springboot的註解之@MapperScan("")分析掃描包流程

前言：其實一般不寫這樣的分析的，因爲學會了分析過程，就知道寫這樣的博客就感覺是在水一樣。但是這次呢一是爲了記錄下來分析過程，二是給大家分享一下@MapperScan註解掃描包的流程吧。

提出問題：@MapperScan("com.fast")掃描的是com.fast這個包下面的bean是毋庸置疑的，但是包括子包下面的bean嗎？

疑問案例：比如com.fast.master.dao,還有com.fast.second.dao這些包下面的bean是否會一起被掃描到？

開始分析：

1.查看MapperScan註解，掃描包的時候主要是這個@Import({MapperScannerRegistrar.class})

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
@Import({MapperScannerRegistrar.class})
@Repeatable(MapperScans.class)
public @interface MapperScan {
    String[] value() default {};

    String[] basePackages() default {};

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

    Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;

    Class<? extends Annotation> annotationClass() default Annotation.class;

    Class<?> markerInterface() default Class.class;

    String sqlSessionTemplateRef() default "";

    String sqlSessionFactoryRef() default "";

    Class<? extends MapperFactoryBean> factoryBean() default MapperFactoryBean.class;
}

2.找到MapperScannerRegistrar.class看實現過程，就不全貼了，主要是這個註解這一塊

    void registerBeanDefinitions(AnnotationAttributes annoAttrs, BeanDefinitionRegistry registry) {
        ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
        Optional var10000 = Optional.ofNullable(this.resourceLoader);
        Objects.requireNonNull(scanner);
        var10000.ifPresent(scanner::setResourceLoader);
        Class<? extends Annotation> annotationClass = annoAttrs.getClass("annotationClass");
        if (!Annotation.class.equals(annotationClass)) {
            scanner.setAnnotationClass(annotationClass);
        }

        Class<?> markerInterface = annoAttrs.getClass("markerInterface");
        if (!Class.class.equals(markerInterface)) {
            scanner.setMarkerInterface(markerInterface);
        }

        Class<? extends BeanNameGenerator> generatorClass = annoAttrs.getClass("nameGenerator");
        if (!BeanNameGenerator.class.equals(generatorClass)) {
            scanner.setBeanNameGenerator((BeanNameGenerator)BeanUtils.instantiateClass(generatorClass));
        }

        Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
        if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
            scanner.setMapperFactoryBeanClass(mapperFactoryBeanClass);
        }

        scanner.setSqlSessionTemplateBeanName(annoAttrs.getString("sqlSessionTemplateRef"));
        scanner.setSqlSessionFactoryBeanName(annoAttrs.getString("sqlSessionFactoryRef"));
        List<String> basePackages = new ArrayList();
        basePackages.addAll((Collection)Arrays.stream(annoAttrs.getStringArray("value")).filter(StringUtils::hasText).collect(Collectors.toList()));
        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();
        scanner.doScan(StringUtils.toStringArray(basePackages));
    }

這句周圍的是不是很熟悉，就是MapperScan實現的註解，value，basePackages，basePackageClasses這幾個

basePackages.addAll((Collection)Arrays.stream(annoAttrs.getStringArray("value")).filter(StringUtils::hasText).collect(Collectors.toList()));
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();
scanner.doScan(StringUtils.toStringArray(basePackages));

從scanner.doScan這句進去，這裏是開始掃描包的地方

3.打開調用的方法

private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
        Iterator var3 = beanDefinitions.iterator();

        while(var3.hasNext()) {
            BeanDefinitionHolder holder = (BeanDefinitionHolder)var3.next();
            GenericBeanDefinition definition = (GenericBeanDefinition)holder.getBeanDefinition();
            String beanClassName = definition.getBeanClassName();
            LOGGER.debug(() -> {
                return "Creating MapperFactoryBean with name '" + holder.getBeanName() + "' and '" + beanClassName + "' mapperInterface";
            });
            definition.getConstructorArgumentValues().addGenericArgumentValue(beanClassName);
            definition.setBeanClass(this.mapperFactoryBeanClass);
            definition.getPropertyValues().add("addToConfig", this.addToConfig);
            boolean explicitFactoryUsed = false;
            if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
                definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
                explicitFactoryUsed = true;
            } else if (this.sqlSessionFactory != null) {
                definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
                explicitFactoryUsed = true;
            }

            if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
                if (explicitFactoryUsed) {
                    LOGGER.warn(() -> {
                        return "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.";
                    });
                }

                definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
                explicitFactoryUsed = true;
            } else if (this.sqlSessionTemplate != null) {
                if (explicitFactoryUsed) {
                    LOGGER.warn(() -> {
                        return "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.";
                    });
                }

                definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
                explicitFactoryUsed = true;
            }

            if (!explicitFactoryUsed) {
                LOGGER.debug(() -> {
                    return "Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.";
                });
                definition.setAutowireMode(2);
            }
        }

    }

4.從這個方法第一行開始debug，這裏我使用@MapperScan("com.fast.framework.dao") 是掃描的com.fast.framework.dao包

這個是掃描到的包，說明會掃描到子包，perfect。解決了開始提出的問題。

總結：其實這裏的分析過程不是特別詳細，因爲到這裏是證明掃描出來的包，從而間接證明掃描到的包都會被使用。剩下的：上一步怎麼掃描的全部包，還有掃描到包怎麼初始化的都沒有詳細分析。所以也是小水一篇吧，主要是要明白@MapperScan註解會掃描包的子包和學會這種分析思路。