对于我的 android 应用程序,我想使用一个大型数据库(大约 45 MB)。
一种解决方案是将(拆分的)数据库包含在 assets 文件夹中,并在第一次启动时将其复制到数据库目录中。
但这会消耗两次磁盘空间 - 一次在无法删除文件的资产文件夹中,一次在已复制到的数据库目录中。
所以我宁愿在第一次启动时从互联网(网络服务器)下载数据库。我怎么能这样做?我可以下载完整的 SQLite 文件并将其保存到数据库目录吗?还是我应该使用用于填充数据库的 JSON 数据文件?
一种解决方案是将(拆分的)数据库包含在 assets 文件夹中,并在第一次启动时将其复制到数据库目录中。
它不必拆分,只需压缩即可。参见SQLiteAssetHelper
示例。
我怎么能这样做?
使用HttpUrlConnection
. 或者,使用HttpClient
.
我可以下载完整的 SQLite 文件并将其保存到数据库目录吗?
是的。用于getDatabasePath()
获取要使用的正确本地路径。
还是我应该使用用于填充数据库的 JSON 数据文件?
你可以,但是对于 45MB,这将是非常缓慢的。
有人问我最终得到了什么解决方案,这是我使用的代码(大致)。它可能不再完整,也不优雅或干净。但也许它对你有帮助。
我的活动.java
public class MyActivity extends Activity {
private static final String SD_CARD_FOLDER = "MyApp";
private static final String DB_DOWNLOAD_PATH = "http://www.example.org/downloads/dictionary.sqlite";
private Database mDB = null;
private DatabaseDownloadTask mDatabaseDownloadTask = null;
private DatabaseOpenTask mDatabaseOpenTask = null;
private class DatabaseDownloadTask extends AsyncTask<Context, Integer, Boolean> {
@Override
protected void onPreExecute() {
mProgressDialog = new ProgressDialog(MyActivity.this);
mProgressDialog.setTitle(getString(R.string.please_wait));
mProgressDialog.setMessage(getString(R.string.downloading_database));
mProgressDialog.setIndeterminate(false);
mProgressDialog.setMax(100);
mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
mProgressDialog.setCancelable(false);
mProgressDialog.show();
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
}
@Override
protected Boolean doInBackground(Context... params) {
try {
File dbDownloadPath = new File(Database.getDatabaseFolder());
if (!dbDownloadPath.exists()) {
dbDownloadPath.mkdirs();
}
HttpParams httpParameters = new BasicHttpParams();
HttpConnectionParams.setConnectionTimeout(httpParameters, 5000);
HttpConnectionParams.setSoTimeout(httpParameters, 5000);
DefaultHttpClient client = new DefaultHttpClient(httpParameters);
HttpGet httpGet = new HttpGet(DB_DOWNLOAD_PATH);
InputStream content = null;
try {
HttpResponse execute = client.execute(httpGet);
if (execute.getStatusLine().getStatusCode() != 200) { return null; }
content = execute.getEntity().getContent();
long downloadSize = execute.getEntity().getContentLength();
FileOutputStream fos = new FileOutputStream(Database.getDatabaseFolder()+Database.DATABASE_NAME+".sqlite");
byte[] buffer = new byte[256];
int read;
long downloadedAlready = 0;
while ((read = content.read(buffer)) != -1) {
fos.write(buffer, 0, read);
downloadedAlready += read;
publishProgress((int) (downloadedAlready*100/downloadSize));
}
fos.flush();
fos.close();
content.close();
return true;
}
catch (Exception e) {
if (content != null) {
try {
content.close();
}
catch (IOException e1) {}
}
return false;
}
}
catch (Exception e) {
return false;
}
}
protected void onProgressUpdate(Integer... values) {
if (mProgressDialog != null) {
if (mProgressDialog.isShowing()) {
mProgressDialog.setProgress(values[0]);
}
}
}
@Override
protected void onPostExecute(Boolean result) {
if (mProgressDialog != null) {
mProgressDialog.dismiss();
mProgressDialog = null;
}
if (result.equals(Boolean.TRUE)) {
Toast.makeText(MyActivity.this, getString(R.string.database_download_success), Toast.LENGTH_LONG).show();
mDatabaseOpenTask = new DatabaseOpenTask();
mDatabaseOpenTask.execute(new Context[] { MyActivity.this });
}
else {
Toast.makeText(getApplicationContext(), getString(R.string.database_download_fail), Toast.LENGTH_LONG).show();
finish();
}
}
}
private class DatabaseOpenTask extends AsyncTask<Context, Void, Database> {
@Override
protected Database doInBackground(Context ... ctx) {
try {
String externalBaseDir = Environment.getExternalStorageDirectory().getAbsolutePath();
// DELETE OLD DATABASE ANFANG
File oldFolder = new File(Environment.getExternalStorageDirectory().getAbsolutePath()+"/"+SD_CARD_FOLDER);
File oldFile = new File(oldFolder, "dictionary.sqlite");
if (oldFile.exists()) {
oldFile.delete();
}
if (oldFolder.exists()) {
oldFolder.delete();
}
// DELETE OLD DATABASE ENDE
File newDB = new File(Database.getDatabaseFolder()+"dictionary.sqlite");
if (newDB.exists()) {
return new Database(ctx[0]);
}
else {
return null;
}
}
catch (Exception e) {
return null;
}
}
@Override
protected void onPreExecute() {
mProgressDialog = ProgressDialog.show(MainActivity.this, getString(R.string.please_wait), "Loading the database! This may take some time ...", true);
}
@Override
protected void onPostExecute(Database newDB) {
if (mProgressDialog != null) {
mProgressDialog.dismiss();
mProgressDialog = null;
}
if (newDB == null) {
mDB = null;
AlertDialog.Builder downloadDatabase = new AlertDialog.Builder(MyActivity.this);
downloadDatabase.setTitle(getString(R.string.downloadDatabase));
downloadDatabase.setCancelable(false);
downloadDatabase.setMessage(getString(R.string.wantToDownloadDatabaseNow));
downloadDatabase.setPositiveButton(getString(R.string.download), new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
mDatabaseDownloadTask = new DatabaseDownloadTask();
mDatabaseDownloadTask.execute();
}
});
downloadDatabase.setNegativeButton(getString(R.string.cancel), new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
finish();
}
});
downloadDatabase.show();
}
else {
mDB = newDB;
}
}
}
@Override
public void onDestroy() {
super.onDestroy();
if (mDatabaseDownloadTask != null) {
if (mDatabaseDownloadTask.getStatus() != AsyncTask.Status.FINISHED) {
mDatabaseDownloadTask.cancel(true);
}
}
if (mDatabaseOpenTask != null) {
if (mDatabaseOpenTask.getStatus() != AsyncTask.Status.FINISHED) {
mDatabaseOpenTask.cancel(true);
}
}
if (mProgressDialog != null) {
mProgressDialog.dismiss();
mProgressDialog = null;
}
if (mDB != null) {
mDB.close();
mDB = null;
}
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
if (!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
Toast.makeText(getApplicationContext(), getString(R.string.sd_card_not_found), Toast.LENGTH_LONG).show();
finish();
}
mDatabaseOpenTask = new DatabaseOpenTask();
mDatabaseOpenTask.execute(new Context[] { this });
}
}
数据库.java
公共类数据库扩展 SQLiteOpenHelper {
private static final String DATABASE_NAME = "dictionary";
private String DATABASE_PATH = null;
private static final int DATABASE_VERSION = 1;
private static final String PACKAGE_NAME = "com.my.package";
private SQLiteDatabase db;
public Database(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
DATABASE_PATH = getDatabaseFolder()+DATABASE_NAME+".sqlite";
db = getWritableDatabase();
}
public static String getDatabaseFolder() {
return Environment.getExternalStorageDirectory().getAbsolutePath()+"/Android/data/"+PACKAGE_NAME+"/databases/";
}
@Override
public synchronized SQLiteDatabase getWritableDatabase() {
try {
if (db != null) {
if (db.isOpen()) {
return db;
}
}
return SQLiteDatabase.openDatabase(DATABASE_PATH, null, SQLiteDatabase.OPEN_READWRITE | SQLiteDatabase.NO_LOCALIZED_COLLATORS);
}
catch (Exception e) {
return null;
}
}
@Override
public synchronized void close() {
if (db != null) {
db.close();
db = null;
}
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) { }
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { }
}
如果您的数据库那么大,我认为 JSON 方法会是一个更好的主意。
我不是 100% 确定,但我相信当您发布应用程序更新时,您的设备会下载整个应用程序。如果您将一个 45mb 的文件与您的应用程序捆绑在一起,这意味着每次您推送更新时,您的用户都会被下载一个 45mb 的文件所困扰。不是一个好主意。
您可以做的是在您的应用程序中包含没有数据的结构正确的数据库。当用户打开应用程序时,它可以连接到您的 Web 服务器并获取 JSON 数据以填充数据库。这样,当用户更新您的应用程序时,他们就不会因下载新的大文件而陷入困境。更新不会清除现有数据库。
您甚至可以通过 JSON 来幻想并获取部分数据库,直到用户拥有一切。这样,如果你正在做一个怪物查询并且他们失去了与互联网的连接,那么不会发生太糟糕的事情。