面试题：Java中基于HTTP协议的网络请求优化

1. 连接管理

使用连接池：在高并发场景下，频繁创建和销毁HTTP连接开销很大。通过使用连接池，可以复用现有的连接，减少连接建立的时间。在Java中，可以使用Apache HttpClient库的PoolingHttpClientConnectionManager来实现连接池。

import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;

public class HttpConnectionPoolExample {
    private static final PoolingHttpClientConnectionManager cm;
    private static final CloseableHttpClient httpClient;

    static {
        cm = new PoolingHttpClientConnectionManager();
        cm.setMaxTotal(100);
        cm.setDefaultMaxPerRoute(20);

        httpClient = HttpClients.custom()
               .setConnectionManager(cm)
               .build();
    }

    public static CloseableHttpClient getHttpClient() {
        return httpClient;
    }
}

然后在发起请求时使用这个httpClient：

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.util.EntityUtils;

public class HttpRequestExample {
    public static void main(String[] args) throws Exception {
        CloseableHttpClient httpClient = HttpConnectionPoolExample.getHttpClient();
        HttpGet httpGet = new HttpGet("http://example.com/api");
        HttpResponse response = httpClient.execute(httpGet);
        String responseBody = EntityUtils.toString(response.getEntity());
        System.out.println(responseBody);
    }
}

2. 缓存策略

客户端缓存：对于一些不经常变化的数据，可以在客户端进行缓存。在Java中，可以使用Guava Cache来实现简单的本地缓存。

import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;

import java.util.concurrent.TimeUnit;

public class HttpCacheExample {
    private static final Cache<String, String> cache = CacheBuilder.newBuilder()
           .maximumSize(1000)
           .expireAfterWrite(10, TimeUnit.MINUTES)
           .build();

    public static String getFromCacheOrFetch(String url) {
        String result = cache.getIfPresent(url);
        if (result != null) {
            return result;
        }
        // 实际发起HTTP请求获取数据
        String data = fetchDataFromHttp(url);
        cache.put(url, data);
        return data;
    }

    private static String fetchDataFromHttp(String url) {
        // 这里实现实际的HTTP请求逻辑
        return "example data";
    }
}

在需要发起HTTP请求时调用getFromCacheOrFetch方法：

public class Main {
    public static void main(String[] args) {
        String result = HttpCacheExample.getFromCacheOrFetch("http://example.com/api");
        System.out.println(result);
    }
}

3. 优化请求头

压缩：启用HTTP压缩可以减少数据传输量。在Apache HttpClient中，可以通过在请求头中设置Accept-Encoding: gzip, deflate来表明支持压缩。

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class HttpCompressionExample {
    public static void main(String[] args) throws Exception {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpGet httpGet = new HttpGet("http://example.com/api");
        httpGet.addHeader("Accept-Encoding", "gzip, deflate");
        HttpResponse response = httpClient.execute(httpGet);
        String responseBody = EntityUtils.toString(response.getEntity());
        System.out.println(responseBody);
    }
}

4. 异步请求

使用异步库：在Java 8及以上版本，可以使用CompletableFuture结合HttpClient（Java 11的java.net.http.HttpClient）来实现异步HTTP请求，提高系统的并发处理能力。

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 AsyncHttpRequestExample {
    public static void main(String[] args) {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
               .uri(URI.create("http://example.com/api"))
               .build();

        CompletableFuture<HttpResponse<String>> future = client.sendAsync(request, HttpResponse.BodyHandlers.ofString());
        future.thenApply(HttpResponse::body)
               .thenAccept(System.out::println)
               .join();
    }
}

星途面试题库

面试题：Java中基于HTTP协议的网络请求优化

知识考点

面试题答案

1. 连接管理

2. 缓存策略

3. 优化请求头

4. 异步请求