Android开发之断点续传（下载）

downloadutils

public class downloadutils {
 private static final string tag = "downloadutils";
 private static volatile downloadutils instance;
 private file file;
 private string filepath;

 private okhttpclient client;
 private file downloadfile;
 private long startposition;
 private call call;

 private downloadutils() {
  client = new okhttpclient();
 }

 private downloadlistener listener;

 public void setlistener(downloadlistener listener) {
  this.listener = listener;
 }

 /**
  * 初始化下载父路径
  *
  * @param path
  */
 public void initdownload(string path) {
  file = new file(path);
  if (!file.getparentfile().exists()) {
file.getparentfile().mkdir();
  }
  if (!file.exists()) {
file.mkdir();
  }
  filepath = file.getabsolutepath();
  log.i(tag, "initdownload: " + filepath);
 }

 public static downloadutils getinstance() {
  if (null == instance) {
synchronized (downloadutils.class) {
 if (instance == null) {
  instance = new downloadutils();
 }
}
  }
  return instance;
 }

 public void startdownload(string url) {
  if (textutils.isempty(url)) {
return;
  }


  if (url.contains(".")) {
string typename = url.substring(url.lastindexof(".") + 1);
if (url.contains("/")) {
 string name = url.substring(url.lastindexof("/") + 1, url.lastindexof("."));
 string fn = name + "." + typename;

 downloadfile = new file(file, fn);
}
  }
  startposition = 0;
  if (downloadfile.exists()) {
startposition = downloadfile.length();
  }

  request request = new request.builder()
 .addheader("range", "bytes=" + startposition + "-")
 .url(url)
 .build();

  call = client.newcall(request);
  call.enqueue(new callback() {
@override
public void onfailure(call call, ioexception e) {

}

@override
public void onresponse(call call, response response) throws ioexception {
 listener.startdownload();
 responsebody body = response.body();
 long totallength = body.contentlength() + startposition;
 log.i(tag, "totallength: " + totallength + "----");
 inputstream is = body.bytestream();
 byte[] buf = new byte[2048];
 int length = 0;
 long totalnum = startposition;
 randomaccessfile raf = new randomaccessfile(downloadfile, "rw");
 raf.seek(totalnum);
 while ((length = is.read(buf, 0, buf.length)) != -1) {
  raf.write(buf, 0, length);
  totalnum += length;
  listener.downloadprogress(totalnum * 100 / totallength);

 }
 log.i(tag, "totalnum==" + totalnum + "---");
 listener.finishdownload(downloadfile.getabsolutepath());
 body.close();
}
  });


 }

 public void pausedownload() {
  listener.pausedownload();
  if (call != null && call.isexecuted()) {
call.cancel();
  }
 }
}

downloadlistener

public interface downloadlistener {
 void startdownload();

 void pausedownload();

 void finishdownload(string path);

 void downloadprogress(long progress);
}

mainactivity

public class mainactivity extends appcompatactivity implements view.onclicklistener {

 private textview tv_pro;
 private progressbar progressbar;
 private button btn_start;
 private button btn_pause;
 private string downloadurl = "https://acj3.pc6.com/pc6_soure/2017-12/com.yek.android.kfc.activitys_3820.apk";

 @override
 protected void oncreate(bundle savedinstancestate) {
  super.oncreate(savedinstancestate);
  setcontentview(r.layout.activity_main);
  tv_pro = findviewbyid(r.id.tv_pro);
  progressbar = findviewbyid(r.id.progressbar);
  btn_start = findviewbyid(r.id.start);
  btn_pause = findviewbyid(r.id.pause);
  btn_start.setonclicklistener(this);
  btn_pause.setonclicklistener(this);
  if (environment.getexternalstoragestate().equals(environment.media_mounted)) {
file storagedirectory = environment.getexternalstoragedirectory();
string absolutepath = storagedirectory.getabsolutepath();
final string path = absolutepath + "/download/";
log.i("zzz", "下载路径 " + path);
downloadutils.getinstance().initdownload(path);
downloadutils.getinstance().setlistener(new downloadlistener() {
 @override
 public void startdownload() {

 }

 @override
 public void pausedownload() {

 }

 @override
 public void finishdownload(string path) {
  installapk(new file(path));
 }


 @override
 public void downloadprogress(final long progress) {
  runonuithread(new runnable() {
@override
public void run() {
 tv_pro.settext((int)progress + "%");
 progressbar.setprogress((int) progress);
}
  });
 }
});
  }
 }

 @override
 public void onclick(view view) {
  switch (view.getid()) {
case r.id.start:
 downloadutils.getinstance().startdownload(downloadurl);
 break;
case r.id.pause:
 downloadutils.getinstance().pausedownload();
 break;
  }
 }
 /**
  * 安装apk
  *
  * @param file
  */
 private void installapk(file file) {
  intent intent = new intent();
  intent.setaction(intent.action_view);
  intent.addcategory("android.intent.category.default");
  intent.addflags(intent.flag_activity_new_task);
  intent.setdataandtype(uri.fromfile(file), "application/vnd.android.package-archive");
  startactivity(intent);
  android.os.process.killprocess(android.os.process.mypid());
 }
}

activity_main.xml