In-depth research on the technical principles of the HTTP client in the Java class library

In -depth research on the technical principles of the HTTP client in the Java class library Abstract: HTTP client is usually used to communicate with the server through the network.The Java class library provides many HTTP client frameworks. These frameworks provide simple and flexible methods to handle HTTP requests and responses.This article will study the technical principles of the general framework of the HTTP client in the Java library and provide some related Java code examples. 1 Introduction HTTP is a protocol for communicating on the web.By sending HTTP requests, the client can request resources or send data from the server and receive the server's response.In the Java class library, there are many HTTP client frameworks to choose from, such as HTTPURLCONNECTION in the Java standard library, and third -party libraries such as Apache HttpClient or OKHTTP.These frameworks provide various functions and characteristics to meet different needs. 2. HTTP request HTTP request consists of a request line, a request header and a request body.The request line contains the request method, URL and protocol version.The request head contains some metadata related to requests, such as Content-Type, User-Agent, etc.The request body is available to send data to the server.Below is a simple Java code example, showing how to use HTTPURLCONNECTION to send GET requests: import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.net.HttpURLConnection; import java.net.URL; public class HttpClientExample { public static void main(String[] args) throws IOException { URL url = new URL("http://example.com"); HttpURLConnection connection = (HttpURLConnection) url.openConnection(); connection.setRequestMethod("GET"); int responseCode = connection.getResponseCode(); System.out.println("Response Code: " + responseCode); BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream())); String line; StringBuilder response = new StringBuilder(); while ((line = reader.readLine()) != null) { response.append(line); } reader.close(); System.out.println("Response Body: " + response.toString()); } } In the above example, we use the HttpurlConnection class to establish a connection to the server and send a GET request.We can set the requesting request by setting the request method, the request head, and the request body. 3. HTTP response HTTP response consists of response, response head, and response.The response contains the description of the response status code and response.The response head contains some metadata related to response, such as Content-Type, Content-Length, etc.The response body contains data returned by the server.Below is a simple Java code example, showing how to use HTTPURLCONNECTION to receive response: import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.net.HttpURLConnection; import java.net.URL; public class HttpClientExample { public static void main(String[] args) throws IOException { URL url = new URL("http://example.com"); HttpURLConnection connection = (HttpURLConnection) url.openConnection(); connection.setRequestMethod("GET"); int responseCode = connection.getResponseCode(); System.out.println("Response Code: " + responseCode); BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream())); String line; StringBuilder response = new StringBuilder(); while ((line = reader.readLine()) != null) { response.append(line); } reader.close(); System.out.println("Response Body: " + response.toString()); } } In the above example, we obtained the response status code by calling the connection.getResponsecode () method, and the input stream of the response was obtained by calling the connection.getInputStream () method, and the data in the input stream was read into the string. 4. HTTP client framework In addition to the HTTPURLCONNECTION of the Java standard library, many third -party libraries provide more HTTP client functions.Among them, Apache httpclient and OKHTTP are two more commonly used frameworks. Apache HTTPClient is a mature, functional HTTP client framework, which provides various functions, such as connecting reuse, connecting pool management, and authentication.Below is a simple example, showing how to use Apache httpclient to send GET requests: import org.apache.http.HttpResponse; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.HttpGet; import org.apache.http.impl.client.HttpClientBuilder; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class HttpClientExample { public static void main(String[] args) throws IOException { HttpClient client = HttpClientBuilder.create().build(); HttpGet request = new HttpGet("http://example.com"); HttpResponse response = client.execute(request); System.out.println("Response Code: " + response.getStatusLine().getStatusCode()); BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent())); String line; StringBuilder responseBody = new StringBuilder(); while ((line = reader.readLine()) != null) { responseBody.append(line); } reader.close(); System.out.println("Response Body: " + responseBody.toString()); } } In the above example, we use the Apache Httpclient library to send a request and get a response.Using the httpclientbuilder class can easily create an HTTPClient instance, and the HTTPGET class represents a get request. OKHTTP is another popular HTTP client framework, which provides simple API and high performance.The following is a simple example, showing how to use OKHTTP to send GET requests: import okhttp3.OkHttpClient; import okhttp3.Request; import okhttp3.Response; import java.io.IOException; public class HttpClientExample { public static void main(String[] args) throws IOException { OkHttpClient client = new OkHttpClient(); Request request = new Request.Builder() .url("http://example.com") .build(); Response response = client.newCall(request).execute(); System.out.println("Response Code: " + response.code()); String responseBody = response.body().string(); System.out.println("Response Body: " + responseBody); } } In the above example, we use the Okhttpclient class to create an Okhttp client instance and use the Request.Builder class to build a request.Call the response.code () method to get the response status code, call response.body (). String () method to obtain the string form of the response. 5 Conclusion This article conducts in -depth research on the technical principles of the HTTP client universal framework in the Java library, and provides some related Java code examples.By learning how to use these frameworks, we can better understand the working principles of the HTTP client and be able to handle HTTP requests and response operations flexibly.Whether using the HTTPURLCONNECTION in the Java Standard Library, or using a third -party library such as Apache Httpclient or OKHTTP, we can choose the appropriate framework according to the needs and develop it in practical applications.