再讀Android sqlite
再讀Android sqlite
Android原生支持sqlite數據庫操做，sqlite時輕量級關係型數據庫，支持標準sql語句。Android對sqlite進行良好的接口封裝來避免sql注入等安全問題。android
本文解決的問題：
一、Android App內如何建立數據庫
二、Android App內建立數據庫如何自定義文件路徑
三、Android App內獲取數據庫流程解析
四、無Context模式使用數據庫，可在uiautomator1.0測試框架和其餘app_process啓動的進程內使用數據庫。sql
App內常規使用數據庫
Android應用內使用數據庫須要藉助於SQLiteOpenHelper類實現對數據庫的操做，使用數據庫經過如下幾步：
一、建立私有類集成自SQLiteOpenHelper方法，並覆寫onCreate、onUpdate方法實現對數據庫升級降級操做。
二、獲取SQLiteOpenHelper對象實例。
三、獲取只讀、讀寫類型數據庫SQLiteDatabase對象實例（getReadableDatabase()/getWritableDatabase()），當數據庫升級或建立時纔會調用onCreate、onUpdate方法。
四、使用SQLiteDatabase接口實現數據庫操做（增刪改查）數據庫
//一、建立私有SQLiteOpenHelper類
class DatabaseHelper extends SQLiteOpenHelper {
public DatabaseHelper(Context context, String dbName, int version) {
super(context, dbName, null, version);
LogUtil.print("DatabaseHelper dbName[%s] version[%d]",dbName+"",version);
}
@Override
public void onCreate(SQLiteDatabase db) {
//數據庫建立時調用
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//數據庫升級時調用
}
}
//二、獲取SQLiteOpenHelper對象實例。
int dbVersion=0;
DatabaseHelper databaseHelper=new (context,"test.db",dbVersion);
//三、獲取只讀、讀寫類型數據庫SQLiteDatabase對象實例
SQLiteDatabase db = databaseHelper.getWritableDatabase();
//四、使用SQLiteDatabase接口實現數據庫操做（增刪改查）
String sql = "select * from testTable where id=?"
Cursor cursor = db.rawQuery(sql, new String[]{"1111"});
數據庫源碼解析
一、SQLiteOpenHelper構造方法僅初始化參數：版本號必須大於0緩存
public SQLiteOpenHelper(Context context, String name, CursorFactory factory, int version,
int minimumSupportedVersion, DatabaseErrorHandler errorHandler) {
if (version < 1) throw new IllegalArgumentException("Version must be >= 1, was " + version);
mContext = context;
mName = name;
mFactory = factory;
mNewVersion = version;
mErrorHandler = errorHandler;
mMinimumSupportedVersion = Math.max(0, minimumSupportedVersion);
}
二、獲取數據庫實例：真正建立數據庫文件安全
- Android8.0及如下版本：區分writeable和readable數據庫
private SQLiteDatabase getDatabaseLocked(boolean writable) {
if (mDatabase != null) {
if (!mDatabase.isOpen()) {
// Darn! The user closed the database by calling mDatabase.close().
mDatabase = null;
//若是獲取只讀數據庫且緩存了可寫數據庫則直接返回
} else if (!writable || !mDatabase.isReadOnly()) {
// The database is already open for business.
return mDatabase;
}
}
if (mIsInitializing) {
throw new IllegalStateException("getDatabase called recursively");
}
SQLiteDatabase db = mDatabase;
try {
mIsInitializing = true;
if (db != null) {
//若是獲取可寫數據庫，複用緩存的只讀數據庫
if (writable && db.isReadOnly()) {
db.reopenReadWrite();
}
} else if (mName == null) {
db = SQLiteDatabase.create(null);
} else {
try {
//獲取只讀類型數據庫實例
if (DEBUG_STRICT_READONLY && !writable) {
final String path = mContext.getDatabasePath(mName).getPath();
db = SQLiteDatabase.openDatabase(path, mFactory,
SQLiteDatabase.OPEN_READONLY, mErrorHandler);
} else {
//獲取可讀寫數據庫實例
db = mContext.openOrCreateDatabase(mName, mEnableWriteAheadLogging ?
Context.MODE_ENABLE_WRITE_AHEAD_LOGGING : 0,
mFactory, mErrorHandler);
}
} catch (SQLiteException ex) {
//獲取數據庫異常時，若是獲取可寫數據庫，則直接拋出
if (writable) {
throw ex;
}
Log.e(TAG, "Couldn't open " + mName
+ " for writing (will try read-only):", ex);
//獲取數據庫異常時，若是獲取只讀數據庫，重試獲取只讀類型數據庫。
final String path = mContext.getDatabasePath(mName).getPath();
db = SQLiteDatabase.openDatabase(path, mFactory,
SQLiteDatabase.OPEN_READONLY, mErrorHandler);
}
}
onConfigure(db);
final int version = db.getVersion();
//數據庫升級處理邏輯
if (version != mNewVersion) {
if (db.isReadOnly()) {
throw new SQLiteException("Can't upgrade read-only database from version " +
db.getVersion() + " to " + mNewVersion + ": " + mName);
}
//程序運行時更新數據庫：使用緩存數據庫時走此邏輯，從新加載數據庫
if (version > 0 && version < mMinimumSupportedVersion) {
File databaseFile = new File(db.getPath());
onBeforeDelete(db);
db.close();
if (SQLiteDatabase.deleteDatabase(databaseFile)) {
mIsInitializing = false;
return getDatabaseLocked(writable);
} else {
throw new IllegalStateException("Unable to delete obsolete database "
+ mName + " with version " + version);
}
} else {
//事務更新（降級/升級）數據庫
db.beginTransaction();
try {
if (version == 0) {
onCreate(db);
} else {
if (version > mNewVersion) {
onDowngrade(db, version, mNewVersion);
} else {
onUpgrade(db, version, mNewVersion);
}
}
db.setVersion(mNewVersion);
db.setTransactionSuccessful();
} finally {
db.endTransaction();
}
}
}
onOpen(db);
if (db.isReadOnly()) {
Log.w(TAG, "Opened " + mName + " in read-only mode");
}
mDatabase = db;
return db;
} finally {
mIsInitializing = false;
if (db != null && db != mDatabase) {
db.close();
}
}
}
- Android8.1.0及以上版本：均獲取writable類型數據庫，僅在發生異常時返回readable類型數據庫
private SQLiteDatabase getDatabaseLocked(boolean writable) {
if (mDatabase != null) {
if (!mDatabase.isOpen()) {
// Darn! The user closed the database by calling mDatabase.close().
mDatabase = null;
} else if (!writable || !mDatabase.isReadOnly()) {
//若是獲取只讀數據庫且緩存了可寫數據庫則直接返回
// The database is already open for business.
return mDatabase;
}
}
if (mIsInitializing) {
throw new IllegalStateException("getDatabase called recursively");
}
SQLiteDatabase db = mDatabase;
try {
mIsInitializing = true;
if (db != null) {
//若是緩存的數據庫爲只讀類型的，而且當次獲取可寫類型數據庫，則覆用緩存數據庫
if (writable && db.isReadOnly()) {
db.reopenReadWrite();
}
} else if (mName == null) {
db = SQLiteDatabase.createInMemory(mOpenParamsBuilder.build());
} else {
//獲取數據庫的存儲路徑：注-僅次一處使用到了context對象
final File filePath = mContext.getDatabasePath(mName);
SQLiteDatabase.OpenParams params = mOpenParamsBuilder.build();
try {
//打開數據庫實例對象
db = SQLiteDatabase.openDatabase(filePath, params);
// Keep pre-O-MR1 behavior by resetting file permissions to
setFilePermissionsForDb(filePath.getPath());
} catch (SQLException ex) {
if (writable) {
throw ex;
}
Log.e(TAG, "Couldn't open " + mName
+ " for writing (will try read-only):", ex);
params = params.toBuilder().addOpenFlags(SQLiteDatabase.OPEN_READONLY).build();
db = SQLiteDatabase.openDatabase(filePath, params);
}
}
onConfigure(db);
final int version = db.getVersion();
if (version != mNewVersion) {
if (db.isReadOnly()) {
throw new SQLiteException("Can't upgrade read-only database from version " +
db.getVersion() + " to " + mNewVersion + ": " + mName);
}
//程序運行時更新數據庫：使用緩存數據庫時走此邏輯，從新加載數據庫
if (version > 0 && version < mMinimumSupportedVersion) {
File databaseFile = new File(db.getPath());
onBeforeDelete(db);
db.close();
if (SQLiteDatabase.deleteDatabase(databaseFile)) {
mIsInitializing = false;
return getDatabaseLocked(writable);
} else {
throw new IllegalStateException("Unable to delete obsolete database "
+ mName + " with version " + version);
}
} else {
//事務更新（降級/升級）數據庫
db.beginTransaction();
try {
if (version == 0) {
onCreate(db);
} else {
if (version > mNewVersion) {
onDowngrade(db, version, mNewVersion);
} else {
onUpgrade(db, version, mNewVersion);
}
}
db.setVersion(mNewVersion);
db.setTransactionSuccessful();
} finally {
db.endTransaction();
}
}
}
onOpen(db);
if (db.isReadOnly()) {
Log.w(TAG, "Opened " + mName + " in read-only mode");
}
mDatabase = db;
return db;
} finally {
mIsInitializing = false;
if (db != null && db != mDatabase) {
db.close();
}
}
}
三、ContextImpl獲取數據庫路徑app
public File getDatabasePath(String name) {
File dir;
File f;
if (name.charAt(0) == File.separatorChar) {
//數據庫文件名爲絕對路徑時，例如（/sdcard/test.db）則返回該絕對路徑的文件對象。
String dirPath = name.substring(0, name.lastIndexOf(File.separatorChar));
dir = new File(dirPath);
name = name.substring(name.lastIndexOf(File.separatorChar));
f = new File(dir, name);
if (!dir.isDirectory() && dir.mkdir()) {
FileUtils.setPermissions(dir.getPath(), 505, -1, -1);
}
} else {
//若是僅指定文件名稱時，經過conext對象獲取數據庫文件存儲目錄，獲取該目錄下的數據庫文件對象想。
dir = this.getDatabasesDir();
f = this.makeFilename(dir, name);
}
return f;
}
數據庫本地文件路徑
經過上面源碼分析發現獲取數據庫對象的具體調用邏輯：框架
一、經過getWritableDatabase()方法獲取數據庫對象，實際是調用getDatabaseLocked(true)方法。ide
public SQLiteDatabase getWritableDatabase() {
synchronized (this) {
return getDatabaseLocked(true);
}
}
getDatabaseLocked（true）方法獲取數據庫實例：獲取數據庫路徑源碼源碼分析
private SQLiteDatabase getDatabaseLocked(boolean writable) {
SQLiteDatabase db = mDatabase;
try {
mIsInitializing = true;
if (db != null) {
...
} else if (mName == null) {
...
} else {
final File filePath = mContext.getDatabasePath(mName);
SQLiteDatabase.OpenParams params = mOpenParamsBuilder.build();
try {
db = SQLiteDatabase.openDatabase(filePath, params);
...
} catch (SQLException ex) {
...
db = SQLiteDatabase.openDatabase(filePath, params);
}
}
...
mDatabase = db;
return db;
} finally {
...
}
}
在getDatabaseLocked（true）獲取數據庫存儲路徑是調用Context的getDatabasePath(mName)方法，在Android中contex的具體實現類爲ContextImpl，因此獲取數據庫存儲路徑要看ContextImpl.getDatabasePath(String)方法的實現。測試
public File getDatabasePath(String name) {
File dir;
File f;
if (name.charAt(0) == File.separatorChar) {
//數據庫文件名爲絕對路徑時，例如（/sdcard/test.db）則返回該絕對路徑的文件對象。
String dirPath = name.substring(0, name.lastIndexOf(File.separatorChar));
dir = new File(dirPath);
name = name.substring(name.lastIndexOf(File.separatorChar));
f = new File(dir, name);
if (!dir.isDirectory() && dir.mkdir()) {
FileUtils.setPermissions(dir.getPath(), 505, -1, -1);
}
} else {
//若是僅指定文件名稱時，經過conext對象獲取數據庫文件存儲目錄，獲取該目錄下的數據庫文件對象想。
dir = this.getDatabasesDir();
f = this.makeFilename(dir, name);
}
return f;
}
自定義本地數據庫文件路徑
咱們在使用數據庫時有時候須要自定義數據庫存儲路徑，下面介紹三種改變數據庫文件路徑的方法。
- 1、更改context中getDatabasesDir()的返回值
一、自定義Application
二、覆寫Application的getDatabasePath(String name)方法，在方法內指定自定義路徑。
三、在AndroidManifest.xml中指定自定義Application
一、自定義Application
public class MyApplication extends Application{
public static MyApplication getInstance()
{
return mInstance;
}
@Override
public void onCreate()
{
super.onCreate();
}
@Override
public File getDatabasePath(String name) {
return new File("/sdcard/");
}
}
二、在manifest文件中指定application
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.qihoo.qa">
//申請權限
...
<application
android:name=".MyApplication"
android:label="@string/app_name"
android:icon="@drawable/ic_launcher"
android:supportsRtl="true"
android:theme="@style/AppTheme">
</application>
</manifest>
四、獲取DatabaseHelper,數據庫文件爲/sdcard/test.db
DatabaseHelper dataBaseHelper = new DatabaseHelper(context, "test.db", 0);
- 2、構建數據庫時傳入絕對路徑
//獲取DatabaseHelper,數據庫文件爲/sdcard/test.db DatabaseHelper dataBaseHelper = new DatabaseHelper(context, "/sdcard/test.db", 0);
- 3、在SQLiteOpenHelper子類中覆寫getWritableDatabase()和getReadableDatabase()
class DatabaseHelper extends SQLiteOpenHelper {
//一、指定數據庫文件名
String dbName="/sdcard/test.db";
int version;
public DatabaseHelper(Context context, String dbName, int version) {
super(context, dbName, null, version);
}
@Override
public void onCreate(SQLiteDatabase db) {
//數據庫建立時調用
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//數據庫升級時調用
}
//覆寫獲取數據庫實現
@Override
public SQLiteDatabase getWritableDatabase() {
return getDataBase(dbName, version);
}
//覆寫獲取數據庫實現
@Override
public SQLiteDatabase getReadableDatabase() {
return getDataBase(dbName, version);
}
//實現獲取數據庫具體邏輯
private SQLiteDatabase getDataBase(String fileName, int version){
try {
SQLiteDatabase database = SQLiteDatabase.openOrCreateDatabase(fileName, null);
int oldVer = database.getVersion();
database.setVersion(version);
if (version > oldVer) {
this.onUpgrade(database, oldVer, version);
}
if(version<oldVer){
this.onDowngrade(database, oldVer, version);
}
return database;
} catch (Exception var4) {
LogUtil.e(var4);
return super.getWritableDatabase();
}
}
注意
方法1、方法二須要傳遞context對象，若是Context爲null，獲取數據庫實例時會致使空指針異常。
方法三的實現不依賴Context對象，能夠將Context指定爲null。
使用數據庫的一些建議
- 調用getWritableDatabase（）獲取數據庫時會從新建立數據庫實例，通常在程序中複用該數據庫實例便可，若是保存多份數據庫實例會致使OOM異常。
- 數據庫插入數據時使用SQLiteStatement對數據進行封裝，避免sql注入相關問題。
- 數據庫查詢中使用方法Cursor rawQuery(String sql, String[] selectionArgs)指定動態參數，防止sql注入及異常字符問題。
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