BeanFactory概述及使用方法

1.BeanFactory概述

Spring的本质是一个bean工厂(beanFactory)或者说bean容器，它按照我们的要求，生产我们需要的各种各样的bean，提供给我们使用。只是在生产bean的过程中，需要解决bean之间的依赖问题，才引入了依赖注入(DI)这种技术。也就是说依赖注入是beanFactory生产bean时为了解决bean之间的依赖的一种技术而已。那么我们为什么需要Spring框架来给我们提供这个beanFactory的功能呢？第一个原因是，我们可以将原来硬编码的对象依赖通过Spring这个beanFactory这个工厂来注入依赖，也就是说原来只有依赖方和被依赖方，现在我们引入了第三方spring这个beanFactory，由它来解决bean之间的依赖问题，达到了对象间松耦合的效果；还有一个更加重要的原因：在没有spring这个beanFactory之前，我们都是直接通过new来实例化各种对象，现在各种对象bean的生产都是通过beanFactory来实例化的，这样的话，spring这个beanFactory就可以在实例化bean的过程中，做一些小动作——在实例化bean的各个阶段进行一些额外的处理，也就是说beanFactory会在bean的生命周期的各个阶段中对bean进行各种管理，并且spring将这些阶段通过各种接口暴露给我们，让我们可以对bean进行各种处理，我们只要让bean实现对应的接口，那么spring就会在bean的生命周期调用我们实现的接口来处理该bean。下面我们看是如何实现这一点的。

bean容器的启动—bean在实例化之前，必须是在bean容器启动之后。所以就有了两个阶段：bean容器的启动阶段；容器中bean的实例化阶段；

在启动阶段，1>首先是读取bean的xml配置文件，然后解析xml文件中的各种bean的定义，将xml文件中的每一个元素分别转换成一个BeanDefinition对象，其中保存了从配置文件中读取到的该bean的各种信息：

public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccessor
  implements BeanDefinition, Cloneable {
 private volatile Object beanClass;
 private String scope = SCOPE_DEFAULT;
 private boolean abstractFlag = false;
 private boolean lazyInit = false;
 private int autowireMode = AUTOWIRE_NO;
 private int dependencyCheck = DEPENDENCY_CHECK_NONE;
 private String[] dependsOn;private ConstructorArgumentValues constructorArgumentValues;
 private MutablePropertyValues propertyValues;private String factoryBeanName;
 private String factoryMethodName;
 private String initMethodName;
 private String destroyMethodName;

beanClass保存bean的class属性，scop保存bean是否单例，abstractFlag保存该bean是否抽象，lazyInit保存是否延迟初始化，autowireMode保存是否自动装配，dependencyCheck保存是否坚持依赖，dependsOn保存该bean依赖于哪些bean(这些bean必须提取初始化)，constructorArgumentValues保存通过构造函数注入的依赖，propertyValues保存通过setter方法注入的依赖，factoryBeanName和factoryMethodName用于factorybean，也就是工厂类型的bean，initMethodName和destroyMethodName分别对应bean的init-method和destory-method属性，比如：

读完配置文件之后，得到了很多的BeanDefinition对象，2>然后通过BeanDefinitionRegistry将这些bean注册到beanFactory中：

public interface BeanDefinitionRegistry extends AliasRegistry {
 void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)throws BeanDefinitionStoreException;
 void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;
 BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;
 boolean containsBeanDefinition(String beanName);
 String[] getBeanDefinitionNames();
 int getBeanDefinitionCount();
 boolean isBeanNameInUse(String beanName);
}

BeanFactory的实现类，需要实现BeanDefinitionRegistry 接口：

@SuppressWarnings("serial")
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
  implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
 /** Map of bean definition objects, keyed by bean name */
 private final Map beanDefinitionMap = new ConcurrentHashMap(64);
 
 @Override
 public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
throws BeanDefinitionStoreException {
  // ... ...
 this.beanDefinitionMap.put(beanName, beanDefinition);
 // ... ...
 }

我们看到BeanDefinition被注册到了 DefaultListableBeanFactory， 保存在它的一个ConcurrentHashMap中。将BeanDefinition注册到了beanFactory之后，在这里Spring为我们提供了一个扩展的切口，允许我们通过实现接口BeanFactoryPostProcessor 在此处来插入我们定义的代码：

public interface BeanFactoryPostProcessor {
 /**
  * Modify the application context's internal bean factory after its standard
  * initialization. All bean definitions will have been loaded, but no beans
  * will have been instantiated yet. This allows for overriding or adding
  * properties even to eager-initializing beans.
  * @param beanFactory the bean factory used by the application context
  * @throws org.springframework.beans.BeansException in case of errors
  */
 void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
}

典型的例子就是：PropertyPlaceholderConfigurer，我们一般在配置数据库的dataSource时使用到的占位符的值，就是它注入进去的：

public abstract class PropertyResourceConfigurer extends PropertiesLoaderSupport
  implements BeanFactoryPostProcessor, PriorityOrdered {
 @Override
 public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
  try {
Properties mergedProps = mergeProperties();
// Convert the merged properties, if necessary.
convertProperties(mergedProps);
// Let the subclass process the properties.
processProperties(beanFactory, mergedProps);
  }
  catch (IOException ex) {
throw new BeanInitializationException("Could not load properties", ex);
  }
 }

processProperties(beanFactory, mergedProps);在子类中实现的，功能就是将

 ${jdbc_username}等等这些替换成实际值。

bean的实例化阶段。实例化阶段主要是通过反射或者CGLIB对bean进行实例化，在这个阶段Spring又给我们暴露了很多的扩展点：1>各种的Aware接口，比如 BeanFactoryAware，MessageSourceAware，ApplicationContextAware对于实现了这些Aware接口的bean，在实例化bean时Spring会帮我们注入对应的：BeanFactory， MessageSource，ApplicationContext的实例：

public interface BeanFactoryAware extends Aware {
 /**
  * Callback that supplies the owning factory to a bean instance.
  * 

Invoked after the population of normal bean properties * but before an initialization callback such as * {@link InitializingBean#afterPropertiesSet()} or a custom init-method. * @param beanFactory owning BeanFactory (never {@code null}). * The bean can immediately call methods on the factory. * @throws BeansException in case of initialization errors * @see BeanInitializationException */ void setBeanFactory(BeanFactory beanFactory) throws BeansException; }

public interface ApplicationContextAware extends Aware {
 /**
  * Set the ApplicationContext that this object runs in.
  * Normally this call will be used to initialize the object.
  * 

Invoked after population of normal bean properties but before an init callback such * as {@link org.springframework.beans.factory.InitializingBean#afterPropertiesSet()} * or a custom init-method. Invoked after {@link ResourceLoaderAware#setResourceLoader}, * {@link ApplicationEventPublisherAware#setApplicationEventPublisher} and * {@link MessageSourceAware}, if applicable. * @param applicationContext the ApplicationContext object to be used by this object * @throws ApplicationContextException in case of context initialization errors * @throws BeansException if thrown by application context methods * @see org.springframework.beans.factory.BeanInitializationException */ void setApplicationContext(ApplicationContext applicationContext) throws BeansException; }

public interface MessageSourceAware extends Aware {
 /**
  * Set the MessageSource that this object runs in.
  * 

Invoked after population of normal bean properties but before an init * callback like InitializingBean's afterPropertiesSet or a custom init-method. * Invoked before ApplicationContextAware's setApplicationContext. * @param messageSource message sourceto be used by this object */ void setMessageSource(MessageSource messageSource); }

2>BeanPostProcessor接口：实现了BeanPostProcessor接口的bean，在实例化bean时Spring会帮我们调用接口中的方法：

public interface BeanPostProcessor {
 /**
  * Apply this BeanPostProcessor to the given new bean instance before any bean
  * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
  * or a custom init-method). The bean will already be populated with property values.
  * The returned bean instance may be a wrapper around the original.*/
 Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
 /**
  * Apply this BeanPostProcessor to the given new bean instance after any bean
  * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
  * or a custom init-method). The bean will already be populated with property values.
  * The returned bean instance may be a wrapper around the original.*/
 Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
}

从注释中可以知道postProcessBeforeInitialization方法在InitializingBean接口的afterPropertiesSet方法之前执行，而postProcessAfterInitialization方法在InitializingBean接口的afterPropertiesSet方法之后执行。3>InitializingBean接口实现了InitializingBean接口的bean，在实例化bean时Spring会帮我们调用接口中的方法：

public interface InitializingBean {
 /**
  * Invoked by a BeanFactory after it has set all bean properties supplied
  * (and satisfied BeanFactoryAware and ApplicationContextAware).
  * 

This method allows the bean instance to perform initialization only * possible when all bean properties have been set and to throw an * exception in the event of misconfiguration. * @throws Exception in the event of misconfiguration (such * as failure to set an essential property) or if initialization fails. */ void afterPropertiesSet() throws Exception; }

4>DisposableBean接口：实现了BeanPostProcessor接口的bean，在该bean死亡时Spring会帮我们调用接口中的方法：

public interface DisposableBean {
 /**
  * Invoked by a BeanFactory on destruction of a singleton.
  * @throws Exception in case of shutdown errors.
  * Exceptions will get logged but not rethrown to allow
  * other beans to release their resources too.
  */
 void destroy() throws Exception;
}

InitializingBean接口 和 DisposableBean接口对应于 的 init-method 和 destory-method 属性，其经典的例子就是dataSource:所以在Spring初始化 dataSource 这个bean之后会调用 DruidDataSource.init 方法:

 public void init() throws SQLException {
  // ... ...try {
lock.lockInterruptibly();
  } catch (InterruptedException e) {
throw new SQLException("interrupt", e);
  }
  boolean init = false;
  try {  
connections = new DruidConnectionHolder[maxActive];
SQLException connectError = null;
try { 
 for (int i = 0, size = getInitialSize(); i < size; ++i) {
  Connection conn = createPhysicalConnection();
  DruidConnectionHolder holder = new DruidConnectionHolder(this, conn);
  connections[poolingCount++] = holder;
 }
 if (poolingCount > 0) {
  poolingPeak = poolingCount;
  poolingPeakTime = System.currentTimeMillis();
 }
} catch (SQLException ex) {
 LOG.error("init datasource error", ex);
 connectError = ex;
} 
  } catch (SQLException e) {
LOG.error("dataSource init error", e);
throw e;
  } catch (InterruptedException e) {
throw new SQLException(e.getMessage(), e);
  } finally {
inited = true;
lock.unlock();
  }
 }

基本就是初始化数据库连接池。

在dataSource 这个bean死亡时会调用 DruidDataSource.close()方法:

public void close() {
  lock.lock();
  try {
 for (int i = 0; i < poolingCount; ++i) {
 try {
  DruidConnectionHolder connHolder = connections[i];
  for (PreparedStatementHolder stmtHolder : connHolder.getStatementPool().getMap().values()) {
connHolder.getStatementPool().closeRemovedStatement(stmtHolder);
  }
  connHolder.getStatementPool().getMap().clear();
  Connection physicalConnection = connHolder.getConnection();
  physicalConnection.close();
  connections[i] = null;
  destroyCount.incrementAndGet();
 } catch (Exception ex) {
  LOG.warn("close connection error", ex);
 }
} 
  } finally {
lock.unlock();
  }
 }

基本就是关闭连接池中的连接。另外注解 @PostConstruct 和 @PreDestroy 也能达到InitializingBean接口和DisposableBean接口的效果。

2. 总结

spring容器接管了bean的实例化，不仅仅是通过依赖注入达到了松耦合的效果，同时给我们提供了各种的扩展接口，来在bean的生命周期的各个时期插入我们自己的代码：

BeanFactoryPostProcessor接口(在容器启动阶段)各种的Aware接口BeanPostProcessor接口InitializingBean接口(@PostConstruct， init-method)DisposableBean接口(@PreDestroy, destory-method)

3.FactoryBean接口

实现了FactoryBean接口的bean是一类叫做factory的bean。其特点是，spring会在使用getBean()调用获得该bean时，会自动调用该bean的getObject()方法，所以返回的不是factory这个bean，而是这个bean.getOjbect()方法的返回值：

public interface FactoryBean {
 T getObject() throws Exception;
 Class getObjectType();
 boolean isSingleton();
}

典型的例子有spring与mybatis的结合：

我们看上面该bean，因为实现了FactoryBean接口，所以返回的不是 SqlSessionFactoryBean 的实例，而是她的 SqlSessionFactoryBean.getObject() 的返回值：

public class SqlSessionFactoryBean implements FactoryBean, InitializingBean, ApplicationListener {

  private static final Log logger = LogFactory.getLog(SqlSessionFactoryBean.class);

  private Resource configLocation;

  private Resource[] mapperLocations;

  private DataSource dataSource;
  
  public SqlSessionFactory getObject() throws Exception {
 if (this.sqlSessionFactory == null) {
afterPropertiesSet();
 }

 return this.sqlSessionFactory;
  }

其实他是一个专门生产sqlSessionFactory的工厂，所以才叫 SqlSessionFactoryBean。 而SqlSessionFactory又是生产SqlSession的工厂。还有spring与ibatis的结合：

public class SqlMapClientFactoryBean implements FactoryBean, InitializingBean {
 private Resource[] configLocations;
 private Resource[] mappingLocations;
 private Properties sqlMapClientProperties;
 private DataSource dataSource;
 private boolean useTransactionAwareDataSource = true;
 private Class transactionConfigClass = ExternalTransactionConfig.class;
 private Properties transactionConfigProperties;
 private LobHandler lobHandler;
 private SqlMapClient sqlMapClient;
 public SqlMapClient getObject() {
  return this.sqlMapClient;
 }

SqlMapClientFactoryBean返回的是getObject()中返回的sqlMapClient,而不是SqlMapClientFactoryBean自己的实例。

4.依赖注入(DI)

1）依赖注入的方式分为接口注入、构造函数注入和setter方法注入：

构造函数注入使用：，，对于非简单参数，需要使用ref

setter方法注入使用, 非简单类型属性使用ref

2）集合等复杂类型的注入：

 
 
  
administrator@example.org
support@example.org
development@example.org
  
 
 
 
  
a list element followed by a reference

  
 
 
 
 
 
 
  
just some string

  
 

也很简单，list属性就是 里面包含或者或者, set也类似。map是

5. 元素可以配置的属性

除了 id 和 class 属性之外，还有一些可选的属性:

1)scope属性，默认 的 scope就是singleton="true", springmvc和struts2的重要区别之一就是spring的controll是单例的，而struts2的action是：scope="prototype" ，还有 scope="request" ， scope="session"，scope="globalSession"(仅用于portlet)；

2）abstract属性，是否是抽象的bean：

3）depends-on 依赖于某个bean，其必须先初始化：；

4）lazy-init="true" 是否延迟初始化，默认为 false；

5)dependency-check 是否对bean依赖的其它bean进行检查，默认值为 none，可取值有：none, simple, object, all等；

6）factory-method 和 factory-bean用于静态工厂和非静态工厂：

7）init-method, destory-method 指定bean初始化和死亡时调用的方法，常用于 dataSource的连接池的配置；

8)lookup-method 方法注入：

表示 mockPersister 有一个依赖属性 newsBean，该属性的每次注入都是通过调用newsBean.getNewsBean() 方法获得的。

9)autowire 是否启用自动装配依赖，默认为 no, 其它取值还有：byName, byType, constructor。