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

Java

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

Java

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

text

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

text

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

方法	作用	是否有请求体
GET	获取资源	无
POST	提交数据	有
PUT	更新资源	有
DELETE	删除资源	可选
HEAD	获取响应头	无
OPTIONS	获取支持方法	无

HTTP状态码

状态码	类别	示例
1xx	信息响应	100 Continue
2xx	成功	200 OK, 201 Created
3xx	重定向	301 Moved, 304 Not Modified
4xx	客户端错误	400 Bad Request, 404 Not Found
5xx	服务端错误	500 Internal Error, 503 Unavailable

常用请求头

请求头	作用
Host	目标主机
Content-Type	请求体类型
Content-Length	请求体长度
Accept	可接受的响应类型
User-Agent	客户端标识
Authorization	认证信息
Cookie	会话标识

常用响应头

响应头	作用
Content-Type	响应体类型
Content-Length	响应体长度
Set-Cookie	设置Cookie
Location	重定向地址
Cache-Control	缓存控制
Expires	过期时间

Java HTTP客户端

HttpURLConnection（传统方式）

text

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+）

text

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

类型	说明
application/json	JSON数据
application/xml	XML数据
text/html	HTML页面
text/plain	纯文本
multipart/form-data	表单上传文件
application/x-www-form-urlencoded	表单数据

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

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