我有一个包含大约 15MB 数据的 sqlite 数据库（太大而无法存储在每个设备上）。我正在构建一个应用程序来与这些数据进行交互。如何从存储应用程序的任何位置访问数据库。我不是要求某人为我做这件事，而是我该去哪里研究如何做这件事。在传递一个 ip 地址（或 FTP 服务器 IP？）后，是否有一个 android 模块可以做到这一点。我从哪里开始研究托管数据库然后将其链接到我的应用程序的最佳方式？这是如何完成的高级简报是什么？谢谢！
【问题讨论】：
标签： android database sqlite data-transfer
两种方式
您可以向 Web 服务器发送查询并检索结果（您需要接收查询并通过 HTTP 发送结果的 Web 服务器 URL）。
可以下载数据库，放到app数据库目录下，就可以查询这个数据库了。
【讨论】：
试试这个，
将您的 externalDB 文件放入 assets 文件夹并打开此文件并写入您的数据库，然后访问它，请参阅以下示例 my externalDB 文件在 assets 文件夹中。
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<Button android:id="@+id/button01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Copy Database">
</Button>
</LinearLayout>
DatabaseHelper.java
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DatabaseHelper extends SQLiteOpenHelper{
//The Android's default system path of your application database.
String DB_PATH =null;
private static String DB_NAME = "extenalDB";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
DB_PATH="/data/data/"+context.getPackageName()+"/"+"databases/";
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}else{
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each time you open the application.
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
}
if(checkDB != null){
checkDB.close();
}
Log.v("check DB", ""+checkDB);
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transfering bytestream.
* */
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
// Log.v("read", "1"+myInput.read(buffer));
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
//return cursor
public Cursor query(String table,String[] columns, String selection,String[] selectionArgs,String groupBy,String having,String orderBy){
return myDataBase.query("EMP_TABLE", null, null, null, null, null, null);
}
}
Main.java
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
public class CopyDbActivity extends Activity {
/** Called when the activity is first created. */
Cursor c=null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
((Button)findViewById(R.id.button01)).setOnClickListener(new View.OnClickListener(){
@Override
public void onClick(View v) {
DatabaseHelper myDbHelper = new DatabaseHelper(CopyDbActivity.this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
myDbHelper.openDataBase();
}catch(SQLException sqle){
throw sqle;
}
Toast.makeText(CopyDbActivity.this, "Success", Toast.LENGTH_SHORT).show();
c=myDbHelper.query("EMP_TABLE", null, null, null, null,null, null);
if(c.moveToFirst())
{
do {
Toast.makeText(CopyDbActivity.this,
"_id: " + c.getString(0) + "\n" +
"E_NAME: " + c.getString(1) + "\n" +
"E_AGE: " + c.getString(2) + "\n" +
"E_DEPT: " + c.getString(3),
Toast.LENGTH_LONG).show();
} while (c.moveToNext());
}
}
});
}
}
很高兴为您提供帮助。
【讨论】：