Spring学习笔记(2)实现 Bean 的定义、注册、获取

代码目录结构

small-spring-step-02
└── src
    ├── main
    │   └── java
    │       └── cn.bugstack.springframework.beans
    │           ├── factory
    │           │   ├── factory
    │           │   │   ├── BeanDefinition.java
    │           │   │   └── SingletonBeanRegistry.java
    │           │   ├── support
    │           │   │   ├── AbstractAutowireCapableBeanFactory.java
    │           │   │   ├── AbstractBeanFactory.java
    │           │   │   ├── BeanDefinitionRegistry.java
    │           │   │   ├── DefaultListableBeanFactory.java
    │           │   │   └── DefaultSingletonBeanRegistry.java
    │           │   └── BeanFactory.java
    │           └── BeansException.java
    └── test
        └── java
            └── cn.bugstack.springframework.test
                ├── bean
                │   └── UserService.java
                └── ApiTest.java

实现代码

BeansException异常类

public class BeansException extends RuntimeException {

  public BeansException(String msg) {
    super(msg);
  }

  public BeansException(String msg, Throwable cause) {
    super(msg, cause);
  }
}

BeanFactory工厂接口

public interface BeanFactory {

  Object getBean(String name) throws BeansException;

}

Bean的定义类

@SuppressWarnings({"rawtypes"})
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;
  }
}

单例注册接口定义和实现接口

public interface SingletonBeanRegistry {

  Object getSingleton(String beanName);
}

bean工厂的基类

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) throws BeansException;

  protected abstract Object createBean(String beanName, BeanDefinition beanDefinition) throws BeansException;

}

bean自动装配工厂的基类

public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFactory {

  @Override
  protected Object createBean(String beanName, BeanDefinition beanDefinition) throws BeansException {
    Object bean;
    try {
      bean = beanDefinition.getBeanClass().getDeclaredConstructor().newInstance();
    } catch (InstantiationException | IllegalAccessException | NoSuchMethodException | InvocationTargetException e) {
      throw new BeansException("Instantiation of bean failed", e);
    }

    addSingleton(beanName, bean);
    return bean;
  }
}

注册bean的接口

public interface BeanDefinitionRegistry {
  /**
   * 向注册表中注册 BeanDefinition
   *
   * @param beanName
   * @param beanDefinition
   */
  void registerBeanDefinition(String beanName, BeanDefinition beanDefinition);
}

bean的注册类

public class DefaultSingletonBeanRegistry implements SingletonBeanRegistry {

  private final Map<String, Object> singletonObjects = new HashMap<>();

  @Override
  public Object getSingleton(String beanName) {
    return singletonObjects.get(beanName);
  }

  protected void addSingleton(String beanName, Object singletonObject) {
    singletonObjects.put(beanName, singletonObject);
  }
}

bean工厂的核心实现类

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory implements BeanDefinitionRegistry {

  private final Map<String, BeanDefinition> beanDefinitionMap = new HashMap<>();

  @Override
  public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) {
    beanDefinitionMap.put(beanName, beanDefinition);
  }

  @Override
  public BeanDefinition getBeanDefinition(String beanName) throws BeansException {
    BeanDefinition beanDefinition = beanDefinitionMap.get(beanName);
    if (beanDefinition == null) throw new BeansException("No bean named '" + beanName + "' is defined");
    return beanDefinition;
  }

}

测试代码

UserService

public class UserService {
  public void queryUserInfo() {
    System.out.println("查询用户信息");
  }
}

ApiTest

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(UserService.class);
    beanFactory.registerBeanDefinition("userService", beanDefinition);

    // 3.第一次获取 bean
    UserService userService = (UserService) beanFactory.getBean("userService");
    userService.queryUserInfo();

    // 4.第二次获取 bean from Singleton
    UserService userService_singleton = (UserService) beanFactory.getSingleton("userService");
    userService_singleton.queryUserInfo();
  }
}

两次调用queryUserInfo成功.

原文地址：http://www.cnblogs.com/haoqirui/p/16890037.html