刚好之前折腾过RestTemplate的HTTP/2配置，给你捋捋清楚：RestTemplate本身只是个上层封装，它的HTTP协议支持完全靠底层的ClientHttpRequestFactory实现。默认的SimpleClientHttpRequestFactory基于JDK自带的HttpURLConnection，根本不支持HTTP/2，所以得换成支持HTTP/2的客户端实现，比如Apache HttpClient 5或者OkHttp。

方案一：使用Apache HttpClient 5配置 #

1. 引入依赖（Maven为例） #

<dependency>
    <groupId>org.apache.httpcomponents.client5</groupId>
    <artifactId>httpclient5</artifactId>
    <version>5.2.1</version> <!-- 用最新稳定版即可 -->
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents.core5</groupId>
    <artifactId>httpcore5-h2</artifactId>
    <version>5.2.1</version>
</dependency>

2. 配置HTTP/2支持的HttpClient并注入RestTemplate #

import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManagerBuilder;
import org.apache.hc.client5.http.io.HttpClientConnectionManager;
import org.apache.hc.client5.http.ssl.SSLConnectionSocketFactory;
import org.apache.hc.core5.http.config.Registry;
import org.apache.hc.core5.http.config.RegistryBuilder;
import org.apache.hc.core5.http.io.SocketConfig;
import org.apache.hc.core5.http.ssl.TLS;
import org.apache.hc.core5.ssl.SSLContexts;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;

import javax.net.ssl.SSLContext;
import java.security.KeyManagementException;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;

@Configuration
public class RestTemplateConfig {

    @Bean
    public RestTemplate http2RestTemplate() throws NoSuchAlgorithmException, KeyStoreException, KeyManagementException {
        // 构建支持HTTP/2的SSL上下文（HTTP/2要求TLS 1.2+）
        SSLContext sslContext = SSLContexts.custom()
                .setProtocol(TLS.V_1_2)
                .build();

        // 注册HTTP/1.1和HTTP/2的Socket工厂
        Registry<SSLConnectionSocketFactory> socketFactoryRegistry = RegistryBuilder.<SSLConnectionSocketFactory>create()
                .register("http", SSLConnectionSocketFactory.getSocketFactory())
                .register("https", new SSLConnectionSocketFactory(sslContext, TLS.V_1_2, null, null))
                .build();

        // 配置连接管理器，启用HTTP/2支持
        HttpClientConnectionManager connectionManager = PoolingHttpClientConnectionManagerBuilder.create()
                .setSSLSocketFactoryRegistry(socketFactoryRegistry)
                .setDefaultSocketConfig(SocketConfig.custom()
                        .setSoTimeout(5000)
                        .build())
                .build();

        // 创建支持HTTP/2的HttpClient实例
        org.apache.hc.client5.http.classic.HttpClient httpClient = HttpClients.custom()
                .setConnectionManager(connectionManager)
                .build();

        // 包装成RestTemplate可用的请求工厂
        HttpComponentsClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory(httpClient);
        requestFactory.setConnectTimeout(5000);
        requestFactory.setReadTimeout(5000);

        return new RestTemplate(requestFactory);
    }
}

方案二：使用OkHttp配置 #

OkHttp对HTTP/2的支持更省心，默认就启用了HTTP/2协商（只要服务器支持）。

1. 引入依赖（Maven为例） #

<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>4.10.0</version> <!-- 最新稳定版 -->
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId> <!-- Spring Boot项目自带RestTemplate基础依赖 -->
</dependency>

2. 配置OkHttpClient并注入RestTemplate #

import okhttp3.OkHttpClient;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.OkHttp3ClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;

import java.time.Duration;

@Configuration
public class RestTemplateConfig {

    @Bean
    public RestTemplate http2RestTemplate() {
        OkHttpClient okHttpClient = new OkHttpClient.Builder()
                .connectTimeout(Duration.ofSeconds(5))
                .readTimeout(Duration.ofSeconds(5))
                .writeTimeout(Duration.ofSeconds(5))
                // OkHttp默认启用HTTP/2，无需额外配置，服务器支持就会自动切换
                .build();

        OkHttp3ClientHttpRequestFactory requestFactory = new OkHttp3ClientHttpRequestFactory(okHttpClient);
        return new RestTemplate(requestFactory);
    }
}

关于Spring生态中支持HTTP/2的客户端选项 #

除了给RestTemplate换底层工厂，还有几个更推荐的选择：

• WebClient（Spring 5+官方推荐）：这是Spring主推的非阻塞、响应式HTTP客户端，天然支持HTTP/2（底层依赖的Reactor Netty默认支持HTTP/2）。RestTemplate已经进入维护模式，如果你的项目是Spring Boot 2.x+或者Spring 5+，更建议用WebClient替代。

• Spring Cloud LoadBalancer + WebClient：如果需要负载均衡，结合Spring Cloud LoadBalancer的WebClient客户端也能轻松支持HTTP/2。

最后要注意：不管用哪种客户端，服务器端必须支持HTTP/2，否则客户端会自动降级到HTTP/1.1。你可以通过查看响应头的HTTP/2标识或者抓包工具（比如Wireshark）来验证是否成功使用了HTTP/2。

内容的提问来源于stack exchange，提问作者the_kaba