Android實現多線程斷點下載的方法

Android實現多線程斷點下載的方法

 　　本文執行個體講述了Android實現多線程斷點下載的方法。分享給大家供大家參考。具體實現方法如下：

　　?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217

package cn.itcast.download; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.ProtocolException; import java.net.URL; import cn.itcast.mutiledownload.StreamTool; import android.app.Activity; import android.os.Bundle; import android.os.Handler; import android.os.Message; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.EditText; import android.widget.ProgressBar; import android.widget.TextView; import android.widget.Toast; public class MutiledownloadActivity extends Activity implements OnClickListener { private ProgressBar pb; private Button bt; private TextView tv; private EditText et; boolean flag = true; boolean stopflag = false; private Handler handler = new Handler() { @Override public void handleMessage(Message msg) { pb.setProgress(total); int max = pb.getMax(); if (total >= (max - 1)) { total = max; flag = false; } int result = total * 100 / max; tv.setText("當前進度 :" + result + "%"); super.handleMessage(msg); } }; int total = 0; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); pb = (ProgressBar) this.findViewById(R.id.pb); bt = (Button) this.findViewById(R.id.bt); tv = (TextView) this.findViewById(R.id.tv_process); et = (EditText) this.findViewById(R.id.et); bt.setOnClickListener(this); } @Override public void onClick(View v) { switch (v.getId()) { case R.id.bt: // 建立一個子線程 週期性更新ui if("開始下載".equals(bt.getText().toString())){ bt.setText("暫停"); stopflag = false; //開始下載 } else { bt.setText("開始下載"); stopflag = true; } new Thread() { @Override public void run() { super.run(); while (flag) { try { sleep(1000); // 如果total > = 檔案長度 Message msg = new Message(); handler.sendMessage(msg); } catch (InterruptedException e) { e.printStackTrace(); } } } }.start();   // 開始執行下載的操作 String path = et.getText().toString().trim(); if ("".equals(path)) { Toast.makeText(this, "路徑不可為空", 1).show(); return; } try { URL url = new URL(path); HttpURLConnection conn = (HttpURLConnection) url .openConnection(); conn.setRequestMethod("GET"); conn.setConnectTimeout(5000); conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)"); int code = conn.getResponseCode(); if (code == 200) { int len = conn.getContentLength(); RandomAccessFile file = new RandomAccessFile( "/mnt/sdcard/" + getFilenName(path), "rwd"); // 1.設定本地檔案大小跟伺服器的檔案大小一致 file.setLength(len); // 設定進度條的最大值 pb.setMax(len); // 2 .假設開啟3 個線程 int threadnumber = 3; int blocksize = len / threadnumber; /** * 線程1 0~ blocksize 線程2 1*bolocksize ~ 2*blocksize 線程3 * 2*blocksize ~ 檔案末尾 */ for (int i = 0; i < threadnumber; i++) { int startposition = i * blocksize; int endpositon = (i + 1) * blocksize; if (i == (threadnumber - 1)) { // 最後一個線程 endpositon = len; } DownLoadTask task = new DownLoadTask(i, path, startposition, endpositon); task.start(); } } } catch (Exception e) { Toast.makeText(this, "下載出現異常", 0).show(); e.printStackTrace(); } break; } } class DownLoadTask extends Thread { int threadid; String filepath; int startposition; int endpositon; public DownLoadTask(int threadid, String filepath, int startposition, int endpositon) { this.threadid = threadid; this.filepath = filepath; this.startposition = startposition; this.endpositon = endpositon; } @Override public void run() { try { File postionfile = new File("/mnt/sdcard/" + threadid + ".txt"); URL url = new URL(filepath); HttpURLConnection conn = (HttpURLConnection) url .openConnection(); System.out.println("線程" + threadid + "正在下載 " + "開始位置 : " + startposition + "結束位置 " + endpositon); if (postionfile.exists()) { FileInputStream fis = new FileInputStream(postionfile); byte[] result = StreamTool.getBytes(fis); String str = new String(result); if (!"".equals(str)) { int newstartposition = Integer.parseInt(str); if (newstartposition > startposition) { startposition = newstartposition; } } } // "Range", "bytes=2097152-4194303") conn.setRequestProperty("Range", "bytes=" + startposition + "-" + endpositon); conn.setRequestMethod("GET"); conn.setConnectTimeout(5000); conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)"); InputStream is = conn.getInputStream(); RandomAccessFile file = new RandomAccessFile("/mnt/sdcard/" + getFilenName(filepath), "rwd"); // 設定 資料從檔案哪個位置開始寫 file.seek(startposition); byte[] buffer = new byte[1024]; int len = 0; // 代表當前讀到的伺服器資料的位置 ,同時這個值已經儲存的檔案的位置 int currentPostion = startposition; // 建立一個檔案對象 ,記錄當前某個檔案的下載位置 while ((len = is.read(buffer)) != -1) { if (stopflag) { return; } file.write(buffer, 0, len); synchronized (MutiledownloadActivity.this) { total += len; } currentPostion += len; // 需要把currentPostion 資訊給持久化到存放裝置 String position = currentPostion + ""; FileOutputStream fos = new FileOutputStream(postionfile); fos.write(position.getBytes()); fos.flush(); fos.close(); } file.close(); System.out.println("線程" + threadid + "下載完畢"); // 當線程下載完畢後 把檔案刪除掉 if (postionfile.exists()) { postionfile.delete(); } } catch (Exception e) { e.printStackTrace(); } super.run(); } } public String getFilenName(String path) { int start = path.lastIndexOf("/") + 1; return path.substring(start, path.length()); } }

　　希望本文所述對大家的Android程式設計有所協助。