Android 学习之--android多线程断点下载
我们平时都用"迅雷"下载软件，当下载到一半的时候突然断网，下次开启的时候能够从上次下载的地方继续下载，而且下载速度很快，那么这是怎么做到的呢！
其实它的“快”其实就是多线程的下载实现的，断点下载的原理是将每次下载的字节数存取下来，保证存取的子节点跟下载的同步，并在用户下次下载的时候自动读取
存储点，并以存储点为开始值继续下载。那么android里面如何实现这么断点的下载呢？
在res的布局文件里面先画一个带有进度条的下载界面
activity_main.xml
<LinearLayout 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" android:orientation="vertical" tools:context="com.example.thread.MainActivity" > <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="下载文件" /> <Button android:layout_width="fill_parent" android:layout_height="wrap_content" android:onClick="downLoad" android:text="下载" /> <ProgressBar android:id="@+id/pd" style="?android:attr/progressBarStyleHorizontal" android:layout_width="fill_parent" android:layout_height="wrap_content" /> <TextView android:id="@+id/tv" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="下载进度" /> </LinearLayout>
package com.example.thread; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.URL; import android.app.Activity; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.text.TextUtils; import android.view.View; import android.widget.EditText; import android.widget.ProgressBar; import android.widget.TextView; import android.widget.Toast; public class MainActivity extends Activity { private static EditText et_path; private static ProgressBar pb; private static TextView tv; public static int runningThread = 3; protected static final int DOWN_LOAD_ERROR = 1; protected static final int SERVER_ERROR = 2; protected static final int DOWN_LOAD_FINSIH = 3; protected static final int SHOW_TEXT = 4; public static int currentProcess = 0;// 当前进度 private Handler handler = new Handler() { public void handleMessage(android.os.Message msg) { switch (msg.what) { case DOWN_LOAD_ERROR: Toast.makeText(getApplicationContext(), "下载失败", 0).show(); break; case SERVER_ERROR: Toast.makeText(getApplicationContext(), "服务器异常", 0).show(); break; case DOWN_LOAD_FINSIH: Toast.makeText(getApplicationContext(), "文件下载完毕", 0).show(); break; case SHOW_TEXT: Toast.makeText(getApplicationContext(), "下载进度" + pb.getProgress() * 100 / pb.getMax() + "%", 0) .show(); break; default: break; } }; }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); et_path = (EditText) findViewById(R.id.et_path); pb = (ProgressBar) findViewById(R.id.pd); tv = (TextView) findViewById(R.id.tv); } public void downLoad(View view) { String path = et_path.getText().toString().trim(); final int thread = 3; if (TextUtils.isEmpty(path)) { Toast.makeText(this, "路径读取失败", 0).show(); return; } new Thread() { public void run() { try { // 1:连接服务器，获取一个文件，获取文件的长度，在本地创建一个大小跟服务器文件大小 String path = "http://dldx.csdn.net/fd.php?i=545080895071440&s=28f87f3d754b743fc81fb8b82848dcd1"; URL url = new URL(path); HttpURLConnection conn = (HttpURLConnection) url .openConnection(); conn.setConnectTimeout(5000); conn.setRequestMethod("GET"); int code = conn.getResponseCode(); if (code == 200) { // 服务器返回的数据的长度 int length = conn.getContentLength(); pb.setMax(length);// 设置进度条的最大值 System.out.println("文件总长度" + length); // 在客户端本地创建出来一个大小跟服务器端文件大小的临时文件 RandomAccessFile raFile = new RandomAccessFile( "/sdcard/spider_demo.rar", "rwd"); // 指定创建的这个文件的长度 raFile.setLength(length); raFile.close(); // 平均每一个线程下载的文件的大小 int blockSize = length / thread; for (int i = 1; i <= thread - 1; i++) { // 第一个线程下载的开始位置 int startIndex = (i - 1) * blockSize; int endIndex = i * blockSize - 1; if (i == thread) {// 最后一个线程的长度要稍微长一点 endIndex = length; } System.out.println("线程:" + i + "下载:----" + startIndex + "----->" + endIndex); new DownLoadthread(i, startIndex, endIndex, path) .start(); } } else { Message msg = new Message(); msg.what = SERVER_ERROR; handler.sendMessage(msg); } } catch (Exception e) { e.printStackTrace(); Message msg = new Message(); msg.what = DOWN_LOAD_ERROR; handler.sendMessage(msg); } }; }.start(); } /** * 下载文件的子线程，每一个线程下载对应位置的文件 * * */ public class DownLoadthread extends Thread { private int threadId; private int startIndex; private int endIndex; private String path; /** * @param threadId线程id * @param startIndex * 线程下载的开始位置 * @param endIndex * 线程下载的结束位置 * @param path下载文件在服务器上的路径 * * */ public DownLoadthread(int threadId, int startIndex, int endIndex, String path) { this.threadId = threadId; this.startIndex = startIndex; this.endIndex = endIndex; this.path = path; } @Override public void run() { try { // 检查是否存在记录下载的文件,如果存在读取这个文件的数据 // ----------------------替换成数据库---------------------------- File tempFile = new File("/sdcard/" + threadId + ".txt"); if (tempFile.exists() && tempFile.length() > 0) { FileInputStream fis = new FileInputStream(tempFile); byte[] temp = new byte[1024]; int leng = fis.read(temp); String downloadLen = new String(temp, 0, leng); int downloadInt = Integer.parseInt(downloadLen); startIndex += downloadInt;// 修改下载的真正的开始位置 fis.close(); } // ----------------------替换成数据库---------------------------- URL url = new URL(path); HttpURLConnection conn = (HttpURLConnection) url .openConnection(); conn.setConnectTimeout(5000); conn.setRequestMethod("GET"); // 重要:请求服务器下载部分的文件，需要置顶文件的位置 conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex); // 从服务器请求全部资源,如果从服务器请求部分资源为206 int code = conn.getResponseCode(); System.out.println("code=" + code); /* * if (code == 200) { InputStream is = * conn.getInputStream();//返回全部的资源 } */ InputStream is = conn.getInputStream();// 返回部分的资源 RandomAccessFile raFile = new RandomAccessFile( "/sdcard/spider_demo.rar", "rwd"); // 随机写文件的时候，从哪个文件开始写 raFile.seek(startIndex); int len = 0; byte[] buffer = new byte[1024]; int total = 0;// 已经下载的数据的长度 File file = new File("/sdcard/" + threadId + ".txt");// 作用:记录当前线程下载的数据长度 while ((len = is.read(buffer)) != -1) { // 如果你是固态硬盘,那么必须这样写数据 // RandomAccessFile info = new RandomAccessFile( // threadId + ".txt", "rwd"); FileOutputStream fos = new FileOutputStream(file); raFile.write(buffer, 0, len); total += len; fos.write(String.valueOf(total).getBytes()); fos.close(); // 更新进度条 synchronized (MainActivity.this) { currentProcess += len;// 获取所以进程下载的总进度总进度 pb.setProgress(currentProcess);// 更该界面上progressbar进度条的进度 Message message = Message.obtain();// 返回一个消息实例，防止创建太多对象 message.what = SHOW_TEXT; // message.obj handler.sendMessage(message); // 特殊情况，progressbar // progressdialog进度条对话框可以直接在子线程里面更新界面，它内部处理过了 } } is.close(); raFile.close(); System.out.println("线程:" + threadId + "下载完毕了..."); File deleteFile = new File("/sdcard/" + threadId + ".txt"); deleteFile.delete(); } catch (Exception e) { // TODO Auto-generated catch block e.printStackTrace(); } finally { threadFinish(); } } private synchronized void threadFinish() { runningThread--; if (runningThread == 0) { for (int i = 1; i <= 3; i++) { File file = new File("/sdcard/" + i + ".txt"); file.delete(); } System.out.println("文件下载完毕,删除所以的下载记录"); Message msg = new Message(); msg.what = DOWN_LOAD_FINSIH; handler.sendMessage(msg); } } } }
在清单文件里面加入权限
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.thread" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="21" /> <uses-permission android:name="android.permission.INTERNET"/> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> <application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <activity android:name=".MainActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest>
最终显示断点下载
