有条件的春豆创作 [英] Conditional spring bean creation

问题描述

我对Spring注释配置有疑问。我有一个bean：

I have a question about Spring annotation configurations. I have a bean:

@Bean 
public ObservationWebSocketClient observationWebSocketClient(){
    log.info("creating web socket connection...");
    return new ObservationWebSocketClient();
}

我有一个属性文件：

@Autowired
Environment env;

在属性文件中我想要一个特殊的布尔属性

In the property file I want to have a special boolean property

createWebsocket=true/false

标志是否应创建bean ObservationWebSocketClient。如果属性值为false，我根本不想建立Web套接字连接。

which signs whether a bean ObservationWebSocketClient should be created. If property value is false I don't want to establich web socket connection at all.

是否有任何技术可能实现这一点？

Is there any technical possibility to realize this?

推荐答案

虽然我没有使用过这个功能，但是看起来你可以用Spring 4的 @Conditional 注释。

Though I've not used this functionality, it appears that you can do this with spring 4's @Conditional annotation.

首先，创建一个 Condition 类，其中 ConditionContext 可以访问环境：

First, create a Condition class, in which the ConditionContext has access to the Environment:

public class MyCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, 
                           AnnotatedTypeMetadata metadata) {
        Environment env = context.getEnvironment();
        return null != env 
               && "true".equals(env.getProperty("createWebSocket"));
    }
}

然后注释你的bean：

Then annotate your bean:

@Bean
@Conditional(MyCondition.class)
public ObservationWebSocketClient observationWebSocketClient(){
    log.info("creating web socket connection...");
    return new ObservationWebSocketClient();
}

编辑 春天-boot 注释 @ConditionalOnProperty 已经实现了这一点;用于评估它的条件的源代码。如果您发现自己经常需要这种功能，那么使用类似的实现是可取的，而不是进行大量的自定义条件实现。

edit The spring-boot annotation @ConditionalOnProperty has implemented this generically; the source code for the Condition used to evaluate it is available on github here for those interested. If you find yourself often needing this funcitonality, using a similar implementation would be advisable rather than making lots of custom Condition implementations.

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