Spring中BeanFactory与FactoryBean的区别
Spring中BeanFactory与FactoryBean的区别
为了搞明白这个问题，下载了spring源码在本地ide编译调试，debug进去一步步跟踪查看spring的启动流程，运行机制。
之前一直有在小破站看过spring源码的课程，但spring的源码还是太过强大，类库多，各种设计模式灵活运用，有时候一个小的方法跟进去就有好多相关的扩展代码，跟着跟着就偏离了原来的的代码逻辑，方法的调用链很深，幸好看过spring源码的课程讲解，对spring源码的整体启动流程和大体逻辑有所了解，不然看spring源码会懵逼，即便这样，在看debug跟spring源码到具体的一些细节的时候还是会略显吃力，总体来讲还是对spring底层的一些类库和设计的理解有限吧，大体上知道，具体细节到各个具体的类，就还需要再次看代码逻辑
至此，我们切入今天的主题Spring中BeanFactory 和FactoryBean的区别：
先谈谈我个人的理解：
1.这两个类 在spring中都是接口类，属性和方法如下：
2.由两个接口类的名字和方法可以看出
BeanFactory 是生产Bean实例的一个工厂(Factory),通过这个接口下的方法来获取spring IOC容器中的各种bean实例，在Spring中所有的Bean 都是由 BeanFactory来管理的
FactoryBean 是一个工厂Bean，实际上也是一个Bean 由BeanFactory 创建，只是这个FactoryBean 有点不一样，是一个能生产或修饰对象生成的工厂Bean
个人理解比较浅薄，来抄作业
在网上找找资料总结如下：
一、BeanFactory 接口
beanFactory 接口是spring容器的核心接口，负责：实例化，定位配置应用程序中的对象及建立这些对象间的依赖
spring 提供了多个易用的BeanFactory的实现, 在spring启动中常用的有DefaultListableBeanFactory, AbstractBeanFactory, AbstractAutoCapableBeanFactory
二、FactoryBean接口
FactoryBean 接口是spring的核心接口，用于编写增强一些逻辑复杂的bean，在bean创建时可以添加逻辑
public interface FactoryBean<T> {
/**
* 返回对象的实例
*/
T getObject() throws Exception;
/**
* 返回对象的类型
*/
Class<?> getObjectType();
/**
* 是否是单例
*/
boolean isSingleton();
}
简单实现
/**
* @author xiaolong.ge
* @since 08 五月 2022
*/
@Component
public class MyFactoryBean implements FactoryBean<UserService> {
@Override
public boolean isSingleton() {
return true;
}
@Override
public UserService getObject() throws Exception {
System.out.println("MyFactoryBean-->getObject()实例化。。。");
UserService userService = new UserServiceImpl();
return userService;
}
@Override
public Class<?> getObjectType() {
return UserService.class;
}
}
public class AppTest {
public static void main(String[] args) throws Exception {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(App.class);
UserService us = (UserService)context.getBean("myFactoryBean");
System.out.println(us);
MyFactoryBean myFactoryBean = (MyFactoryBean)context.getBean("&myFactoryBean");
UserService us2 = myFactoryBean.getObject();
System.out.println(us2);
System.out.println(us == us2);
}
// 输出结果:
MyFactoryBean-->getObject()实例化。。。
com.gexl.service.impl.UserServiceImpl@1440c311
MyFactoryBean-->getObject()实例化。。。
com.gexl.service.impl.UserServiceImpl@189b5fb1
false
增强实现
/**
* @author xiaolong.ge
* @since 08 五月 2022
*/
@Component
public class MyFactoryBean implements FactoryBean<UserService>, InitializingBean, DisposableBean {
private Object proxyObject;
private Object target;
private String interfaceName;
public MyFactoryBean() {
this.interfaceName = UserService.class.getName();
this.target = new UserServiceImpl();
}
@Override
public UserService getObject() throws Exception {
return (UserService) proxyObject;
}
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("myFactoryBean afterPropertiesSet..");
proxyObject = Proxy.newProxyInstance(this.getClass().getClassLoader(), new Class[]{Class.forName(interfaceName)}, new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("方法调用之前增强。。。method="+method.getName());
Object obj = method.invoke(target,args);
System.out.println("方法调用之后增强。。。method="+method.getName());
return obj;
}
});
}
@Override
public Class<?> getObjectType() {
return proxyObject == null ? Object.class : proxyObject.getClass();
}
@Override
public boolean isSingleton() {
return true;
}
@Override
public void destroy() throws Exception {
System.out.println("destory...");
}
public Object getTarget() {
return target;
}
public void setTarget(Object target) {
this.target = target;
}
public String getInterfaceName() {
return interfaceName;
}
public void setInterfaceName(String interfaceName) {
this.interfaceName = interfaceName;
}
}
public class AppTest {
@Test
public void testFactoryBean() throws Exception {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(App.class);
MyFactoryBean myFactoryBean = (MyFactoryBean) context.getBean("&myFactoryBean");
System.out.println("myFactoryBean="+myFactoryBean);
UserService userService = myFactoryBean.getObject();
System.out.println("userService="+userService);
UserServiceImpl targetService = (UserServiceImpl)myFactoryBean.getTarget();
String beanName = "userDao";
UserDao userDao = (UserDao)context.getBean(beanName);
Field field = targetService.getClass().getDeclaredField(beanName);
field.setAccessible(true);
field.set(targetService,userDao);
// 调用方法
userService.getById(1);
}
}
// 输出结果：
myFactoryBean afterPropertiesSet..
myFactoryBean=com.gexl.service.impl.MyFactoryBean@65bb9029
方法调用之前增强。。。method=toString
方法调用之后增强。。。method=toString
userService=com.gexl.service.impl.UserServiceImpl@1bfe3203
方法调用之前增强。。。method=getById
方法调用之后增强。。。method=getById
应用实例
Spring在整合mybatis框架时 SqlSessionFactoryBean 就是应用的FactoryBean
Spring会调用SqlSessionFactoryBean这个实现了FactoryBean的工厂Bean 同时加载dataSource,Mapper文件的路径,对sqlSessionFactory进行初始化。
public class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>, InitializingBean, ApplicationListener<ApplicationEvent> {
.....
@Override
public void afterPropertiesSet() throws Exception {
notNull(dataSource, "Property 'dataSource' is required");
notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
"Property 'configuration' and 'configLocation' can not specified with together");
// 创建 sqlSessionFactory
this.sqlSessionFactory = buildSqlSessionFactory();
}
/**
* Build a {@code SqlSessionFactory} instance.
*
* The default implementation uses the standard MyBatis {@code XMLConfigBuilder} API to build a
* {@code SqlSessionFactory} instance based on an Reader.
* Since 1.3.0, it can be specified a {@link Configuration} instance directly(without config file).
*
* @return SqlSessionFactory
* @throws Exception if configuration is failed
*/
protected SqlSessionFactory buildSqlSessionFactory() throws Exception {
final Configuration targetConfiguration;
XMLConfigBuilder xmlConfigBuilder = null;
if (this.configuration != null) {
targetConfiguration = this.configuration;
if (targetConfiguration.getVariables() == null) {
targetConfiguration.setVariables(this.configurationProperties);
} else if (this.configurationProperties != null) {
targetConfiguration.getVariables().putAll(this.configurationProperties);
}
} else if (this.configLocation != null) {
xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
targetConfiguration = xmlConfigBuilder.getConfiguration();
} else {
LOGGER.debug(() -> "Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration");
targetConfiguration = new Configuration();
Optional.ofNullable(this.configurationProperties).ifPresent(targetConfiguration::setVariables);
}
... 省略
Optional.ofNullable(this.cache).ifPresent(targetConfiguration::addCache);
... 省略
if (this.mapperLocations != null) {
if (this.mapperLocations.length == 0) {
LOGGER.warn(() -> "Property 'mapperLocations' was specified but matching resources are not found.");
} else {
for (Resource mapperLocation : this.mapperLocations) {
if (mapperLocation == null) {
continue;
}
try {
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
xmlMapperBuilder.parse();
} catch (Exception e) {
throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
} finally {
ErrorContext.instance().reset();
}
LOGGER.debug(() -> "Parsed mapper file: '" + mapperLocation + "'");
}
}
} else {
LOGGER.debug(() -> "Property 'mapperLocations' was not specified.");
}
return this.sqlSessionFactoryBuilder.build(targetConfiguration);
}
...
}
三、总结
BeanFactory是Spring中IOC容器最核心的接口，遵循了IOC容器中所需的基本接口。比如：ApplicationContext, AbstractBeanFactory等 都使用了BeanFactory接口。
FactoryBean是工厂类接口，只想简单构造Bean，不希望实现原有大量的方法。它是一个Bean，不过这个Bean能够做为工厂去创建Bean, 同时还能修饰对象的生成
FactoryBean比BeanFactory在生产Bean的时候灵活，还能修饰对象，带有工厂模式和装饰模式的意思在里面，不过它的存在还是以Bean的形式存在