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I. Introduction

In modern software development, it is often necessary to communicate with remote servers, such as getting or sending data. Apache HttpClient is a popular Java HTTP client library that simplifies the initiation and response processing of HTTP requests. This article will introduce how to use a custom HttpClientUtils Class to use Apache HttpClient to initiate POST requests and manage connection pools to optimize performance.

1. HttpClientUtils Class Overview

public class HttpClientUtils {
    // 静态常量和变量声明
    private static final int MAX_TOTAL_CONN = 600;
    private static final int MAX_CONN_PER_HOST = 300;
    private static final int SOCKET_TIMEOUT = 5000;
    private static final int CONNECTION_TIMEOUT = 200;
    private static final int CONNECTION_MANAGER_TIMEOUT = 100;

    private static CloseableHttpClient httpclient;
    private static PoolingHttpClientConnectionManager connMrg;
    private static String encoding = StandardCharsets.UTF_8.name();
    private static Logger log = LoggerFactory.getLogger(HttpClientUtils.class);
    private static final ScheduledExecutorService scheduledService = Executors.newScheduledThreadPool(2);

    // 静态代码块，用于初始化 HttpClient 和连接管理器，并设置 JVM 退出时关闭 HttpClient
    static {
        init();
        destroyByJvmExit();
    }

    // 初始化连接管理器和 HttpClient
    private static void init() {
        connMrg = new PoolingHttpClientConnectionManager();
        connMrg.setMaxTotal(MAX_TOTAL_CONN);
        connMrg.setDefaultMaxPerRoute(MAX_CONN_PER_HOST);

        httpclient = HttpClients.custom()
                .setConnectionManager(connMrg)
                .setDefaultRequestConfig(HttpClientUtils.defaultRequestConfig())
                .build();

        // 定时任务，定期清理过期和空闲连接
        scheduledService.scheduleAtFixedRate(() -> {
            connMrg.closeExpiredConnections();
            connMrg.closeIdleConnections(CONNECTION_MANAGER_TIMEOUT, TimeUnit.MILLISECONDS);
        }, 0, CONNECTION_MANAGER_TIMEOUT, TimeUnit.MILLISECONDS);
    }

    // JVM 退出时关闭 HttpClient
    private static void destroyByJvmExit() {
        Runtime.getRuntime().addShutdownHook(new Thread(() -> {
            try {
                httpclient.close();
            } catch (IOException e) {
                log.error("Error closing HttpClient: {}", e.getMessage());
            }
        }));
    }

    // 创建 HttpClientContext
    private static HttpClientContext createContext() {
        return HttpClientContext.create();
    }

    // 创建默认的 RequestConfig
    private static RequestConfig defaultRequestConfig() {
        return RequestConfig.custom()
                .setConnectTimeout(CONNECTION_TIMEOUT)
                .setSocketTimeout(SOCKET_TIMEOUT)
                .setConnectionRequestTimeout(CONNECTION_MANAGER_TIMEOUT)
                .build();
    }

    // 发起带参数的 POST 表单请求，返回字符串结果
    public static String postWithParamsForString(String url, List<NameValuePair> params) {
        HttpPost httpPost = new HttpPost();
        try {
            URI uri = new URIBuilder(url).build();
            httpPost.setURI(uri);
            httpPost.setEntity(new UrlEncodedFormEntity(params, StandardCharsets.UTF_8));

            return executeRequest(httpPost);
        } catch (URISyntaxException | IOException e) {
            log.error("Error executing POST request: {}", e.getMessage());
        } finally {
            httpPost.releaseConnection();
        }
        return null;
    }
    
    // 发起 GET 请求，返回字符串结果
    public static String get(String url, List<NameValuePair> params) {
        HttpGet httpGet = new HttpGet();
        try {
            URI uri = new URIBuilder(url).setParameters(params).build();
            httpGet.setURI(uri);

            return executeRequest(httpGet);
        } catch (URISyntaxException | IOException e) {
            log.error("HTTP GET request failed", e);
        } finally {
            httpGet.releaseConnection();
        }
        return null;
    }

    // 发起 Post 请求，返回字符串结果
    public static String post(String url, List<NameValuePair> params) {
        HttpPost httpPost = new HttpPost();
        try {
            httpPost.setURI(new URI(url));
            httpPost.setEntity(new UrlEncodedFormEntity(params, StandardCharsets.UTF_8));

            return executeRequest(httpPost);
        } catch (URISyntaxException | IOException e) {
            log.error("HTTP POST request failed", e);
        } finally {
            httpPost.releaseConnection();
        }
        return null;
    }

    // 执行 HTTP 请求并处理响应
    private static String executeRequest(HttpUriRequest request) throws IOException {
        try (CloseableHttpResponse response = httpclient.execute(request, createContext())) {
            int statusCode = response.getStatusLine().getStatusCode();
            if (statusCode == HttpStatus.SC_OK) {
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    return EntityUtils.toString(entity, encoding);
                } else {
                    log.warn("Empty response entity");
                }
            } else {
                log.error("HTTP request failed with status code: {}", statusCode);
            }
        } catch (IOException e) {
            log.error("HTTP request execution failed: {}", e.getMessage());
            throw e;
        }
        return null;
    }
}
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2. Parsing the HttpClientUtils class

1. Static constants and variables:

   • Defines constants and variables such as the maximum number of connections, connection timeout, and socket timeout.

2. Initialization and destruction:

   • Initialized in a static code block HttpClient and Connection ManagerPoolingHttpClientConnectionManager。
   • use ScheduledExecutorService Regularly clean up expired and idle connections.
   • exist destroyByJvmExit In the method, a JVM exit hook is registered to ensure that it is closed when the JVM is shut down.HttpClient。

3. HTTP Request Method:

   • postWithParamsForString Method is used to perform a POST request with parameters.
   • use HttpPost Build the request, set the URL and request parameters, and finally callexecuteRequest Method execution request.

4. Executing requests and handling responses:

   • executeRequest Method ReceiveHttpUriRequest, execute HTTP requests and handle responses.
   • Check the response status code, if it is 200 (OK), read the response entity and convert it to a string and return it.
   • Use logging to record error and warning information to ensure the robustness and reliability of the code.

3. Using the HttpClientUtils class

use HttpClientUtils The class can simplify the preparation and management of HTTP requests. The specific steps are as follows:

public class Main {
    public static void main(String[] args) {
        List<NameValuePair> params = new ArrayList<>();
        params.add(new BasicNameValuePair("param1", "value1"));
        params.add(new BasicNameValuePair("param2", "value2"));

        String response = HttpClientUtils.postWithParamsForString("http://example.com/api", params);
        if (response != null) {
            System.out.println("Response: " + response);
        } else {
            System.err.println("Failed to execute POST request");
        }
    }
}
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After learning the above, you should now understand how to use HttpClientUtils Class to manage HTTP clients and initiate requests. This approach can help you handle HTTP communication more efficiently in Java applications, while improving performance and stability through connection pools and periodic cleanup mechanisms.