OKhttp框架实现断点续传

1.什么是断点续传

FTP（文件传输协议的简称）（File Transfer Protocol、 FTP）客户端软件断点续传指的是在下载或上传时，将下载或上传任务（一个文件或一个压缩包）人为的划分为几个部分，每一个部分采用一个线程进行上传或下载，如果碰到网络故障，可以从已经上传或下载的部分开始继续上传下载未完成的部分，而没有必要从头开始上传下载。用户可以节省时间，提高速度。

 

有时用户上传下载文件需要历时数小时，万一线路中断，不具备断点续传的FTP服务器或下载软件就只能从头重传，比较好的FTP服务器或下载软件具有FTP断点续传能力，允许用户从上传下载断线的地方继续传送，这样大大减少了用户的烦恼。

 

 

 

2.代码讲解

 

ProgressDownloader类

package com.wjn.okhttpmvpdemo.mode.breakpointcontinuingly;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.Interceptor;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.ResponseBody;

public class ProgressDownloader {
    private ProgressResponseBody.ProgressListener progressListener;
    private String url;
    private OkHttpClient client;
    private File destination;
    private Call call;

    public ProgressDownloader(String url, File destination, ProgressResponseBody.ProgressListener progressListener) {
        this.url = url;
        this.destination = destination;
        this.progressListener = progressListener;
        //在下载、暂停后的继续下载中可复用同一个client对象
        client = getProgressClient();
    }

    //每次下载需要新建新的Call对象
    private Call newCall(long startPoints) {
        Request request = new Request.Builder()
                .url(url)
                .header("RANGE", "bytes=" + startPoints + "-")//断点续传要用到的，指示下载的区间
                .build();
        return client.newCall(request);
    }

    public OkHttpClient getProgressClient() {
        // 拦截器，用上ProgressResponseBody
        Interceptor interceptor = new Interceptor() {
            @Override
            public Response intercept(Chain chain) throws IOException {
                Response originalResponse = chain.proceed(chain.request());
                return originalResponse.newBuilder()
                        .body(new ProgressResponseBody(originalResponse.body(), progressListener))
                        .build();
            }
        };
        return new OkHttpClient.Builder()
                .addNetworkInterceptor(interceptor)
                .build();
    }

    // startsPoint指定开始下载的点
    public void download(final long startsPoint) {
        call = newCall(startsPoint);
        call.enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                save(response, startsPoint);
            }
        });
    }

    public void pause() {
        if (call != null) {
            call.cancel();
        }
    }

    private void save(Response response, long startsPoint) {
        ResponseBody body = response.body();
        InputStream in = body.byteStream();
        FileChannel channelOut = null;
        // 随机访问文件，可以指定断点续传的起始位置
        RandomAccessFile randomAccessFile = null;
        try {
            randomAccessFile = new RandomAccessFile(destination, "rwd");
            //Chanel NIO中的用法，由于RandomAccessFile没有使用缓存策略，直接使用会使得下载速度变慢，亲测缓存下载3.3秒的文件，用普通的RandomAccessFile需要20多秒。
            channelOut = randomAccessFile.getChannel();
            // 内存映射，直接使用RandomAccessFile，是用其seek方法指定下载的起始位置，使用缓存下载，在这里指定下载位置。
            MappedByteBuffer mappedBuffer = channelOut.map(FileChannel.MapMode.READ_WRITE, startsPoint, body.contentLength());
            byte[] buffer = new byte[1024];
            int len;
            while ((len = in.read(buffer)) != -1) {
                mappedBuffer.put(buffer, 0, len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                in.close();
                if (channelOut != null) {
                    channelOut.close();
                }
                if (randomAccessFile != null) {
                    randomAccessFile.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

 

 

 

ProgressResponseBody类

package com.wjn.okhttpmvpdemo.mode.breakpointcontinuingly;

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 {
    //设置对外访问的进度监听
    public interface ProgressListener {
        void onPreExecute(long contentLength);

        void update(long totalBytes, boolean done);
    }

    private final ResponseBody responseBody;
    private final ProgressListener progressListener;
    private BufferedSource bufferedSource;

    public ProgressResponseBody(ResponseBody responseBody,
                                ProgressListener progressListener) {
        this.responseBody = responseBody;
        this.progressListener = progressListener;
        if (progressListener != null) {
            progressListener.onPreExecute(contentLength());
        }
    }

    @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 totalBytes = 0L;

            @Override
            public long read(Buffer sink, long byteCount) throws IOException {
                long bytesRead = super.read(sink, byteCount);
                // read() returns the number of bytes read, or -1 if this source is exhausted.
                totalBytes += bytesRead != -1 ? bytesRead : 0;
                if (null != progressListener) {
                    progressListener.update(totalBytes, bytesRead == -1);
                }
                return bytesRead;
            }
        };
    }
}

 

 

BreakpointContinuinglyActivity类

package com.wjn.okhttpmvpdemo.view.impl.activity;

import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.Toast;

import com.wjn.okhttpmvpdemo.R;
import com.wjn.okhttpmvpdemo.mode.breakpointcontinuingly.ProgressDownloader;
import com.wjn.okhttpmvpdemo.mode.breakpointcontinuingly.ProgressResponseBody;
import com.wjn.okhttpmvpdemo.mode.utils.ui.StatusBarUtil;

import java.io.File;

import rx.Observable;
import rx.android.schedulers.AndroidSchedulers;
import rx.functions.Action0;

public class BreakpointContinuinglyActivity extends AppCompatActivity implements ProgressResponseBody.ProgressListener {

    public static final String PACKAGE_URL = "http://gdown.baidu.com/data/wisegame/df65a597122796a4/weixin_821.apk";
    private ProgressBar progressBar;
    private Button button1, button2, button3;
    private long breakPoints;
    private ProgressDownloader downloader;
    private File file;
    private long totalBytes;
    private long contentLength;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_breakpointcontinuingly);

        //根据状态栏颜色来决定 状态栏背景 用黑色还是白色 true:是否修改状态栏字体颜色
        StatusBarUtil.setStatusBarMode(this, true, false, R.color.baise);

        progressBar = findViewById(R.id.progressBar);
        button1 = findViewById(R.id.downloadButton);
        button2 = findViewById(R.id.cancel_button);
        button3 = findViewById(R.id.continue_button);

        //下载
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                breakPoints = 0L;
                file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), "sample.apk");
                downloader = new ProgressDownloader(PACKAGE_URL, file, BreakpointContinuinglyActivity.this);
                downloader.download(0L);
            }
        });
        //暂停
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloader.pause();
                Toast.makeText(BreakpointContinuinglyActivity.this, "下载暂停", Toast.LENGTH_SHORT).show();
                // 存储此时的totalBytes，即断点位置。
                breakPoints = totalBytes;
            }
        });
        //继续
        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                downloader.download(breakPoints);
            }
        });
    }

    @Override
    public void onPreExecute(long contentLength) {
        // 文件总长只需记录一次，要注意断点续传后的contentLength只是剩余部分的长度
        if (this.contentLength == 0L) {
            this.contentLength = contentLength;
            progressBar.setMax((int) (contentLength / 1024));
        }
    }

    @Override
    public void update(long totalBytes, boolean done) {
        // 注意加上断点的长度
        this.totalBytes = totalBytes + breakPoints;
        progressBar.setProgress((int) (totalBytes + breakPoints) / 1024);
        if (done) {
            // 切换到主线程
            Observable.empty()
                    .observeOn(AndroidSchedulers.mainThread())
                    .doOnCompleted(new Action0() {
                        @Override
                        public void call() {
                            Toast.makeText(BreakpointContinuinglyActivity.this, "下载完成", Toast.LENGTH_SHORT).show();
                        }
                    })
                    .subscribe();
        }
    }
}

 

 

activity_breakpointcontinuingly布局

 

 

效果