自动装配两个实现相同接口的bean - 如何将默认bean设置为autowire？ [英] Autowiring two beans implementing same interface - how to set default bean to autowire?

问题描述

我有一个Spring 2.5 / Java / Tomcat应用程序。有以下bean，在很多地方的应用程序中使用

I have a Spring 2.5/Java/Tomcat application. There is the following bean, which is used throughout the application in many places

public class HibernateDeviceDao implements DeviceDao

以及下面的新豆：

public class JdbcDeviceDao implements DeviceDao

第一个bean配置如此（所有bean都在包括在内）

The first bean is configured so (all beans in the package are included)

<context:component-scan base-package="com.initech.service.dao.hibernate" />

第二个（新）bean单独配置

The second (new) bean is configured separately

<bean id="jdbcDeviceDao" class="com.initech.service.dao.jdbc.JdbcDeviceDao">
    <property name="dataSource" ref="jdbcDataSource">
</bean>

当启动服务器时，这会导致（当然）异常：

This results (of course) in an exception when starting the server:

嵌套异常是org.springframework.beans.factory.NoSuchBeanDefinitionException：没有定义[com.sevenp.mobile.samplemgmt.service.dao.DeviceDao]类型的唯一bean ：期望的单个匹配bean，但找到2：[deviceDao，jdbcDeviceDao]

nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [com.sevenp.mobile.samplemgmt.service.dao.DeviceDao] is defined: expected single matching bean but found 2: [deviceDao, jdbcDeviceDao]

来自尝试像这样自动装配bean的类

from a class trying to autowire the bean like this

@Autowired
private DeviceDao hibernateDevicDao;

因为有两个bean实现了相同的接口。

because there are two beans implementing the same interface.

是否可以配置bean以便

1。我不必对已有 HibernateDeviceDao autowired

1. I don't have to make changes to existing classes, which already have the HibernateDeviceDao autowired

2. 仍然可以像这样使用第二个（新）bean：

2. still being able to use the second (new) bean like this:

@Autowired
@Qualifier("jdbcDeviceDao")

即我需要一种方法来配置 HibernateDeviceDao bean作为要自动装配的默认bean，同时允许使用 JdbcDeviceDao 使用 @Qualifier 注释显式指定时。

I.e. i would need a way to configure the HibernateDeviceDao bean as the default bean to be autowired, simultaneously allowing the usage of a the JdbcDeviceDao when explicitly specifying so with the @Qualifier annotation.

我尝试设置属性

autowire-candidate="false"

在JdbcDeviceDao的bean配置中：

in the bean configuration for JdbcDeviceDao:

<bean id="jdbcDeviceDao" class="com.initech.service.dao.jdbc.JdbcDeviceDao" autowire-candidate="false">
    <property name="dataSource" ref="jdbcDataSource"/>
</bean>

因为Spring文档说

because the Spring documentation says that

指示当
寻找匹配的候选者以满足另一个bean的
自动装配要求时是否应该考虑这个bean。 请注意，这不会影响名称显式的
引用，即使指定的
bean未标记为autowire候选，也会解析它。*

我解释为我仍然可以使用 @自动装载 JdbcDeviceDao 限定符注释并将 HibernateDeviceDao 作为默认bean。显然我的解释是不正确的，因为这会在启动服务器时导致以下错误消息：

which I interpreted to mean that I could still autowire JdbcDeviceDao using the @Qualifier annotation and have the HibernateDeviceDao as default bean. Apparently my interpretation was not correct, though, as this results in the following error message when starting the server:

类型[class]的不满意依赖性com.sevenp.mobile.samplemgmt.service.dao.jdbc.JdbcDeviceDao]：预计至少有1个匹配的bean

Unsatisfied dependency of type [class com.sevenp.mobile.samplemgmt.service.dao.jdbc.JdbcDeviceDao]: expected at least 1 matching bean

来自班级我尝试使用限定符自动装配bean：

coming from the class where I've tried autowiring the bean with a qualifier:

@Autowired
@Qualifier("jdbcDeviceDao")

解决方案：

skaffman 建议尝试@Resource注释工作。因此，对于jdbcDeviceDao，配置的autowire-candidate设置为false，当使用jdbcDeviceDao时，我使用@Resource注释（而不是@Qualifier）引用它：

Solution:

skaffman's suggestion to try the @Resource annotation worked. So the configuration has autowire-candidate set to false for jdbcDeviceDao and when using the jdbcDeviceDao I refer to it using the @Resource annotation (instead of @Qualifier):

@Resource(name = "jdbcDeviceDao")
private JdbcDeviceListItemDao jdbcDeviceDao;

推荐答案

我建议用<标记Hibernate DAO类a href =http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/context/annotation/Primary.html =noreferrer> @Primary ，即（假设您在 HibernateDeviceDao 上使用 @Repository ） ：

I'd suggest marking the Hibernate DAO class with @Primary, i.e. (assuming you used @Repository on HibernateDeviceDao):

@Primary
@Repository
public class HibernateDeviceDao implements DeviceDao

这样它将被选为默认的autowire候选者，不需要 autowire-candidate 另一个bean。

This way it will be selected as the default autowire candididate, with no need to autowire-candidate on the other bean.

此外，我发现它更多，而不是使用 @Autowired @Qualifier 优雅使用 @Resource 来挑选特定的豆类，即

Also, rather than using @Autowired @Qualifier, I find it more elegant to use @Resource for picking specific beans, i.e.

@Resource(name="jdbcDeviceDao")
DeviceDao deviceDao;

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