# Spring Boot課程筆記3: URL路由器&注解說明
## 1.RESTful URL
### 典型的前後端分離URL設計風格
* **GET http://localhost:8080/aip/v1/books 獲取所有讀書清單列表**
* **POST http://localhost:8080/aip/v1/books 新增一個書單**
* **GET http://localhost:8080/aip/v1/books/{id} 獲取一個指定書單**
* **PUT http://localhost:8080/aip/v1/books 更新書單**
* **DELETE http://localhost:8080/aip/v1/books/{id} 刪除一個書單**
-每個URL都代表一個資源或著是資源的狀態轉換
-通常定義URL皆用名詞且大多為複數 EX: *books*
-所有資源狀態轉換都是根據不同請求類型作為區分
## 2.注解
### @RestController
* **將被標注的類別定義為Web Controller**
-凡是被標注的類別，裡面method如值為Spring則直接return，如為物件則會透過Json格式return
### @RequestMapping
* **通常應用在method或class上**
-根據value參數中相對應URL的Web請求，並於method中進行映射處理
-根據method參數中的定義決定進行何種請求處理(常見的GET/ POST/ PUT/ DELETE)，如未定義 RequestMethod則默認接受所有請求類型
`@RequestMapping(value = "/say", method = RequestMethod.GET)`
-如定義在類別上則提供最初步的URL定義訊息，如下方CODE其URL即為*http://localhost:8080/api/says*

    @RestController
    @RequestMapping("/api")
    public class HelloController {
        @RequestMapping(value = "/say", method = RequestMethod.GET)
        public String hello() {
            return "Hello Spring Boot";
        }
    }

* **@RequestMapping簡寫方式**
-例如 *@PostMapping* 則支援POST請求，以此類推

    @RestController
    @RequestMapping("/api")
    public class HelloController {
        //@RequestMapping(value = "/say", method = RequestMethod.GET)
        @PostMapping("/say")
        public String hello() {
            return "Hello Spring Boot";
        }
    }

### @Controller
* **非Rest風格返回值**
-透過映射方法中的return值找尋相對應的template，如範例程式 http://localhost:8080/api/books 該連結會映射至resources中template資料夾的books.html

  //@RestController
    @Controller
    @RequestMapping("/api")
    public class HelloController {
        //@RequestMapping(value = "/say", method = RequestMethod.GET)
        @PostMapping("/say")
        public String hello() {
            return "Hello Spring Boot";
        }
        @GetMapping("/books")
        public String getAll() {
            return "books";
        }
    }

-@ResponseBody標注method則可在@Contoller類別中實現與RestController一樣的效果，下方範例程式中 http://localhost:8080/api/books 會透過Json格式返回Map物件
`{
"name": "hello",
"age": 18
}`

  //@RestController
    @Controller
    @RequestMapping("/api")
    public class HelloController {
        //@RequestMapping(value = "/say", method = RequestMethod.GET)
        @PostMapping("/say")
        public String hello() {
            return "Hello Spring Boot";
        }
        @GetMapping("/books")
        @ResponseBody
        public Object getAll() {

            Map<String, Object> map = new HashMap<>();
            map.put("name", "hello");
            map.put("age", 18);
            return map;
        }
    }

[RESTful API學習資源](https://www.ruanyifeng.com/blog/2014/05/restful_api.html)
[參考課程Reference](https://www.udemy.com/course/spring-boot-u/)
###### tags: `Spring Boot`