java - 非 JSR299 bean 无法代理生产者方法

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(inject)。

我对此的解释是，如果我想使用带有参数的构造函数来注入(inject)一个 bean，我可以通过使用生产者方法来实现。

但是，当我这样做时，我在部署时遇到以下异常:

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()]. 

这是制作人:

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);
    }
}

用法如下:

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());
    }

 }

我是否错过了一些非常明显的事情？

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);
}

要了解详情，您可以查看 this SO answer .

顺便说一句: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代理的第3部分类，并且我们无法更改它。所以我们可能的解决方案是:

• 使用@Singleton伪作用域。
• 创建一个接口(interface)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)。