Spring bean 依赖查找

悠悠 2022-10-30 01:26 180阅读 0赞

Spring bean 的依赖查找，可以

*  根据名称查找
 *  根据类型查找单个和所有 bean
 *  根据 名称 + 类型 查找
 *  根据注解查找
 *  延迟查找

配置文件

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    
        <bean id="user1" class="constxiong.User"/>
    
        <bean id="user2" class="constxiong.User" primary="true">
            <property name="id" value="2" />
            <property name="name" value="user2" />
        </bean>
    
        <bean id="lazyUser" class="org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean">
            <property name="targetBeanName" value="user1"/>
        </bean>
    
    </beans>

自定义注解，为演示可以通过注解查找到 bean 而创建

package constxiong;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    /**
     * 注解
     */
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface ConstXiong {
    }

bean 类

package constxiong;
    
    @ConstXiong
    public class User {
    
        private Integer id = 1;
    
        private String name = "Constxiong";
    
        public Integer getId() {
            return id;
        }
    
        public void setId(Integer id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        @Override
        public String toString() {
            return "User{" +
                    "id=" + id +
                    ", name='" + name + ''' +
                    '}';
        }
    }

测试代码

package constxiong;
    
    import java.util.Map;
    
    import org.springframework.beans.factory.BeanFactory;
    import org.springframework.beans.factory.ListableBeanFactory;
    import org.springframework.beans.factory.ObjectFactory;
    import org.springframework.beans.factory.xml.XmlBeanFactory;
    import org.springframework.core.io.ClassPathResource;
    
    /**
     * 依赖查找
     */
    @SuppressWarnings("deprecation")
    public class Test {
    
        public static void main(String[] args) {
            BeanFactory factory = new XmlBeanFactory(new ClassPathResource("META-INF/spring-dependency-lookup.xml"));
            findByName(factory);
            findPrimaryByType(factory);
            findAllByType(factory);
            findByNameAndType(factory);
            findByAnnotation(factory);
            findInLazy(factory);
        }
    
        /**
         * 根据名称查找
         */
        public static void findByName(BeanFactory factory) {
            User user = (User)factory.getBean("user1");
            System.out.println("根据名称查找: " + user);
        }
    
        /**
         * 根据类型查找 primary
         */
        private static void findPrimaryByType(BeanFactory factory) {
            //根据类型查找如何存在多个同一类型的bean，需要制定 primary 属性为 true
            User user = factory.getBean(User.class);
            System.out.println("根据类型查找 priary: " + user);
        }
    
        /**
         * 根据类型查找所有
         */
        private static void findAllByType(BeanFactory factory) {
            //ListableBeanFactory，具有查询所有类型的能力
            Map<String, User> beans = ((ListableBeanFactory) factory).getBeansOfType(User.class);
            System.out.println("根据类型查找所有: " + beans);
        }
    
        /**
         * 根据 名称 + 类型 查找
         */
        private static void findByNameAndType(BeanFactory factory) {
            User user = factory.getBean("user1", User.class);
            System.out.println("根据 名称 + 类型 查找: " + user);
        }
    
        /**
         * 根据注解查找
         */
        private static void findByAnnotation(BeanFactory factory) {
            //ListableBeanFactory，具有根据注解查找 bean 的能力
            Map<String, Object> beans = ((ListableBeanFactory) factory).getBeansWithAnnotation(ConstXiong.class);
            System.out.println("根据注解查找: " + beans);
        }
    
        /**
         * 延迟查找
         */
        private static void findInLazy(BeanFactory factory) {
            ObjectFactory<User> objectFactory = (ObjectFactory<User>)factory.getBean("lazyUser");
            User user = objectFactory.getObject();
            System.out.println("延迟查找: " + user);
        }
    
    }

打印结果

根据名称查找: User{id=1, name='Constxiong'}
    根据类型查找 priary: User{id=2, name='user2'}
    根据类型查找所有: {user1=User{id=1, name='Constxiong'}, user2=User{id=2, name='user2'}}
    根据 名称 + 类型 查找: User{id=1, name='Constxiong'}
    根据注解查找: {user1=User{id=1, name='Constxiong'}, user2=User{id=2, name='user2'}}
    延迟查找: User{id=1, name='Constxiong'}

ps：

*  XmlBeanFactory 已经是一个废弃的类，但这个示例不想引入 spring-context、XmlBeanFactory 加载 xml 的代码比较直接，所以仍使用了
 *  根据类型查到单个 bean 时，如果存在多个同类型的 bean，需要给 bean 设置 primary 属性
 *  ListableBeanFactory 具有根据注解查找 bean、查询同一类型多个 bean 的能力
 *  延迟查找可以借助 ObjectFactoryCreatingFactoryBean 类实现

--------------------

### 【Java学习资源】整理推荐 ###

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 *  [BeanFactory 与 FactoryBean 的区别][BeanFactory _ FactoryBean]
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 *  [Spring IoC 依赖注入的实现方式][Spring IoC 1]
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--------------------

### 【Java面试题与答案】整理推荐 ###

*  [基础与语法][Link 1]
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 *  [异常][Link 9]
 *  [文件解析与生成][Link 10]
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[Spring _ DependencyDescriptor]: https://www.javanav.com/val/152161d266a94fd38efb365a78d8f9a3.html
[Spring _ Aware]: https://www.javanav.com/val/089b3993c8bc4dec891ea677c104c5e4.html
[Spring Bean _ Exception]: https://www.javanav.com/val/2b31b7061b3342c0a67f8d7fc7373ed3.html
[Spring _ Bean]: https://www.javanav.com/val/92f9e0951b19454196b645bb3cb1a0b9.html
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[Spring IoC]: https://www.javanav.com/val/d382c8380fc2480788a35a7e671b5e9b.html
[BeanFactory _ FactoryBean]: https://www.javanav.com/val/173e873a2c98499a8a08a13b4f88ae10.html
[BeanFactory _ ApplicationContext]: https://www.javanav.com/val/bbc2c9580b7045e583855925d5f1a50b.html
[Spring IoC 1]: https://www.javanav.com/val/a835e6c709ea439ebb21a80f1bf77926.html
[Spring IoC 2]: https://www.javanav.com/val/e377beac22644c2c85308079b239a0fd.html
[Spring bean]: https://www.javanav.com/val/7f8c2e1f24db46e79bc4b9b04f9ad715.html
[Spring-IoC]: https://www.javanav.com/val/a412668efda74412a13f6df9a6d2c714.html
[Spring]: https://www.javanav.com/val/6eac12a548ea40c68ff64b1af307563a.html
[Link 1]: https://www.javanav.com/interview/93b0069472fd479393006c0e73043fc4.html
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[Link 4]: https://www.javanav.com/interview/36a24fa3258e45c89873f474ce914912.html
[Web]: https://www.javanav.com/interview/4e27cb63adb440c6825a159d35cf4010.html
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[Link 9]: https://www.javanav.com/interview/d3f058cfc05d4c6dadd821b622e84d36.html
[Link 10]: https://www.javanav.com/interview/67a50996c28f418e83b109ea42fc3eff.html
[Linux]: https://www.javanav.com/interview/00cccb81729540d1923bd0a0ef49533a.html
[MySQL]: https://www.javanav.com/interview/d311e78502a845f1a4bb307bd6aec2b3.html
[Oracle]: https://www.javanav.com/interview/5f29e9677edf4a16be3dce30d257c9ab.html
[Redis]: https://www.javanav.com/interview/066c62b3af4d4827b2243a822c3084a9.html
[Dubbo]: https://www.javanav.com/interview/9a3e7a7740324757abaab953f7ebc455.html