[TIL] Spring Basics - Request Data Handling

What to do today

What I studied

Path Variable and Request Param

• When sending an HTTP request from the client (browser) to the server, data can be sent together.

Path Variable method

You can add the data you want to send to the server to the URL path. 🌐 GET http://localhost:8080/hello/request/star/Robbie/age/95

// [Request sample]
// GET http://localhost:8080/hello/request/star/Robbie/age/95
@GetMapping("/star/{name}/age/{age}")
@ResponseBody
public String helloRequestPath(@PathVariable String name, @PathVariable int age)
{
  return String.format("Hello, @PathVariable.<br> name = %s, age = %d", name, age);
}

Request Param method

You can add the data you want to send to the server using ? and & at the end of the URL path. 🌐 GET http://localhost:8080/hello/request/form/param?name=Robbie&age=95

// [Request sample]
// GET http://localhost:8080/hello/request/form/param?name=Robbie&age=95
@GetMapping("/form/param")
@ResponseBody
public String helloGetRequestParam(@RequestParam String name, @RequestParam int age) {
  return String.format("Hello, @RequestParam.<br> name = %s, age = %d", name, age);
}

form tag POST

You can send an HTTP request using the POST method using the HTML form tag. 🌐 POST http://localhost:8080/hello/request/form/param

• At this time, the data is delivered to the server in the form of name=Robbie&age=95 in the HTTP body. ``` html

이름:

나이:

``` java
// [Request sample]
// POST http://localhost:8080/hello/request/form/param
// Header
//  Content type: application/x-www-form-urlencoded
// Body
//  name=Robbie&age=95
@PostMapping("/form/param")
@ResponseBody
public String helloPostRequestParam(@RequestParam String name, @RequestParam int age) {
    return String.format("Hello, @RequestParam.<br> name = %s, age = %d", name, age);
}

• @RequestParam can be omitted -@RequestParam(required = false)

  • If the required option is set to false, an error will not occur even if the corresponding value is not included in the values received from the client.
  • The variable that did not receive a value from the client is initialized to null. (If required = false is not set, an error occurs)

How to process HTTP data as objects

@ModelAttribute

• form tag POST 🌐 POST http://localhost:8080/hello/request/form/model

  // [Request sample]
  // POST http://localhost:8080/hello/request/form/model
  // Header
  //  Content type: application/x-www-form-urlencoded
  // Body
  //  name=Robbie&age=95
  @PostMapping("/form/model")
  @ResponseBody
  public String helloRequestBodyForm(@ModelAttribute Star star) {
    return String.format("Hello, @ModelAttribute.<br> (name = %s, age = %d) ", star.name, star.age);
  }
  

  • You can send an HTTP request using the POST method using the HTML form tag. -> At this time, the data is delivered to the server in the form of name=Robbie&age=95 in the HTTP body.
  • After using the @ModelAttribute annotation, body data is declared as an object to receive Star star.
• Query String method 🌐 GET http://localhost:8080/hello/request/form/param/model?name=Robbie&age=95

  // [Request sample]
  // GET http://localhost:8080/hello/request/form/param/model?name=Robbie&age=95
  @GetMapping("/form/param/model")
  @ResponseBody
  public String helloRequestParam(@ModelAttribute Star star) {
    return String.format("Hello, @ModelAttribute.<br> (name = %s, age = %d) ", star.name, star.age);
  }
  

  • If there are only two pieces of data like ?name=Robbie&age=95, it is okay, but if there are multiple pieces of data, it may be difficult to receive them one by one with the @RequestParam annotation. -> At this time, you can receive data as a Java object by using @ModelAttribute. - The Star object declared in the parameter is created and contains the value of name & age requested through the overloaded constructor or Setter method.

• @ModelAttribute can be omitted.
• Both @ModelAttribute and @RequestParam can be omitted. How to distinguish them in Spring
  • Spring considers the parameter as @RequestParam if it is SimpleType; otherwise, it determines that @ModelAttribute is omitted.

@RequestBody

• When sending JSON data to the server in the HTTP Body, the body data can be delivered as a Java object.
• Body JSON data 🌐 POST http://localhost:8080/hello/request/form/json

  // [Request sample]
  // POST http://localhost:8080/hello/request/form/json
  // Header
  //  Content type: application/json
  // Body
  //  {"name":"Robbie","age":"95"}
  @PostMapping("/form/json")
  @ResponseBody
  public String helloPostRequestJson(@RequestBody Star star) {
    return String.format("Hello, @RequestBody.<br> (name = %s, age = %d) ", star.name, star.age);
  }
  

• When data is delivered to the server in the form of {"name":"Robbie","age";"95"} JSON in the HTTP Body, the data can be received in object form using the @RequestBody annotation.

• Things to keep in mind when receiving data as an object
  • A set or get method or overloaded constructor is required to insert data into the field of the object.

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Issues & Errors

What to do tomorrow