Before understanding Java Web development in depth, we need to understand the basic concepts of HTTP (Hypertext Transfer Protocol, Hypertext Transfer Protocol). HTTP is the most commonly used application layer protocol in web applications, which defines the rules for exchanging data between clients and servers. Key features of HTTP include:
- Stateless: Each HTTP request is independent, and the server does not save state information between requests.
- Request/response model: the client sends a request and the server returns a response.
- Support multiple data types: HTML, pictures, audio, video, etc.
Below we discuss some of the key components of HTTP, including request methods, status codes, request headers, and response headers.
8.2.1. HTTP request method
The HTTP protocol defines a variety of request methods, representing different operations on resources. The most commonly used request methods are:
- GET: Request the specified resource.
- POST: Submit data to create a new resource.
- PUT: Update the specified resource.
- DELETE: Delete the specified resource.
8.2.2. HTTP Status Codes
The HTTP status code indicates the processing result of the server on the request. Status codes are divided into five categories:
- 1xx (Information): Indicates that the request has been received and the server continues processing.
- 2xx (Success): Indicates that the request was processed successfully.
- 200 OK: The request was successful.
- 3xx (Redirect): Indicates that further action is required to complete the request.
- 302 Found: Temporary redirection.
- 4xx (Client Error): Indicates that the request contained incorrect syntax or could not be completed.
- 400 Bad Request: The request is invalid.
- 404 Not Found: The resource was not found.
- 5xx (Server Error): Indicates that the server failed to properly process a valid request.
- 500 Internal Server Error: Internal server error.
8.2.3. HTTP request and response headers
HTTP request and response headers provide metadata about the request and response. Common request headers include:
- Accept: The media types supported by the client.
- Content-Type: The media type of the request body.
- Content-Length: The length of the request body.
- User-Agent: Client information.
Common response headers include:
- Content-Type: The media type of the response body.
- Content-Length: The length of the response body.
- Set-Cookie: Set Cookie.
- Cache-Control: cache control strategy.
Armed with a basic understanding of the HTTP protocol, we will learn how to handle HTTP requests using Java Servlets in the next section. We will learn how to read request data, how to generate response data, and how to handle GET and POST requests, etc. Recommended reading: