Spring MVC 中接受参数的方式_请求 principal如何传

Spring MVC 接受参数的方式：

1. 无注解方式
2. @RequestParam 方式：参数绑定
3. @PathVariable 方式：url 匹配
4. @RequestBody 方式：请求对象 $\to$ JSON

@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {
  private String name;
  private int age;
}
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@RestController
public class ParamController {
  //无注解方式
  @GetMapping("noAnnotation")
  public User noAnnotation(User user) {
    return user;
  }

  // @RequestParams 方式：url上的参数与方法上参数绑定
  @GetMapping("/requestParam")
  public User requestParams(@RequestParam String name, @RequestParam int age) {
    return new User(name, age);
  }

  // @PathVariable 方式：获取 url 上的路径
  @GetMapping("/pathVariable/{name}/{age}")
  public User pathVariable(@PathVariable String name, @PathVariable int age) {
    return new User(name, age);
  }

  // @RequestBody 方式：对象 -> JSON
  @PostMapping("/requestBody")
  public User requestBody(@RequestBody User user) {
    System.out.println("user = " + user);
    return user;
  }
}
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使用 HTTP Request 请求

### 无注解方式
GET http://localhost:8080/noAnnotation?name=foo&age=20
Accept: application/json

### @RequestParams 方式
GET http://localhost:8080/requestParam?name=foo&age=20
Accept: application/json

### @PathVariable 方式
GET http://localhost:8080/pathVariable/foo/20
Accept: application/json

### @RequestBody 方式
POST http://localhost:8080/requestBody
Content-Type: application/json

{
  "name": "foo",
  "age": 20
}
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添加 value 的作用: 参数转换

// name -> qwe
@GetMapping("/requestParam2")
public User requestParams2(@RequestParam(value = "qwe") String name, @RequestParam int age) {
  return new User(name, age);
}

// name -> qwe
@GetMapping("/pathVariable2/{qwe}/{age}")
public User pathVariable2(@PathVariable(value = "qwe") String name, @PathVariable int age) {
  return new User(name, age);
}
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### @RequestParams2 方式
GET http://localhost:8080/requestParam2?qwe=foo&age=20
Accept: application/json

### @PathVariable2 方式
GET http://localhost:8080/pathVariable2/qwe/20
Accept: application/json
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