Spring - When to use Setter Injection over Constructor Injection in Spring

Setter Injection has upper hand over Constructor Injection in terms of readability. Since for configuring Spring we use XML files, readability is much bigger concern. Also drawback of setter Injection around ensuring mandatory dependency injected or not can be handled by configuring Spring to check dependency using "dependency-check" attribute of  tag or tag. Another worth noting point to remember while comparing Setter Injection vs Constructor Injection is that, once number of dependency crossed a threshold e.g. 5 or 6 its handy manageable to passing dependency via constructor. Setter Injection is preferred choice when number of dependency to be injected is lot more than normal, if some of those arguments is optional than using Builder design pattern is also a good option.

In Summary both Setter Injection and Constructor Injection has there own advantage and disadvantage. Good thing about Spring is that it doesn't restrict you to use either Setter Injection or Constructor Injection and you are free to use both of them in one Spring configuration file. Use Setter injection when number of dependency is more or you need readability. Use Constructor Injection when Object must be created with all of its dependency.