Java HTTP协议

HTTP（HyperText Transfer Protocol）是Web应用的基础协议，无状态、基于请求-响应模式。

HTTP请求结构

请求行：方法 URL 协议版本
请求头：HeaderName: HeaderValue
请求体：数据内容

请求示例

POST /api/user HTTP/1.1
Host: www.example.com
Content-Type: application/json
Content-Length: 25
User-Agent: Java/11

{"name":"张三","age":25}

HTTP响应结构

状态行：协议版本 状态码 状态描述
响应头：HeaderName: HeaderValue
响应体：数据内容

响应示例

HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 42
Date: Sat, 11 May 2026 08:00:00 GMT

{"id":1,"name":"张三","age":25}

HTTP方法

HTTP状态码

常用请求头

常用响应头

Java HTTP客户端

HttpURLConnection（传统方式）

public class HttpUtil {
    public static String get(String url) throws IOException {
        HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
        conn.setRequestMethod("GET");
        conn.setConnectTimeout(5000);
        conn.setReadTimeout(5000);

        int code = conn.getResponseCode();
        if (code == 200) {
            BufferedReader reader = new BufferedReader(
                new InputStreamReader(conn.getInputStream()));
            StringBuilder result = new StringBuilder();
            String line;
            while ((line = reader.readLine()) != null) {
                result.append(line);
            }
            reader.close();
            return result.toString();
        }
        conn.disconnect();
        return null;
    }

    public static String post(String url, String body) throws IOException {
        HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
        conn.setRequestMethod("POST");
        conn.setDoOutput(true);
        conn.setRequestProperty("Content-Type", "application/json");

        OutputStream out = conn.getOutputStream();
        out.write(body.getBytes());
        out.flush();

        int code = conn.getResponseCode();
        if (code == 200) {
            InputStream in = conn.getInputStream();
            // 读取响应...
        }
        conn.disconnect();
        return null;
    }
}

HttpClient（Java 11+）

import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

public class ModernHttpClient {
    private static final HttpClient client = HttpClient.newHttpClient();

    // GET请求
    public static String get(String url) throws Exception {
        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create(url))
            .GET()
            .build();

        HttpResponse<String> response = client.send(request,
            HttpResponse.BodyHandlers.ofString());
        return response.body();
    }

    // POST请求
    public static String post(String url, String body) throws Exception {
        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create(url))
            .header("Content-Type", "application/json")
            .POST(HttpRequest.BodyPublishers.ofString(body))
            .build();

        HttpResponse<String> response = client.send(request,
            HttpResponse.BodyHandlers.ofString());
        return response.body();
    }

    // 异步请求
    public static CompletableFuture<String> getAsync(String url) {
        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create(url))
            .GET()
            .build();

        return client.sendAsync(request,
            HttpResponse.BodyHandlers.ofString())
            .thenApply(HttpResponse::body);
    }
}

Content-Type常见值

注意事项

HTTP/1.1 默认持久连接，Connection: keep-alive

POST请求需设置 Content-Type 和 Content-Length

状态码4xx表示客户端问题，5xx表示服务端问题

HttpURLConnection 只支持HTTP协议，HTTPS需设置SSL

要点总结

1. HTTP请求包含请求行、请求头、请求体
2. 常用方法：GET获取、POST提交、PUT更新、DELETE删除
3. 状态码2xx成功、4xx客户端错误、5xx服务端错误
4. Java 11+ 推荐使用 HttpClient，支持同步和异步
5. 重要请求头：Content-Type、Accept、Authorization