平时开发我们可以使用 Autowired，Resource 注入 spring 容器。
如何使用编程的方式将一个 bean 注入spring 容器 ？

1.set 方法注入

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2.构造方法注入

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3.指定构造方法参数顺序注入

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4.通过 BeanDefinitionBuilder 注入

1.定义一个基础配置类

  1. public class DataSourceConfig {
  3.     private String dataSourceName;
  5.     private String url;
  7.     private String password;
  9.     public String getDataSourceName() {
  10.         return dataSourceName;
  11.     }
  13.     public void setDataSourceName(String dataSourceName) {
  14.         this.dataSourceName = dataSourceName;
  15.     }
  17.     public String getUrl() {
  18.         return url;
  19.     }
  21.     public void setUrl(String url) {
  22.         this.url = url;
  23.     }
  25.     public String getPassword() {
  26.         return password;
  27.     }
  29.     public void setPassword(String password) {
  30.         this.password = password;
  31.     }
  32. }

2.注入spring容器

  1. @SpringBootTest
  2. @RunWith(SpringRunner.class)
  3. public class DatasourceTest {
  5.     @Autowired
  6.     private ApplicationContext applicationContext;
  8.     @Test
  9.     public void testInject() {
  10.         BeanDefinitionBuilder beanDefinitionBuilder = BeanDefinitionBuilder.genericBeanDefinition(DataSourceConfig.class);
  11.         beanDefinitionBuilder.addPropertyValue("dataSourceName", "busi");
  12.         beanDefinitionBuilder.addPropertyValue("url", "xxx");
  13.         beanDefinitionBuilder.addPropertyValue("password", "123456");
  14.         DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory) applicationContext.getAutowireCapableBeanFactory();
  15.         beanFactory.registerBeanDefinition("busiDatasourceConfig", beanDefinitionBuilder.getBeanDefinition());
  16.         Assert.assertNotNull(applicationContext.getBean(DataSourceConfig.class));
  17.         Assert.assertEquals(applicationContext.getBean(DataSourceConfig.class).getDataSourceName(), "busi");
  18.         Assert.assertEquals(applicationContext.getBean(DataSourceConfig.class).getPassword(), "123456");
  19.         Assert.assertEquals(applicationContext.getBean(DataSourceConfig.class).getUrl(), "xxx");
  20.     }
  22. }

5.ObjectProvider

实现宽松的依赖注入，当 spring 容器没有该 Bean 时也不会报错。
什么时候使用ObjectProvider接口？
如果待注入参数的Bean为空或有多个时，便是ObjectProvider发挥作用的时候了。
如果注入实例为空时，使用ObjectProvider则避免了强依赖导致的依赖对象不存在异常；如果有多个实例，ObjectProvider的方法会根据Bean实现的Ordered接口或@Order注解指定的先后顺序获取一个Bean。从而了提供了一个更加宽松的依赖注入方式。

  1. /**
  2.  * A variant of {@link ObjectFactory} designed specifically for injection points,
  3.  * allowing for programmatic optionality and lenient not-unique handling.
  4.  *
  5.  * @author Juergen Hoeller
  6.  * @since 4.3
  7.  */
  8. public interface ObjectProvider<T> extends ObjectFactory<T> {
  10.     /**
  11.      * Return an instance (possibly shared or independent) of the object
  12.      * managed by this factory.
  13.      * <p>Allows for specifying explicit construction arguments, along the
  14.      * lines of {@link BeanFactory#getBean(String, Object...)}.
  15.      * @param args arguments to use when creating a corresponding instance
  16.      * @return an instance of the bean
  17.      * @throws BeansException in case of creation errors
  18.      * @see #getObject()
  19.      */
  20.     T getObject(Object... args) throws BeansException;
  22. }