前言

APP中难免会使用到下载文件、更新APP的功能，而我们自己处理下载流程往往都很复杂的，要考虑http请求、下载进度监听、下载UI提示信息等等。google官方已经封装好了专门用于下载的类，我们可以直接使用这个类进行下载即可。

DownloadManger是android 2.3（API 9）开始提供的系统服务，用于处理长时间的下载操作。应用场景是客户端请求一个URL地址去下载一个目标文件。DownloadManger可以构建一个后台下载服务，在发生故障或连接更改、重新启动系统等情况后，处理HTTP连接并重试下载。

代码

下载监听接口

package com.hyfun.downloadmanager.support;

/**
 * Created by HyFun on 2019/05/27.
 * Email: 775183940@qq.com
 * Description:
 */
public interface AndroidDownloadManagerListener {
    void onPrepare();

    void onSuccess(String path);

    void onFailed(Throwable throwable);
}

下载管理类

package com.hyfun.downloadmanager.support;

import android.app.DownloadManager;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.database.Cursor;
import android.net.Uri;
import android.os.Environment;
import android.util.Log;

import java.io.File;

/**
 * Created by HyFun on 2019/05/27.
 * Email: 775183940@qq.com
 * <p>
 * https://qd.myapp.com/myapp/qqteam/AndroidQQ/mobileqq_android.apk
 * <p>
 * Description: 使用android系统自带的download manager 进行下载apk文件
 * <p>
 * 只负责下载
 */
public class AndroidDownloadManager {
    private DownloadManager downloadManager;
    private Context context;
    private long downloadId;
    private String url;
    private String name;

    private String path;

    private AndroidDownloadManagerListener listener;

    public AndroidDownloadManager(Context context, String url) {
        this(context, url, getFileNameByUrl(url));
    }

    public AndroidDownloadManager(Context context, String url, String name) {
        this.context = context;
        this.url = url;
        this.name = name;
    }

    public AndroidDownloadManager setListener(AndroidDownloadManagerListener listener) {
        this.listener = listener;
        return this;
    }

    /**
     * 开始下载
     */
    public void download() {
        DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
        //移动网络情况下是否允许漫游
        request.setAllowedOverRoaming(false);
        //在通知栏中显示，默认就是显示的
        request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE);
        request.setTitle(name);
        request.setDescription("文件正在下载中......");
        request.setVisibleInDownloadsUi(true);

        //设置下载的路径
        File file = new File(context.getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS), name);
        request.setDestinationUri(Uri.fromFile(file));
        path = file.getAbsolutePath();

        //获取DownloadManager
        if (downloadManager == null) {
            downloadManager = (DownloadManager) context.getSystemService(Context.DOWNLOAD_SERVICE);
        }
        //将下载请求加入下载队列，加入下载队列后会给该任务返回一个long型的id，通过该id可以取消任务，重启任务、获取下载的文件等等
        if (downloadManager != null) {
            if (listener != null) {
                listener.onPrepare();
            }
            downloadId = downloadManager.enqueue(request);
        }

        //注册广播接收者，监听下载状态
        context.registerReceiver(receiver, new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
    }

    //广播监听下载的各个状态
    private BroadcastReceiver receiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            DownloadManager.Query query = new DownloadManager.Query();
            //通过下载的id查找
            query.setFilterById(downloadId);
            Cursor cursor = downloadManager.query(query);
            if (cursor.moveToFirst()) {
                int status = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_STATUS));
                switch (status) {
                    //下载暂停
                    case DownloadManager.STATUS_PAUSED:
                        break;
                    //下载延迟
                    case DownloadManager.STATUS_PENDING:
                        break;
                    //正在下载
                    case DownloadManager.STATUS_RUNNING:
                        break;
                    //下载完成
                    case DownloadManager.STATUS_SUCCESSFUL:
                        if (listener != null) {
                            listener.onSuccess(path);
                        }
                        cursor.close();
                        context.unregisterReceiver(receiver);
                        break;
                    //下载失败
                    case DownloadManager.STATUS_FAILED:
                        if (listener != null) {
                            listener.onFailed(new Exception("下载失败"));
                        }
                        cursor.close();
                        context.unregisterReceiver(receiver);
                        break;
                }
            }
        }
    };


    // ——————————————————————私有方法———————————————————————

    /**
     * 通过URL获取文件名
     *
     * @param url
     * @return
     */
    private static final String getFileNameByUrl(String url) {
        String filename = url.substring(url.lastIndexOf("/") + 1);
        filename = filename.substring(0, filename.indexOf("?") == -1 ? filename.length() : filename.indexOf("?"));
        return filename;
    }

}

使用

new AndroidDownloadManager(this, url)
        .setListener(new AndroidDownloadManagerListener() {
            @Override
            public void onPrepare() {
                Log.d(TAG, "onPrepare");
            }

            @Override
            public void onSuccess(String path) {
                Log.d(TAG, "onSuccess >>>>" + path);
            }

            @Override
            public void onFailed(Throwable throwable) {
                Log.e(TAG, "onFailed", throwable);
            }
        })
        .download();

---