实例化Bean

/**
 * 一个简单的Beans工厂，实例化具体的Bean
 */
public class BeansFactory {
  private ConcurrentHashMap<String, Object> singletonObjects = new ConcurrentHashMap<>();
  private ConcurrentHashMap<String, BeanDefinition> beanDefinitions = new ConcurrentHashMap<>();


  @VisibleForTesting
  protected Object createBean(BeanDefinition beanDefinition) {
    // 类对象的实例
    Object bean = null;
    try {
      // 根据字符串得到类
      Class beanClass = Class.forName(beanDefinition.getClassName());
      List<BeanDefinition.ConstructorArg> args = beanDefinition.getConstructorArgs();
      if (args.isEmpty()) {
        bean = beanClass.newInstance();
      } else {
        Class[] argClasses = new Class[args.size()];
        Object[] argObjects = new Object[args.size()];
        for (int i = 0; i < args.size(); ++i) {
          BeanDefinition.ConstructorArg arg = args.get(i);
          // 如果不是引用
          if (!arg.getIsRef()) {
            // 得到对象参数的类型
            argClasses[i] = arg.getType();
            // 得到对象参数的值
            argObjects[i] = arg.getArg();
          } else { // 是引用，则根据参数值获取容器中的对象
            BeanDefinition refBeanDefinition = beanDefinitions.get(arg.getArg());
            if (refBeanDefinition == null) {
              throw new NoSuchBeanDefinitionException("Bean is not defined: " + arg.getArg());
            }
            argClasses[i] = Class.forName(refBeanDefinition.getClassName());
            argObjects[i] = createBean(refBeanDefinition);
          }
        }
        // 调用构造函数，实例化对象
        bean = beanClass.getConstructor(argClasses).newInstance(argObjects);
      }
    } catch (ClassNotFoundException | IllegalAccessException
            | InstantiationException | NoSuchMethodException | InvocationTargetException e) {
      throw new BeanCreationFailureException("", e);
    }

    if (bean != null && beanDefinition.isSingleton()) {
      singletonObjects.putIfAbsent(beanDefinition.getId(), bean);
      return singletonObjects.get(beanDefinition.getId());
    }
    return bean;
  }
}

 

来源：oschina

链接：https://my.oschina.net/u/3777515/blog/3167511