源码分析@Autowired注解原理

原理肯定是java反射，但具体是怎么做的，是通过AutowiredAnnotationBeanPostProcessor来进行处理，并且@Autowired也可以消除setter和getter方法。

在AutowiredAnnotationBeanPostProcessor中处理字段注入的内部类：

private class AutowiredFieldElement extends InjectionMetadata.InjectedElement {

		private final boolean required;

		private volatile boolean cached = false;

		private volatile Object cachedFieldValue;

		public AutowiredFieldElement(Field field, boolean required) {
			super(field, null);
			this.required = required;
		}

		@Override
		protected void inject(Object bean, String beanName, PropertyValues pvs) throws Throwable {
			Field field = (Field) this.member;
			try {
				Object value;
				if (this.cached) {
					value = resolvedCachedArgument(beanName, this.cachedFieldValue);
				}
				else {
					DependencyDescriptor descriptor = new DependencyDescriptor(field, this.required);
					Set<String> autowiredBeanNames = new LinkedHashSet<String>(1);
					TypeConverter typeConverter = beanFactory.getTypeConverter();
					value = beanFactory.resolveDependency(descriptor, beanName, autowiredBeanNames, typeConverter);
					synchronized (this) {
						if (!this.cached) {
							if (value != null || this.required) {
								this.cachedFieldValue = descriptor;
								registerDependentBeans(beanName, autowiredBeanNames);
								if (autowiredBeanNames.size() == 1) {
									String autowiredBeanName = autowiredBeanNames.iterator().next();
									if (beanFactory.containsBean(autowiredBeanName)) {
										if (beanFactory.isTypeMatch(autowiredBeanName, field.getType())) {
											this.cachedFieldValue = new RuntimeBeanReference(autowiredBeanName);
										}
									}
								}
							}
							else {
								this.cachedFieldValue = null;
							}
							this.cached = true;
						}
					}
				}
				if (value != null) {
					ReflectionUtils.makeAccessible(field);
					field.set(bean, value);
				}
			}
			catch (Throwable ex) {
				throw new BeanCreationException("Could not autowire field: " + field, ex);
			}
		}
	}
           

关键代码：

if (value != null) {
					ReflectionUtils.makeAccessible(field);
					field.set(bean, value);
				}
           

处理方法注入的内容类：

/**
	 * Class representing injection information about an annotated method.
	 */
	private class AutowiredMethodElement extends InjectionMetadata.InjectedElement {

		private final boolean required;

		private volatile boolean cached = false;

		private volatile Object[] cachedMethodArguments;

		public AutowiredMethodElement(Method method, boolean required, PropertyDescriptor pd) {
			super(method, pd);
			this.required = required;
		}

		@Override
		protected void inject(Object bean, String beanName, PropertyValues pvs) throws Throwable {
			if (checkPropertySkipping(pvs)) {
				return;
			}
			Method method = (Method) this.member;
			try {
				Object[] arguments;
				if (this.cached) {
					// Shortcut for avoiding synchronization...
					arguments = resolveCachedArguments(beanName);
				}
				else {
					Class<?>[] paramTypes = method.getParameterTypes();
					arguments = new Object[paramTypes.length];
					DependencyDescriptor[] descriptors = new DependencyDescriptor[paramTypes.length];
					Set<String> autowiredBeanNames = new LinkedHashSet<String>(paramTypes.length);
					TypeConverter typeConverter = beanFactory.getTypeConverter();
					for (int i = 0; i < arguments.length; i++) {
						MethodParameter methodParam = new MethodParameter(method, i);
						GenericTypeResolver.resolveParameterType(methodParam, bean.getClass());
						descriptors[i] = new DependencyDescriptor(methodParam, this.required);
						arguments[i] = beanFactory.resolveDependency(
								descriptors[i], beanName, autowiredBeanNames, typeConverter);
						if (arguments[i] == null && !this.required) {
							arguments = null;
							break;
						}
					}
					synchronized (this) {
						if (!this.cached) {
							if (arguments != null) {
								this.cachedMethodArguments = new Object[arguments.length];
								for (int i = 0; i < arguments.length; i++) {
									this.cachedMethodArguments[i] = descriptors[i];
								}
								registerDependentBeans(beanName, autowiredBeanNames);
								if (autowiredBeanNames.size() == paramTypes.length) {
									Iterator<String> it = autowiredBeanNames.iterator();
									for (int i = 0; i < paramTypes.length; i++) {
										String autowiredBeanName = it.next();
										if (beanFactory.containsBean(autowiredBeanName)) {
											if (beanFactory.isTypeMatch(autowiredBeanName, paramTypes[i])) {
												this.cachedMethodArguments[i] = new RuntimeBeanReference(autowiredBeanName);
											}
										}
									}
								}
							}
							else {
								this.cachedMethodArguments = null;
							}
							this.cached = true;
						}
					}
				}
				if (arguments != null) {
					ReflectionUtils.makeAccessible(method);
					method.invoke(bean, arguments);
				}
			}
			catch (InvocationTargetException ex) {
				throw ex.getTargetException();
			}
			catch (Throwable ex) {
				throw new BeanCreationException("Could not autowire method: " + method, ex);
			}
		}

		private Object[] resolveCachedArguments(String beanName) {
			if (this.cachedMethodArguments == null) {
				return null;
			}
			Object[] arguments = new Object[this.cachedMethodArguments.length];
			for (int i = 0; i < arguments.length; i++) {
				arguments[i] = resolvedCachedArgument(beanName, this.cachedMethodArguments[i]);
			}
			return arguments;
		}
	}