学习了多线程下载，而且可以断点续传的逻辑，线程数量可以自己选择，但是线程数量过多手机就承受不起，导致闪退，好在有断点续传。
步骤写在了代码的注释里。大概就是获取服务器文件的大小，在本地新建一个相同大小的文件用来申请空间，然后将服务器的文件读下来写到申请的文件中去。若开多线程，将文件分块，计算每个线程下载的开始位置和结束位置。若断点传输，则保存断开后下载的位置，下次将此位置赋给开始下载的位置即可。细节见代码。
下面是效果图：
布局文件activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<EditText
android:id="@ id/et_path"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="请输入下载路径"
android:text="http://10.173.29.234/test.exe" />
<EditText
android:id="@ id/et_threadCount"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="请输入线程数量" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="click"
android:text="下载" />
<LinearLayout
android:id="@ id/ll_pb"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#455eee"
android:orientation="vertical">
</LinearLayout>
</LinearLayout>
</android.support.constraint.ConstraintLayout>
创建布局文件，用来动态显示每个线程的进度条
layout.xml:
<?xml version="1.0" encoding="utf-8"?> <ProgressBar xmlns:android="http://schemas.android.com/apk/res/android" android:id="@ id/progressBar" style="?android:attr/progressBarStyleHorizontal" android:layout_width="match_parent" android:layout_height="wrap_content" />
MainActivity.java:
import...;
public class MainActivity extends AppCompatActivity {
private EditText et_path;
private EditText et_threadCount;
private LinearLayout ll_pb;
private String path;
private static int runningThread;// 代表正在运行的线程
private int threadCount;
private List<ProgressBar> pbList;//集合存储进度条的引用
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
et_path = findViewById(R.id.et_path);
et_threadCount = findViewById(R.id.et_threadCount);
ll_pb = findViewById(R.id.ll_pb);
//添加一个进度条的引用
pbList = new ArrayList<ProgressBar>();
}
//点击按钮实现下载逻辑
public void click(View view) {
//获取下载路径
path = et_path.getText().toString().trim();
//获取线程数量
String threadCounts = et_threadCount.getText().toString().trim();
//移除以前的进度条添加新的进度条
ll_pb.removeAllViews();
threadCount = Integer.parseInt(threadCounts);
pbList.clear();
for (int i = 0; i < threadCount; i ) {
ProgressBar v = (ProgressBar) View.inflate(getApplicationContext(), R.layout.layout, null);
//把v添加到几何中
pbList.add(v);
//动态获取进度条
ll_pb.addView(v);
}
//java逻辑移植
new Thread() {
@Override
public void run() {
/*************/
System.out.println("你好");
try {
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
int code = conn.getResponseCode();
if (code == 200) {
int length = conn.getContentLength();
// 把运行线程的数量赋值给runningThread
runningThread = threadCount;
System.out.println("length=" length);
// 创建一个和服务器的文件一样大小的文件，提前申请空间
RandomAccessFile randomAccessFile = new RandomAccessFile(getFileName(path), "rw");
randomAccessFile.setLength(length);
// 算出每个线程下载的大小
int blockSize = length / threadCount;
// 计算每个线程下载的开始位置和结束位置
for (int i = 0; i < length; i ) {
int startIndex = i * blockSize;// 开始位置
int endIndex = (i 1) * blockSize;// 结束位置
// 特殊情况就是最后一个线程
if (i == threadCount - 1) {
// 说明是最后一个线程
endIndex = length - 1;
}
// 开启线程去服务器下载
DownLoadThread downLoadThread = new DownLoadThread(startIndex, endIndex, i);
downLoadThread.start();
}
}
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
/*************/
}
}.start();
}
private class DownLoadThread extends Thread {
// 通过构造方法吧每个线程的开始位置和结束位置传进来
private int startIndex;
private int endIndex;
private int threadID;
private int PbMaxSize;//代表当前下载（进度条）的最大值
private int pblastPosition;//如果中断过，这是进度条上次的位置
public DownLoadThread(int startIndex, int endIndex, int threadID) {
this.startIndex = startIndex;
this.endIndex = endIndex;
this.threadID = threadID;
}
@Override
public void run() {
// 实现去服务器下载文件
try {
//计算进度条最大值
PbMaxSize = endIndex - startIndex;
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
// 如果中间断过，接着上次的位置继续下载，聪慧文件中读取上次下载的位置
File file = new File(getFileName(path) threadID ".txt");
if (file.exists() && file.length() > 0) {
FileInputStream fis = new FileInputStream(file);
BufferedReader bufr = new BufferedReader(new InputStreamReader(fis));
String lastPosition = bufr.readLine();
int lastPosition1 = Integer.parseInt(lastPosition);
//赋值给进度条位置
pblastPosition = lastPosition1 - startIndex;
// 改变一下startIndex的值
startIndex = lastPosition1 1;
System.out.println("线程id：" threadID "真实下载的位置：" lastPosition "-------" endIndex);
bufr.close();
fis.close();
}
conn.setRequestProperty("Range", "bytes=" startIndex "-" endIndex);
int code = conn.getResponseCode();
if (code == 206) {
// 随机读写文件对象
RandomAccessFile raf = new RandomAccessFile(getFileName(path), "rw");
// 每个线程从自己的位置开始写
raf.seek(startIndex);
InputStream in = conn.getInputStream();
// 把数据写到文件中
int len = -1;
byte[] buffer = new byte[1024];
int totle = 0;// 代表当前线程下载的大小
while ((len = in.read(buffer)) != -1) {
raf.write(buffer, 0, len);
totle = len;
// 实现断点续传就是把当前线程下载的位置保存起来，下次再下载的时候按照上次下载的位置继续下载
int currentThreadPosition = startIndex totle;// 存到一个txt文本中
// 用来存储当前线程当前下载的位置
RandomAccessFile raff = new RandomAccessFile(getFileName(path) threadID ".txt", "rwd");
raff.write(String.valueOf(currentThreadPosition).getBytes());
raff.close();
//设置进度条当前的进度
pbList.get(threadID).setMax(PbMaxSize);
pbList.get(threadID).setProgress(pblastPosition totle);
}
raf.close();
System.out.println("线程ID:" threadID "下载完成");
// 将产生的txt文件删除，每个线程下载完成的具体时间不知道
synchronized (DownLoadThread.class) {
runningThread--;
if (runningThread == 0) {
//说明线程执行完毕
for (int i = 0; i < threadCount; i ) {
File filedel = new File(getFileName(path) i ".txt");
filedel.delete();
}
}
}
}
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public String getFileName(String path) {
int start = path.lastIndexOf("/") 1;
String subString = path.substring(start);
String fileName = "/data/data/com.lgqrlchinese.heima76android_11_mutildownload/" subString;
return fileName;
}
}
在清单文件中添加以下权限
<uses-permission android:name="android.permission.INTERNET"/> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持Devmax。