java 将动态参数传递给注释？
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Passing dynamic parameters to an annotation?
提问by Nicholas DiPiazza
I am using the following annotation:
我正在使用以下注释：
@ActivationConfigProperty(
propertyName = "connectionParameters",
propertyValue = "host=127.0.0.1;port=5445,host=127.0.0.1;port=6600"),
public class TestMDB implements MessageDrivenBean, MessageListener
I would like to pull each of these IP addresses and ports and store them in a file jmsendpoints.properties... then load them dynamically. Something like this:
我想提取这些 IP 地址和端口中的每一个并将它们存储在一个文件中jmsendpoints.properties……然后动态加载它们。像这样的东西：
@ActivationConfigProperty(
propertyName = "connectionParameters",
propertyValue = jmsEndpointsProperties.getConnectionParameters()),
public class TestMDB implements MessageDrivenBean, MessageListener
Is there a way to do that?
有没有办法做到这一点？
回答by Johan Sj?berg
No.The annotation processor (the annotation-based framework you're using) needs to implement an approach to handling placeholders.
不可以。注释处理器（您正在使用的基于注释的框架）需要实现一种处理占位符的方法。
As an example, a similar technique is implemented in Spring
例如，类似的技术在 Spring
@Value("#{systemProperties.dbName}")
Here Springimplements an approach to parsingthat particular syntax, which in this case translates to something similar to System.getProperty("dbName");
HereSpring实现了一种解析该特定语法的方法，在这种情况下转换为类似于System.getProperty("dbName");
回答by FThompson
Annotations are not designed to be modifiable at runtime, but you might be able to utilize a bytecode engineering library such as ASMin order to edit the annotation values dynamically.
注释不是为了在运行时可修改而设计的，但您可以利用字节码工程库（例如ASM）来动态编辑注释值。
Instead, I recommend creating an interface in which you could modify these values.
相反，我建议创建一个界面，您可以在其中修改这些值。
public interface Configurable {
public String getConnectionParameters();
}
public class TestMDB implements MessageDrivenBean, MessageListener, Configurable {
public String getConnectionParameters() {
return jmsEndpointsProperties.getConnectionParameters();
}
//...
}
You might wish to create a more key-value oriented interface, but that's the general concept of it.
您可能希望创建一个更面向键值的界面，但这是它的一般概念。
