Spring-依赖查找

June

Java技术栈/Spring

发布于：2020年7月14日

依赖查找

历史

单一类型依赖查找

JNDI - javax.naming.Context#lookup*(javax.naming.Name);
JavaBeans - java.beans.beancontext.BeanContext

BeanFactory:
- 根据bean名称查找
  - getBean(String);
  - getBean(String,Object…) //覆盖默认参数
- 根据Bean类型查找
  - bean实时查找
    - getBean(Class)
    - getBean(Class,Object…)//覆盖默认参数
  - bean延时查找
    - getBeanProvider(Class);
    - getBeanProvider(String,Class);
- 根据Bean名称和类型查找
  - getBean(String,Class);

/**
 * 通过 {@link org.springframework.beans.factory.ObjectProvider} 进行依赖查找
 */
public class ObjectProviderDemo {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
        applicationContext.register(ObjectProviderDemo.class);
        applicationContext.refresh();
        lookupByObjectProvider(applicationContext);
        applicationContext.close();
    }

    @Bean
    public String helloWorld() {
        return "Hello World";
    }
    private static void lookupByObjectProvider(AnnotationConfigApplicationContext applicationContext) {
        ObjectProvider<String> objectProvider = applicationContext.getBeanProvider(String.class);
        System.out.println(objectProvider.getObject());
    }
}

集合类型依赖查找

java.beans.beancontext.BeanContext

ListableBeanFactory

是针对某个类型去查找一个集合列表。
一种是查询bean的名称，一种是查询bean的实例。
一般情况下应该使用bean的名称来判断当前bean是否存在，或者进一步判断BeanDefinition是否存在。
而查询bean实例会提早初始化bean实例，造成初始化不完整。

根据Bean类型查找
- 获取同类型Bean名称列表
  - getBeanNamesForType(Class)
  - getBeanNamesForType(ResolvableType)
- 获取痛类型Bean实例列表
  - getBeansOfType(Class)以及重载方法
根据注解类型查找
- 获取标注类型Bean 名称列表
  - getBeanNamesForAnnotation(Class<? extends Annotation>);
- 获取标注类型Bean实例列表
  - getBeansWithAnnotation(Class<? extends Annotation>);
- 获取指定名称+标注类型实例
  - findAnnotationOnBean(String,Class<? extends Annotation>);

层次性依赖查找

java.beans.beancontext.BeanContext

HierachicalBeanFactory

双亲 BeanFactory: getParentBeanFactory();
- 层次查找
- 根据Bean名称查找
  - 基于containsLocalBean方法实现
- 根据Bean类型查找实例列表
  - 单一类型：BeanFactoryUtils#beanOfType
  - 集合类型：BeanFactoryUtils#beansOfTypeIncludingAncestors
- 根据Java注解查找名称列表
  - BeanFactoryUtils#beanNamesForTypeIncludingAncestors

public class HierarchicalDependencyLookupDemo {


    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();

        ConfigurableListableBeanFactory beanFactory = applicationContext.getBeanFactory();

        HierarchicalBeanFactory parentBeanFactory = createParentBeanFactory();

        beanFactory.setParentBeanFactory(parentBeanFactory);

        displayContainsLocalBean(beanFactory, "user"); //false
        displayContainsLocalBean(parentBeanFactory, "user"); //true
        
        displayContainsBean(beanFactory, "user"); //true
        displayContainsBean(parentBeanFactory,"user");//true

        applicationContext.refresh();
        applicationContext.close();
    }


    private static void displayContainsBean(HierarchicalBeanFactory beanFactory, String beanName) {
        System.out.printf("当前 BeanFactory [%s] 是否包含  bean[name:%s]  %s\n", beanFactory, beanName, containsBean(beanFactory,beanName));

    }

    private static boolean containsBean(HierarchicalBeanFactory beanFactory, String beanName) {
        BeanFactory parentBeanFactory = beanFactory.getParentBeanFactory();
        if (parentBeanFactory instanceof HierarchicalBeanFactory) {
            HierarchicalBeanFactory parentHierarchicalBeanFactory = HierarchicalBeanFactory.class.cast(parentBeanFactory);
            if (containsBean(parentHierarchicalBeanFactory, beanName)) {
                return true;
            }
        }
        return beanFactory.containsLocalBean(beanName);
    }

    private static void displayContainsLocalBean(HierarchicalBeanFactory parentBeanFactory, String user) {
        System.out.printf("当前 BeanFactory [%s] 是否包含 Local bean[name:%s]  %s\n", parentBeanFactory, user, parentBeanFactory.containsLocalBean(user));
    }

    private static HierarchicalBeanFactory createParentBeanFactory() {
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
        XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(beanFactory);
        String location = "classpath:applicationContext-lookup.xml";
        reader.loadBeanDefinitions(location);
        return beanFactory;
    }
}

延迟依赖查找

Bean延迟依赖查找接口
- org.springframework.beans.factory.ObjectFactory#getObject();
- org.springframework.beans.factory.ObjectProvider
  - Spring5对于Java8的特性扩展
  - 函数式接口
    - getIfAvailable(Supplier)
    - ifAvailable(Consumer)
  - Stream扩展 - stream()

/**
 * 通过 {@link org.springframework.beans.factory.ObjectProvider} 进行依赖查找
 */
public class ObjectProviderDemo {


    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
        applicationContext.register(ObjectProviderDemo.class);
        applicationContext.refresh();

        lookupByObjectProvider(applicationContext);
        lookupIfAvailable(applicationContext);
        lookupByStream(applicationContext);
        applicationContext.close();
    }

    private static void lookupByStream(AnnotationConfigApplicationContext applicationContext) {
        ObjectProvider<String> objectProvider = applicationContext.getBeanProvider(String.class);
//        Iterator<String> iterator = objectProvider.iterator();
//        while(iterator.hasNext()){
//            System.out.println(iterator.next());
//        }
        objectProvider.stream().forEach(System.out::println);
    }

    private static void lookupIfAvailable(AnnotationConfigApplicationContext applicationContext) {
        ObjectProvider<User> userObjectProvider = applicationContext.getBeanProvider(User.class);
        User user = userObjectProvider.getIfAvailable(User::new);
        System.out.println(user);

    }

    @Bean
    @Primary
    public String helloWorld() {
        return "Hello World";
    }

    @Bean
    public String message(){
        return "message";
    }

    private static void lookupByObjectProvider(AnnotationConfigApplicationContext applicationContext) {
        ObjectProvider<String> objectProvider = applicationContext.getBeanProvider(String.class);
        System.out.println(objectProvider.getObject());
    }
}

安全依赖查找

依赖查找安全性对比

依赖查找类型	代表实现	是否安全
单一类型查找	BeanFactory#getBean	否
	ObjectFactory#getObject	否
	ObjectProvider#getIfAvailable	是
集合类型查找	ListableBeanFactory#getBeansOfType	是
	ObjectProvider.stream	是

import com.github.springframework.models.User;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.*;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class TypeSafetyDependencyLookupDemo {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
        applicationContext.register(TypeSafetyDependencyLookupDemo.class);
        applicationContext.refresh();

        displayBeanFactoryGetBean(applicationContext);
        displayObjectFactoryGetObject(applicationContext);
        displayObjectProviderIfAvailable(applicationContext);

        displayListableBeanFactoryGetBeansOfType(applicationContext);

        displayObjectProviderStreamOps(applicationContext);
        applicationContext.close();
    }

    public static void displayObjectProviderStreamOps(AnnotationConfigApplicationContext beanFactory){
        ObjectProvider<User> userObjectFactory = beanFactory.getBeanProvider(User.class);
        printException("displayObjectProviderStreamOps", ()->userObjectFactory.forEach(System.out::println));
    }

    public static void displayListableBeanFactoryGetBeansOfType(ListableBeanFactory beanFactory){
        printException("displayListableBeanFactoryGetBeansOfType", ()->beanFactory.getBeansOfType(User.class));
    }

    public static void displayObjectProviderIfAvailable(BeanFactory beanFactory){
        ObjectProvider<User> userObjectFactory = beanFactory.getBeanProvider(User.class);
        printException("displayObjectProviderIfAvailable", ()->userObjectFactory.getIfAvailable());
    }

    public static void displayObjectFactoryGetObject(BeanFactory beanFactory){
        ObjectProvider<User> userObjectFactory = beanFactory.getBeanProvider(User.class);
        printException("displayObjectFactoryGetObject", ()->userObjectFactory.getObject());
    }

    public static void displayBeanFactoryGetBean(BeanFactory beanFactory){
        printException("displayBeanFactoryGetBean",()->beanFactory.getBean(User.class));
    }

    public static void printException(String source, Runnable run){
        System.out.println("Source From : " + source);
        System.out.println("======================================");
        try{
            run.run();
        }catch (BeansException e){
            e.printStackTrace();
        }
    }
}

内建可查找的依赖

AbstractApplicationContext 内建可查找依赖

Bean名称	Bean实例	使用场景
environment	Environment对象	外部化配置以及Profiles
systemProperties	java.util.Proerties对象	Java系统属性
systemEnvironment	java.util.Map对象	操作系统环境变量
messageSource	MessageSource对象	国际化文案
lifecycleProcessor	LifecycleProcessor对象	LifecycleBean处理器
applicationEventMulticaster	ApplicationEventMulticaster对象	Spring事件广播器

注解驱动Spring上下文内建可查找的依赖

AnnotationConfigUtils.

Bean名称	Bean实例	使用场景
org.springframework.context.annotation.internalConfigurationAnnotationProcessor	ConfigurationClassPostProcessor对象	处理Spring配置类
org.springframework.context.annotation.internalAutowiredAnnotationProcessor	AutowireAnnotationBeanPostProcessor对象	处理@Autowired以及@Value注解
org.springframework.context.annotation.internalCommonAnnotatinProcessor	CommonAnnotationBeanPostProcessor对象	条件激活处理JSR-250注解，如@PostConstruct
org.springframework.context.event.internalEventListenerProcessor	EventListenerMethodProcessor对象	处理@EventListener的Spring事件监听方法

依赖查找中的异常

NoSuchBeanDefinitionException
NoUniqueBeanDefinitionException
BeanInstantiationException
BeanCreationException
BeanDefinitionStoreException

常见题目

ObjectFactory 和 BeanFactory 的区别
BeanFactory.getBean 的线程安全性

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