android断点下载

断点下载往往用在大文件的下载过程中,如传统的迅雷下载用的就是断点下载技术,说起来原理比较简单:对文件进行分片,并对分片的文件进行标记,然后分片下载,下载完成后对数据流进行重组,写到本地文件。如果涉及到多线程问题,还会涉及到数据的存取操作。为了更加方便的讲解断点下载的原理,我们这里暂时不考虑断点续传问题,及数据库问题。首先来看一一个多线程下载的例子。

多线程下载

我们先看一下单个线程的下载逻辑: SmartDownloadThread.java

import java.io.File;  
import java.io.InputStream;  
import java.io.RandomAccessFile;  
import java.net.HttpURLConnection;  
import java.net.URL;  

import android.util.Log;  

/** 
 * 线程下载 
 * @author Administrator 
 *  
 */  
public class SmartDownloadThread extends Thread {  
    private static final String TAG = "SmartDownloadThread";  
    private File saveFile;  
    private URL downUrl;  
    private int block;  
    /*  *下载开始位置 */  
    private int threadId = -1;  
    private int downLength;  
    private boolean finish = false;  
    private SmartFileDownloader downloader;  

    public SmartDownloadThread(SmartFileDownloader downloader, URL downUrl,  
            File saveFile, int block, int downLength, int threadId) {  
        this.downUrl = downUrl;  
        this.saveFile = saveFile;  
        this.block = block;  
        this.downloader = downloader;  
        this.threadId = threadId;  
        this.downLength = downLength;  
    }  

    @Override  
    public void run() {  
        if (downLength < block) {// 未下载完成  
            try {  
                HttpURLConnection http = (HttpURLConnection) downUrl  
                        .openConnection();  
                http.setConnectTimeout(5 * 1000);  
                http.setRequestMethod("GET");  
                http.setRequestProperty("Accept","image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");  
                http.setRequestProperty("Accept-Language", "zh-CN");  
                http.setRequestProperty("Referer", downUrl.toString());  
                http.setRequestProperty("Charset", "UTF-8");  
                int startPos = block * (threadId - 1) + downLength;// 开始位置  
                int endPos = block * threadId - 1;// 结束位置  
                http.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);// 设置获取实体数据的范围  
                http.setRequestProperty("User-Agent","Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");  
                http.setRequestProperty("Connection", "Keep-Alive");  

                InputStream inStream = http.getInputStream();  
                byte[] buffer = new byte[1024];  
                int offset = 0;  
                print("Thread " + this.threadId + " start download from position " + startPos);  
                RandomAccessFile threadfile = new RandomAccessFile(this.saveFile, "rwd");  
                threadfile.seek(startPos);  
                while ((offset = inStream.read(buffer, 0, 1024)) != -1) {  
                    threadfile.write(buffer, 0, offset);  
                    downLength += offset;  
                    downloader.update(this.threadId, downLength);  
                    downloader.saveLogFile();  
                    downloader.append(offset);  
                }  
                threadfile.close();  
                inStream.close();  
                print("Thread " + this.threadId + " download finish");  
                this.finish = true;  
            } catch (Exception e) {  
                this.downLength = -1;  
                print("Thread " + this.threadId + ":" + e);  
            }  
        }  
    }  

    private static void print(String msg) {  
        Log.i(TAG, msg);  
    }  

    /**  
     * 下载是否完成  
     * @return  
     */  
    public boolean isFinish() {  
        return finish;  
    }  

    /** 
     * 已经下载的内容大小 
     * @return 如果返回值为-1,代表下载失败 
     */  
    public long getDownLength() {  
        return downLength;  
    }  
} 

然后在看一下多个线程下载。 SmartFileDownloader.java

import java.io.File;  
import java.io.RandomAccessFile;  
import java.net.HttpURLConnection;  
import java.net.URL;  
import java.util.LinkedHashMap;  
import java.util.Map;  
import java.util.UUID;  
import java.util.concurrent.ConcurrentHashMap;  
import java.util.regex.Matcher;  
import java.util.regex.Pattern;  

import com.hao.db.DownloadFileService;  

import android.content.Context;  
import android.util.Log;  

/** 
 * 文件下载主程序 
 * @author Administrator 
 *  
 */  
public class SmartFileDownloader {  
    private static final String TAG = "SmartFileDownloader";  
    private Context context;  
    private DownloadFileService fileService;  
    /* 已下载文件长度 */  
    private int downloadSize = 0;  
    /* 原始文件长度 */  
    private int fileSize = 0;  
    /*原始文件名*/  
    private String fileName;  
    /* 线程数 */  
    private SmartDownloadThread[] threads;  
    /* 本地保存文件 */  
    private File saveFile;  
    /* 缓存各线程下载的长度 */  
    private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();  
    /* 每条线程下载的长度 */  
    private int block;  
    /* 下载路径 */  
    private String downloadUrl;  

    /** 
     * 获取文件名 
     */  
    public String getFileName(){  
        return this.fileName;  
    }  
    /** 
     * 获取线程数 
     */  
    public int getThreadSize() {  
        return threads.length;  
    }  

    /** 
     * 获取文件大小 
     * @return 
     */  
    public int getFileSize() {  
        return fileSize;  
    }  

    /** 
     * 累计已下载大小 
     * @param size 
     */  
    protected synchronized void append(int size) {  
        downloadSize += size;  
    }  

    /** 
     * 更新指定线程最后下载的位置 
     * @param threadId 线程id 
     * @param pos 最后下载的位置 
     */  
    protected void update(int threadId, int pos) {  
        this.data.put(threadId, pos);  
    }  

    /** 
     * 保存记录文件 
     */  
    protected synchronized void saveLogFile() {  
        this.fileService.update(this.downloadUrl, this.data);  
    }  

    /** 
     * 构建文件下载器 
     * @param downloadUrl 下载路径 
     * @param fileSaveDir 文件保存目录 
     * @param threadNum 下载线程数 
     */  
    public SmartFileDownloader(Context context, String downloadUrl,  
            File fileSaveDir, int threadNum) {  
        try {  
            this.context = context;  
            this.downloadUrl = downloadUrl;  
            fileService = new DownloadFileService(this.context);  
            URL url = new URL(this.downloadUrl);  
            if (!fileSaveDir.exists()) fileSaveDir.mkdirs();  
            this.threads = new SmartDownloadThread[threadNum];  
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();  
            conn.setConnectTimeout(5 * 1000);  
            conn.setRequestMethod("GET");  
            conn.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*");  
            conn.setRequestProperty("Accept-Language", "zh-CN");  
            conn.setRequestProperty("Referer", downloadUrl);  
            conn.setRequestProperty("Charset", "UTF-8");  
            conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");  
            conn.setRequestProperty("Connection", "Keep-Alive");  
            conn.connect();  
            printResponseHeader(conn);  
            if (conn.getResponseCode() == 200) {  
                this.fileSize = conn.getContentLength();// 根据响应获取文件大小  
                if (this.fileSize <= 0)  
                    throw new RuntimeException("Unkown file size ");  

                fileName = getFileName(conn);  
                this.saveFile = new File(fileSaveDir, fileName);/* 保存文件 */  
                Map<Integer, Integer> logdata = fileService.getData(downloadUrl);  
                if (logdata.size() > 0) {  
                    for (Map.Entry<Integer, Integer> entry : logdata.entrySet())  
                        data.put(entry.getKey(), entry.getValue());  
                }  
                //划分每个线程下载文件长度  
                this.block = (this.fileSize % this.threads.length) == 0 ? this.fileSize / this.threads.length  
                        : this.fileSize / this.threads.length + 1;  
                if (this.data.size() == this.threads.length) {  
                    for (int i = 0; i < this.threads.length; i++) {  
                        this.downloadSize += this.data.get(i + 1);  
                    }  
                    print("已经下载的长度" + this.downloadSize);  
                }  
            } else {  
                throw new RuntimeException("server no response ");  
            }  
        } catch (Exception e) {  
            print(e.toString());  
            throw new RuntimeException("don't connection this url");  
        }  
    }  

    /** 
     * 获取文件名 
     */  
    private String getFileName(HttpURLConnection conn) {  
        String filename = this.downloadUrl.substring(this.downloadUrl.lastIndexOf('/') + 1);//链接的最后一个/就是文件名  
        if (filename == null || "".equals(filename.trim())) {// 如果获取不到文件名称  
            for (int i = 0;; i++) {  
                String mine = conn.getHeaderField(i);  
                print("ConnHeader:"+mine+" ");  
                if (mine == null)  
                    break;  
                if ("content-disposition".equals(conn.getHeaderFieldKey(i).toLowerCase())) {  
                    Matcher m = Pattern.compile(".*filename=(.*)").matcher(mine.toLowerCase());  
                    if (m.find())  
                        return m.group(1);  
                }  
            }  
            filename = UUID.randomUUID() + ".tmp";// 默认取一个文件名  
        }  
        return filename;  
    }  

    /** 
     * 开始下载文件 
     *  
     * @param listener 
     *            监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null 
     * @return 已下载文件大小 
     * @throws Exception 
     */  
    public int download(SmartDownloadProgressListener listener)  
            throws Exception {  
        try {  
            RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");  
            if (this.fileSize > 0)  
                randOut.setLength(this.fileSize);  
            randOut.close();  
            URL url = new URL(this.downloadUrl);  
            if (this.data.size() != this.threads.length) {  
                this.data.clear();// 清除数据  
                for (int i = 0; i < this.threads.length; i++) {  
                    this.data.put(i + 1, 0);  
                }  
            }  
            for (int i = 0; i < this.threads.length; i++) {  
                int downLength = this.data.get(i + 1);  
                if (downLength < this.block && this.downloadSize < this.fileSize) { // 该线程未完成下载时,继续下载  
                    this.threads[i] = new SmartDownloadThread(this, url,  
                            this.saveFile, this.block, this.data.get(i + 1), i + 1);  
                    this.threads[i].setPriority(7);  
                    this.threads[i].start();  
                } else {  
                    this.threads[i] = null;  
                }  
            }  
            this.fileService.save(this.downloadUrl, this.data);  
            boolean notFinish = true;// 下载未完成  
            while (notFinish) {// 循环判断是否下载完毕  
                Thread.sleep(900);  
                notFinish = false;// 假定下载完成  
                for (int i = 0; i < this.threads.length; i++) {  
                    if (this.threads[i] != null && !this.threads[i].isFinish()) {  
                        notFinish = true;// 下载没有完成  
                        if (this.threads[i].getDownLength() == -1) {// 如果下载失败,再重新下载  
                            this.threads[i] = new SmartDownloadThread(this,  
                                    url, this.saveFile, this.block, this.data.get(i + 1), i + 1);  
                            this.threads[i].setPriority(7);  
                            this.threads[i].start();  
                        }  
                    }  
                }  
                if (listener != null)  
                    listener.onDownloadSize(this.downloadSize);  
            }  
            fileService.delete(this.downloadUrl);  
        } catch (Exception e) {  
            print(e.toString());  
            throw new Exception("file download fail");  
        }  
        return this.downloadSize;  
    }  

    /** 
     * 获取Http响应头字段 
     *  
     * @param http 
     * @return 
     */  
    public static Map<String, String> getHttpResponseHeader(  
            HttpURLConnection http) {  
        Map<String, String> header = new LinkedHashMap<String, String>();  
        for (int i = 0;; i++) {  
            String mine = http.getHeaderField(i);  
            if (mine == null)  
                break;  
            header.put(http.getHeaderFieldKey(i), mine);  
        }  
        return header;  
    }  

    /** 
     * 打印Http头字段 
     *  
     * @param http 
     */  
    public static void printResponseHeader(HttpURLConnection http) {  
        Map<String, String> header = getHttpResponseHeader(http);  
        for (Map.Entry<String, String> entry : header.entrySet()) {  
            String key = entry.getKey() != null ? entry.getKey() + ":" : "";  
            print(key + entry.getValue());  
        }  
    }  

    // 打印日志  
    private static void print(String msg) {  
        Log.i(TAG, msg);  
    }  

    public interface SmartDownloadProgressListener {  
        public void onDownloadSize(int size);  
    }  
}  

最后是对下载的文件进行组装。 DownloadActivity.java

import java.io.File;  

import com.hao.R;  
import com.hao.R.id;  
import com.hao.R.layout;  
import com.hao.download.SmartFileDownloader;  
import com.hao.download.SmartFileDownloader.SmartDownloadProgressListener;  
import com.hao.util.ConstantValues;  

import android.app.Activity;  
import android.os.Bundle;  
import android.os.Environment;  
import android.os.Handler;  
import android.os.Message;  
import android.view.View;  
import android.widget.Button;  
import android.widget.ProgressBar;  
import android.widget.TextView;  
import android.widget.Toast;  

/** 
 *  
 * @author Administrator 
 *  
 */  
public class SmartDownloadActivity extends Activity {  
    private ProgressBar downloadbar;  
    private TextView resultView;  
    private String path = ConstantValues.DOWNLOAD_URL;  
    SmartFileDownloader loader;  
    private Handler handler = new Handler() {  
        @Override  
        // 信息  
        public void handleMessage(Message msg) {  
            switch (msg.what) {  
            case 1:  
                int size = msg.getData().getInt("size");  
                downloadbar.setProgress(size);  
                float result = (float) downloadbar.getProgress() / (float) downloadbar.getMax();  
                int p = (int) (result * 100);  
                resultView.setText(p + "%");  
                if (downloadbar.getProgress() == downloadbar.getMax())  
                    Toast.makeText(SmartDownloadActivity.this, "下载成功", 1).show();  
                break;  
            case -1:  
                Toast.makeText(SmartDownloadActivity.this, msg.getData().getString("error"), 1).show();  
                break;  
            }  

        }  
    };  

    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.download);  

        Button button = (Button) this.findViewById(R.id.button);  
        Button closeConn = (Button) findViewById(R.id.closeConn);  
        closeConn.setOnClickListener(new View.OnClickListener() {  

            @Override  
            public void onClick(View v) {  
                // TODO Auto-generated method stub  
                if(loader != null){  
                    finish();  
                }else{  
                    Toast.makeText(SmartDownloadActivity.this, "还没有开始下载,不能暂停", 1).show();  
                }  
            }  
        });  
        downloadbar = (ProgressBar) this.findViewById(R.id.downloadbar);  
        resultView = (TextView) this.findViewById(R.id.result);  
        resultView.setText(path);  
        button.setOnClickListener(new View.OnClickListener() {  
            @Override  
            public void onClick(View v) {  
                if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {  
                    download(path, ConstantValues.FILE_PATH);  
                } else {  
                    Toast.makeText(SmartDownloadActivity.this, "没有SDCard", 1).show();  
                }  
            }  
        });  
    }  

    // 对于UI控件的更新只能由主线程(UI线程)负责,如果在非UI线程更新UI控件,更新的结果不会反映在屏幕上,某些控件还会出错  
    private void download(final String path, final File dir) {  
        new Thread(new Runnable() {  
            @Override  
            public void run() {  
                try {  
                    loader = new SmartFileDownloader(SmartDownloadActivity.this, path, dir, 3);  
                    int length = loader.getFileSize();// 获取文件的长度  
                    downloadbar.setMax(length);  
                    loader.download(new SmartDownloadProgressListener() {  
                        @Override  
                        public void onDownloadSize(int size) {// 可以实时得到文件下载的长度  
                            Message msg = new Message();  
                            msg.what = 1;  
                            msg.getData().putInt("size", size);  
                            handler.sendMessage(msg);  
                        }  
                    });  
                } catch (Exception e) {  
                    Message msg = new Message();// 信息提示  
                    msg.what = -1;  
                    msg.getData().putString("error", "下载失败");// 如果下载错误,显示提示失败!  
                    handler.sendMessage(msg);  
                }  
            }  
        }).start();// 开始  

    }  
}  

Android聊天文件分片下载

在很多聊天程序中,都涉及到发送图片的功能,而展示在聊天界面的图片大多数是缩略图,然后点击查看大图,对于一些直接使用第三方库的开发者来说,可以自己维护一个图片服务器,然后通过Http请求,然后通过一些第三方的加载库(如Glide,fresco等)来加载图片。而有些项目,由于项目的历史问题,往往走的是Socket,就像我们的项目。 首先给大家看看实际的效果吧。

首先来分析下流程:首先到本地文件判断,是否有本地大图的缓存,如果有,直接预览本地大图,否则启动下载文件线程去下载文件,一不下载文件(分片下载),下载完成缓存到本地,同事更新数据库记录。简单的流程图如下:

涉及到的核心代码: 首先判断本地文件是否有缓存,没有启动异步线程下载(下载主要有三个方面需要注意:文件总的大小,文件片,下载文件的服务器的id)

if (!TextUtils.isEmpty(picInfo.bigImage)){
            CommonImageLoader.imageLoader("file://"+picInfo.bigImage, holder.img);
        }else {
            asynImage(holder,picInfo, tag);
        }

启动异步线程下载:

if (!TextUtils.isEmpty(picInfo.bigImage)){
            CommonImageLoader.imageLoader("file://"+picInfo.bigImage, holder.img);
        }else {
            asynImage(holder,picInfo, tag);
        }

下载核心类:

public String loadImagePath(final String tag,final String pic,final ImageCallback imageCallback,final ImageProgressCallback imageProgressCallback){
        String result = null;
        ChatPicInfo chatPicInfo = ChatPicInfo.getInfo(pic);
        if(chatPicInfo != null){
            if(chatPicInfo.local != null && new File(chatPicInfo.local).exists()){
                return chatPicInfo.local;
            }
            if(chatPicInfo.fileId != null){
                String filePath = FileUtils.getChatPath(chatPicInfo.fileId);
                if(!downloadingFileId.contains(chatPicInfo.fileId)){//不存在下载列表里面
                    WeimiHttpUtils.getWeimiHttp().downloadFile(chatPicInfo.fileId, filePath,chatPicInfo.fileLength,chatPicInfo.pieceSize);
                }
                removeData(chatPicInfo.fileId);
                downloadingFileId.add(chatPicInfo.fileId);
                fileId2Tag.put(chatPicInfo.fileId, tag);
                fileId2ImagePath.put(chatPicInfo.fileId, filePath);
                fileId2ImageCallback.put(chatPicInfo.fileId, imageCallback);
                fileId2ImageProgressCallback.put(chatPicInfo.fileId, imageProgressCallback);
            }
        }
        return result;
    }

核心下载的回调:

public String loadImagePath(final String tag,final String pic,final ImageCallback imageCallback,final ImageProgressCallback imageProgressCallback){
        String result = null;
        ChatPicInfo chatPicInfo = ChatPicInfo.getInfo(pic);
        if(chatPicInfo != null){
            if(chatPicInfo.local != null && new File(chatPicInfo.local).exists()){
                return chatPicInfo.local;
            }
            if(chatPicInfo.fileId != null){
                String filePath = FileUtils.getChatPath(chatPicInfo.fileId);
                if(!downloadingFileId.contains(chatPicInfo.fileId)){//不存在下载列表里面
                    WeimiHttpUtils.getWeimiHttp().downloadFile(chatPicInfo.fileId, filePath,chatPicInfo.fileLength,chatPicInfo.pieceSize);
                }
                removeData(chatPicInfo.fileId);
                downloadingFileId.add(chatPicInfo.fileId);
                fileId2Tag.put(chatPicInfo.fileId, tag);
                fileId2ImagePath.put(chatPicInfo.fileId, filePath);
                fileId2ImageCallback.put(chatPicInfo.fileId, imageCallback);
                fileId2ImageProgressCallback.put(chatPicInfo.fileId, imageProgressCallback);
            }
        }
        return result;
    }  

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前面已经写过一篇java实现最基础的socket网络通信,这篇和之前那篇大同小异,只是将客户端代码移植到手机中,然后获取本机IP的方法略有不同。 先讲一下本篇中...

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来自专栏指尖下的Android

菜鸡的MVP架构漫谈

相信大家在网上看过关于MVP架构的博客数不胜数,至于MVP到底是什么,也不需要我再从百度百科复制一遍了,通俗的说MVP就是解决Model和View的耦合,没有使...

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来自专栏张高兴的博客

张高兴的 Xamarin.Android 学习笔记:(三)活动生命周期

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