项目中经常会用到向第三方系统发送请求来传递数据或者获得信息，一般用的比较多的为HttpClient 和 HttpRequest，这里简要总结一下 HttpClient 和 HttpRequest 的用法

一、HttpClient

1. 发送get请求

public static String get(String url, Map<String, String> headMap, int timeout) {
    String result = null;
    CloseableHttpClient httpclient = HttpClients.createDefault();
    CloseableHttpResponse response = null;
    try {
        HttpGet httpGet = new HttpGet(url);
        RequestConfig requestConfig = RequestConfig.custom().setConnectTimeout(timeout).build();
        httpGet.setConfig(requestConfig);
        setHead(httpGet, headMap);
        response = httpclient.execute(httpGet);
        HttpEntity entity = response.getEntity();
        result = EntityUtils.toString(entity, "UTF-8");
        EntityUtils.consume(entity);
    } catch (Exception e) {
        LOG.error("HttpGet [{}] error: {}", url, e.getMessage(), e);
        throw new RuntimeException(e.getMessage(), e);
    } finally {
        try {
            if (null != response) {
                response.close();  
            }
            httpclient.close();
        } catch (IOException e) {
            LOG.error("HttpGet [{}] httpclient close error: {}", url, e.getMessage(), e);
        }
    }
    return result;
}

1. 发送post请求

public static String postJson(String url, String body, Map<String, String> headMap, int timeout) {
    CloseableHttpClient httpClient = HttpClients.createDefault();
    CloseableHttpResponse response = null;
    try {
        HttpPost httpPost = new HttpPost(url);
        httpPost.addHeader("Content-Type", "application/json;charset=utf-8");
        setHead(httpPost, headMap);
        RequestConfig requestConfig = RequestConfig.custom().setConnectTimeout(timeout).build();
        httpPost.setConfig(requestConfig);
        httpPost.setEntity(new StringEntity(body, "UTF-8"));
        response = httpClient.execute(httpPost);
        HttpEntity entity = response.getEntity();
        String responseContent = EntityUtils.toString(entity, "UTF-8");
        EntityUtils.consume(entity);
        return responseContent;
    } catch (Exception e) {
        LOG.error("HttpPostJson [{}] error: {}", url, e.getMessage(), e);
        throw new RuntimeException(e.getMessage(), e);
    } finally {
        try {
            response.close();
            httpClient.close();
        } catch (IOException e) {
            LOG.error("HttpPostJson [{}] httpclient close error: {}", url, e.getMessage(), e);
        }
    }
}

private static void setHead(HttpRequestBase httpRequestBase, Map<String, String> headMap) {
    if (headMap != null && headMap.size() > 0) {
        Set<String> keySet = headMap.keySet();
        for (String key : keySet) {
            httpRequestBase.addHeader(key, headMap.get(key));
        }
    }
}

优点：连接池（复用HTTP连接）、重试、代理机制，社区活跃，性能更加优异

缺点：配置和API使用较为复杂

二、HttpRequest

1. 发送get请求

public static String get(String methodName, String url, Map<String, Object> paramMap, Map<String, String> headers){
    return HttpRequest.get(url).addHeaders(headers).form(paramMap).execute().body();
}

2. 发送post请求

public static String postForm(String methodName, String url, Map<String, Object> paramMap, Map<String, String> headers, String paramStr){
    return HttpRequest.post(url).addHeaders(headers).form(paramMap).body(paramStr).execute().body();
}

优点：功能简单，整体比较易用

缺点：性能一般，社区支持较弱

三、对比

hutool 的 HttpRequest 底层是基于 HttpClient 的，是对其进行了封装，提供了更加简便的API请求，使用 HttpRequest 可在一行代码中实现发送简单的HTTP请求，如果需要使用 HttpClient 更加复杂的操作，则可以通过自定义 HttpClient 并通过 setHttpClient() 方法传入 HttpClient

例如通过自定义Httpclient实现设置最大连接数量

// 创建连接池管理器
PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
connectionManager.setMaxTotal(100); // 设置最大连接数
connectionManager.setDefaultMaxPerRoute(20); // 设置每个路由的最大连接数

// 创建自定义的HttpClient
HttpClientBuilder httpClientBuilder = HttpClientBuilder.create()
        .setConnectionManager(connectionManager);

// 使用 Hutool 的 HttpRequest 发送请求
HttpResponse response = HttpRequest.get("https://example.com")
        .timeout(5000) // 设置超时时间
        .setHttpClient(httpClientBuilder.build()) // 设置自定义的HttpClient
        .execute();

总结：

1. 小型简单项目可使用 HttpRequest 快速请求，较大型复杂项目适合使用 HttpClient
2. HttpClient 引入 httpclient 依赖，HttpRequest 引入 hutool 依赖
3. 如果有连接池、重试、代理等机制的需求则可使用 HttpClient
4. 高性能，高并发，有复杂Http操作的场景则可使用 HttpClient