如何将HttpUrlConnection转换为OkHttpClient？或适配ApolloClient的HttpEngine？

1. 能否将HttpUrlConnection转换为OkHttpClient？ #

不行。HttpUrlConnection和OkHttpClient是完全独立的两套HTTP客户端实现，底层架构、API设计逻辑差异极大，没有直接的实例转换方式。如果你的遗留代码只能提供HttpUrlConnection实例，没法把它转换成OkHttpClient给ApolloClient使用。

2. 能否用HttpUrlConnection实现Apollo的HttpEngine？ #

可以。ApolloClient的HttpEngine是一个抽象扩展层，专门用来支持自定义HTTP客户端接入。你只需要实现Apollo提供的HttpEngine接口（或继承BaseHttpEngine抽象类），在实现类里封装HttpUrlConnection的请求/响应处理逻辑，就能让ApolloClient通过HttpUrlConnection发送GraphQL请求。

简单实现示例 #

class HttpUrlConnectionEngine implements HttpEngine {
    @Override
    public HttpResponse execute(HttpRequest request) throws IOException {
        // 解析Apollo HttpRequest的参数
        URL url = new URL(request.url().toString());
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();

        // 设置请求方法与请求头
        connection.setRequestMethod(request.method());
        for (Map.Entry<String, String> header : request.headers().entrySet()) {
            connection.setRequestProperty(header.getKey(), header.getValue());
        }

        // 处理请求体（针对POST等带body的请求）
        if (request.hasBody()) {
            connection.setDoOutput(true);
            try (OutputStream outputStream = connection.getOutputStream()) {
                request.body().writeTo(outputStream);
            }
        }

        // 读取响应并封装成Apollo HttpResponse
        int statusCode = connection.getResponseCode();
        Headers responseHeaders = Headers.of(connection.getHeaderFields());
        InputStream responseStream = statusCode >= 200 && statusCode < 300
                ? connection.getInputStream()
                : connection.getErrorStream();

        return HttpResponse.builder()
                .statusCode(statusCode)
                .headers(responseHeaders)
                .body(responseStream)
                .build();
    }

    @Override
    public void dispose() {
        // 按需清理资源，比如关闭未释放的连接等
    }

    @Override
    public boolean isCanceled() {
        return false;
    }

    @Override
    public void cancel() {
        // 实现取消请求逻辑
    }
}

接入ApolloClient #

把自定义的HttpEngine传入ApolloClient构建器即可：

ApolloClient apolloClient = ApolloClient.builder()
        .serverUrl("你的GraphQL服务地址")
        .httpEngine(new HttpUrlConnectionEngine())
        .build();

内容的提问来源于stack exchange，提问作者Vinod Jayachandran