Java中 HttpURLConnection 和 HttpClient 详解（初学者友好）

Java中`HttpURLConnection`和`HttpClient`详解（初学者友好）

在Java开发中，向服务器发送HTTP请求是常见的需求，比如调用API接口或获取远程数据。在JDK中，主要有两种方式实现HTTP通信：

使用 HttpURLConnection（JDK自带）。
使用 HttpClient（JDK 11 引入的新API，推荐方式）。

本文将全面讲解这两种方式，包括基本用法、优缺点以及适用场景。

一、`HttpURLConnection`详解

HttpURLConnection 是JDK内置的HTTP请求工具类，无需额外依赖库。它适用于简单的HTTP请求处理。

1. 基本用法

下面是使用 HttpURLConnection 发送 GET 和 POST 请求的示例代码。

（1）GET 请求示例

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;public class HttpURLConnectionGetExample {public static void main(String[] args) {try {String urlString = "https://jsonplaceholder.typicode.com/posts/1";URL url = new URL(urlString);HttpURLConnection connection = (HttpURLConnection) url.openConnection();connection.setRequestMethod("GET");// 设置请求头connection.setRequestProperty("User-Agent", "Mozilla/5.0");// 检查响应码int responseCode = connection.getResponseCode();System.out.println("Response Code: " + responseCode);// 读取响应if (responseCode == HttpURLConnection.HTTP_OK) { // 200BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));String inputLine;StringBuilder response = new StringBuilder();while ((inputLine = in.readLine()) != null) {response.append(inputLine);}in.close();System.out.println("Response: " + response.toString());} else {System.out.println("GET request failed.");}} catch (Exception e) {e.printStackTrace();}}
}

（2）POST 请求示例

import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;public class HttpURLConnectionPostExample {public static void main(String[] args) {try {String urlString = "https://jsonplaceholder.typicode.com/posts";URL url = new URL(urlString);HttpURLConnection connection = (HttpURLConnection) url.openConnection();connection.setRequestMethod("POST");// 设置请求头connection.setRequestProperty("Content-Type", "application/json; utf-8");connection.setRequestProperty("Accept", "application/json");connection.setDoOutput(true); // 用于设置HTTP请求是否允许向服务器发送数据// 请求体String jsonInputString = "{ \"title\": \"foo\", \"body\": \"bar\", \"userId\": 1 }";// 发送数据try (OutputStream os = connection.getOutputStream()) {byte[] input = jsonInputString.getBytes("utf-8");os.write(input, 0, input.length);}// 检查响应码int responseCode = connection.getResponseCode();System.out.println("Response Code: " + responseCode);if (responseCode == HttpURLConnection.HTTP_CREATED) { // 201System.out.println("POST request successful.");} else {System.out.println("POST request failed.");}} catch (Exception e) {e.printStackTrace();}}
}

2. 优缺点

优点：

内置类，无需添加依赖。
易于实现简单的HTTP请求。

缺点：

使用较复杂，代码冗长。
不支持异步。
不便于维护和扩展。

二、`HttpClient`详解

HttpClient 是 JDK 11 新引入的 HTTP 通信工具，功能强大，支持同步和异步模式。

1. 基本用法

（1）GET 请求示例

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;public class HttpClientGetExample {public static void main(String[] args) {try {HttpClient client = HttpClient.newHttpClient();HttpRequest request = HttpRequest.newBuilder().uri(URI.create("https://jsonplaceholder.typicode.com/posts/1")).GET().build();HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());System.out.println("Response Code: " + response.statusCode());System.out.println("Response Body: " + response.body());} catch (Exception e) {e.printStackTrace();}}
}

（2）POST 请求示例

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;public class HttpClientPostExample {public static void main(String[] args) {try {HttpClient client = HttpClient.newHttpClient();String jsonInputString = "{ \"title\": \"foo\", \"body\": \"bar\", \"userId\": 1 }";HttpRequest request = HttpRequest.newBuilder().uri(URI.create("https://jsonplaceholder.typicode.com/posts")).header("Content-Type", "application/json").POST(HttpRequest.BodyPublishers.ofString(jsonInputString)).build();HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());System.out.println("Response Code: " + response.statusCode());System.out.println("Response Body: " + response.body());} catch (Exception e) {e.printStackTrace();}}
}

（3）异步请求示例

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.util.concurrent.CompletableFuture;public class HttpClientAsyncExample {public static void main(String[] args) {HttpClient client = HttpClient.newHttpClient();HttpRequest request = HttpRequest.newBuilder().uri(URI.create("https://jsonplaceholder.typicode.com/posts/1")).build();CompletableFuture<HttpResponse<String>> responseFuture = client.sendAsync(request, HttpResponse.BodyHandlers.ofString());responseFuture.thenAccept(response -> {System.out.println("Response Code: " + response.statusCode());System.out.println("Response Body: " + response.body());}).join(); //这里的 .join()是一个阻塞方法，调用这个方法，可以使当前线程（通常是主线程）等待//直到responseFuture完成，避免程序过早退出（单元测试和多异步任务结果合并时常用join方法）}
}