本文共 5055 字，大约阅读时间需要 16 分钟。

两者区别

• 共同点：BeanFactory 和 FactoryBean 两者都是接口

• package org.springframework.beans.factory;public interface FactoryBean
        
          {  String OBJECT_TYPE_ATTRIBUTE = "factoryBeanObjectType";  /**   * Return an instance (possibly shared or independent) of the object   * managed by this factory.   */  @Nullable  T getObject() throws Exception;  /**   * Return the type of object that this FactoryBean creates,   * or {@code null} if not known in advance.   */  @Nullable  Class
          getObjectType();  /**   * Is the object managed by this factory a singleton? That is,   * will {@link #getObject()} always return the same object   * (a reference that can be cached)?   */  default boolean isSingleton() {    return true;  }}
        

• package org.springframework.beans.factory;public interface BeanFactory {  String FACTORY_BEAN_PREFIX = "&";  // Return an instance, which may be shared or independent, of the specified bean.  Object getBean(String name) throws BeansException;  //  Return an instance, which may be shared or independent, of the specified bean.  
        
          T getBean(String name, Class
         
           requiredType) throws BeansException;  // Return an instance, which may be shared or independent, of the specified bean.  Object getBean(String name, Object... args) throws BeansException;  // Return the bean instance that uniquely matches the given object type, if any.  
          
            T getBean(Class
           
             requiredType) throws BeansException;  // Return an instance, which may be shared or independent, of the specified bean.  
            
              T getBean(Class
             
               requiredType, Object... args) throws BeansException; /** * Return a provider for the specified bean, allowing for lazy on-demand retrieval * of instances, including availability and uniqueness options. */ 
              
                ObjectProvider
               
                 getBeanProvider(Class
                
                  requiredType); /** * Return a provider for the specified bean, allowing for lazy on-demand retrieval * of instances, including availability and uniqueness options. */ 
                 
                   ObjectProvider
                  
                    getBeanProvider(ResolvableType requiredType); boolean containsBean(String name); boolean isSingleton(String name) throws NoSuchBeanDefinitionException; boolean isPrototype(String name) throws NoSuchBeanDefinitionException; /** * Check whether the bean with the given name matches the specified type. * More specifically, check whether a {@link #getBean} call for the given name * would return an object that is assignable to the specified target type. */ boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException; boolean isTypeMatch(String name, Class
                    typeToMatch) throws NoSuchBeanDefinitionException; /** * Determine the type of the bean with the given name. More specifically, * determine the type of object that {@link #getBean} would return for the given name. */ @Nullable Class
                    getType(String name) throws NoSuchBeanDefinitionException; /** * Determine the type of the bean with the given name. More specifically, * determine the type of object that {@link #getBean} would return for the given name. */ @Nullable Class
                    getType(String name, boolean allowFactoryBeanInit) throws NoSuchBeanDefinitionException; // Return the aliases for the given bean name, if any. String[] getAliases(String name);}
                  
                 
                
               
              
             
            
           
          
         
        

• 不同点：
  • BeanFactory：表示一个 Bean 的工厂，用来管理 Bean 的工厂，Spring中，所有的 Bean 都是由 BeanFactory 进行管理的，也就是 Ioc 容器。通过 getBean() 方法可以得到一个对象的 Bean。

  • BeanFactory beanFactory = new ClassPathXmlApplicationContext("xxx");beanFactory.getBean(xxx.class);

  • FactoryBean：它是一个 Bean，可以用于产生对象或者用于修饰对象的工厂 Bean。也就是说，一个类如果实现了 FactoryBean，那么这个类中存在两个对象，一个是 getObject() 方法返回的 Object(TempDaoFactoryBean)，另一个是当前对象 (DaoFactoryBean)。

  • public class TempDaoFactoryBean {    public void test() {        System.out.println("FactoryBean");    }}//----------------------------------------------@Component("daoFactoryBean")public class DaoFactoryBean implements FactoryBean {    @Override    public Object getObject() throws Exception {        return new TempDaoFactoryBean();    }    @Override    public Class
             getObjectType() {        return TempDaoFactoryBean.class;    }    @Override    public boolean isSingleton() {        return false;    }    public void testBean() {        System.out.println("testBean");    }}

  • 注意：getObject() 得到的对象存储的是当前类指定的名字，如果在调用 getBean() 时，在当前类 (DaoFactoryBean) 的前边加上字符 &，那么可以调用当前对象。

  • DaoFactoryBean daoFactoryBean = (DaoFactoryBean) context.getBean("&daoFactoryBean");daoFactoryBean.testBean();// 不加字符 &，只能调用指定的类TempDaoFactoryBean tempDaoFactoryBean = (TempDaoFactoryBean) context.getBean("daoFactoryBean");tempDaoFactoryBean.test();

使用场景

• BeanFactory：大部分情况我们只会用到 BeanFactory，直接调用 getBean() 方法就可以得到这个对象的实例，从而调用这个对象中的方法。

• FactoryBean：当一个类的依赖关系很复杂的时候,我们又想对外提供简单的配置关系(外部可以配置这个类)，可以使用 FactoryBean。

  • 例如：sqlSessionFactoryBean，这个类实现了 FactoryBean，我们不需要去维护 sqlSessionFactoryBean 类的依赖关系，把它交给 FactoryBean，我们只需要调用实现 FactoryBean 的这个类就能实现简单配置，从而可以使用这个类，平时我们配置 MyBatis 最简单的，就是只需要添加 MySQL 的 user、password、driverClass、jdbcUrl，其他的则不需要我们关心。

  • 

有兴趣的同学可以关注我的个人公众号，期待我们共同进步！！！

转载地址：http://hxzad.baihongyu.com/