彻底搞明白Spring中的自动装配和Autowired注解的使用

public interface AutowireCapableBeanFactory{

 //无需自动装配
 int AUTOWIRE_NO = 0;

 //按名称自动装配bean属性
 int AUTOWIRE_BY_NAME = 1;

 //按类型自动装配bean属性
 int AUTOWIRE_BY_TYPE = 2;

 //按构造器自动装配
 int AUTOWIRE_CONSTRUCTOR = 3;

 //过时方法，Spring3.0之后不再支持
 @Deprecated
 int AUTOWIRE_AUTODETECT = 4;
}

public class User{
 private Role myRole;
}
public class Role {
 private String id; 
 private String name;
}

<bean id="myRole" class="com.viewscenes.netsupervisor.entity.Role">
 <property name="id" value="1001"></property>
 <property name="name" value="管理员"></property>
</bean>

<bean id="user" class="com.viewscenes.netsupervisor.entity.User" autowire="byName"></bean>

<bean class="com.viewscenes.netsupervisor.entity.Role">
 <property name="id" value="1001"></property>
 <property name="name" value="管理员"></property>
</bean>

<bean id="user" class="com.viewscenes.netsupervisor.entity.User" autowire="byType"></bean>

public class User{
 private Role role;

 public User(Role role) {
 this.role = role;
 }
}

<bean id="user" class="com.viewscenes.netsupervisor.entity.User" autowire="constructor"></bean>

<beans default-autowire="byType">

@Autowired
UserService userService;

public Object doResolveDependency(DependencyDescriptor descriptor, String beanName,
  Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {
 
 //查找Bean
 Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
 //如果拿到的Bean集合为空，且isRequired，就抛出异常。
 if (matchingBeans.isEmpty()) {
 if (descriptor.isRequired()) {
  raiseNoSuchBeanDefinitionException(type, "", descriptor);
 }
 return null;
 }
}

@Autowired(required=false)
UserService userService;

protected Map<String, Object> findAutowireCandidates(
 String beanName, Class<?> requiredType, DependencyDescriptor descriptor) {
 
 //获取给定类型的所有bean名称，里面实际循环所有的beanName，获取它的实例
 //再通过isTypeMatch方法来确定
 String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
  this, requiredType, true, descriptor.isEager());
  
 Map<String, Object> result = new LinkedHashMap<String, Object>(candidateNames.length);
 
 //根据返回的beanName，获取其实例返回
 for (String candidateName : candidateNames) {
 if (!isSelfReference(beanName, candidateName) && isAutowireCandidate(candidateName, descriptor)) {
  result.put(candidateName, getBean(candidateName));
 }
 }
 return result;
}

@Autowired
UserService UserServiceImpl2;

public Object doResolveDependency(DependencyDescriptor descriptor, String beanName,
  Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {
  
 //按照类型查找Bean实例
 Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
 //如果Bean集合为空，且isRequired成立就抛出异常
 if (matchingBeans.isEmpty()) {
 if (descriptor.isRequired()) {
  raiseNoSuchBeanDefinitionException(type, "", descriptor);
 }
 return null;
 }
 //如果查找的Bean实例大于1个
 if (matchingBeans.size() > 1) {
 //找到最合适的那个，如果没有合适的。。也抛出异常
 String primaryBeanName = determineAutowireCandidate(matchingBeans, descriptor);
 if (primaryBeanName == null) {
  throw new NoUniqueBeanDefinitionException(type, matchingBeans.keySet());
 }
 if (autowiredBeanNames != null) {
  autowiredBeanNames.add(primaryBeanName);
 }
 return matchingBeans.get(primaryBeanName);
 } 
}

protected String determineAutowireCandidate(Map<String, Object> candidateBeans, 
  DependencyDescriptor descriptor) {
 //循环拿到的Bean集合
 for (Map.Entry<String, Object> entry : candidateBeans.entrySet()) {
 String candidateBeanName = entry.getKey();
 Object beanInstance = entry.getValue();
 //通过matchesBeanName方法来确定bean集合中的名称是否与属性的名称相同
 if (matchesBeanName(candidateBeanName, descriptor.getDependencyName())) {
  return candidateBeanName;
 }
 }
 return null;
}

protected String determineAutowireCandidate(Map<String, Object> candidateBeans, 
  DependencyDescriptor descriptor) {
 Class<?> requiredType = descriptor.getDependencyType();
 //通过@Primary注解来标识Bean
 String primaryCandidate = determinePrimaryCandidate(candidateBeans, requiredType);
 if (primaryCandidate != null) {
 return primaryCandidate;
 }
 //通过@Priority(value = 0)注解来标识Bean value为优先级大小
 String priorityCandidate = determineHighestPriorityCandidate(candidateBeans, requiredType);
 if (priorityCandidate != null) {
 return priorityCandidate;
 }
 return null;
}

protected String determinePrimaryCandidate(Map<String, Object> candidateBeans, Class<?> requiredType) {
 String primaryBeanName = null;
 for (Map.Entry<String, Object> entry : candidateBeans.entrySet()) {
 String candidateBeanName = entry.getKey();
 Object beanInstance = entry.getValue();
 if (isPrimary(candidateBeanName, beanInstance)) {
  if (primaryBeanName != null) {
  boolean candidateLocal = containsBeanDefinition(candidateBeanName);
  boolean primaryLocal = containsBeanDefinition(primaryBeanName);
  if (candidateLocal && primaryLocal) {
   throw new NoUniqueBeanDefinitionException(requiredType, candidateBeans.size(),
    "more than one 'primary' bean found among candidates: " + candidateBeans.keySet());
  }
  else if (candidateLocal) {
   primaryBeanName = candidateBeanName;
  }
  }
  else {
  primaryBeanName = candidateBeanName;
  }
 }
 }
 return primaryBeanName;
}

protected String determineHighestPriorityCandidate(Map<String, Object> candidateBeans, 
     Class<?> requiredType) {
 String highestPriorityBeanName = null;
 Integer highestPriority = null;
 for (Map.Entry<String, Object> entry : candidateBeans.entrySet()) {
 String candidateBeanName = entry.getKey();
 Object beanInstance = entry.getValue();
 Integer candidatePriority = getPriority(beanInstance);
 if (candidatePriority != null) {
  if (highestPriorityBeanName != null) {
  //如果优先级大小相同
  if (candidatePriority.equals(highestPriority)) {
   throw new NoUniqueBeanDefinitionException(requiredType, candidateBeans.size(),
   "Multiple beans found with the same priority ('" + highestPriority + "') " +
    "among candidates: " + candidateBeans.keySet());
  }
  else if (candidatePriority < highestPriority) {
   highestPriorityBeanName = candidateBeanName;
   highestPriority = candidatePriority;
  }
  }
  else {
  highestPriorityBeanName = candidateBeanName;
  highestPriority = candidatePriority;
  }
 }
 }
 return highestPriorityBeanName;
}

<dependency>
 <groupId>javax.annotation</groupId>
 <artifactId>javax.annotation-api</artifactId>
 <version>1.2</version>
</dependency>