OkHttp的HTTP连接基础
虽然在使用 OkHttp 发送 HTTP 请求时只需要提供 URL 即可，OkHttp 在实现中需要综合考虑 3 种不同的要素来确定与 HTTP 服务器之间实际建立的 HTTP 连接。这样做的目的是为了达到最佳的性能。
首先第一个考虑的要素是 URL 本身。URL 给出了要访问的资源的路径。比如 URL http://。每个地址都有对应的配置，包括端口号，HTTPS 连接设置和网络传输协议。同一个地址上的 URL 可以共享同一个底层 TCP 套接字连接。通过共享连接可以有显著的性能提升。OkHttp 提供了一个连接池来复用连接。
第三个要素是连接 HTTP 服务器时使用的路由。路由包括具体连接的 IP 地址（通过 DNS 查询来发现）和所使用的代理服务器。对于 HTTPS 连接还包括通讯协商时使用的 TLS 版本。对于同一个地址，可能有多个不同的路由。OkHttp 在遇到访问错误时会自动尝试备选路由。
当通过 OkHttp 来请求某个 URL 时，OkHttp 首先从 URL 中得到地址信息，再从连接池中根据地址来获取连接。如果在连接池中没有找到连接，则选择一个路由来尝试连接。尝试连接需要通过 DNS 查询来得到服务器的 IP 地址，也会用到代理服务器和 TLS 版本等信息。当实际的连接建立之后，OkHttp 发送 HTTP 请求并获取响应。当连接出现问题时，OkHttp 会自动选择另外的路由进行尝试。这使得 OkHttp 可以自动处理可能出现的网络问题。当成功获取到 HTTP 请求的响应之后，当前的连接会被放回到连接池中，提供给后续的请求来复用。连接池会定期把闲置的连接关闭以释放资源。

文件上传和下载实例：
1.不带参数上传文件

/** * 上传文件 * @param actionUrl 接口地址 * @param filePath 本地文件地址 */ public <T> void upLoadFile(String actionUrl, String filePath, final ReqCallBack<T> callBack) { //补全请求地址 String requestUrl = String.format("%s/%s", BASE_URL, actionUrl); //创建File File file = new File(filePath); //创建RequestBody RequestBody body = RequestBody.create(MEDIA_OBJECT_STREAM, file); //创建Request final Request request = new Request.Builder().url(requestUrl).post(body).build(); final Call call = mOkHttpClient.newBuilder().writeTimeout(50, TimeUnit.SECONDS).build().newCall(request); call.enqueue(new Callback() { @Override public void onFailure(Call call, IOException e) { Log.e(TAG, e.toString()); failedCallBack("上传失败", callBack); } @Override public void onResponse(Call call, Response response) throws IOException { if (response.isSuccessful()) { String string = response.body().string(); Log.e(TAG, "response ----->" + string); successCallBack((T) string, callBack); } else { failedCallBack("上传失败", callBack); } } }); }

2.带参数上传文件

/** *上传文件 * @param actionUrl 接口地址 * @param paramsMap 参数 * @param callBack 回调 * @param <T> */ public <T>void upLoadFile(String actionUrl, HashMap<String, Object> paramsMap, final ReqCallBack<T> callBack) { try { //补全请求地址 String requestUrl = String.format("%s/%s", upload_head, actionUrl); MultipartBody.Builder builder = new MultipartBody.Builder(); //设置类型 builder.setType(MultipartBody.FORM); //追加参数 for (String key : paramsMap.keySet()) { Object object = paramsMap.get(key); if (!(object instanceof File)) { builder.addFormDataPart(key, object.toString()); } else { File file = (File) object; builder.addFormDataPart(key, file.getName(), RequestBody.create(null, file)); } } //创建RequestBody RequestBody body = builder.build(); //创建Request final Request request = new Request.Builder().url(requestUrl).post(body).build(); //单独设置参数 比如读取超时时间 final Call call = mOkHttpClient.newBuilder().writeTimeout(50, TimeUnit.SECONDS).build().newCall(request); call.enqueue(new Callback() { @Override public void onFailure(Call call, IOException e) { Log.e(TAG, e.toString()); failedCallBack("上传失败", callBack); } @Override public void onResponse(Call call, Response response) throws IOException { if (response.isSuccessful()) { String string = response.body().string(); Log.e(TAG, "response ----->" + string); successCallBack((T) string, callBack); } else { failedCallBack("上传失败", callBack); } } }); } catch (Exception e) { Log.e(TAG, e.toString()); } }

3.带参数带进度上传文件

/** *上传文件 * @param actionUrl 接口地址 * @param paramsMap 参数 * @param callBack 回调 * @param <T> */ public <T> void upLoadFile(String actionUrl, HashMap<String, Object> paramsMap, final ReqProgressCallBack<T> callBack) { try { //补全请求地址 String requestUrl = String.format("%s/%s", upload_head, actionUrl); MultipartBody.Builder builder = new MultipartBody.Builder(); //设置类型 builder.setType(MultipartBody.FORM); //追加参数 for (String key : paramsMap.keySet()) { Object object = paramsMap.get(key); if (!(object instanceof File)) { builder.addFormDataPart(key, object.toString()); } else { File file = (File) object; builder.addFormDataPart(key, file.getName(), createProgressRequestBody(MEDIA_OBJECT_STREAM, file, callBack)); } } //创建RequestBody RequestBody body = builder.build(); //创建Request final Request request = new Request.Builder().url(requestUrl).post(body).build(); final Call call = mOkHttpClient.newBuilder().writeTimeout(50, TimeUnit.SECONDS).build().newCall(request); call.enqueue(new Callback() { @Override public void onFailure(Call call, IOException e) { Log.e(TAG, e.toString()); failedCallBack("上传失败", callBack); } @Override public void onResponse(Call call, Response response) throws IOException { if (response.isSuccessful()) { String string = response.body().string(); Log.e(TAG, "response ----->" + string); successCallBack((T) string, callBack); } else { failedCallBack("上传失败", callBack); } } }); } catch (Exception e) { Log.e(TAG, e.toString()); } }

4.创建带进度RequestBody

/** * 创建带进度的RequestBody * @param contentType MediaType * @param file 准备上传的文件 * @param callBack 回调 * @param <T> * @return */ public <T> RequestBody createProgressRequestBody(final MediaType contentType, final File file, final ReqProgressCallBack<T> callBack) { return new RequestBody() { @Override public MediaType contentType() { return contentType; } @Override public long contentLength() { return file.length(); } @Override public void writeTo(BufferedSink sink) throws IOException { Source source; try { source = Okio.source(file); Buffer buf = new Buffer(); long remaining = contentLength(); long current = 0; for (long readCount; (readCount = source.read(buf, 2048)) != -1; ) { sink.write(buf, readCount); current += readCount; Log.e(TAG, "current------>" + current); progressCallBack(remaining, current, callBack); } } catch (Exception e) { e.printStackTrace(); } } }; }

5.不带进度文件下载

/** * 下载文件 * @param fileUrl 文件url * @param destFileDir 存储目标目录 */ public <T> void downLoadFile(String fileUrl, final String destFileDir, final ReqCallBack<T> callBack) { final String fileName = MD5.encode(fileUrl); final File file = new File(destFileDir, fileName); if (file.exists()) { successCallBack((T) file, callBack); return; } final Request request = new Request.Builder().url(fileUrl).build(); final Call call = mOkHttpClient.newCall(request); call.enqueue(new Callback() { @Override public void onFailure(Call call, IOException e) { Log.e(TAG, e.toString()); failedCallBack("下载失败", callBack); } @Override public void onResponse(Call call, Response response) throws IOException { InputStream is = null; byte[] buf = new byte[2048]; int len = 0; FileOutputStream fos = null; try { long total = response.body().contentLength(); Log.e(TAG, "total------>" + total); long current = 0; is = response.body().byteStream(); fos = new FileOutputStream(file); while ((len = is.read(buf)) != -1) { current += len; fos.write(buf, 0, len); Log.e(TAG, "current------>" + current); } fos.flush(); successCallBack((T) file, callBack); } catch (IOException e) { Log.e(TAG, e.toString()); failedCallBack("下载失败", callBack); } finally { try { if (is != null) { is.close(); } if (fos != null) { fos.close(); } } catch (IOException e) { Log.e(TAG, e.toString()); } } } }); }

6.带进度文件下载

/** * 下载文件 * @param fileUrl 文件url * @param destFileDir 存储目标目录 */ public <T> void downLoadFile(String fileUrl, final String destFileDir, final ReqProgressCallBack<T> callBack) { final String fileName = MD5.encode(fileUrl); final File file = new File(destFileDir, fileName); if (file.exists()) { successCallBack((T) file, callBack); return; } final Request request = new Request.Builder().url(fileUrl).build(); final Call call = mOkHttpClient.newCall(request); call.enqueue(new Callback() { @Override public void onFailure(Call call, IOException e) { Log.e(TAG, e.toString()); failedCallBack("下载失败", callBack); } @Override public void onResponse(Call call, Response response) throws IOException { InputStream is = null; byte[] buf = new byte[2048]; int len = 0; FileOutputStream fos = null; try { long total = response.body().contentLength(); Log.e(TAG, "total------>" + total); long current = 0; is = response.body().byteStream(); fos = new FileOutputStream(file); while ((len = is.read(buf)) != -1) { current += len; fos.write(buf, 0, len); Log.e(TAG, "current------>" + current); progressCallBack(total, current, callBack); } fos.flush(); successCallBack((T) file, callBack); } catch (IOException e) { Log.e(TAG, e.toString()); failedCallBack("下载失败", callBack); } finally { try { if (is != null) { is.close(); } if (fos != null) { fos.close(); } } catch (IOException e) { Log.e(TAG, e.toString()); } } } }); }7.接口ReqProgressCallBack.java实现
public interface ReqProgressCallBack<T> extends ReqCallBack<T>{ /** * 响应进度更新 */ void onProgress(long total, long current);}8.进度回调实现 /** * 统一处理进度信息 * @param total 总计大小 * @param current 当前进度 * @param callBack * @param <T> */ private <T> void progressCallBack(final long total, final long current, final ReqProgressCallBack<T> callBack) { okHttpHandler.post(new Runnable() { @Override public void run() { if (callBack != null) { callBack.onProgress(total, current); } } }); }