Android中实现下载URL地址的网络资源的实例分享

package com.example.threaddown; 
 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.RandomAccessFile; 
import java.net.HttpURLConnection; 
import java.net.MalformedURLException; 
import java.net.URL; 
 
public class DownUtil { 
 
  // 定义下载资源的路径 
  private String path; 
  // 指定所下载的文件的保存位置 
  private String targetFile; 
  // 定义需要使用多少线程下载资源 
  private int threadNum; 
  // 定义下载的线程对象 
  private DownThread[] threads; 
  // 定义下载的文件总大小 
  private int fileSize; 
 
  public DownUtil(String path, String targetFile, int threadNum) { 
    this.path = path; 
    this.targetFile = targetFile; 
    this.threadNum = threadNum; 
  } 
 
  public void download() throws IOException { 
    URL url = new URL(path); 
    HttpURLConnection conn = (HttpURLConnection) url.openConnection(); 
    conn.setConnectTimeout(5000); 
    conn.setRequestMethod("GET"); 
    conn.setRequestProperty("Accept", "*/*"); 
    conn.setRequestProperty("Accept-Language", "zh-CN"); 
    conn.setRequestProperty("Charset", "UTF-8"); 
    conn.setRequestProperty("Connection", "Keep-Alive"); 
    // 得到文件的大小 
    fileSize = conn.getContentLength(); 
    conn.disconnect(); 
    int currentPartsSize = fileSize / threadNum + 1; 
    RandomAccessFile file = new RandomAccessFile(targetFile, "rw"); 
    // 设置本地文件的大小 
    file.setLength(fileSize); 
    file.close(); 
    for (int i = 0; i < threadNum; i++) { 
      // 计算每条线程的下载位置 
      int startPos = i * currentPartsSize; 
      // 每个线程使用一个RandomAccessFile进行下载 
      RandomAccessFile current = new RandomAccessFile(targetFile, "rw"); 
      // 定义该线程的下载位置 
      current.seek(startPos); 
      // 创建下载线程 
      threads[i] = new DownThread(startPos, currentPartsSize, current); 
      // 启动线程下载 
      threads[i].start(); 
    } 
 
  } 
 
  // 获取下载的完成百分比 
  public double getCompleteRate() { 
    // 统计多条线程已经下载的总大小 
    int sumSize = 0; 
    for (int i = 0; i < threadNum; i++) { 
      sumSize += threads[i].length; 
    } 
    return sumSize * 1.0 / fileSize; 
  } 
 
  private class DownThread extends Thread { 
    // 定义当前线程下载的位置 
    private int startPos; 
    // 定义当前线程下载文件的大小 
    private int currentPartsSize; 
    // 当前线程下载的文件块 
    private RandomAccessFile currentPart; 
    // 定义该线程已下载的字节数 
    private int length; 
 
    public DownThread(int startPos, int currentPartsSize, 
        RandomAccessFile currentPart) { 
      this.startPos = startPos; 
      this.currentPart = currentPart; 
      this.currentPartsSize = currentPartsSize; 
 
    } 
 
    @Override 
    public void run() { 
      try { 
        URL url = new URL(path); 
        HttpURLConnection conn = (HttpURLConnection) url 
            .openConnection(); 
        conn.setConnectTimeout(5000); 
        conn.setRequestMethod("GET"); 
        conn.setRequestProperty("Accept", "*/*"); 
        conn.setRequestProperty("Accept-Language", "zh-CN"); 
        conn.setRequestProperty("Charset", "UTF-8"); 
        conn.setRequestProperty("Connection", "Keep-Alive"); 
        InputStream in = conn.getInputStream(); 
        in.skip(startPos); 
        int hasRead = 0; 
        byte[] buffer = new byte[1024]; 
        // 读取网络数据，并写入本地文件 
        while (length < currentPartsSize 
            && (hasRead = in.read(buffer)) > 0) { 
          currentPart.write(buffer, 0, hasRead); 
          // 累计该线程下载的总大小 
          length += hasRead; 
        } 
        currentPart.close(); 
        in.close(); 
 
      } catch (Exception e) { 
        e.printStackTrace(); 
      } 
 
    } 
 
  } 
 
} 
								 
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