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Spring Request mapping

  • @RequestMapping annotation is one of the main annotation to map web requests to spring controller .
  • Request mapping takes value which holds the path of the request and the HTTPrequest.get to determine the type of request we will use .
  • HTTPrequest doesn't have a default value and should be determined .
  • You can also specify a head sent with the request mapping pararmeter list as key value pair .
  • Request can have multiple header by wrapping them in curly braces .
  • Request mapping can accept types of data using accept header .
  • The produce header can be sent to the mapping annotation with one or multiple values like json or xml .
  • @PathVariable can be used in the request mapping and if it matches the same variable name it can be sent without value .
  • More than one path variable can be used in the request mapping annotation .
  • It can be sent as regex to ensure some specific data to be there .
  • Request mapping can be used to easily map request parameters specified with @Requestparam annotation .
  • Also we can determine our parameters in the body of the request mapping .
  • When sending multiple values to the value attribute the request is mapped to the same method .
  • Also multiple request methods can be mapped to the same controller .
  • To implement a fallback request for all methods we use the star sign as a place holder in the value attribute .
  • Spring will throw if two request mappings have the same value header , method and return type .
  • New Annotation introduced by spring based on request mapping :
    • @GetMaping
    • @PostMaping
    • @PutMaping
    • @DeleteMaping
    • @PatchMaping

Accessing Data with JPA

  • First Steps to do is what I introduced previously is using the spring initializer :

  • Launch start.spring.io to Land on the home page .

  • Specify Project ,team ,package names .

  • Specify the language and version .

  • Inject dependencies .

  • Click on generate .

  • Download the zip file which will contain your initialized project .

Defining a simple entity

  • Starts by defining a class with it's members and constructor including getters and setters if wanted .
  • Then You have to annotate the class with @Entity annotation .
  • After that start by adding an id as a data member annotated with @Id and @GeneratedValue with (strategy = GenerationType.Auto) This means that the id value will be generated automatically .
  • In entity the default constructor must be declared .
  • The arg-Constructor is used to create objects and save in the database .

Create Simple Queries

  • In order to make queries and operation to the entity we should make a new repository interface .
  • That interface should extend JpaRepository to take all the operations on the database from Jpa .
  • In that interface you are allowed to define methods by adding their signature to the interface .
  • You can add data to the database by making an object of the entity class .
  • Then use the save method to save the object in the database .

Spring Data Repository

  • Every repository in spring data extends repository interface .

CrudRepository

  • Provide CRUD functions .
  • If we don't the full functionality we can simply implement this repository .
  • Provides all query abstractions needed in application .
  • Example methods : count , find , findall .

PagingAndSortingRepository

  • Provide pagination and sorting functions .

JpaRepository

  • Extends PagingAndSortingRepository and CrudRepository .
  • Provides Jpa related methods like flushing deleting records .
  • Easily implementing it and providing the method signature will implement the method for us .
Down Sides of Repositories :
- Couple the code to the library . 
- By extending the CrudRpository we expose a whole set of methods which we want to gain more control on .