我第一次运行应用程序并将createDefaultUser()的数据插入storage.db（数据库版本1）。
第二次，我运行了应用程序（数据库版本2），DatabaseManager.java函数onUpgrade()。 Logcats表现良好。
但是onUpgrade()存在一个问题，即SQLiteDatabase.exe(sql)在sql不是“null”的地方插入任何内容，并且是从文件读取的字符串。
这是MainActivity.java：
package com.example.textbase;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new AsyncDatabase().execute();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
private class AsyncDatabase extends AsyncTask<Void, Void, Void> {
@Override
protected Void doInBackground(Void... params) {
DatabaseManager db = new DatabaseManager(getApplicationContext());
db.createDatabase();
db.getWritableDatabase();
//db.createDefaultUser();
return null;
}
@Override
protected void onPostExecute(Void result) {
TextView txt=(TextView)findViewById(R.id.textView);
txt.setText("Done");
}
@Override
protected void onPreExecute() {
TextView txt=(TextView)findViewById(R.id.textView);
txt.setText("Loading");
}
@Override
protected void onProgressUpdate(Void... values) {
}
}
}
这是DatabaseManager.java：
package com.example.textbase;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DatabaseManager extends SQLiteOpenHelper{
private static final String DATABASE_PATH = "/data/data/com.example.textbase/databases/";
private static final String DATABASE_NAME = "storage.db";
private static final String CACHE_NAME="temp_favourite";
private static final int DATABASE_VERSION =2;
private final Context context;
public DatabaseManager(Context context){
super(context, DATABASE_NAME, null, DATABASE_VERSION);
this.context=context;
}
@Override
public void onCreate(SQLiteDatabase database) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
if(oldVersion<newVersion){
Log.i("Database","New database is being upgraded.");
exportFavourite(db);
Log.i("Favourite","Favourite file has been exported.");
File f=new File(DATABASE_PATH+DATABASE_NAME);
f.delete();
Log.i("Database","Old database has been deleted.");
copyDatabase();
Log.i("Database","New database has been created.");
importFavourite(db);
Log.i("Favourite","Favourite file has been imported into database.");
f=new File(context.getFilesDir()+"/"+CACHE_NAME);
f.delete();
Log.i("Favourite","Favourite file has been deleted.");
}
}
public void createDatabase(){
boolean dbExist=checkDatabase();
if(dbExist){
Log.i("Database","Database exists.");
}else{
copyDatabase();
}
}
private void copyDatabase(){
File databaseFile = new File(DATABASE_PATH);
// check if databases folder exists, if not create one and its subfolders
if (!databaseFile.exists()){
databaseFile.mkdir();
Log.i("Directory","Database directory has been created.");
}
String outFilename =null;
outFilename = DATABASE_PATH +DATABASE_NAME;
File sampleFile = new File(outFilename);
try {
InputStream in = context.getAssets().open(DATABASE_NAME);
OutputStream out = new FileOutputStream(outFilename);
byte[] buf = new byte[1024];
int len;
while ((len = in.read(buf)) > 0) {
out.write(buf, 0, len);
}
out.flush();
out.close();
in.close();
Log.i("Database","Database has been copied from asset folder.");
}catch(IOException e) {
}
}
private boolean checkDatabase() {
SQLiteDatabase checkDB = null;
try {
String fullPath = DATABASE_PATH + DATABASE_NAME;
checkDB = SQLiteDatabase.openDatabase(fullPath, null,SQLiteDatabase.OPEN_READONLY);
} catch (SQLiteException e) {
e.printStackTrace();
}
if (checkDB != null) {
checkDB.close();
}
return checkDB != null ? true : false;
}
private void setQuerytoFile(String str){
FileOutputStream outputStream;
try {
outputStream = context.openFileOutput(CACHE_NAME, Context.MODE_APPEND);
outputStream.write(str.getBytes());
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
}
}
public void exportFavourite(SQLiteDatabase db){
String sql = "SELECT * FROM user";
Cursor cursor = db.rawQuery(sql, null);
if (cursor.moveToFirst()) {
do {
String username=cursor.getString(1);
int password=Integer.parseInt(cursor.getString(2));
String query="insert into user(username,password) values('"+username+"',"+password+");";
setQuerytoFile(query);
} while (cursor.moveToNext());
}
}
private String getQueryfromFile() throws IOException{
BufferedReader in = null;
File file=new File(context.getFilesDir()+"/"+CACHE_NAME);
FileInputStream fin=new FileInputStream(file);
InputStream is=fin;
try
{
in = new BufferedReader(new InputStreamReader(is));
String line;
final StringBuilder buffer = new StringBuilder();
while ((line = in.readLine()) != null)
{
buffer.append(line);
}
return buffer.toString();
}
catch (final IOException e)
{
return "";
}
finally
{
try
{
in.close();
}
catch (IOException e)
{
// ignore //
}
}
}
private void importFavourite(SQLiteDatabase db){
File f=new File(context.getFilesDir()+"/"+CACHE_NAME);
if(f.exists()){
String sql;
try {
sql = getQueryfromFile();
Log.i("SQL Query",sql);
db.execSQL(sql);
Log.i("Database","Favourite backup has been imported.");
f.delete();
Log.i("File","Favourite backup file has been deleted.");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}else{
Log.i("File","Favourite backup file does not exist.");
}
}
public void createDefaultUser(){
String sql="insert into user(username,password) values('Administrator','123');";
getWritableDatabase().execSQL(sql);
Log.i("User","Created default user");
}
}
这是升级数据库时的Logcat：
12-11 21:19:37.320: I/Database(4358): Database exists.
12-11 21:19:37.590: I/Database(4358): New database is being upgraded.
12-11 21:19:37.620: I/Favourite(4358): Favourite file has been exported.
12-11 21:19:37.620: I/Database(4358): Old database has been deleted.
12-11 21:19:37.630: I/Database(4358): Database has been copied from asset folder.
12-11 21:19:37.630: I/Database(4358): New database has been created.
12-11 21:19:37.650: I/SQL Query(4358): insert into user(username,password) values('Administrator',123);insert into user(username,password) values('Administrator',123);insert into user(username,password) values('Administrator',123);
12-11 21:19:37.660: I/Database(4358): Favourite backup has been imported.
12-11 21:19:37.660: I/File(4358): Favourite backup file has been deleted.
12-11 21:19:37.660: I/Favourite(4358): Favourite file has been imported into database.
12-11 21:19:37.660: I/Favourite(4358): Favourite file has been deleted.
这是数据库（storage.db）表格方案：
CREATE TABLE "android_metadata" ("locale" TEXT DEFAULT 'en_US');
CREATE TABLE [user] (
[user_id] INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
[username] VARCHAR(255) NULL,
[password] VARCHAR(255) NULL
);
我想成功执行exec（sql）。我怎么能？
为什么SQLiteDatabase.exec（）什么都不插入？
答案 0 :(得分：0)
您可以阅读the official docs：
public void execSQL（String sql） 执行一个非SELECT的SQL语句或任何其他返回数据的SQL语句。
<强>参数
sql要执行的SQL语句。 多个陈述 不支持以分号分隔。
在使用任何函数之前阅读和理解参考文献很重要。