Let's create a TODO application in Java 12 Processing when a request comes in with an unused HttpMethod ・ Processing when an error occurs in the server
Hello.
Let's continue to implement exception handling until the last time!
TODO application creation link collection
1: [Understanding the super basics] A brief description of MVC 2: [Prepare a template] I want to create a template with Spring Initializr and do Hello world 3: [Connection / Settings / Data display with MySQL] Save temporary data in MySQL-> Get all-> Display on top 4: [POST function] Implementation of posting function 5: [PATCH function] Switch TODO display 6: [Easy to use JpaRepository] Implementation of search function [7: [Common with Thymeleaf template fragment] Create Header] (https://qiita.com/nomad_kartman/items/8c33eca2880c43a06e40) [8: [PUT function] Implementation of editing function] (https://qiita.com/nomad_kartman/items/66578f3f91a422f9207d) [9: [Tweak] Sort TODO display in chronological order + Set due date default to today's date] (https://qiita.com/nomad_kartman/items/5ee2b13a701cf3eaeb15) 10: [Exception handling with spring] A brief summary of exception handling [11: [Exception handling in spring] Exception handling when accessing TODO with non-existent ID] (https://qiita.com/nomad_kartman/items/a486838153a563767169) 12: [Exception handling in spring] Processing when a request comes in with an unused HttpMethod-Processing when an error occurs in the server
A brief description of HttpMethod
What is an HTTP method? I think there are many people who think that, so this time it's a rough sketch, but I'll explain what it is like.
A light understanding of what it means to visit a website
First of all, I would like you to understand
Access the Internet site = Access the server on the Internet
about it.
HP is displayed and various functions (such as TODO function) are placed in this server, and if accessed, it should work as expected by the creator.
By the way, the TODO app we are currently creating is not published on the web, but since we are creating a temporary server on our local, we can access localhost: 8080 when we run the app. It is.
URL and HttpMethod
Well, I found out that you can use HP by accessing the server.
What do I need to access?
First of all, you need the address of that site!
If the site is like a house, the address will be the address!
If you just use HP normally, you only need to know the address, but when you actually make HP as a web creator, you have to understand another concept HttpMethod.
Actually, when accessing the site, we use something called HttpMethod to request access.
By requesting the site URL + HttpMethod at the same time, the site is determining which page the user wants to visit!
For example, take the following example.
com/example/todo/TodoController.java
@Controller
public class TodoController {
@GetMapping("/top")
public String top(Model model){
return "top";
}
This is the part that displays the top page of the TODO application, but what I want to pay attention to is
This is the part of @GetMapping ("/ top").
This annotation is for the user
The site URL / top has the role of clearly stating what you want to do when you make a request with the GET method.
So if the user makes such a request, the function top will run.
If your site is home and your address is an address, HttpMethod may be like a key.
It's like the key needed to enter the room that displays the top page of the house.
You can access the same URL by changing the HttpMethod.
For example, take the example below
com/example/todo/TodoController.java
@Controller
public class TodoController {
@GetMapping("/top")
public String top(Model model){
return "top";
}
@PostMapping("/top")
public String top(Model model){
//Post processing
}
I added the process when / top is accessed by POST method.
The URL itself to access is the same, but different processing can be realized by changing the HTTP method at the time of request.
Various HttpMethod
Well, there are various types of HttpMethod, but let's summarize the typical ones and their roles.
- GET
- Used when retrieving resources in the site (Example: Display TODO (resource) obtained from DB on the top page)
- POST
- Used when posting something (example: when posting TODO)
- PUT
- Replace the contents of the data (eg upload a file and change the whole contents)
- PATCH
- Update, modify and save part or all of the data (example: when editing TODO)
Exception handling when requested by an unused HttpMethod
com/example/todo/exception/TodoControllerAdvice.java
@ResponseStatus(HttpStatus.METHOD_NOT_ALLOWED)
@ExceptionHandler(HttpRequestMethodNotSupportedException.class)
public String badMethod() {
log.warn("Bad Request");
return "error/405.html";
}
templates/error/405.html
<!DOCTYPE html>
<html lang="ja">
<head>
<meta charset="UTF-8">
<title>405</title>
</head>
<body>
405!
</body>
</html>
Let's add the above two.
You can see how to write Controller Advice by looking at the previous article.
Here, 405.html is displayed when HttpRequestMethodNotSupportedException (an exception class that occurs when a request for HttpMethod that does not exist is thrown) occurs.
Let's use the Curl command to throw an HttpMethod that doesn't actually exist!
Launch the Todo app and in the terminal
$ curl -X POST "http://localhost:8080/top"
Type. This is making an access request with POST to / top, which originally implements processing only with GET.
Then the result is
It should look like this! You can see that 405 is displayed as expected.
Next, set it when an error occurs in the server.
com/example/todo/exception/TodoControllerAdvice.java
@ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
@ExceptionHandler(Exception.class)
public String otherErrors() {
log.error("Something went wrong");
return "error/500.html";
}
templates/error/500.html
<!DOCTYPE html>
<html lang="ja">
<head>
<meta charset="UTF-8">
<title>500</title>
</head>
<body>
500!
</body>
</html>
By adding these, you can now display a page with a 500 error when the ʻException class occurs!
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