SpringBoot實現自定義包掃描

最近很好奇在SpringBoot項目上加@MapperScan(basePackages = "xxx") 註解就能掃描到執行的包下面的東西。於是研究了一下Mybatis怎麼實現的。大致是根據Mybatis依葫蘆畫瓢

於是點開@MapperScan類,看到類結構如下:


@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
@Import({MapperScannerRegistrar.class})  //MapperScannerRegistrar這個類纔是真正的註冊邏輯
@Repeatable(MapperScans.class)
public @interface MapperScan {
    String[] value() default {};

    String[] basePackages() default {};

    Class<?>[] basePackageClasses() default {};
	
    ...
}

然後點開MapperScannerRegistrar,看一下類結構


//當使用@Import標籤,實現ImportBeanDefinitionRegistrar 接口,那麼可以自定義擴展beanDefinition
public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {
    
    //資源加載器
    private ResourceLoader resourceLoader;


    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }

    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        //從啓動類上面獲取MapperScan註解
        AnnotationAttributes mapperScanAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
        if (mapperScanAttrs != null) {
            //存在的話那麼註冊自己的BeanDefinitions
            this.registerBeanDefinitions(mapperScanAttrs, registry);
        }

    }

    //已將不重要的內容刪除
    void registerBeanDefinitions(AnnotationAttributes annoAttrs, BeanDefinitionRegistry registry) {
        //自定義註解掃描器
        ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);

        Class<? extends BeanNameGenerator> generatorClass = annoAttrs.getClass("nameGenerator");
        if (!BeanNameGenerator.class.equals(generatorClass)) {
           //這裏是對應處理bean scanner.setBeanNameGenerator((BeanNameGenerator)BeanUtils.instantiateClass(generatorClass));
        }
       //獲取註解basePackages value   basePackages.addAll((Collection)Arrays.stream(annoAttrs.getStringArray("basePackages")).filter(StringUtils::hasText).collect(Collectors.toList()));
        basePackages.addAll((Collection)Arrays.stream(annoAttrs.getClassArray("basePackageClasses")).map(ClassUtils::getPackageName).collect(Collectors.toList()));
        scanner.registerFilters();
        //獲取到包,開始進行掃描, 
        scanner.doScan(StringUtils.toStringArray(basePackages));
    }
}

這裏是doScan的邏輯,Spring的代碼中,一般已do開頭的都是具體做事情的,這裏返回掃描包下面的的beanDefinitions集合,如果存在的話,那麼會調用對應的BeanNameGenerator 方法,對應上面scanner.setBeanNameGenerator

    public Set<BeanDefinitionHolder> doScan(String... basePackages) {
        Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
        return beanDefinitions;
    }

大概思路瞭解了,那我們也整一個

定義啓動類需要配置的掃描註解


import org.springframework.context.annotation.Import;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * ClassName: MyAOP
 * @Description:
 * @author leegoo
 * @date 2020年03月14日
 */
@Retention(RetentionPolicy.RUNTIME)//注意用這個註解才能在運行時使用反射
@Target({ElementType.TYPE})
@Documented
@Import({CustomerScanRegister.class})
public @interface CustomerScan {
    //掃描包路徑
    String[] basePackages() default {};
    //掃描類
    Class<?>[] basePackageClasses() default {};
}

定義CustomerScanRegister以及實現


import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.context.ResourceLoaderAware;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.lang.NonNull;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;


public class CustomerScanRegister implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, BeanFactoryAware {
    private ResourceLoader resourceLoader;

    private BeanFactory beanFactory;

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = beanFactory;
    }

    @Override
    public void setResourceLoader(@NonNull ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,@NonNull BeanDefinitionRegistry registry) {
        //這裏是獲取cn.withmes.springboot.my.aop.SpringBootMyAopApplication類上對應的註解
        //MergedAnnotations annotations = importingClassMetadata.getAnnotations();
        //這裏判斷是否存在MyAOP註解
        AnnotationAttributes mapperScanAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(CustomerScan.class.getName()));
        if (mapperScanAttrs == null)  return;

        this.registerBeanDefinitions(mapperScanAttrs, registry);
    }


    private  Set<BeanDefinitionHolder> registerBeanDefinitions(AnnotationAttributes annoAttrs, BeanDefinitionRegistry registry) {
        List<String> basePackages = new ArrayList<>();
        //取到所有屬性的值
        basePackages.addAll(Arrays.stream(annoAttrs.getStringArray("basePackages")).filter(StringUtils::hasText).collect(Collectors.toList()));
        basePackages.addAll(Arrays.stream(annoAttrs.getClassArray("basePackageClasses")).map(ClassUtils::getPackageName).collect(Collectors.toList()));
        CustomerScanner scanner = new CustomerScanner(registry);
        scanner.setBeanNameGenerator(( beanDefinition,beanDefinitionRegistry)->{
            String beanClassName = beanDefinition.getBeanClassName();
            try {
                Class<?> clz = Class.forName(beanClassName);
                MyService at = clz.getAnnotation(MyService.class);
                if (null == at) return null;
                //如果@MyService沒有指定名字,那麼默認首字母小寫進行註冊
                if (at.name().equalsIgnoreCase("")  ) {
                    String clzSimpleName = clz.getSimpleName();
                    String first = String.valueOf(clzSimpleName.charAt(0));
                    return clzSimpleName.replaceFirst(first,first.toLowerCase());
                }
                return at.name();
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
                return null;
            }
        });
        if(resourceLoader != null){
            scanner.setResourceLoader(resourceLoader);
        }
        
        return scanner.doScan(StringUtils.toStringArray(basePackages));
    }

自定義掃描器


import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.context.annotation.ClassPathBeanDefinitionScanner;
import org.springframework.core.type.filter.AnnotationTypeFilter;

import java.util.Set;


public class CustomerScanner extends ClassPathBeanDefinitionScanner {

    public CustomerScanner(BeanDefinitionRegistry registry) {
        super(registry, false);
    }

    @Override
    public Set<BeanDefinitionHolder> doScan(String... basePackages) {
        //添加過濾條件，這裏是只添加了@MyService的註解纔會被掃描到
        addIncludeFilter(new AnnotationTypeFilter(MyService.class));
        return super.doScan(basePackages);
    }

}

寫一個接口和兩個實現類,試下不同的方式注入(這裏把所有類的代碼放在一起了)


public interface UserService {
    User findUser(Integer id) ;
}


@MyService // 使用自定義註解,注入spring容器
public class UserServiceImpl implements UserService {

    @Resource
    private Data data;

    @Override
    public User findUser(Integer id)  {
        return data.users.get(id);
    }

}

@MyService(name = "lsUser") // 使用自定義註解,注入spring容器
public class UserServiceImpl2 implements UserService {

    @Resource
    private Data data;

    @Override
    public User findUser(Integer id)  {
        return data.users.get(id);
    }

}


//實現CommandLineRunner,應用初始化後,去執行一段代碼塊邏輯,這段初始化代碼在整個應用生命週期內只會執行一次
@Service
public class Data  implements CommandLineRunner {
    public Map<Integer, User> users = new HashMap<>(

    );


    @Override
    public void run(String... args) throws Exception {
        users.put(1, new User(1, "小紅"));
        users.put(2, new User(2, "小明"));
        users.put(3, new User(3, "小三"));
        System.out.println("初始化數據:"+users);
    }

    public User getUsers(Integer id) {
        return users.get(id);
    }

}

開始測試

@SpringBootTest
class SpringBootMyAopApplicationTests {

    //這裏userServiceImpl 會報紅,但是還是能夠執行,因爲我們沒有使用spring註解進行Bean注入,所以會提示我們可能找不到bean
    @Resource(name = "userServiceImpl")
    private UserService  userService;

    @Resource(name = "lsUser")
    private UserService  lsUser;

    @Test
    void testCustomerAnnotation() {
        User user = userService.findUser(1);
        System.out.println("user:"+user); //user:User{id=1, name='小紅'}
        User ls = lsUser.findUser(2);
        System.out.println("ls:"+ls);//ls:User{id=2, name='小明'}
    }

}

代碼已上傳github(github主頁:https://github.com/q920447939/java-study)

SpringBoot實現自定義包掃描

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