Spring实战系列（四）-动态注入接口Bean

小鱼儿 2022-05-22 23:57 468阅读 1赞

"对于Spring框架，现实公司使用的非常广泛，但是由于业务的复杂程度不同，了解到很多小伙伴们利用Spring开发仅仅是利用了Spring的IOC，即使是AOP也很少用，但是目前的Spring是一个大家族，形成了一个很大的生态，覆盖了我们平时开发的方方面面，抛开特殊的苛刻要求之外，Spring的生态其实已经很全面了，所以在此开个系列来研究下Spring提供给我们的一些平时不太却又很实用的内容。"

上一篇我们分析了BeanPostProcessor的基本使用，接下来我们分析下如何使用该类实现动态的接口注入，示例说明：在BeetlSQL框架中，在使用自动扫描注入时，我们通常只需要配置上要扫描的包路径，然后在该路径下声明对应的Dao接口类，这些接口类都默认继承BaseMapper接口类，然后我们在使用这些Dao类的时候，直接根据类型注入（@Autowired）即可使用，这个其实和Mybatis的那一套相似，也和Spring自身的Spring-data框架也类似。这个经常用于框架的开发，那么我就该部分的实现做相应的解释，这三个框架具体实现可能有差距，感兴趣的小伙伴自行去查看源码，我会以一个很简单的例子来讲解大概的实现逻辑。

问题描述：

继承Spring框架，实现声明某个自定义接口（UserMapper）,改接口继承通用接口BaseMapper，（通用接口BaseMapper有默认的实现类），实现通过类型注入UserMapper类，然后通过Spring框架的上下文类（ApplicationContext实现类）的getBean（）方法拿到UserMapper类来调用内部提供的方法。

1、声明BaseMapper接口类

public interface BaseMapper {
    
        /**
         * @param value
         */
        public void add(String value);
    
        /**
         * @param key
         */
        public void remove(String key);
    }

2、默认BaseMapper实现类：CustomBaseMapper

public class CustomBaseMapper implements BaseMapper {
        private final Logger logger = Logger.getLogger(this.getClass().getName());
        private List<String> dataList = new CopyOnWriteArrayList<>();
    
        /**
         * @param value
         */
        @Override
        public void add(String value) {
            logger.info("添加数据:" + value);
            dataList.add(value);
        }
    
        /**
         * @param key
         */
        @Override
        public void remove(String key) {
            if (dataList.isEmpty())
                throw new IllegalArgumentException("Can't remove because the list is Empty!");
    
        }
    }

接下来是继承Spring的核心代码

3、首先我们要先定义一个扫描某路径下的类，该类继承ClassPathBeanDefinitionScanner，自定义扫描类：DefaultClassPathScanner

public class DefaultClassPathScanner extends ClassPathBeanDefinitionScanner {
    
        private final String DEFAULT_MAPPER_SUFFIX = "Mapper";
    
        public DefaultClassPathScanner(BeanDefinitionRegistry registry) {
            super(registry, false);
        }
    
        private String mapperManagerFactoryBean;
    
        /**
         * 扫描包下的类-完成自定义的Bean定义类
         *
         * @param basePackages
         * @return
         */
        @Override
        protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
            Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
            // 如果指定的基础包路径中不存在任何类对象，则提示
            if (beanDefinitions.isEmpty()) {
                logger.warn("系统没有在 '" + Arrays.toString(basePackages) + "' 包中找到任何Mapper，请检查配置");
            } else {
                processBeanDefinitions(beanDefinitions);
            }
            return beanDefinitions;
        }
    
        /**
         * 注册过滤器-保证正确的类被扫描注入
         */
        protected void registerFilters() {
            addIncludeFilter(new TypeFilter() {
                @Override
                public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory)
                        throws IOException {
                    String className = metadataReader.getClassMetadata().getClassName();
                    //TODO 这里设置包含条件-此处是个扩展点，可以根据自定义的类后缀过滤出需要的类
                    return className.endsWith(DEFAULT_MAPPER_SUFFIX);
                }
            });
            addExcludeFilter(new TypeFilter() {
                @Override
                public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory)
                        throws IOException {
                    String className = metadataReader.getClassMetadata().getClassName();
                    return className.endsWith("package-info");
                }
            });
        }
    
        /**
         * 重写父类的判断是否能够实例化的组件-该方法是在确认是否真的是isCandidateComponent
         * 原方法解释：
         * 确定给定的bean定义是否有资格成为候选人。
         * 默认实现检查类是否不是接口，也不依赖于封闭类。
         * 以在子类中重写。
         *
         * @param beanDefinition
         * @return
         */
        protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition) {
            // 原方法这里是判断是否为顶级类和是否是依赖类（即接口会被排除掉-由于我们需要将接口加进来，所以需要覆盖该方法）
            return beanDefinition.getMetadata().isInterface() && beanDefinition.getMetadata().isIndependent();
        }
    
        /**
         * 扩展方法-对扫描到的含有BeetlSqlFactoryBean的Bean描述信息进行遍历
         *
         * @param beanDefinitions
         */
        void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
            GenericBeanDefinition definition;
            for (BeanDefinitionHolder holder : beanDefinitions) {
                definition = (GenericBeanDefinition) holder.getBeanDefinition();
                String mapperClassName = definition.getBeanClassName();
                // 必须在这里加入泛型限定，要不然在spring下会有循环引用的问题
                definition.getConstructorArgumentValues().addGenericArgumentValue(mapperClassName);
                //依赖注入
                definition.getPropertyValues().add("mapperInterface", mapperClassName);
                // 根据工厂的名称创建出默认的BaseMapper实现
                definition.getPropertyValues().add("mapperManagerFactoryBean", new RuntimeBeanReference(this.mapperManagerFactoryBean));
                definition.setBeanClass(BaseMapperFactoryBean.class);
                // 设置Mapper按照接口组装
                definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
                logger.info("已开启自动按照类型注入 '" + holder.getBeanName() + "'.");
            }
        }
    
        public void setMapperManagerFactoryBean(String mapperManagerFactoryBean) {
            this.mapperManagerFactoryBean = mapperManagerFactoryBean;
        }
    }

4、核心的接口实现类：BaseMapperFactoryBean

public class BaseMapperFactoryBean<T> implements FactoryBean<T>, InitializingBean, ApplicationListener<ApplicationEvent>, ApplicationContextAware {
        /**
         * 要注入的接口类定义
         */
        private Class<T> mapperInterface;
    
        /**
         * Spring上下文
         */
        private ApplicationContext applicationContext;
    
        //也因该走工厂方法注入得来
    
        private BaseMapper mapperManagerFactoryBean;
    
        public BaseMapperFactoryBean(Class<T> mapperInterface) {
            this.mapperInterface = mapperInterface;
        }
    
        @Override
        public T getObject() throws Exception {
            //采用动态代理生成接口实现类，核心实现
            return (T) Proxy.newProxyInstance(applicationContext.getClassLoader(), new Class[]{mapperInterface}, new MapperJavaProxy(mapperManagerFactoryBean, mapperInterface));
        }
    
        @Override
        public Class<?> getObjectType() {
            return this.mapperInterface;
        }
    
        @Override
        public boolean isSingleton() {
            return true;
        }
    
        @Override
        public void afterPropertiesSet() throws Exception {
            //TODO 判断属性的注入是否正确-如mapperInterface判空
            if (null == mapperInterface)
                throw new IllegalArgumentException("Mapper Interface Can't Be Null!!");
        }
    
        /**
         * Handle an application event.
         *
         * @param event the event to respond to
         */
        @Override
        public void onApplicationEvent(ApplicationEvent event) {
            //TODO 可依据事件进行扩展
        }
    
    
        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            this.applicationContext = applicationContext;
        }
    
        public void setMapperInterface(Class<T> mapperInterface) {
            this.mapperInterface = mapperInterface;
        }
    
    
        public void setMapperManagerFactoryBean(BaseMapper mapperManagerFactoryBean) {
            this.mapperManagerFactoryBean = mapperManagerFactoryBean;
        }
    }

5、定义默认的BaseMapper的FactoryBean-MapperManagerFactoryBean

public class MapperManagerFactoryBean implements FactoryBean<BaseMapper>, InitializingBean, ApplicationListener<ApplicationEvent> {
    
        @Override
        public BaseMapper getObject() throws Exception {
            return new CustomBaseMapper();
        }
    
        @Override
        public Class<?> getObjectType() {
            return BaseMapper.class;
        }
    
        @Override
        public boolean isSingleton() {
            return true;
        }
    
        @Override
        public void afterPropertiesSet() throws Exception {
            //TODO 判断属性的注入是否正确
        }
    
        /**
         * Handle an application event.
         *
         * @param event the event to respond to
         */
        @Override
        public void onApplicationEvent(ApplicationEvent event) {
            System.out.println(event.toString());
        }
    }

6、核心的java动态代理类：MapperJavaProxy

public class MapperJavaProxy implements InvocationHandler {
    
        private BaseMapper baseMapper;
    
        private Class<?> interfaceClass;
    
        public MapperJavaProxy(BaseMapper baseMapper, Class<?> interfaceClass) {
            this.baseMapper = baseMapper;
            this.interfaceClass = interfaceClass;
        }
    
        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            if (!interfaceClass.isInterface()) {
                throw new IllegalArgumentException("mapperInterface is not interface.");
            }
    
            if (baseMapper == null) {
                baseMapper = new CustomBaseMapper();
            }
            return method.invoke(baseMapper, args);
        }
    }

7、调用时的核心配置类：DefaultClassRegistryBeanFactory

public class DefaultClassRegistryBeanFactory implements ApplicationContextAware, BeanDefinitionRegistryPostProcessor, BeanNameAware {
    
        private String scanPackage;
    
        private String beanName;
    
        private String mapperManagerFactoryBean;
    
        private ApplicationContext applicationContext;
    
        public String getScanPackage() {
            return scanPackage;
        }
    
        public void setScanPackage(String scanPackage) {
            this.scanPackage = scanPackage;
        }
    
        public String getMapperManagerFactoryBean() {
            return mapperManagerFactoryBean;
        }
    
        public void setMapperManagerFactoryBean(String mapperManagerFactoryBean) {
            this.mapperManagerFactoryBean = mapperManagerFactoryBean;
        }
    
        @Override
        public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException {
            if (StringUtils.isEmpty(this.scanPackage)) {
                throw new IllegalArgumentException("scanPackage can't be null");
            }
            String basePackage2 = this.applicationContext.getEnvironment().resolvePlaceholders(this.scanPackage);
            String[] packages = StringUtils.tokenizeToStringArray(basePackage2, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
            DefaultClassPathScanner defaultClassPathScanner = new DefaultClassPathScanner(beanDefinitionRegistry);
            defaultClassPathScanner.setMapperManagerFactoryBean(mapperManagerFactoryBean);
            defaultClassPathScanner.registerFilters();
    
            defaultClassPathScanner.doScan(packages);
        }
    
        @Override
        public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
    
        }
    
        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            this.applicationContext = applicationContext;
        }
    
        @Override
        public void setBeanName(String name) {
            this.beanName = name;
        }
    }

8、调用测试

8.1、假设你在包目录：colin.spring.basic.advanced.inject.dao下声明自定义的类UserMapper

public interface UserMapper extends BaseMapper {
    }

8.2、声明配置类：ClassRegistryBeanScannerConfig

@Configuration
    public class ClassRegistryBeanScannerConfig {
    
        @Bean(name = "mapperManagerFactoryBean")
        public MapperManagerFactoryBean configMapperManagerFactoryBean() {
            MapperManagerFactoryBean mapperManagerFactoryBean = new MapperManagerFactoryBean();
            return mapperManagerFactoryBean;
        }
    
        @Bean
        public DefaultClassRegistryBeanFactory configDefaultClassRegistryBeanFactory() {
            DefaultClassRegistryBeanFactory defaultClassRegistryBeanFactory = new DefaultClassRegistryBeanFactory();
            defaultClassRegistryBeanFactory.setScanPackage("colin.spring.basic.advanced.inject.dao");
            defaultClassRegistryBeanFactory.setMapperManagerFactoryBean("mapperManagerFactoryBean");
            return defaultClassRegistryBeanFactory;
        }
    }

8.3、测试调用

public static void main(String[] args) {
            AnnotationConfigApplicationContext acApplicationCOntext = new AnnotationConfigApplicationContext("colin.spring.basic.advanced.inject");
            UserMapper userMapper = acApplicationCOntext.getBean(UserMapper.class);
            userMapper.add("lalaldsf");
            acApplicationCOntext.stop();
        }

总结：

此处对于BeanPostProcessor接口的调用应该属于高级应用了，该思路常用来解决扩展或集成Spring框架，其核心的思路可以分为以下几步：

1、自定义实现类路径扫描类，决定哪些类应该被注入进Spring容器。

2、采用Java动态代理来动态实现对于声明接口类的注入。

3、实现BeanDefinitionRegistryPostProcessor，在Spring初始化初期将需要扫描导入Spring容器的类进行注入。

（PS:需要对Spring的BeanDefinition类有一定的了解，下一张我们来分析该类的）