文件多线程下载实现

布局文件

- <RelativeLayout 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" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context=".MainActivity">
- <LinearLayout android:id="@+id/ll" android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal">
- <EditText android:id="@+id/pathET" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:inputType="textUri" android:text="http://192.168.1.251:8080/WebServer/FeiQ.exe">
  <requestFocus /> 
  </EditText>
  <ImageButton android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="download" android:src="@android:drawable/ic_media_play" /> 
  </LinearLayout>
  <ProgressBar android:id="@+id/downloadPB" style="?android:attr/progressBarStyleHorizontal" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_below="@id/ll" android:layout_marginTop="20dp" /> 
  <TextView android:id="@+id/percentTV" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_below="@id/downloadPB" android:text="0%" /> 
  <TextView android:id="@+id/progressTV" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentRight="true" android:layout_below="@id/downloadPB" android:text="0/0" /> 
  </RelativeLayout>

MyHandler.java

package com.itheima.download;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

import org.apache.http.HttpEntity;

import android.content.Context;

import com.loopj.android.http.FileAsyncHttpResponseHandler;

public abstract class MyFileHandler extends FileAsyncHttpResponseHandler {
    private boolean isCancel;

    public MyFileHandler(Context context) {
        super(context);
    }

    public MyFileHandler(File file) {
        super(file);
    }

    @Override
    protected byte[] getResponseData(HttpEntity entity) throws IOException {
        if (entity != null) {
            InputStream instream = entity.getContent();
            long contentLength = entity.getContentLength();
            FileOutputStream buffer = new FileOutputStream(getTargetFile(), true);
            if (instream != null) {
                try {
                    byte[] tmp = new byte[BUFFER_SIZE];
                    int l, count = 0;
                    // do not send messages if request has been cancelled
                    while ((l = instream.read(tmp)) != -1 && !Thread.currentThread().isInterrupted()) {
                        if (isCancel)
                            break;
                        count += l;
                        buffer.write(tmp, 0, l);
                        sendProgressMessage(count, (int) contentLength);
                    }
                } finally {
                    instream.close();
                    buffer.flush();
                    buffer.close();
                }
            }
        }
        return null;
    }
    
    public void cancel() {
        isCancel = true;
    }

}

MainActivity.java

package com.itheima.download;

import java.io.File;

import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ProgressBar;
import android.widget.TextView;

public class MainActivity extends Activity {

//    private AsyncHttpClient client;
    
    private EditText pathET;
    private ProgressBar downloadPB;
    private TextView percentTV;
    private TextView progressTV;
    private DownloadTask task;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        pathET = (EditText) findViewById(R.id.pathET);
        downloadPB = (ProgressBar) findViewById(R.id.downloadPB);
        percentTV = (TextView) findViewById(R.id.percentTV);
        progressTV = (TextView) findViewById(R.id.progressTV);
        
//        client = new AsyncHttpClient();
    }
    
    public void download(View v) {
        ImageButton ib = (ImageButton) v;
        
        if (task == null) {
            String targetUrl = pathET.getText().toString().trim();
            File localFile = new File(Environment.getExternalStorageDirectory(), targetUrl.substring(targetUrl.lastIndexOf("/") + 1));
            task = new DownloadTask(targetUrl, localFile, 3, this, downloadPB, percentTV, progressTV);
            task.execute();
            ib.setImageResource(android.R.drawable.ic_media_pause);
        } else {
            task.stop();
            task = null;
            ib.setImageResource(android.R.drawable.ic_media_play);
        }
    }

    /*
    public void classicDownload(View v) {
        String path = pathET.getText().toString().trim();
        File file = new File("/mnt/sdcard/", path.substring(path.lastIndexOf("/") + 1));
        
        client.get(path, new FileAsyncHttpResponseHandler(file) {        // 处理文件传输的处理器
            public void onSuccess(int statusCode, Header[] headers, File file) {
                Toast.makeText(getApplicationContext(), "下载成功", Toast.LENGTH_SHORT).show();
            }
            public void onFailure(int statusCode, Header[] headers, Throwable throwable, File file) {
                Toast.makeText(getApplicationContext(), "下载失败 " + statusCode, Toast.LENGTH_SHORT).show();
                throwable.printStackTrace();
            }
            public void onProgress(int bytesWritten, int totalSize) {    // 下载或上传的进度
                System.out.println(bytesWritten + " / " + totalSize + " (" + bytesWritten * 100 / totalSize + "%)");
            }
        });
    }
    */

}

DownloadTask.java

package com.itheima.download;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.ArrayList;

import org.apache.http.Header;

import android.content.Context;
import android.widget.ProgressBar;
import android.widget.TextView;

import com.loopj.android.http.AsyncHttpClient;
import com.loopj.android.http.AsyncHttpResponseHandler;

public class DownloadTask {
    private String targetUrl;
    private File localFile;
    private int threadAmount;
    private Context context;
    private ProgressBar downloadPB;
    private TextView percentTV;
    private TextView progressTV;

    private long contentLength;
    private long threadLength;
    private ArrayList<File> cacheList = new ArrayList<File>();
    private ArrayList<MyFileHandler> handlerList = new ArrayList<MyFileHandler>();
    
    /**
     * 创建下载任务
     * @param targetUrl        目标地址
     * @param localFile        本地路径
     * @param threadAmount    线程数量
     * @param context        应用环境
     * @param downloadPB 
     * @param progressTV 
     * @param percentTV 
     */
    public DownloadTask(String targetUrl, File localFile, int threadAmount, Context context, ProgressBar downloadPB, TextView percentTV, TextView progressTV) {
        super();
        this.targetUrl = targetUrl;
        this.localFile = localFile;
        this.threadAmount = threadAmount;
        this.context = context;
        this.downloadPB = downloadPB;
        this.percentTV = percentTV;
        this.progressTV = progressTV;
    }

    public void execute() {
        new AsyncHttpClient().head(targetUrl, new AsyncHttpResponseHandler() {        // 根据URL向服务器发起一个请求, 获取响应头
            public void onSuccess(int statusCode, Header[] headers, byte[] responseBody) {
                caculateLength(headers);    // 获取文件总长度, 计算每个线程负责的长度
                beginDownload();            // 开启多个线程下载
            }
            public void onFailure(int statusCode, Header[] headers, byte[] responseBody, Throwable error) {
            }
        });
    }
    
    private void caculateLength(Header[] headers) {        
        for (Header header : headers) 
            if ("Content-Length".equals(header.getName())) 
                contentLength = Long.parseLong(header.getValue());            // 从相应头中获取文件总大小
        threadLength = (contentLength + threadAmount - 1) / threadAmount;    // 计算每个线程负责多少
        downloadPB.setMax((int) contentLength);        // 设置进度条的最大刻度为文件总大小
    }
    
    private void beginDownload() {
        for (int i = 0; i < threadAmount; i++) {    // 定义循环, 每次循环启动1个线程下载
            File cacheFile = new File(context.getCacheDir(), localFile.getName() + ".temp" + i);    // 定义临时文件的路径
            cacheList.add(cacheFile);                // 把文件装入集合
            
            long begin = i * threadLength + cacheFile.length();        // 计算开始位置
            long end = i * threadLength + threadLength - 1;            // 计算结束位置
            System.out.println(i + ": " + begin + " - " + end);
            if (begin > end)
                continue;
            
            MyFileHandler fileHandler = new MyFileHandler(cacheFile) {            // 发送请求, 下载数据, 存储到临时文件
                private long ms;
                public void onSuccess(int statusCode, Header[] headers, File file) {
                    System.out.println(Thread.currentThread().getName() + ": " + file + " 下载完成");
                    checkOtherThread();                // 检查其他线程是否下载完毕, 如果都完了, 合并文件
                }
                public void onFailure(int statusCode, Header[] headers, Throwable throwable, File file) {
                }
                public void onProgress(int bytesWritten, int totalSize) {    // 运行频率非常高
                    if (System.currentTimeMillis() - ms > 100) {
                        ms = System.currentTimeMillis();
                        updateProgress();
                    }
                }
            };
            handlerList.add(fileHandler);
            
            AsyncHttpClient client = new AsyncHttpClient();
            client.addHeader("Range", "bytes=" + begin + "-" + end);        // 设置请求数据的范围
            client.get(targetUrl, fileHandler);
        }
    }
    
    private void updateProgress() {
        long finishLength = getFinishLength();
        if (finishLength == 0)
            return;
        downloadPB.setProgress((int) finishLength);
        percentTV.setText(finishLength * 1000 / contentLength / 10f + "%"); 
        progressTV.setText(finishLength + "/" + contentLength);
    }
    
    private long getFinishLength() {
        long finishLength = 0;
        for (File cacheFile : cacheList)             // 遍历所有临时文件
            finishLength += cacheFile.length();        // 统计总长度
        return finishLength;
    }

    private void checkOtherThread() {
        if (getFinishLength() == contentLength) {     // 如果文件长度和ContentLength相等, 代表下载完成
            updateProgress();
            merge();                                // 合并所有的临时文件
        }
    }

    private void merge() {
        try {
            FileOutputStream out = new FileOutputStream(localFile);        
            for (File cacheFile : cacheList) {                                // 遍历所有临时文件
                FileInputStream in = new FileInputStream(cacheFile);        
                byte[] buffer = new byte[8192];
                int length;
                while ((length = in.read(buffer)) != -1)    // 读取每个文件
                    out.write(buffer, 0, length);            // 把每个文件的数据都写出到localFile
                in.close();
                cacheFile.delete();
            }
            out.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
    
    public void stop() {
        for (MyFileHandler fileHandler : handlerList) {
            fileHandler.cancel();
        }
    }
}