用java写一个http连接池，支持不同域名访问的连接池

好的，下面是一个简单的Java HTTP连接池，支持不同域名访问的连接池。该连接池使用Apache HttpClient库来管理HTTP连接。请注意，这只是一个示例，您需要根据您的具体需求进行修改。

import org.apache.http.HttpEntity;
import org.apache.http.HttpHost;
import org.apache.http.HttpResponse;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.client.utils.URIBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;

import java.io.IOException;
import java.net.URISyntaxException;
import java.util.HashMap;
import java.util.Map;

public class HttpConnectionPool {
    private static final int MAX_TOTAL_CONNECTIONS = 100;
    private static final int MAX_CONNECTIONS_PER_ROUTE = 20;
    private static final int CONNECTION_TIMEOUT = 5000; // in milliseconds
    private static final int SOCKET_TIMEOUT = 5000; // in milliseconds

    private PoolingHttpClientConnectionManager connectionManager;
    private Map<String, CloseableHttpClient> httpClientMap;

    public HttpConnectionPool() {
        connectionManager = new PoolingHttpClientConnectionManager();
        connectionManager.setMaxTotal(MAX_TOTAL_CONNECTIONS);
        connectionManager.setDefaultMaxPerRoute(MAX_CONNECTIONS_PER_ROUTE);

        httpClientMap = new HashMap<>();
    }

    public String doGet(String baseUrl, Map<String, String> params) throws IOException, URISyntaxException {
        String domain = new URIBuilder(baseUrl).getHost();
        CloseableHttpClient httpClient = getHttpClient(domain);

        HttpUriRequest request = new HttpGet(baseUrl);
        if (params != null && !params.isEmpty()) {
            URIBuilder uriBuilder = new URIBuilder(baseUrl);
            for (Map.Entry<String, String> entry : params.entrySet()) {
                uriBuilder.addParameter(entry.getKey(), entry.getValue());
            }
            request = new HttpGet(uriBuilder.build());
        }

        RequestConfig config = RequestConfig.custom()
                .setConnectTimeout(CONNECTION_TIMEOUT)
                .setSocketTimeout(SOCKET_TIMEOUT)
                .setProxy(new HttpHost(domain, 80))
                .build();
        request.setConfig(config);

        HttpResponse response = httpClient.execute(request);
        HttpEntity entity = response.getEntity();

        String result = "";
        if (entity != null) {
            result = EntityUtils.toString(entity);
        }

        return result;
    }

    private CloseableHttpClient getHttpClient(String domain) {
        CloseableHttpClient httpClient = httpClientMap.get(domain);
        if (httpClient == null) {
            httpClient = HttpClientBuilder.create()
                    .setConnectionManager(connectionManager)
                    .build();
            httpClientMap.put(domain, httpClient);
        }
        return httpClient;
    }
}

使用示例：

HttpConnectionPool pool = new HttpConnectionPool();
Map<String, String> params = new HashMap<>();
params.put("key", "value");
String result = pool.doGet("https://www.example.com/path", params);
System.out.println(result);

在这个示例中，我们使用了一个HashMap来缓存已经创建的HttpClient。每当需要发送HTTP请求时，我们首先从请求的URL中提取出域名，然后从缓存中获取对应的HttpClient。如果缓存中没有对应的HttpClient，则创建一个新的HttpClient，并将其添加到缓存中。这样可以避免为每个请求都创建一个新的HttpClient，从而减少资源消耗。同时，我们使用了连接池来管理HTTP连接，确保连接得到重复利用，从而提高性能。

请注意，该示例中使用了HTTP代理，您需要根据您的具体情况进行修改。