前言
前面介绍了很多关于Retrofit2的基本使用，下面就单独介绍一下如何使用Retrofit2实现文件上传和文件下载，并且做了一点拓展，重点介绍了一下上传和下载过程中进度的显示。
文件上传
定义接口
@Multipart
@POST("url")
Call<Result> uploadFile(@Part RequestBody file);
构造所要上传的RequestBody
File file = new File(filePath);
RequestBody body = RequestBody.create(MediaType.parse("multipart/form-data"), file);
Call<String> call = fileService.uploadFile(body);
call.enqueue(callback);
通过Retrofit提供的方法就可以很简单的将文件上传到服务器，但通常上传文件时，都会加上文件的上传进度，这样交互会显得更加友好。而Retrofit本身是不支持文件上传进度显示的，所以就需要我们自己扩展OkHttp来实现文件上传进度。
我的做法是直接扩展一个RequestBody来实现进度显示，实现完成之后只需要将上面body进行包装转换即可。
首先封装一个RetrofitCallback，用于进度的回调。
public abstract class RetrofitCallback<T> implements Callback<T> {
@Override
public void onResponse(Call<T> call, Response<T> response) {
if(response.isSuccessful()) {
onSuccess(call, response);
} else {
onFailure(call, new Throwable(response.message()));
}
}
public abstract void onSuccess(Call<T> call, Response<T> response);
//用于进度的回调
public abstract void onLoading(long total, long progress) ;
}
第二步，扩展OkHttp的请求体，编写包装类FileRequestBody，对RequestBody进行包装
public final class FileRequestBody<T> extends RequestBody {
/**
* 实际请求体
*/
private RequestBody requestBody;
/**
* 上传回调接口
*/
private RetrofitCallback<T> callback;
/**
* 包装完成的BufferedSink
*/
private BufferedSink bufferedSink;
public FileRequestBody(RequestBody requestBody, RetrofitCallback<T> callback) {
super();
this.requestBody = requestBody;
this.callback = callback;
}
@Override
public long contentLength() throws IOException {
return requestBody.contentLength();
}
@Override
public MediaType contentType() {
return requestBody.contentType();
}
@Override
public void writeTo(BufferedSink sink) throws IOException {
bufferedSink = Okio.buffer(sink(sink));
//写入
requestBody.writeTo(bufferedSink);
//必须调用flush，否则最后一部分数据可能不会被写入
bufferedSink.flush();
}
/**
* 写入，回调进度接口
* @param sink Sink
* @return Sink
*/
private Sink sink(Sink sink) {
return new ForwardingSink(sink) {
//当前写入字节数
long bytesWritten = 0L;
//总字节长度，避免多次调用contentLength()方法
long contentLength = 0L;
@Override
public void write(Buffer source, long byteCount) throws IOException {
super.write(source, byteCount);
if (contentLength == 0) {
//获得contentLength的值，后续不再调用
contentLength = contentLength();
}
//增加当前写入的字节数
bytesWritten += byteCount;
//回调
callback.onLoading(contentLength, bytesWritten);
}
};
}
}
最后，通过onLoading(long total, long progress) ，更新上传进度
RetrofitCallback< String > callback = new RetrofitCallback< Result >() {
@Override
public void onSuccess(Call< String > call, Response< String > response) {
runOnUIThread(activity, response.body().toString());
//进度更新结束
}
@Override
public void onFailure(Call< String > call, Throwable t) {
runOnUIThread(activity, t.getMessage());
//进度更新结束
}
@Override
public void onLoading(long total, long progress) {
super.onLoading(total, progress);
//此处进行进度更新
}
};
RequestBody resquestBody = RequestBody.create(MediaType.parse("multipart/form-data"), file);
//通过该行代码将RequestBody转换成特定的FileRequestBody
FileRequestBody body = new FileRequestBody(resquestBody, callback);
Call<String> call = fileService.uploadOneFile(body);
call.enqueue(callback);
文件下载
接口定义
文件下载请求与普通的Get和Post请求是一样的，只是他们的返回值不一样而已，文件下载请求的返回值一般定义成ResponseBody
//这里只举例POST方式进行文件下载
@FormUrlEncoded
@POST("fileService")
Call<ResponseBody> downloadFile(@Field("param") String param);
发起请求
RetrofitCallback<ResponseBody> callback = new RetrofitCallback<ResponseBody>() {
@Override
public void onSuccess(Call<ResponseBody> call, Response<ResponseBody> response) {
try {
InputStream is = response.body().byteStream();
String path = Util.getSdCardPath();
File file = new File(path, "download.jpg");
FileOutputStream fos = new FileOutputStream(file);
BufferedInputStream bis = new BufferedInputStream(is);
byte[] buffer = new byte[1024];
int len;
while ((len = bis.read(buffer)) != -1) {
fos.write(buffer, 0, len);
}
fos.flush();
fos.close();
bis.close();
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void onFailure(Call<ResponseBody> call, Throwable t) {
runOnUIThread(activity, t.getMessage());
}
@Override
public void onLoading(long total, long progress){
//更新下载进度
}
};
Call<ResponseBody> call = getRetrofitService(callback).downloadFile(param);
call.enqueue(callback);
下载进度显示
通过OkHttp设置拦截器将ResponseBody进行转换成我们扩展后的ResponseBody
** 扩展ResponseBody设置OkHttp拦截器**
private <T> RetrofitService getRetrofitService(final RetrofitCallback<T> callback) {
OkHttpClient.Builder clientBuilder = new OkHttpClient.Builder();
clientBuilder.addInterceptor(new Interceptor() {
@Override
public okhttp3.Response intercept(Chain chain) throws IOException {
okhttp3.Response response = chain.proceed(chain.request());
//将ResponseBody转换成我们需要的FileResponseBody
return response.newBuilder().body(new FileResponseBody<T>(response.body(), callback)).build();
}
});
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(BASE_URL)
.client(clientBuilder.build())
.addConverterFactory(GsonConverterFactory.create())
.build();
RetrofitService service = retrofit.create(RetrofitService.class);
return service ;
}
//通过上面的设置后，我们需要在回调RetrofitCallback中实现onLoading方法来进行进度的更新操作，与上传文件的方法相同
FileResponseBody
/**
* 扩展OkHttp的请求体，实现上传时的进度提示
*
* @param <T>
*/
public final class FileResponseBody<T> extends ResponseBody {
/**
* 实际请求体
*/
private ResponseBody mResponseBody;
/**
* 下载回调接口
*/
private RetrofitCallback<T> mCallback;
/**
* BufferedSource
*/
private BufferedSource mBufferedSource;
public FileResponseBody(ResponseBody responseBody, RetrofitCallback<T> callback) {
super();
this.mResponseBody = responseBody;
this.mCallback = callback;
}
@Override
public BufferedSource source() {
if (mBufferedSource == null) {
mBufferedSource = Okio.buffer(source(mResponseBody.source()));
}
return mBufferedSource;
}
@Override
public long contentLength() {
return mResponseBody.contentLength();
}
@Override
public MediaType contentType() {
return mResponseBody.contentType();
}
/**
* 回调进度接口
* @param source
* @return Source
*/
private Source source(Source source) {
return new ForwardingSource(source) {
long totalBytesRead = 0L;
@Override
public long read(Buffer sink, long byteCount) throws IOException {
long bytesRead = super.read(sink, byteCount);
totalBytesRead += bytesRead != -1 ? bytesRead : 0;
mCallback.onLoading(mResponseBody.contentLength(), totalBytesRead);
return bytesRead;
}
};
}
}
总结
依照惯例，最后都要有一个总结，先感叹一下retrofit的强大。ok，再来说一下使用过程中的感受，从本文中也感受的到，就是retrofit大量的引入了对okhttp 应用，所以要想用好retrofit ，学好okhttp 也是必须的，不说了，啃代码去了。
