HTTPDNS:Android で WebView と OkHttp を使用した HTTPDNS のベストプラクティス

webview.webViewClient = object : WebViewClient() {
    override fun shouldInterceptRequest(
        view: WebView?,
        request: WebResourceRequest?
    ): WebResourceResponse? {
        if (shouldIntercept(request)) {
            return getResponseByOkHttp(request)
        }
        return super.shouldInterceptRequest(view, request)
    }
}

webview.setWebViewClient(new WebViewClient(){
    @Nullable
    @Override
    public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request) {
        if (shouldIntercept(request)) {
            return getResponseByOkHttp(request);
        }
        return super.shouldInterceptRequest(view, request);
    }
});

private fun shouldIntercept(webResourceRequest: WebResourceRequest?): Boolean {
    if (webResourceRequest == null) {
        return false
    }
    val url = webResourceRequest.url ?: return false
    // HTTP 以外のリクエストはインターセプトされません。
    if ("https" != url.scheme && "http" != url.scheme) {
        return false
    }
    // GET リクエストのみがインターセプトされます。
    if ("GET".equals(webResourceRequest.method, true)) {
        return true
    }
    return false
}

private boolean shouldIntercept(WebResourceRequest request) {
    if (request == null || request.getUrl() == null) {
        return false;
    }
    // HTTP 以外のリクエストはインターセプトされません。
    if (!"http".equals(request.getUrl().getScheme()) && !"https".equals(request.getUrl().getScheme())) {
        return false;
    }
    // GET リクエストのみがインターセプトされます。
    if ("GET".equalsIgnoreCase(request.getMethod())) {
        return true;
    }

    return false;
}

private fun getResponseByOkHttp(webResourceRequest: WebResourceRequest?): WebResourceResponse? {
    if (webResourceRequest == null) {return null}
    try {
        val url = webResourceRequest.url.toString()
        val requestBuilder =
            Request.Builder().url(url).method(webResourceRequest.method, null)
        val requestHeaders = webResourceRequest.requestHeaders
        if (!requestHeaders.isNullOrEmpty()) {
            requestHeaders.forEach {
                requestBuilder.addHeader(it.key, it.value)
            }
        }
        val response = okHttpClient.newCall(requestBuilder.build()).execute()
        val code = response.code
        if (code != 200) {
            return null
        }
        val body = response.body
        if (body != null) {
            val contentType = body.contentType()
            val encoding = contentType?.charset()
            val mediaType = contentType?.toString()
            var mimeType = "text/plain"
            if (!TextUtils.isEmpty(mediaType)) {
                val mediaTypeElements = mediaType?.split(";")
                if (!mediaTypeElements.isNullOrEmpty()) {
                    mimeType = mediaTypeElements[0]
                }
            }
            val responseHeaders = mutableMapOf<String, String>()
            for (header in response.headers) {
                responseHeaders[header.first] = header.second
            }
            var message = response.message
            if (message.isBlank()) {
                message = "OK"
            }
            val resourceResponse =
                WebResourceResponse(mimeType, encoding?.name(), body.byteStream())
            resourceResponse.responseHeaders = responseHeaders
            resourceResponse.setStatusCodeAndReasonPhrase(code, message)
            return resourceResponse
        }
    } catch (e: Throwable) {
        e.printStackTrace()
    }
    return null
}

private WebResourceResponse getResponseByOkHttp(WebResourceRequest request) {
    try {
        String url = request.getUrl().toString();
        Request.Builder requestBuilder = new Request.Builder()
                .url(url)
                .method(request.getMethod(), null);
        Map<String, String> requestHeaders = request.getRequestHeaders();
        if (requestHeaders != null) {
            for (Map.Entry<String, String> entry : requestHeaders.entrySet()) {
                requestBuilder.addHeader(entry.getKey(), entry.getValue());
            }
        }
        Response response = okHttpClient.newCall(requestBuilder.build()).execute();
        if (200 != response.code()) {
            return null;
        }
        ResponseBody body = response.body();
        if (body != null) {
            MediaType contentType = body.contentType();
            if (contentType != null) {
                Charset encoding = contentType.charset();
                String mediaType = contentType.toString();
                String mimeType = "text/plain";
                if (!TextUtils.isEmpty(mediaType)) {
                    String[] mediaTypeElements = mediaType.split(";");
                    if (mediaTypeElements.length > 0) {
                       mimeType = mediaTypeElements[0];
                    }
                }
                Map<String, String> responseHeaders = new HashMap<>();
                for (String key : response.headers().names()) {
                    responseHeaders.put(key, response.header(key));
                }
                String message = response.message();
                if (TextUtils.isEmpty(message)) {
                    message = "OK";
                }
                WebResourceResponse resourceResponse = new WebResourceResponse(mimeType, encoding.name(), body.byteStream());
                resourceResponse.setResponseHeaders(responseHeaders);
                resourceResponse.setStatusCodeAndReasonPhrase(response.code(), message);
                return resourceResponse;
            }

        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}