Android使用DownloadManager下载文件

前言

DownloadManager是处理长时间HTTP下载的系统服务，客户端可以将指定内容下载到某一特定的目录。DownloadManager会在后台进行下载工作，自己会处理下载失败、网络变换或系统重启等问题。接下来说一下如何使用DownloadManager。

代码实现

AndroidManifest.xml

AndroidManifest.xml中需要添加以下权限：

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

MainActivity.java

使用DownloadManager下载指定url的文件：

package com.andlink.downloadtest;

import androidx.appcompat.app.AppCompatActivity;

import android.app.DownloadManager;
import android.database.Cursor;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

    //下载地址必须用https
    private String apkUrl = "https://XXX.apk";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        downloadFile();
    }

    private void downloadFile() {
        DownloadManager downloadManager = (DownloadManager)getSystemService(this.DOWNLOAD_SERVICE);

		//通过DownloadManager.Request调整请求参数
        DownloadManager.Request request = new DownloadManager.Request(Uri.parse(apkUrl));
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
            request.setRequiresCharging(false).setAllowedOverMetered(true);
        }
        //request.setAllowedNetworkTypes(DownloadManager.Request.NETWORK_WIFI); //可以指定在何种网络状态下进行下载
        
        //将下载任务加到队列
        long requestId = downloadManager.enqueue(request);

		//使用DownloadManager.Query可以查询下载状态
        DownloadManager.Query query = new DownloadManager.Query();
        query.setFilterById(requestId);
        try {
            boolean flag = true;
            while(flag) {
                Cursor cursor = downloadManager.query(query);
                if (cursor != null && cursor.moveToFirst()) {
                    int status = cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_STATUS)); //获取下载状态
                    //String path = cursor.getString(cursor.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI)); //获取保存路径
                    switch(status){
                        //判断下载状态
                        case DownloadManager.STATUS_SUCCESSFUL:
                            flag = false;
                            Log.d("Jason", "download success");
                            break;
                        case DownloadManager.STATUS_FAILED:
                            flag = false;
                            Log.d("Jason", "download fail");
                            break;
                    }
                }

                if(cursor != null) {
                    cursor.close();
                }
            }
        }catch(Exception e) {
            e.printStackTrace();
        }
    }
}