Spring 自定义bean的生命周期（@Scope）

迷南。 2021-09-20 18:24 295阅读 0赞

### **一，背景** ###

Scope注解主要用于配置bean在容器中的生命周期，除了可以配置为singleton和prototype，在Web环境还可以配置为request、session等 值，表示容器会为一次请求或一个会话分配一个bean的实例。如果对bean的生命周期有特殊需求，可以使用自定义的Scope。比如实现一个bean被使用3次后，就获取新的bean实例。

### 二，实现 ###

下面以Spring boot 进行演示

pom.xml

<dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <optional>true</optional>
            </dependency>

MyBean.java

@Data
    public class MyBean {
    
        public MyBean(String id) {
            this.id = id;
        }
    
        private String id;
    }

MyScope.java

import org.springframework.beans.factory.ObjectFactory;
    import org.springframework.beans.factory.config.Scope;
    
    import java.util.concurrent.ConcurrentHashMap;
    
    /**
     * @author lwc
     */
    public class MyScope implements Scope {
    
        /**
         * 记录bean的使用次数
         */
        private static ConcurrentHashMap<String, Integer> beanCounts = new ConcurrentHashMap<>();
    
        /**
         * 保存实例
         */
        private ConcurrentHashMap<String, Object> beans = new ConcurrentHashMap<String, Object>();
    
        @Override
        public Object get(String s, ObjectFactory<?> objectFactory) {
            beanCounts.putIfAbsent(s, 0);
            //第一次使用，放到实例的Map中
            Integer beanCount = beanCounts.get(s);
            if (beanCount == 0) {
                Object newObject = objectFactory.getObject();
                beans.put(s, newObject);
            }
            Object bean = beans.get(s);
            //计数器加1
            int newBeanCount = beanCount + 1;
            if (newBeanCount >= 3) {
                newBeanCount = 0;
            }
            //设置新的次数
            beanCounts.put(s, newBeanCount);
            return bean;
        }
    
        @Override
        public Object remove(String s) {
            return null;
        }
    
        @Override
        public void registerDestructionCallback(String s, Runnable runnable) {
    
        }
    
        @Override
        public Object resolveContextualObject(String s) {
            return null;
        }
    
        @Override
        public String getConversationId() {
            return null;
        }
    }

MyConfig.java

import org.springframework.beans.factory.BeanFactory;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
    import org.springframework.beans.factory.config.CustomScopeConfigurer;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.context.annotation.Scope;
    
    import javax.annotation.PostConstruct;
    
    /**
     * 配置
     *
     * @author lwc
     */
    @Configuration
    public class MyConfig {
    
        @Autowired
        BeanFactory factory;
    
        @PostConstruct
        public void customScopeConfigurer() {
            CustomScopeConfigurer config = new CustomScopeConfigurer();
            config.addScope("three", new MyScope());
            config.postProcessBeanFactory((ConfigurableListableBeanFactory) factory);
        }
    
        @Bean
        @Scope(scopeName = "three")
        public MyBean bean1() {
            return new MyBean("1");
        }
    }

DemoController.java

import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.ApplicationContext;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RestController;
    
    /**
     * @author lwc
     */
    @RestController
    public class DemoController {
    
        @Autowired
        ApplicationContext ctx;
    
        @RequestMapping(value = "/")
        public String index() {
            for (int i = 0; i < 5; i++) {
                System.out.println(ctx.getBean("bean1"));
            }
            return "";
        }
    }

### 三，测试 ###

com.g7go.springannotation.MyBean@7e05c996
    com.g7go.springannotation.MyBean@7e05c996
    com.g7go.springannotation.MyBean@7e05c996
    com.g7go.springannotation.MyBean@2ef5859d
    com.g7go.springannotation.MyBean@2ef5859d

和我们要的相符，当然这里仅仅是一个下例子，更多使用场景还需要大家慢慢发现。