spring注入相关注解

　　本次主要整理四个注解 @ComponentScan、@Scope、@Conditional、@Import

1. @ComponentScan(value = "com.xiaoguo") 报扫描注解： 扫描该路径下的@controller @component @service 等等注解并将其交给spring容器管理。可以选择只扫描那些组件或是排除那些组件： includeFilters=Filter[]：指定只包含的组件
excludeFilters=Filter[]：指定需要排除的组件；

注解：

 @ComponentScan(value = "com.xiaoguo.annotation", excludeFilters = {
         @ComponentScan.Filter(type = FilterType.CUSTOM, classes = {MyTypeFilter.class})
 })

自定义过滤类：

 package com.xiaoguo.annotation.filter;

 import com.xiaoguo.annotation.beans.Car;
 import org.springframework.core.io.Resource;
 import org.springframework.core.type.AnnotationMetadata;
 import org.springframework.core.type.ClassMetadata;
 import org.springframework.core.type.classreading.MetadataReader;
 import org.springframework.core.type.classreading.MetadataReaderFactory;
 import org.springframework.core.type.filter.TypeFilter;

 import java.io.IOException;

 /**
  * @author xiaoguo
  * @date 2019-10-14 下午 9:11
  */
 public class MyTypeFilter implements TypeFilter {

     @Override
     public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
         //获取当前正在扫描的类的类信息
         ClassMetadata classMetadata = metadataReader.getClassMetadata();
         String className = classMetadata.getClassName();
         Class<?> forName = null;
         try {
             forName = Class.forName(className);
             if (Car.class.isAssignableFrom(forName)) {
                 // true就加载到IOC容器
                 return true;
             }
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         }
         return false;
     }
 }

2. @Scope("prototype") 此注解表示交给容器管理的对象为多例模式，不加默认为但例模式，加此注解每次从容器获取对象都是新new的对象。

3. @Conditional({WindowsCondition.class}) 按照一定的条件满足条件的则注册bean到容器中

注解：

 @Conditional({LinuxCondition.class})
     @Bean("linux")
     public Person person03() {
         return new Person("linux", 25);
     }

自定义条件类：

 package com.xiaoguo.annotation.condition;

 import org.springframework.context.annotation.Condition;
 import org.springframework.context.annotation.ConditionContext;
 import org.springframework.core.env.Environment;
 import org.springframework.core.type.AnnotatedTypeMetadata;

 /**
  * @author xiaoguo
  * @date 2019-10-11 下午 8:12
  */
 public class LinuxCondition implements Condition {

     @Override
     public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {

         //3.获取到当前环境信息
         Environment environment = context.getEnvironment();

         String property = environment.getProperty("os.name");
         if (property.contains("linux")) {
             //true 注入bean
             return true;
         }
         return false;
     }
 }

4. @Import({Car.class}) 快速将Car导入到spring容器中

ImportSelector 注册类到容器中:

 @Import({MyImportSelector.class})

 public class MyImportSelector implements ImportSelector {

     /**
      * 返回值就是导入容器中的组件全类名
      *
      * @param importingClassMetadata
      * @return
      */
     @Override
     public String[] selectImports(AnnotationMetadata importingClassMetadata) {
         return new String[]{"com.xiaoguo.annotation.beans.Red"};
     }
 }

ImportBeanDefinitionRegistrar与上同理:

 public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {

     /**
      *
      * @param importingClassMetadata 当前类的注解信息
      * @param registry BeanDefinition注册类
      */
     @Override
     public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
         boolean tf = registry.containsBeanDefinition("com.xiaoguo.annotation.beans.Red");
         if (tf) {
             RootBeanDefinition beanDefinition = new RootBeanDefinition(XiaoGuo.class);
             registry.registerBeanDefinition("xiaoguo", beanDefinition);
         }
     }
 }