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);
        }
    }
}