Question

如果只存在数据库文件，如何将其复制到SD卡中？这是我的代码：

public boolean checkdatabase() {
        boolean checkdb = false;
        try {
            File databaseFile = myContext.getDatabasePath("database.db");
            checkdb = databaseFile.exists();
        } catch(SQLiteException e) {
            System.out.println("Database doesn't exist");
        }
        return checkdb;
    }

    public void opendatabase() {
        boolean dbexist = checkdatabase();
        if (dbexist) {
            myDatabase = SQLiteDatabase.openDatabase("data/data/***/databases/database.db", null, SQLiteDatabase.OPEN_READWRITE);
        } else {
            createdatabase();
            System.out.println("Database doesn't exist");
            myDatabase = SQLiteDatabase.openDatabase("data/data/***/databases/database.db", null, SQLiteDatabase.OPEN_READWRITE);
        }
    }

    private copydatabase() throws IOException {
            String DB_PATH = "data/data/***/databases/";
            File f = new File(DB_PATH);
            if (!f.exists()) {
            f.mkdir();
            }
            String DATABASE_NAME = "database.db";
            InputStream myInput = myContext.getAssets().open(DATABASE_NAME);
            String outFileName = DB_PATH + DATABASE_NAME;
            OutputStream myOutput = new FileOutputStream(outFileName);
            byte[] buffer = new byte[1024];
            int length;
            while ((length = myInput.read(buffer)) > 0) {
                myOutput.write(buffer, 0, length);
            }

            myOutput.flush();
            myOutput.close();
            myInput.close();
        }

此代码将数据库复制到内部存储器中。我想检查是否存在外部存储器（sdcard），如果确实存在 - 将数据库文件复制到其中，然后在我的应用程序中随处访问它。

Answer 1

试试这个：

try {
        File sd = Environment.getExternalStorageDirectory();
        File data = Environment.getDataDirectory();

        if (sd.canWrite()) {
            String currentDBPath = "//data//{package name}//databases//{database name}";
            String backupDBPath = "{database name}";
            File currentDB = new File(data, currentDBPath);
            File backupDB = new File(sd, backupDBPath);

            if (currentDB.exists()) {
                FileChannel src = new FileInputStream(currentDB).getChannel();
                FileChannel bst = new FileOutputStream(backupDB).getChannel();
                bst.transferFrom(src, 0, src.size());
                src.close();
                bst.close();
            }
        }
    } catch (Exception e) {
    }

不要忘记将其包含在清单文件中：

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

Answer 2

这样的事情应该有效：

String state = Environment.getExternalStorageState();
if (state.equals(Environment.MEDIA_MOUNTED)){
    File root = Environment.getExternalStorageDirectory();

    String DATABASE_NAME = "database.db";
    File destination = new File(root, "nameofthefile");

    try{
        InputStream myInput = myContext.getAssets().open(DATABASE_NAME);
        FileOutputStream myOutput = new FileOutputStream(destination);
        //Handle writing
    }catch(Exception e){ //Change it for appropiate catches
        // Handle exceptions
    }finally{
        myOutput.flush();
        myOutput.close();
        myInput.close();
    }
}else{
    // No SD card or only reading permissions
}

请记住，您需要在AndroidManifest.xml中声明这一点：

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

将数据库复制到SD卡（如果存在）

2 个答案: