Spring Boot 自动装配
在 Spring Boot 场景下，基于约定大于配置的原则，实现 Spring 组件自动装配的目的。
底层装配技术 ：
Spring 模式注解装配 @Configuration
Spring 模块装配 @Enable
Spring 条件装配装配 @Conditional
Spring 工厂加载机制
SpringBoot自动装配的实现类： SpringFactoriesLoader.class
相关配置资源目录和文件： META-INF/spring.factories
自动装配实现例子：
实现HelloWorld自动装配
实现方法：
1）激活自动装配 @EnableAutoConfiguration
2）实现自动装配 – XXXAutoConfiguration
3）配置自动装配实现 – META-INF/spring.factories
# @Enable 模块加载流程： @EnableHelloWorld -> HelloWorldImportSelector -> HelloWorldConfiguration – > helloWorld
项目结构展示：
代码实现：
SpringBootApplication.class
@EnableAutoConfiguration
public class SpringBootApplication {
public static void main(String[] args) {
ConfigurableApplicationContext context = new SpringApplicationBuilder(SpringBootApplication.class)
.web(WebApplicationType.NONE)
.run(args);
String helloWorld = context.getBean("helloWorld", String.class);
System.out.println(helloWorld);
}
}HelloWorldAutoConfiguration .class
@Configuration
@EnableHelloWorld
@SystemPropertiesConditional(name = "name",value = "77")
public class HelloWorldAutoConfiguration {
}@interface EnableHelloWorld
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(HelloWorldImportSelector.class)
public @interface EnableHelloWorld {
}HelloWorldImportSelector.class
public class HelloWorldImportSelector implements ImportSelector {
@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
System.out.println("******进入selector 选择满足的Configuration!!");
return new String[]{HelloWorldConfiguration.class.getName()};
}
}HelloWorldConfiguration.class
@Configuration
public class HelloWorldConfiguration {
@Bean
public String helloWorld(){
return "helloWorldConfiguration";
}
}@interface SystemPropertiesConditional
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnSystemPropertiesCondition.class)
public @interface SystemPropertiesConditional {
String name();
String value();
}OnSystemPropertiesCondition.class
public class OnSystemPropertiesCondition implements Condition {
@Override
public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) {
MultiValueMap<String, Object> allAnnotationAttributes = annotatedTypeMetadata.getAllAnnotationAttributes(SystemPropertiesConditional.class.getName());
String name = String.valueOf(allAnnotationAttributes.get("name"));
String value = String.valueOf(allAnnotationAttributes.get("value"));
System.out.println("条件判断" + name +" "+ value);
System.out.println("****条件满足--启用此AutoConfiguration");
return true;
}
}
spring.factories
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
cn.edu.mju.driver.configuration.HelloWorldAutoConfiguration
启动SpirngBootApplication显示结果：
Git下载：https://github.com/xiezengcheng/dirver