# Spring Boot課程筆記4: 參數處理
## @PathVariable
### 多於GET請求時使用(搜尋指定物件)
* **定義方法**
-透過@GetMapping注解定義該方法，並映射相關URL請求 http://localhost:8080/aip/v1/books/{id}
-於方法中的參數透過@PathVariable定義URL所帶入的參數，如範例程式中getOne()所示如此才會接收到URL所帶入的值

    @RestController
    //@Controller
    @RequestMapping("/api/v1")
    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;
        }

        @GetMapping("/books/{id}")
        public Object getOne(@PathVariable long id) {
            Map<String, Object> book = new HashMap<>();
            book.put("name", "三國演義");
            book.put("isbn", "0800092000");
            book.put("author", "諸葛亮");

            return book;
        }
    }

-帶入的參數Spring Boot會自動幫你轉換成方法中你所定義的型別
-URL中定義參數名需與方法中參數名相同，如需有例外則需在@PathVariable中定義欲映射的URL參數，參考範例程式

        @GetMapping("/books/{id}")
        public Object getOne(@PathVariable("id") long bid) {
            Map<String, Object> book = new HashMap<>();
            book.put("name", "三國演義");
            book.put("isbn", "0800092000");
            book.put("author", "諸葛亮");

            return book;
        }

-如遇複數參數需求也可直接於URL中新增，並於程式內透過注解定義即可。如遇特殊需求可用正則表達式進行簡單處理，範例程式如下

        /**
         * 正則表達式: {參數名: 正則表達式}
         * @param id
         * @param username
         * @return
         */
        @GetMapping("/books/{id}/{username:[a-z_]+}")
        public Object getOne(@PathVariable long id, @PathVariable String username) {
            Map<String, Object> book = new HashMap<>();
            book.put("name", "三國演義");
            book.put("isbn", "0800092000");
            book.put("author", "諸葛亮");
            book.put("username", username);

            return book;
        }

## @RequestParam
### 多於POST請求時使用(傳送表單)
* **定義方法**
-透過@PostMapping注解定義該方法，並映射相關URI請求 http://localhost:8080/aip/v1/books
-於方法中的參數透過@RequestParam定義URI所帶入的參數，如範例程式中post()所示如此才會接收到URI所帶入的值

        @PostMapping("/books")
        public Object post(@RequestParam("name") String name,
                           @RequestParam("author") String author,
                           @RequestParam("isbn") String isbn) {
            Map<String, Object> book = new HashMap<String, Object>();
            book.put("name", name);
            book.put("author", author);
            book.put("isbn", isbn);
            return book;
        }

## 模擬需求情境: 定義分頁頁數與每頁能列出之數量。
* **透過URI中定義參數並帶入後端 http://localhost:8080/api/v1/books?page=1&size=10 ?表示參數開頭，參數之間透過 & 連結**
-選用GET請求，並於後端透過@RequestParam獲取參數進行處理，參考範例程式

        @GetMapping("/books")
        //@ResponseBody
        public Object getAll(@RequestParam("page") int page,
                             @RequestParam("size") int size) {
            Map<String, Object> book = new HashMap<String, Object>();
            book.put("name", "三國演義");
            book.put("isbn", "0800092000");
            book.put("author", "諸葛亮");
            Map<String, Object> book2 = new HashMap<String, Object>();
            book2.put("name", "西遊記");
            book2.put("isbn", "020488995");
            book2.put("author", "孫悟空");

            List<Map> contents = new ArrayList<>();
            contents.add(book);
            contents.add(book2);


            Map<String, Object> pageMap = new HashMap<String, Object>();
            pageMap.put("page", page);
            pageMap.put("size", size);
            pageMap.put("content", contents);
            return pageMap;
        }

-PostMan參考
-也可於參數中透過defaultValue預設默認值，如範例(方法內容省略)

  public Object getAll(@RequestParam("page") int page, 
                       @RequestParam(value = "size", defaultValue = "10") int size)

## 結語
* @PathVariable: 多用於刪除或獲取單一資源
* @RequestParam: 多用於提交/ 新增表單，或透過URI中的參數過濾查詢並回傳

[補充討論: URI與URL區別](https://codertw.com/%E5%89%8D%E7%AB%AF%E9%96%8B%E7%99%BC/53793/)
[參考課程Reference](https://www.udemy.com/course/spring-boot-u/)
###### tags: `Spring Boot`