	 * @return the supplied {@code parameter} or the <em>effective</em> {@code Parameter}
+	 * if the aforementioned bug is in effect
+	 */
+	private static AnnotatedElement getEffectiveAnnotatedParameter(Parameter parameter, int index) {
+		Executable executable = parameter.getDeclaringExecutable();
+		if (executable instanceof Constructor && ClassUtils.isInnerClass(executable.getDeclaringClass()) &&
+				executable.getParameterAnnotations().length == executable.getParameterCount() - 1) {
+			// Bug in javac in JDK <9: annotation array excludes enclosing instance parameter
+			// for inner classes, so access it with the actual parameter index lowered by 1
+			return (index == 0 ? EMPTY_ANNOTATED_ELEMENT : executable.getParameters()[index - 1]);
+		}
+		return parameter;
+	}
+
+}