不能为生产者方法代理非JSR299 bean

Question

我知道，如果通过生产者方法实例化，不符合JSP-299的类可以用于注入。

这意味着，如果我想用一个接受参数的构造函数使bean可注入，我可以通过使用生产者方法来实现。

然而，当我这样做时，我在部署时会遇到以下异常：

2015-11-11T21:35:12.099+0000|Grave: Exception during lifecycle processing
org.glassfish.deployment.common.DeploymentException: CDI deployment failure:Exception List with 2 exceptions:
Exception 0 :
org.jboss.weld.exceptions.DeploymentException: WELD-001435 Normal scoped bean class org.....MongoConfiguration is not proxyable because it has no no-args constructor - Producer Method [MongoConfiguration] with qualifiers [@Any @Default] declared as [[BackedAnnotatedMethod] @Produces @ApplicationScoped public org.....PropertiesProducer.produceMongoConfiguration()]. 

这是生产商：

public class PropertiesProducer {
    private static final String PROPERTIES_FILE = "mongo.properties";
    private Properties properties = new Properties();
    public static final String DATABASE_NAME        = "database.name";
    public static final String PORT                 = "database.port";
    public static final String HOST                 = "database.host";
    public static final String USERNAME             = "database.username";
    public static final String PASSWORD             = "database.password";
    @Produces
    @ApplicationScoped
    public MongoConfiguration produceMongoConfiguration(){
        final InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream(PROPERTIES_FILE);
        if (in == null) {
            return new MongoConfiguration(properties);
        }
        try {
            properties.load(in);
        } catch (IOException e) {
            throw new RuntimeException("Failed to load properties", e);
        }
        finally {
            try {
                if (in != null) {
                    in.close();
                }
            } catch (IOException e) {
                // don't care
            }
        }
        return new MongoConfiguration(properties);
    }
}

以下是用法：

public class MongoDatastore {
    @Inject
    MongoConfiguration mongoConfiguration;
    @Inject
    MongoClient mongoClient;
    Datastore datastore;
    @PostConstruct
    private void setupDatastore() {
        Morphia morphia = new Morphia();
        datastore = morphia.createDatastore(mongoClient, mongoConfiguration.getDatabaseName());
    }
 }

我错过了什么显而易见的东西吗？

Answer 1

最简单的解决方案是将范围从@ApplicationScoped更改为@Singleton:

import javax.inject.Singleton;
@Produces
@Singleton
public MongoConfiguration produceMongoConfiguration(){
     // ...
     return new MongoConfiguration(properties);
}

为了澄清，你可以看到这个SO的回答。

BTW：普通作用域@ApplicationScoped通常优于@Singleton伪作用域。为什么？例如，因为这样的bean的序列化+反序列化将完美地工作。但在日常工作中，有时我们会遇到不可氧化的第三部分类，我们无法更改它。因此，我们有可能的解决方案：

• 使用@Singleton伪作用域
• 创建一个接口，并使用它来代替具体的bean（在生产者方法返回类型和普通代码中）