DownloadDemo.zip

package com.example.ryandu.downloaddemo; import android.os.AsyncTask; import android.os.Environment; import android.print.PageRange; import java.io.File; import java.io.IOException; import java.io.InputStream; import java.io.RandomAccessFile; import okhttp3.OkHttpClient; import okhttp3.Request; import okhttp3.Response; /** * <p>Project:DownloadDemo</p> * <p>Package:com.example.ryandu.downloaddemo</p> * <p>Description:下载AsyncTask</p> * <p>Company:公众号 Coder栈 </p> * * @author ryandu * @date 2017/7/27 * * 泛型说明：String 表示在执行AsyncTask的时候需要传入String参数给后台任务 此处为下载地址 * Integer 表示使用整型作为进度显示单位 * Integer 表示使用整型作为反馈执行结果 */ public class DownloadTask extends AsyncTask<String, Integer, Integer> { public static final int TYPE_SUCCESS = 0;//下载成功 public static final int TYPE_FAILED = 1;//下载失败 public static final int TYPE_PAUSED = 2;//下载暂停 public static final int TYPE_CANCELED = 3;//下载取消 private DownloadListener listener;//下载状态回调监听 private boolean isCanceled = false; private boolean isPaused = false; private int lastProgress; public DownloadTask(DownloadListener listener) { this.listener = listener; } /** * 执行具体下载逻辑 * @param strings * @return 下载状态 */ @Override protected Integer doInBackground(String... strings) { InputStream is = null; RandomAccessFile savedFile = null; File file = null; try { long downloadedLength = 0; //记录已下载文件的长度 String downloadUrl = strings[0];//获取下载地址 String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/")); String directory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getPath(); file = new File(directory + fileName);//将文件指定下载到SD卡的Download目录下 if (file.exists()) {//判断是否已存在文件，是：取出文件大小（字节数） downloadedLength = file.length(); } long contentLength = getContentLength(downloadUrl);//获取待下载文件大小（字节数） if (contentLength == 0) {//长度为0，文件异常，下载失败 return TYPE_FAILED; } else if (contentLength == downloadedLength) {//文件长度等于已下载长度，已下载完，直接返回成功 return TYPE_SUCCESS; } OkHttpClient client = new OkHttpClient(); Request request = new Request.Builder() .addHeader("RANGE", "bytes=" + downloadedLength + "-")//断点下载，指定从哪个字节开始下载 .url(downloadUrl) .build(); Response response = client.newCall(request).execute(); if (response != null) { is = response.body().byteStream(); savedFile = new RandomAccessFile(file, "rw"); savedFile.seek(downloadedLength);//跳过已下载字节 byte[] bytes = new byte[1024]; int total = 0; int len; while ((len = is.read(bytes)) != -1) { if (isCanceled) {//判断是否有取消操作 return TYPE_CANCELED; } else if (isPaused) {//判断是否有暂停操作 return TYPE_PAUSED; } else { total += len; savedFile.write(bytes, 0, len); //计算已下载百分比 int progress = (int) ((total + downloadedLength) * 100 / contentLength); publishProgress(progress); } } } } catch (Exception e) { e.printStackTrace(); } finally { try { } catch (Exception e) { e.printStackTrace(); } } return TYPE_FAILED; } /** * 更新下载进度 * @param values */ @Override protected void onProgressUpdate(Integer... values) { int progress = values[0]; if (progress > lastProgress) { listener.onProgress(progress); lastProgress = progress; } } /** * 通知下载结果 * @param type */ @Override protected void onPostExecute(Integer type) { switch (type) { case TYPE_SUCCESS: listener.onSuccess(); break; case TYPE_FAILED: listener.onFailed(); break; case TYPE_PAUSED: listener.onPaused(); break; case TYPE_CANCELED: listener.onCanceled(); break; default: break; } } public void pauseDownload() { isPaused = true; } public void cancelDownload() { isCanceled = true; } private long getContentLength(String downloadUrl) throws IOException { OkHttpClient client = new OkHttpClient(); Request request = new Request.Builder().url(downloadUrl).build(); Response response = client.newCall(request).execute(); if (response != null && response.isSuccessful()) { long contentLength = response.body().contentLength(); response.body().close(); return contentLength; } return 0; } }