一步步用Rxjava+Retrofit+OKhttp实现下载进度监听

版权声明：本文为博主原创文章，转载请注明原文链接 https://blog.csdn.net/sailist/article/details/82432969

服务器端如何实现下载(Tomcat)可以看我之前写的博客
Tomcat下文件下载与上传的简单实现，这篇博客主要是写安卓端如何监听下载进度，并转到相应的UI界面进行处理。

主要分三步：

• 创建一个Listener接口用于监听下载进度
• 创建一个内置了监听器的ResponseBody的子类用于实时获取进度
• 为OKHttpClient添加拦截器处理原本的Response

第一步：创建一个Listener接口用于监听下载进度

public interface ProgressListener {
    /**
     * @param progress 已经下载或上传字节数
     * @param total    总字节数
     * @param done     是否完成
     */
    void onProgress(long progress, long total, boolean done);
}

第二步：实现继承ResponseBody的子类

import java.io.IOException;

import okhttp3.MediaType;
import okhttp3.ResponseBody;
import okio.Buffer;
import okio.BufferedSource;
import okio.ForwardingSource;
import okio.Okio;
import okio.Source;

public class ProgressResponseBody extends ResponseBody {
    private final ResponseBody responseBody;
    private final ProgressListener progressListener;
    private BufferedSource bufferedSource;

    public ProgressResponseBody(ResponseBody responseBody, ProgressListener progressListener) {
        this.responseBody = responseBody;
        this.progressListener = progressListener;
    }

    @Override
    public MediaType contentType() {
        return responseBody.contentType();
    }


    @Override
    public long contentLength() {
        return responseBody.contentLength();
    }

    @Override
    public BufferedSource source() {
        if (bufferedSource == null) {
            bufferedSource = Okio.buffer(source(responseBody.source()));
        }
        return bufferedSource;
    }

    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;
                progressListener.onProgress(totalBytesRead, responseBody.contentLength(), bytesRead == -1);
                return bytesRead;
            }
        };
    }
}

第三步：为OKHttpClient添加拦截器

OkHttpClient build = new OkHttpClient.Builder()
                .addInterceptor(new Interceptor() {
                    @Override
                    public Response intercept(Chain chain) throws IOException {
                        Response proceed = chain.proceed(chain.request());
                        return proceed.newBuilder().body(new ProgressResponseBody(
                                proceed.body(),
                                new ProgressListener() {
                                    @Override
                                    public void onProgress(long progress, long total, boolean done) {
                                        Log.i(TAG, "onProgress: " + progress + "-" + total + "-" + done);
                                    }
                                }
                        )).build();
                    }
                }).build();

剩下的步骤就是正常的Retrofit请求的步骤了：

Retrofit retrofit = new Retrofit.Builder()
                .client(build)
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .baseUrl(Request.host)
                .build();

Request request = retrofit.create(Request.class);
        ...

之后正常使用，可以发现控制台已经有了相应的输出，这说明监听进度已经实现，接下来就是如何将监听器里原本的输出换成相应的UI更新了，这里不做赘述。