| I'd also like to consider some form of data bound builder class feature so we can avoid using poor Java patterns. Let me give you an example from the Log4j plugin system. The more typical use of DataBoundConstructor is equivalent to PluginFactory in Log4j: https://github.com/apache/logging-log4j2/blob/a6b1cbfc9d4257baaa6760e58426f0f4dfa99b0f/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/FailoverAppender.java#L183 In order to add new options over time, we used to deprecate a factory method, remove the annotation, and move it to the new factory method that contained default values for new parameters (as well as validation; you could return null instead of the plugin object to signify an error without throwing exceptions which was important in this part of our design, but I digress). This pattern was extremely brittle and is fairly similar to DataBoundConstructor. However, in order to follow Effective Java and other similar best practices, we'd still like to prefer that our objects are fully constructed and ready to use as soon as they're "created" whether that be via a constructor, a factory method, a builder class, or whatever. Having to call setters after creating the object leaves the object in intermediary states that typically don't have meaning, and this can cause runtime bugs in practice. This is getting a bit long, so let me wrap it up. My preferred approach would be what we did in Log4j with newer plugins via a builder class pattern: https://github.com/apache/logging-log4j2/blob/a6b1cbfc9d4257baaa6760e58426f0f4dfa99b0f/log4j-core/src/main/java/org/apache/logging/log4j/core/appender/HttpAppender.java#L48 As you can see, due to syntactical features of Java, it is much easier to add and rename things in a builder class over time independently from the implementation details of the plugin class itself. I'd also note that there was a time in Log4j history before there was automatic type conversion in the annotated factory methods, so some old code still have all string parameters with manual type conversion. Also, why do I bring this up in EC2 and not structs or whatever the appropriate plugin is? Good question, but a new issue should likely be filed about it linked back here. |
