开启掘金成长之旅！这是我参与「掘金日新计划 · 12 月更文挑战」的第18天，点击查看活动详情
通过 Spring Bean 容器创建 Bean 对象，而不是在调用时传递一个完成了实例化的Bean对象。单例对象在二次获取对象时，可以从内存中获取。
完善容器设计
在注册对象时，只注册一个类信息，而不是直接实例化，然后在获取Bean对象时再实例化，顺便加个判断当前单例对象是否缓存。
通过使用模版模式，可以统一使用核心方法的调用逻辑和标准定义。
完善容器实现
在Bean对象定义中 Object 替换成 Class。这样可以将Bean对象的实例化放到容器中处理。
Bean 对象的实例化是在初始化调用阶段由 BeanDefinition 构造函数完成。
代码实现
BeansException - 定义 Bean 异常
public class BeansException extends RuntimeException{
public BeansException(String msg) {
super(msg);
}
public BeansException(String msg, Throwable cause) {
super(msg, cause);
}
}
BeanDefinitionRegistry - Bean 定义注册接口
public interface BeanDefinitionRegistry {
/**
* @Author: Take-off
* @Description: //TODO 向注册表中注册 BeanDefinition
* @Date: 10:16 AM 2022/12/12
* @Param: [beanName, beanDefinition]
* @return: void
**/
void registerBeanDefinition(String beanName, BeanDefinition beanDefinition);
}
BeanFactory - 工厂：获取Bean
public interface BeanFactory {
/**
* @Author: Take-off
* @Description: //TODO 返回Bean 的实例对象
* @Date: 10:01 AM 2022/12/12
* @Param: [name]
* @return: java.lang.Object
**/
Object getBean(String name) throws BeansException;
}
SingletonBeanRegistry - 单例Bean 注册表
public interface SingletonBeanRegistry {
/**
* @Author: Take-off
* @Description: //TODO 根据名字获取单例对象
* @Date: 10:03 AM 2022/12/12
* @Param: [beanName]
* @return: java.lang.Object
**/
Object getSingleton(String beanName);
/**
* @Author: Take-off
* @Description: //TODO 注册单例对象
* @Date: 10:03 AM 2022/12/12
* @Param: [beanName, singletonObject]
* @return: void
**/
void registerSingleton(String beanName, Object singletonObject);
}
BeanDefinition - Bean 的定义信息
public class BeanDefinition {
private Class beanClass;
public BeanDefinition(Class beanClass) {
this.beanClass = beanClass;
}
public Class getBeanClass() {
return beanClass;
}
public void setBeanClass(Class beanClass) {
this.beanClass = beanClass;
}
}
DefaultSingletonBeanRegistry - 通用注册表实现
public class DefaultSingletonBeanRegistry implements SingletonBeanRegistry {
private Map<String, Object> singletonObjects = new HashMap<>();
@Override
public Object getSingleton(String beanName) {
return singletonObjects.get(beanName);
}
@Override
public void registerSingleton(String beanName, Object singletonObject) {
singletonObjects.put(beanName,singletonObject);
}
}
DefaultSingletonBeanRegistry - 通用注册表实现
public class DefaultSingletonBeanRegistry implements SingletonBeanRegistry {
private Map<String, Object> singletonObjects = new HashMap<>();
@Override
public Object getSingleton(String beanName) {
return singletonObjects.get(beanName);
}
@Override
public void registerSingleton(String beanName, Object singletonObject) {
singletonObjects.put(beanName,singletonObject);
}
}
AbstractBeanFactory - 抽象的 Bean 工厂基类，定义模板方法
public abstract class AbstractBeanFactory extends DefaultSingletonBeanRegistry implements BeanFactory {
@Override
public Object getBean(String name) throws BeansException {
Object bean = getSingleton(name);
if (bean != null) {
return bean;
}
BeanDefinition beanDefinition = getBeanDefinition(name);
return createBean(name, beanDefinition);
}
protected abstract BeanDefinition getBeanDefinition(String beanName);
protected abstract Object createBean(String beanName, BeanDefinition beanDefinition);
}
AbstractAutowireCapableBeanFactory - 实现默认bean创建的抽象bean工厂超类
public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory{
@Override
protected Object createBean(String beanName, BeanDefinition beanDefinition) throws BeansException {
Object bean = null;
try {
bean = beanDefinition.getBeanClass().newInstance();
} catch (InstantiationException | IllegalAccessException e) {
throw new BeansException("Instantiation of bean failed", e);
}
registerSingleton(beanName, bean);
return bean;
}
}
DefaultListableBeanFactory - 默认的Bean工厂实现类
public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory implements BeanDefinitionRegistry{
private Map<String, BeanDefinition> beanDefinitionMap = new HashMap<>();
@Override
protected BeanDefinition getBeanDefinition(String beanName) {
BeanDefinition beanDefinition = beanDefinitionMap.get(beanName);
if (beanDefinition == null) throw new BeansException("No bean named '" + beanName + "' is defined");
return beanDefinition;
}
@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) {
beanDefinitionMap.put(beanName, beanDefinition);
}
}
测试类 ：
public class ApiTest {
@Test
public void test_BeanFactory(){
// 1.初始化 BeanFactory
DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
// 2.注册 bean
BeanDefinition beanDefinition = new BeanDefinition(User.class);
beanFactory.registerBeanDefinition("user", beanDefinition);
// 3.第一次获取 bean
User userService = (User) beanFactory.getBean("user");
userService.queryUserInfo();
// 4.第二次获取 bean from Singleton
User userService_singleton = (User) beanFactory.getBean("user");
userService_singleton.queryUserInfo();
}
}
public class User {
public void queryUserInfo(){
System.out.println("查询用户信息");
}
}
总结
开始重点关注类之间的职责和关系。所有的接口功能设计都离不开接口、抽象类的实现和继承
