SpringBoot如何动态创建Bean示例代码

package com.spring.configuration; 
 
import org.springframework.beans.factory.annotation.Autowired; 
import org.springframework.beans.factory.support.BeanDefinitionBuilder; 
import org.springframework.beans.factory.support.DefaultListableBeanFactory; 
import org.springframework.boot.autoconfigure.condition.ConditionalOnExpression; 
import org.springframework.context.ApplicationContext; 
import org.springframework.context.ConfigurableApplicationContext; 
import org.springframework.context.annotation.Bean; 
import org.springframework.context.annotation.Configuration; 
import org.springframework.jdbc.core.JdbcTemplate; 
 
@Configuration 
/** 
 * 这里的conditional是一个可选条件，表示当这个表达式为true的时候，才动态创建bean 
 */ 
@ConditionalOnExpression("${my.configuration.enabled}") 
public class DynamicConfiguration 
{ 
 @Autowired 
 private ApplicationContext applicationContext; 
  
 /** 
  * 这个方法返回Runnable只是一个幌子，最重要的是执行方法里面的代码 
  */ 
 @Bean 
 public Runnable dynamicConfiguration() throws Exception 
 { 
  ConfigurableApplicationContext cOntext= (ConfigurableApplicationContext)applicationContext; 
  DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory)context.getBeanFactory(); 
   
  BeanDefinitionBuilder beanDefinitiOnBuilder= BeanDefinitionBuilder.rootBeanDefinition(UserService.class); 
  /** 
   * 设置属性 
   */ 
  beanDefinitionBuilder.addPropertyValue("name", "myConfigure"); 
  beanDefinitionBuilder.addPropertyValue("jdbcTemplate", applicationContext.getBean(JdbcTemplate.class)); 
   
  /** 
   * 注册到spring容器中 
   */ 
  beanFactory.registerBeanDefinition("userService", beanDefinitionBuilder.getBeanDefinition()); 
  return null; 
 } 
} 
class UserService 
{ 
 private String name; 
 private JdbcTemplate jdbcTemplate; 
 public String getName() 
 { 
  return name; 
 } 
 public void setName(String name) 
 { 
  this.name = name; 
 } 
 public JdbcTemplate getJdbcTemplate() 
 { 
  return jdbcTemplate; 
 } 
 public void setJdbcTemplate(JdbcTemplate jdbcTemplate) 
 { 
  this.jdbcTemplate = jdbcTemplate; 
 } 
} 

applicationContext.getBean(UserService.class);
applicationContext.getBean("userService", UserService.class)