1. Spring DI IoC
without frameworks, normally to invoke methods on another class (loose coupling), we need to create an instance of the class, then call the method.
IoC, inversion of control, is pre set up this for us, so called inversion of control. instead we call that method on that object, the object is prepared and injected for us.
DI is one implementation of IoC. Both spring and Guice are DI frameworks.
This saves a lot of efforts for developers, the cost is slower app start up time (so the effort/time is brought forward to spend). This is initial reason why spring started becoming popular even during webwork/struts days.
spring used to use XML for bean creation, and DI. basically tell what’s the beans/class/Objects to be managed by spring bean factory/context. and what’s needed fields/beans for the beans to be created. Spring library would read these configuration and do the set up job.
with the annotation (using reflection) becomes popular, this saves efforts to maintain separate XML files, (at the same time, become less maintainable). So the XML configuration start having the annotation equivalent. @Auowired is the equivalent of telling needed constructs for bean creations in XML.
3. Spring MVC
this is the spring implementation of MVC pattern, corresponding to structs and java default servlet and other framework. basically to tell what’s the URL mapped to which class, and what’s the result(view), with the model passing around. (in XML)
with annotation this become, @RestController @Controller @RequestMapping @RequestParamter etc
4. thread safety in Spring
by default, spring beans are singleton, though this can be changed to be prototype (one bean per each request)
singleton beans are not thread safe, same as servlet, which is shared among requests/threads.
5. spring AOP
AOP is for those code cross cutting or scattering. there are a lot common tasks, like audit or access control, which without AOP, could be duplicating the same code in multiple different places
AOP basically define the point cut (places), cross point and advice (the real business to be done, like audit /access control)
Spring has mostly two proxy mechanism for AOP, default JDK dhynamic proxy or CGLIB (JDK is preferred by spring for performance consideration)
6. spring boot
spring boot trying to make the developers’ job easier, by providing a lot defaults (configuration over convention)
instead of XML, or a lot annotations, Spring boot assume conventions (and library on classpath)to preset up
new Java EE ORM implemntation (no more EJBs), JPA, has same origin as new hibernate implementation. so there are a lot commonality.
Hibernate probably is the most popular JPA provider for now
While hibernate translate between objects and SQLs, where we call objects create/insert/update/delete actually call the hbernate generated SQL to be run on RDBMS (or other DB);
myBatis is more for the reverse. if the DB is old, not possible to change schema, direct SQL is preferred than leaving to Hibernate to construct simple queries.
Even though hibernate has its own HQL, mybatis is since beginning more on the direct SQL type
9. apache camel vs spring integration
both are EIP. Apache Camel has a massive of supported start points/URI, like HTTP, MQ, Timer etc.
With Spring framework become more and more popular, it started to incorporate various other functionality (besides DI), Spring integration is Spring’s counterparts for Camel.