feign 整合 httpclien 连接池

在 Feign 中使用 HttpClient 连接池可以提高性能和资源利用率，避免重复创建和关闭连接。下面是整合的步骤：

1. 添加依赖

在 pom.xml 中添加以下依赖：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.12</version>
</dependency>

2. 配置 HttpClient

在 Spring Boot 中，可以使用 HttpClientBuilder 来构建 HttpClient，并配置连接池参数：

@Configuration
public class HttpClientConfig {

    @Value("${httpclient.max-total}")
    private int maxTotal;

    @Value("${httpclient.default-max-per-route}")
    private int defaultMaxPerRoute;

    @Bean
    public CloseableHttpClient httpClient() {
        PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
        connectionManager.setMaxTotal(maxTotal);
        connectionManager.setDefaultMaxPerRoute(defaultMaxPerRoute);

        return HttpClientBuilder.create()
                .setConnectionManager(connectionManager)
                .build();
    }
}

其中，maxTotal 表示连接池最大连接数，defaultMaxPerRoute 表示每个路由（域名）最大连接数。

3. 配置 Feign

在 Feign 中配置 HttpClient，需要实现 HttpClient 的 Client 接口，具体如下：

public class HttpClientFeignClient implements Client {

    private final CloseableHttpClient httpClient;

    public HttpClientFeignClient(CloseableHttpClient httpClient) {
        this.httpClient = httpClient;
    }

    @Override
    public Response execute(Request request, Request.Options options) throws IOException {
        HttpClientContext context = HttpClientContext.create();
        HttpUriRequest httpUriRequest = toHttpUriRequest(request);

        CloseableHttpResponse httpResponse = httpClient.execute(httpUriRequest, context);
        return toResponse(httpResponse);
    }

    private HttpUriRequest toHttpUriRequest(Request request) {
        String method = request.method();
        String url = request.url();
        Request.Body body = request.body();

        HttpEntityEnclosingRequestBase httpUriRequest;
        switch (method) {
            case "GET":
                httpUriRequest = new HttpGet(url);
                break;
            case "POST":
                httpUriRequest = new HttpPost(url);
                break;
            case "PUT":
                httpUriRequest = new HttpPut(url);
                break;
            case "DELETE":
                httpUriRequest = new HttpDelete(url);
                break;
            default:
                throw new UnsupportedOperationException("unsupported http method: " + method);
        }

        if (body != null) {
            httpUriRequest.setEntity(new ByteArrayEntity(body.asBytes()));
        }

        return httpUriRequest;
    }

    private Response toResponse(CloseableHttpResponse httpResponse) throws IOException {
        int statusCode = httpResponse.getStatusLine().getStatusCode();
        String reasonPhrase = httpResponse.getStatusLine().getReasonPhrase();

        Map<String, Collection<String>> headers = new HashMap<>();
        for (Header header : httpResponse.getAllHeaders()) {
            String name = header.getName();
            String value = header.getValue();
            headers.computeIfAbsent(name, k -> new ArrayList<>()).add(value);
        }

        Response.Builder builder = Response.builder()
                .status(statusCode)
                .reason(reasonPhrase)
                .headers(headers);

        HttpEntity entity = httpResponse.getEntity();
        if (entity != null) {
            InputStream inputStream = entity.getContent();
            byte[] bodyData = ByteStreams.toByteArray(inputStream);
            builder.body(bodyData);
        }

        return builder.build();
    }
}

最后，在 Feign 的配置类中，使用上述实现类作为 Client：

@Configuration
public class FeignConfig {

    @Autowired
    private CloseableHttpClient httpClient;

    @Bean
    public Client feignClient() {
        return new HttpClientFeignClient(httpClient);
    }
}

这样就完成了 Feign 整合 HttpClient 连接池的配置。