java - 从返回的匿名内部类调用 @Bean 方法的线程安全性

假设从多个线程调用以下测试方法，它是否是线程安全的？有时 println 语句显示“null”。

这个想法是返回一个映射，该映射将根据提供的标识符按需创建 bean。请注意，这只是一个简单的示例，用于说明类似的现实生活场景，其中一个 Bean 使用相同的方法未满足其依赖关系(例如，value.x 为 null)。对于奖励积分，是否有另一种(更好)的方法来达到相同的效果？

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import javax.annotation.Resource;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.test.context.support.AnnotationConfigContextLoader;

import com.oanda.bi.rm.test.AnnotationConfigTest.Config;

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = { Config.class }, loader = AnnotationConfigContextLoader.class)
public class AnnotationConfigTest {

    @Resource
    Map<String, Value> map;

    @Test
    public void test() throws InterruptedException {
        ExecutorService service = Executors.newFixedThreadPool( 10 );

        for ( int i = 0; i < 10; i++ ) {
            service.execute( new Runnable() {
                @Override
                public void run() {
                    // Is this thread-safe?
                    Value value = map.get( "value" );

                    // Sometimes null!
                    System.out.println( value.x );
                }
            } );
        }

        service.shutdown();
        service.awaitTermination( 1, TimeUnit.MINUTES );
    }

    public static class Value {
        @Resource
        protected Integer x;
    }

    @Configuration
    public static class Config {

        @Bean
        public Integer x() {
            return 1;
        }

        @Bean
        @Scope("prototype")
        public Value value() {
            return new Value();
        }

        @Bean
        @SuppressWarnings("serial")
        public Map<String, Value> map() {
            // Return a Spring agnostic "bean factory" map
            return Collections.unmodifiableMap( new HashMap<String, Value>() {
                @Override
                public Value get( Object obj ) {
                    String key = (String) obj;

                    if ( key.equals( "value" ) ) {
                        // Create new bean on demand
                        return value();
                    }

                    // Assume other similar branches here...

                    return null;
                }
            } );
        }

    }
}

更新

鉴于 Biju Kunjummen 的富有洞察力的反馈，我尝试了一种直接使用应用程序上下文的不同方法，但它仍然失败。这次我使用 Function 抽象而不是 Map ，这似乎更合适:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import javax.annotation.Resource;

import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.test.context.support.AnnotationConfigContextLoader;

import com.google.common.base.Function;
import com.oanda.bi.rm.test.AnnotationFunctionConfigTest.Config;

/**
 * Unit test that tries to perform the same pattern as {#link ResourceConfig} and ensure
 * thread safety.
 * 
 * @see http://stackoverflow.com/questions/12700239/thread-safety-of-calling-bean-methods-from-returned-annonymous-inner-classes/12700284#comment17146235_12700284
 * @see http://forum.springsource.org/showthread.php?130731-Thread-safety-of-calling-Bean-methods-from-returned-annonymous-inner-classes&p=426403#post426403
 * @author btiernay
 */
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = { Config.class }, loader = AnnotationConfigContextLoader.class)
public class AnnotationFunctionConfigTest {

    @Resource
    Function<String, Value> function;

    @Test
    public void test() throws InterruptedException {
        final int threads = 10;
        ExecutorService service = Executors.newFixedThreadPool( threads );

        for ( int i = 0; i < threads; i++ ) {
            service.execute( new Runnable() {
                @Override
                public void run() {
                    Value value = function.apply( "value" );
                    Assert.assertNotNull( value.x );
                }
            } );
        }

        service.shutdown();
        service.awaitTermination( 1, TimeUnit.MINUTES );
    }

    public static class Value {
        @Resource
        protected Integer x;
    }

    @Configuration
    public static class Config {

        @Bean
        public Integer x() {
            return 1;
        }

        @Bean
        @Scope("prototype")
        public Value value() {
            return new Value();
        }

        @Bean
        public Function<String, Value> function() {
            // Return a Spring agnostic "bean factory" function
            return new Function<String, Value>() {
                @Autowired
                private ApplicationContext applicationContext;

                @Override
                public Value apply( String key ) {
                    if ( key.equals( "value" ) ) {
                        // Create new bean on demand
                        return applicationContext.getBean( key, Value.class );
                    }

                    // Assume other similar branches here...

                    return null;
                }
            };
        }

    }
}

有人愿意评论一下为什么这仍然看起来不安全吗？

更新

这看起来可能是一个 Spring 错误。我提交了 jira 票证:

https://jira.springsource.org/browse/SPR-9852

最佳答案

我不推荐您实现它的方式:

就像 Jordan 所说，那里并不真正需要映射，您根本不将其用作 HashMap ，而只是使用它来调用 .value() 方法。
Spring @Configuration 机制被绕过，Spring 在内部为 @Configuration 类创建一个 CGLIB 代理，并使用它知道哪些依赖项需要注入(inject)到哪里，并创建知道如何管理范围的实例，通过绕过它你基本上不再使用 Spring 来管理您的 bean 实例。

以下内容与您实现的内容类似，但我认为更简单并且每次都能一致地工作 - 这是通过使用应用程序上下文来获取原型(prototype) bean 并以这种方式将其隐藏在自定义工厂后面:

更新实现

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;


@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class AnnotationConfigTest {


    @Autowired PrototypeBeanFactory prototypeFactory;

    @Test
    public void test() throws InterruptedException {
        ExecutorService service = Executors.newFixedThreadPool( 10 );

        for ( int i = 0; i < 10; i++ ) {
            service.execute( new Runnable() {
                @Override
                public void run() {
                    Value value = prototypeFactory.getBean("value", Value.class);
                    System.out.println( "value1.x = "  + value.getX() );
                }
            } );
        }

        service.shutdown();
        service.awaitTermination( 1, TimeUnit.MINUTES );
    }

    public static class Value {
        @Autowired
        private Integer x;

        public Integer getX() {
            return x;
        }

        public void setX(Integer x) {
            this.x = x;
        }
    }



    @Configuration
    public static class Config {

        @Bean
        public Integer x() {
            return 1;
        }

        @Bean
        @Scope(value="prototype")
        public Value value() {
            return new Value();
        }

        @Bean
        public PrototypeBeanFactory prototypeFactory(){
            return new PrototypeBeanFactory();
        }

    }


    public static class PrototypeBeanFactory implements ApplicationContextAware{
        private ApplicationContext applicationContext;
        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            this.applicationContext = applicationContext;
        }

        public<T> T getBean(String name, Class<T> clazz){
            return this.applicationContext.getBean(name, clazz);
        }

    }
}

关于java - 从返回的匿名内部类调用 @Bean 方法的线程安全性，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/12700239/

java - 从返回的匿名内部类调用 @Bean 方法的线程安全性

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