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@Detailed explanation of requestmapping usage

2022-07-29 07:29:00 【A salted fish..】

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Tips ： The following is the main body of this article ,Java The series of learning will be continuously updated

@RequestMapping brief introduction

  stay Spring MVC in ,@RequestMapping The purpose of the annotation is to associate the request with the controller method that processes the request , Establish a mapping relationship .

 @RequestMapping It can modify classes , You can also modify methods . When decorating classes and methods , The access address is class + Method .

Take a look at the source code ：

// Target  These two attributes in represent  @RequestMapping  Annotations can be used on methods and classes 
@Target({
    ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Mapping
public @interface RequestMapping {
    
	String name() default "";
	String[] value() default {
    };
	String[] path() default {
    };
	RequestMethod[] method() default {
    };
	String[] params() default {
    };
	String[] headers() default {
    };
	String[] consumes() default {
    };
	String[] produces() default {
    };
}

@RequestMapping In addition to name() Outside the returned string , There are seven properties .

Property name Attribute specification
value、path Specify the requested url Address .value and path It's the same thing , They can replace each other .value Is the default property , therefore @RequestMapping(value=“/example”) and @RequestMapping(“/example”) It is equivalent. .
method Specify the requested method type , GET( check )、POST( increase )、PUT( Change )、DELETE( Delete ) etc.
params Appoint request Some parameter values must be included in , To be handled by this method .
headers Appoint request Some of the specified header value , To have the method process the request .
consumes Specifies the submitted content type to process the request （Content-Type）, for example application/json, text/html;
produces Specify the type of content returned , Only when the request In the request header (Accept) The specified type is included in the type to return ;

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1. value attribute

value Property matches the request mapping by the request address of the request .valuel Property is an array of string types , Indicates that the request mapping can match the request corresponding to multiple request addresses ,value Property must be set .

1-1 Use a ： Simple jump html page 

@Controller //  Must use  Controller  annotation 
public class Demo1 {
    
    //  Routing rule registration ： Visit the address of the page 
    @RequestMapping("/test1")
    public String sayTest1() {
    
        //  Jump to  templates  Under the  demo2.html
        return "demo2";
    }
}
//  Access address : http://localhost:8080/test1

perhaps 

@Controller //  Must use  Controller  annotation 
@ResponseBody //  Return to one text/html  Information （ Non view file ）
public class Demo2 {
    
    //  Routing rule registration ： Visit the address of the page 
    @RequestMapping("/test2")
    public String sayTest2() {
    
        return "<h1>hello,this is Test</h1>";
    }
}
//  Access address : http://localhost:8080/test2

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1-2 Use two ： Jump html page + Model Data binding

1. First you have to create a data entity class 

import lombok.Data;
// @Data Annotations in lombok Next , Can save code space 
//  With @Data annotation , We don't need to write it manually get、set、toString And the construction method , It has these methods built in 

@Data
public class Student {
    
    private final String name;
    private final String brief;
    private final String birthday;
}

2. Create a view file (just-a-view.html), Internal custom data object 

<!DOCTYPE html>
<html lang="zh-hans">
<head>
    <meta charset="UTF-8">
    <title> Just a view file  |  It is actually a template file </title>
</head>
<body>
    <h1 th:text="${person.name}"> The content here will be replaced </h1>
    <p th:text="${person.brief}"> The content here will be replaced </p>
    <p th:text="${person.birthday}"> The content here will be replaced </p>
</body>
</html>

3. after Controller Conduct Model Data binding 

@Controller
public class DemoController {
    

    //  Support all  HTTP  Method ,@RequestMapping  The default is  get Method request 
    @RequestMapping("/hello")
    public String hello(Model model) {
    
        Student student = new Student(" Zhang San ", " I am Zhang San. , I'm pleased to meet you ", "2000-07-26");
		
		// Forward data , It can be transferred to , Through the expression  ${} Can be obtained 
        model.addAttribute("person", student);

        return "just-a-view";
    }
}
//  Access address : http://localhost:8080/hello

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2. method attribute

@RequestMapping Medium method It is mainly used to define what kind of requests are received from the browser .

Http The specification defines a variety of ways to request resources , There are four basic , Respectively ：GET（ check ）、POST（ increase ）、PUT（ Change ）、DELETE（ Delete ）, and URL Then it is used to locate resources on the network, which is equivalent to the function of address , Cooperate with four request modes , Can realize the right URL Add, delete, modify and query the corresponding resources .

2-1 Process through GET A request sent by 

@Controller
public class UserController1 {
    
 	//  Only support  GET  Method 
	@RequestMapping(value = "/login1", method=RequestMethod.GET)
	public String login1() {
    
		return "success";
	}
	//  It can be abbreviated as 
    @GetMapping("/login2")
    public String login2() {
    
		return "success";
	}
}
//  Access address : http://localhost:8080/login1

At this time , If the request from the browser is not GET Words , You will receive an error prompt returned by the browser , That is, you have to link .

2-2 Process through POST A request sent by 

@Controller
public class UserController2 {
    
	//  Only support  POST  Method 
    @PostMapping("/login3")
	public String login3() {
    
		return "success";
	}
}

At this time , The request must be sent in the form , Otherwise, you will receive an error prompt returned by the browser 

<form action="user/login" method="post">
    <input type="submit" value=" Use Post Send a request "/>
</form>

2-3 Processing multiple requests 

@Controller
public class UserController3 {
    
    //  Support  HTTP GET  and  POST  Method 
    @RequestMapping(value = "/login4", method = {
    RequestMethod.GET, RequestMethod.POST})
    public String login4() {
    
		return "success";
	}
}

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3. params attribute

params Attribute represents the request parameter , That is, add in URL Key value pairs on , Multiple request parameters are expressed in & separate .

Defining entity classes ：

@Data
public class Cat {
    
	public final String name;
	public final int age;
}

Unwanted params Properties :

@Controller
public class ParamsController {
    

    @GetMapping("/cat1")
    @ResponseBody
    public Cat createCat() {
    
    	//  The return object will be  JSON  Output after sequence 
        return new Cat(" kitten ", 3);
    }
}
//  Access address : http://localhost:8080/cat1
//  Web results ：{"name":" kitten ","age":3}

3-1 Request parameters are attribute values 

@Controller
public class ParamsController {
    
    @GetMapping("/cat2")
    @ResponseBody
    public Cat createCat2(String name, String age) {
    
        return new Cat(name, age);
    }
    //  Type the address : http://localhost:8080/cat3?name= millet &age=6

	@GetMapping(value = "cat3", params={
    "name= millet ","age=4"})
    @ResponseBody
    public Cat createCat3(String name, String age) {
    
        return new Cat(name, age);
    }
    //  Fixed address : http://localhost:8080/cat3?name= millet &age=6
}

3-2 Request parameters are objects 

@Controller
public class ParamsController {
    
    @GetMapping("/cat4")
    @ResponseBody
    public Cat createCat4(Cat cat) {
    
        //  You can request directly with objects . As long as you can pass parameters correctly ,Spring Objects are constructed internally 
        return cat;
    }
}
//  Type the address : http://localhost:8080/cat3?name= millet &age=6

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4. headers attribute

adopt @RequestMapping Medium headers attribute , You can restrict requests from clients 

@Controller
public class HeadersController {
    
	//  It means to receive only requests from the local machine 
	@RequestMapping(path = "/login", headers="Host=localhost:8080")
	public String login() {
    
		return "success";
	}
}

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5. produces attribute

produces Property specifies the content type returned , Only when the request In the request header (Accept) The specified type is included in the type to return .

public class DemoController {
    
	//  Specify the output format as  text,  Font is  utf-8
	@RequestMapping(value = "/hello", produces = "text/plain; charset=utf-8")
    @ResponseBody
    public String hello(@RequestParam(value = "target", defaultValue = " The world ") String target) {
    
    	//  Set up  target  The default value is “ The world ”, If the request specifies target  Value , Then the specified value is output 
        return " Hello , " + target;
    }
}
//  Type the address : http://localhost:8080/hello
//  Output results :  Hello , The world 
//  Type the address : http://localhost:8080/hello?target= millet 
//  Output results :  Hello , millet

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summary

  Begin to learn Spring It's been a week , My feeling is that it is difficult to start . You don't need to know the principle of a framework to use it , This really saves a lot of trouble for development . But for beginners , It's really difficult , Because there are too many things in it , If there is no accumulation of time , It's hard for you to know so many tools in a short time , Let alone understand the principle .
  But it will be normal ,“ Everything is difficult at the beginning ”. All we can do is work hard slowly . This article is just a summary of the beginner , The follow-up needs to be constantly supplemented and improved ！！！

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summary :
Tips ： Here is a summary of the article ：
The above is today's learning content , This article is about SpringMVC Learning from , I know another annotation @RequestMapping, And learned its various uses . After that, the learning content will be continuously updated ！！！

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