如何用Apache CloseableHttpClient处理HTTP/2请求（遇505错误）

关键依赖补充 #

首先确保项目中除了httpclient5，还引入HTTP/2支持的核心依赖，版本需与httpclient5保持一致（5.3.1）：

<!-- Maven依赖示例 -->
<dependency>
    <groupId>org.apache.httpcomponents.client5</groupId>
    <artifactId>httpclient5</artifactId>
    <version>5.3.1</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents.core5</groupId>
    <artifactId>httpcore5-h2</artifactId>
    <version>5.3.1</version>
</dependency>

正确配置CloseableHttpClient支持h2c #

默认的CloseableHttpClient未启用HTTP/2协商和h2c升级逻辑，需手动配置连接管理器和版本策略：

import org.apache.hc.client5.http.classic.CloseableHttpClient;
import org.apache.hc.client5.http.classic.methods.HttpGet;
import org.apache.hc.client5.http.impl.classic.CloseableHttpResponse;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManagerBuilder;
import org.apache.hc.core5.http.HttpVersion;
import org.apache.hc.core5.http.config.Registry;
import org.apache.hc.core5.http.config.RegistryBuilder;
import org.apache.hc.core5.http.io.HttpClientConnectionOperator;
import org.apache.hc.core5.http.io.SocketConfig;
import org.apache.hc.core5.http.io.operators.DefaultHttpClientConnectionOperator;
import org.apache.hc.core5.http2.HttpVersionPolicy;
import org.apache.hc.core5.http2.config.H2Config;
import org.apache.hc.core5.http2.impl.nio.DefaultHttp2ClientConnectionOperator;
import org.apache.hc.core5.util.Timeout;

public class H2cSyncClient {
    public static void main(String[] args) throws Exception {
        // 配置HTTP/2基础参数
        H2Config h2Config = H2Config.custom()
                .setPushEnabled(false)
                .build();

        // 注册HTTP/1.1和HTTP/2的连接处理器
        Registry<HttpClientConnectionOperator> connOperatorRegistry = RegistryBuilder.<HttpClientConnectionOperator>create()
                .register(HttpVersion.HTTP_1_1, new DefaultHttpClientConnectionOperator())
                .register(HttpVersion.HTTP_2, new DefaultHttp2ClientConnectionOperator(h2Config))
                .build();

        // 构建支持HTTP/2的连接管理器
        PoolingHttpClientConnectionManager connManager = PoolingHttpClientConnectionManagerBuilder.create()
                .setSocketConfig(SocketConfig.custom()
                        .setSoTimeout(Timeout.ofSeconds(10))
                        .build())
                .setConnectionOperatorRegistry(connOperatorRegistry)
                .build();

        // 创建支持h2c升级的同步HttpClient
        try (CloseableHttpClient httpClient = HttpClients.custom()
                .setConnectionManager(connManager)
                .setVersionPolicy(HttpVersionPolicy.NEGOTIATE) // 允许协商HTTP版本，触发h2c升级
                .build()) {

            HttpGet request = new HttpGet("http://192.168.0.171:20002");
            // 手动添加升级头，确保服务器识别h2c请求（部分服务器需要明确触发）
            request.setHeader("Upgrade", "h2c");
            request.setHeader("Connection", "Upgrade");

            try (CloseableHttpResponse response = httpClient.execute(request)) {
                System.out.println("响应状态码: " + response.getCode());
                System.out.println("使用HTTP版本: " + response.getVersion());
                // 后续处理响应内容逻辑
            }
        }
    }
}

核心配置说明 #

• 依赖补充：httpcore5-h2是HttpClient5支持HTTP/2的核心模块，缺失会导致无法处理HTTP/2连接逻辑。
• 连接管理器配置：注册HTTP/2的连接处理器DefaultHttp2ClientConnectionOperator，让客户端具备处理HTTP/2连接的能力。
• 版本协商策略：HttpVersionPolicy.NEGOTIATE会让客户端主动尝试通过Upgrade头升级到HTTP/2。
• 手动添加升级头：部分服务器需要明确的Upgrade: h2c和Connection: Upgrade头才会触发h2c升级，手动添加可避免自动协商失效的情况。

排查要点 #

• 确认所有HTTP组件版本一致，避免版本不兼容导致的异常。
• 检查是否有请求拦截器或代理修改/移除了Upgrade相关请求头。
• 若服务器要求特定的h2c设置（如设置HTTP2-Settings头），可在请求中添加：request.setHeader("HTTP2-Settings", "AAMAAABkAAQAAP__");（空设置值，符合规范）

内容的提问来源于stack exchange，提问作者dev_jongtae