Five common annotations of springmvc: 1. @RequestMapping, which is an annotation used to process request address mapping; 2. @RequestParam, which is used to map the request parameter area data to the parameters of the function processing method; 3. @PathVariable, used to set request variables.

@RequestMapping

is an annotation used to handle request address mapping
Applicable to classes and methods. Used on a class, it means that all methods in the class that respond to requests use this address as the parent path.

Attribute

value: Specifies the actual address of the request. The value can be an ordinary specific value, or it can be specified as a type of value containing a certain variable (URI Template Patterns with Path Variables)
can be specified as a type of value containing regular expressions (URI Template Patterns with Regular Expressions)
method: Specify the requested method type, GET, POST, PUT, DELETE, etc.
consumes: Specify the submission content type (Content-Type) for processing the request, such as application/json, text/html
produces: Specify the returned content type, only When the (Accept) type in the request header contains the specified type, it will return
params: The specified request must contain certain parameter values ??before the method can process it
headers: The specified request must contain certain specified header values ??in order for this method to process the request

??1.處理get請求:?@RequestMapping(value?=?"index",method?=?RequestMethod.GET)
??2.springboot錯誤處理(使用app客戶端返回json格式，使用瀏覽器返回html錯誤頁)
???@RequestMapping(produces?=?"text/html")
??3.方法僅處理request?Content-Type為“application/json”類型的請求
???@RequestMapping(value?=?"/pets",?consumes="application/json")
??4.僅處理請求中包含了名為“myParam”，值為“myValue”的請求
???@RequestMapping(value?=?"/pets/{petId}",?params="myParam=myValue")?
??5.僅處理request的header中包含了指定“Refer”請求頭和對應值為“http://www.rxy.com/”的請求
???@RequestMapping(value?=?"/pets",?headers="Referer=http://www.rxy.com/")

@RequestParam

is used to map the request parameter area data to the function processing method
Applicable to the parameters: method parameters

Attributes

value/name: Both attributes refer to the parameter name, that is, the request parameter name of the input parameter ( Usually form name attribute)
required: Whether it is required, the default is true, which means that the request must have corresponding parameters, otherwise an exception will be thrown
defaultValue: Default Value, indicating the default value if there is no parameter with the same name in the request. When setting this parameter, required is automatically set to false

??如果是原子類型，不管加沒加注解，都必須有值，否則拋出異常，如果允許空值請使用包裝類代替
??index(@RequestParam?Integer?num){}??表示該參數(shù)必須傳遞，值允許為空
??表示該參數(shù)非必須，如果不傳則默認為0
??getPageData(@RequestParam(name="pageNum",defaultValue="0")?String?pageNo,?String?pageSize)

@PathVariable

is used to map template variables in the request URL Go to the parameters of the function processing method, that is, take out the variables in the uri template as parameters
Applicable: method parameters

Attributes

value: Specify the url template variable name, if the name is the same as the method parameter If the names are different, they need to be specified, otherwise they can be omitted.

????@RequestMapping("/index/{id}")
?????????public?String?index(@PathVariable("id")?String?sdf){
???????????System.out.println(sdf);
???????????return?"index";
?????}

@ResponseBody

This annotation is used to pass the appropriate to the object returned by the Controller method. After HttpMessageConverter is converted to the specified format, it is written to the body data area of ??the Response object. By default, springmvc is returned in the form of json (Use jackson converter)
Applicable: method, when the data returned is not a page with html tags, but data in some other format (such as json, xml, etc.), use
to compare: @RequestBody Convert the HTTP request body to a suitable HttpMessageConverter object
@ResponseBody Return the content or object as the HTTP response body, and call the Adapter conversion object suitable for HttpMessageConverter, write Output stream

@RequestBody

1. This annotation is used to read the body part of the Request request, parse it using the system's default configured HttpMessageConverter, and then bind the corresponding data to the object to be returned. on the object
2. Then bind the object data returned by HttpMessageConverter to the parameters of the method in the controller
Applicable: method parameters, for the Content-Type of the request: application/json, application/xml must use this Note
For application/x-www-form-urlencoded, if the request method is put, it is required,
It is optional for POST/GET method (that is, it is not necessary, because @RequestParam, @ModelAttribute can also be processed)
For multipart/form-data, @RequestBody cannot handle data in this format
Attribute: required: Whether it is required, the default is true, indicating that the request must have corresponding parameters, otherwise an exception will be thrown
Example: Usually the front-end using this annotation sends an ajax request, then the request part is as follows:

?????????$.ajax({
???????????type:?"POST",
???????????url:"/role/saveRole",
???????????contentType:"application/json",
???????????data:?JSON.stringify(_self.form)...

Note: contentType cannot be omitted, data must be converted into a json string through stringify
Then the corresponding The method can be written like this:

@RequestMapping(value?=?"/saveRole",method?=?RequestMethod.POST)
public?String?saveRole(@RequestBody?People?requestJson)?{}

If the front-end passes an array of objects, the backend can also use List to accept it directly. This is the most practical way to bind List data

@CookieValue

You can bind the cookie value in the Request header to the parameters of the method
Applicable to: method parameters

獲取cookie中的JSESSIONID
public?String?index(@CookieValue("JSESSIONID")?String?cookie){}

@RequestHeader

You can bind the Request The value of the request header part is bound to the parameters of the method
Applicable to: method parameters

獲取請求中Accept-Encoding值，返回gzip,?deflate,?br
public?String?index(@RequestHeader("Accept-Encoding")?String?host){return?host;}

@ExceptionHandler

注解在方法上，表示該方法用于處理特定的異常，處理范圍是當前類，如果想要全局捕獲異常，需要使用@ControllerAdvice
當一個Controller中有多個HandleException注解出現(xiàn)時，那么異常被哪個方法捕捉呢？這就存在一個優(yōu)先級的問題
ExceptionHandler的優(yōu)先級是：在異常的體系結構中，哪個異常與目標方法拋出的異常血緣關系越緊密，就會被哪個捕捉到
屬性：value: 需要處理的異常類型集合(Class)
在當前Controller有兩個處理異常的方法，當訪問/index時，頁面顯示: json data

package?com.rxy.controller;

@Controller
public?class?HelloController?{
????
????@ExceptionHandler({?ArithmeticException.class?})
????@ResponseBody
????public?String?handleArithmeticException(Exception?e)?{
????????e.printStackTrace();
????????return?"json?data";
????}
????
????@ExceptionHandler({?IOException.class?})
????public?String?handleIOException(Exception?e)?{
????????e.printStackTrace();
????????//返回錯誤頁面
????????return?"error";
????}

????@RequestMapping("/index")
????public?String?index(){
????????int?i?=?10?/?0;
????????return?"index";
????}

}

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