The SQL ORDER BY Keyword

The ORDER BY keyword is used to sort the result-set in ascending or descending order.

The ORDER BY keyword sorts the records in ascending order by default. To sort the records in descending order, use the DESC keyword.

Example:

To find the recent joining employees in each department:

select * from emp order by deptno,hiredate desc;

Spring4Restful WebServices Annotations

Basically, @RestController , @RequestBody, ResponseEntity & @PathVariable are all you need to know to implement a REST API in Spring 4. Additionally, spring provides several support classes to help you implement something customized.

@RestController
--->@RestController : First of all, we are using Spring 4′s new @RestController annotation. This annotation eliminates the need of annotating each method with @ResponseBody. @RestController is itself annotated with @ResponseBody, and can be considered as combination of @Controller and @ResponseBody.

@RequestBody

--->@RequestBody : If a method parameter is annotated with @RequestBody, Spring will bind the incoming HTTP request body(for the URL mentioned in @RequestMapping for that method) to that parameter. While doing that, Spring will use HTTP Message converters to convert the HTTP request body into domain object [deserialize request body to domain object], based on ACCEPT or Content-Type header present in request.

@ResponseBody

--->@ResponseBody : If a method is annotated with @ResponseBody, Spring will bind the return value to outgoing HTTP response body. While doing that, Spring will use HTTP Message converters to convert the return value to HTTP response body, based on Content-Type present in request HTTP header.

@PathVariable

--->This annotation indicates that a method parameter should be bound to a URI template variable [the one in '{}'].

ResponseEntity

--->ResponseEntity is a real deal. It represents the entire HTTP response. Good thing about it is that you can control anything that goes into it. You can specify status code, headers, and body. It comes with several constructors to carry the information you want to sent in HTTP Response.

MediaType

--->MediaType : With @RequestMapping annotation, you can additionally, specify the MediaType to be produced or consumed (using produces or consumes attributes) by that particular controller method, to further narrow down the mapping.

---> Accept header says about what type client can understand. Content-Type header says what type of data actually 

@Controller VS @RestController in Spring

The key difference between a traditional Spring MVC controller and the RESTful web service controller is the way the HTTP response body is created. While the traditional MVC controller relies on the View technology, the RESTful web service controller simply returns the object and the object data is written directly to the HTTP response as JSON/XML/TEXT