Android中的資料庫操作（保證執行緒安全）

摘要： 類DbHelper： import android.content.Context; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; publi...

類DbHelper：

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DbHelper extends SQLiteOpenHelper {

//資料庫名字
private static final String DATABASE_NAME = "lindb";
//資料庫版本
private static final int DATABASE_VERSION = 100;

private DbHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
super(context, name, factory, version);
}

public DbHelper(Context context) {
this(context, DATABASE_NAME, null, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
//建立學生表
db.execSQL("create table students(id integer primary key autoincrement,name text )");
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
//處理版本升級
}
}

類DbManager：

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

import java.util.concurrent.atomic.AtomicInteger;

public class DbManager {

//執行緒安全的i++或i--操作,初始值為0
private AtomicInteger openCounter = new AtomicInteger(0);
//資料庫管理單例
private static DbManager instance;
//要管理的資料庫
private static SQLiteDatabase database;
private DbHelper dbHelper;

private DbManager(Context context) {
dbHelper = new DbHelper(context);
}

/**
* 需要在Application
* 初始化資料庫單例
*
* @param context
*/
public static void initDbManager(Context context) {
if (instance == null) {
instance = new DbManager(context);
}
}

/**
* 同步獲取該資料庫管理類單例
*/
public static synchronized DbManager getInstance() {
if (instance == null) {
throw new IllegalStateException("DbManager is not init in application");
}
return instance;
}

/**
* 這個方法可能需要很長時間才能返回，
* 所以你不應該從應用程式主執行緒呼叫它，
* 包括from ContentProvider.onCreate()
*/
public SQLiteDatabase openDb() {
Log.v("Lin2", "openDb:" + openCounter.get());
if (openCounter.incrementAndGet() == 1) {
Log.v("Lin2", "打開了db");
database = dbHelper.getWritableDatabase();
} else {
Log.v("Lin2", "返回開啟的db");
}
return database;
}

public void closeDb() {
Log.v("Lin2", "closeDb:" + openCounter.get());
if (openCounter.decrementAndGet() == 0) {
Log.v("Lin2", "關閉了db");
database.close();
} else {
Log.v("Lin2", "還有其他執行緒操作db");
}
}
}

在Application中初始化：

import android.app.Application;

public class AppInit extends Application {
@Override
public void onCreate() {
super.onCreate();
DbManager.initDbManager(getApplicationContext());
}
}

MainActivity：

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

public class MainActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Thread1 T1 = new Thread1();
T1.start();
Thread2 T2 = new Thread2();
T2.start();
}

class Thread1 extends Thread {

public void run() {
Log.v("Lin2", "Running Thread1");
try {
DbManager.getInstance().openDb();
for (int i = 5; i > 0; i--) {
Log.v("Lin2", "Thread: Thread1" + ", " + i);
// 模擬資料庫操作
Thread.sleep(1000);
}
DbManager.getInstance().closeDb();
} catch (InterruptedException e) {
Log.v("Lin2", "Thread: Thread1" + ", " + " interrupted.");
}
Log.v("Lin2", "Thread: Thread1" + ", " + " exiting.");
}


}

class Thread2 extends Thread {


public void run() {
Log.v("Lin2", "Running Thread2");
try {
DbManager.getInstance().openDb();
for (int i = 10; i > 0; i--) {
Log.v("Lin2", "Thread: Thread2" + ", " + i);
// 模擬資料庫操作
Thread.sleep(1000);
}
DbManager.getInstance().closeDb();
} catch (InterruptedException e) {
Log.v("Lin2", "Thread: Thread2" + ", " + " interrupted.");
}
Log.v("Lin2", "Thread: Thread2" + ", " + " exiting.");
}

}
}

列印的資料：

資料庫操作類

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;

import java.util.ArrayList;
import java.util.List;

public class DbHandle {

/**
* 新增名字
*
* @param name
* @return 是否新增成功
*/
public static boolean insertStudents(String name) {

ContentValues contentValues = new ContentValues();
SQLiteDatabase database = DbManager.getInstance().openDb();
database.beginTransaction();
contentValues.put("name", name);
long execSql = database.insert("students", null, contentValues);
contentValues.clear();
database.setTransactionSuccessful();
database.endTransaction();
//關閉database
DbManager.getInstance().closeDb();
return execSql != -1;

}

/**
* 查詢所有的名字
*
* @return 名字列表
*/
public static List<String> getNameList() {
List<String> list = new ArrayList<>();
SQLiteDatabase database = DbManager.getInstance().openDb();

Cursor cursor = database.query("students", null, null,
null, null, null, null);
if (cursor != null) {
while (cursor.moveToNext()) {
list.add(cursor.getString(cursor.getColumnIndex("name")));
}
cursor.close();
}
DbManager.getInstance().closeDb();

return list;
}

/**
* 刪除
*
* @param name
* @return 刪除的行數
*/
public static int delName(String name) {
SQLiteDatabase database = DbManager.getInstance().openDb();
int delNumber = database.delete("students", "name=?", new String[]{name});
DbManager.getInstance().closeDb();
return delNumber;
}

/**
* 修改
*
* @param newName 修改後的
* @param oldName 要修改的
* @return 修改的行數
*/
public static int updateName(String newName, String oldName) {
ContentValues contentValues = new ContentValues();
SQLiteDatabase database = DbManager.getInstance().openDb();
database.beginTransaction();
contentValues.put("name", newName);
int updateNumber = database.update("students", contentValues, "name=?", new String[]{oldName});
contentValues.clear();
database.setTransactionSuccessful();
database.endTransaction();
DbManager.getInstance().closeDb();
return updateNumber;
}

/**
* 以上增刪改查的方法檢視原始碼就會知道最終執行是拼接的sql語句，但這些方法有時候並不能為所欲為。
* 下面是直接運用sql語句來實現增刪改查
*/

//增 insert into students(name) values('xxx')
public static void insertBySql(String name) {
SQLiteDatabase database = DbManager.getInstance().openDb();
database.beginTransaction();
try {
database.execSQL("insert into students(name) values ('" + name + "')");
} catch (Exception e) {
Log.e("Lin2", "students插入失敗原因:" + e.getMessage());
} finally {
database.setTransactionSuccessful();
database.endTransaction();
DbManager.getInstance().closeDb();
}
}

//刪 delete from students where name='xxx'
public static void delBySql(String name) {
SQLiteDatabase database = DbManager.getInstance().openDb();
try {
database.execSQL("delete from students where name='" + name + "'");
} catch (Exception e) {
Log.e("Lin2", "students刪除失敗原因:" + e.getMessage());
} finally {
DbManager.getInstance().closeDb();
}
}

//改 update students set name='xx' where name='xx'
public static void updateBySql(String newName, String oldName) {
SQLiteDatabase database = DbManager.getInstance().openDb();
database.beginTransaction();
try {
database.execSQL("update students set name='" + newName + "'" + "where name='" + oldName + "'");
} catch (Exception e) {
Log.e("Lin2", "students更新失敗原因:" + e.getMessage());
} finally {
database.setTransactionSuccessful();
database.endTransaction();
DbManager.getInstance().closeDb();
}
}

//查 select * from students
public static List<String> getListBySql() {
List<String> list = new ArrayList<>();
SQLiteDatabase database = DbManager.getInstance().openDb();
try {
Cursor cursor = database.rawQuery("select * from students", null);
if (cursor != null) {
while (cursor.moveToNext()) {
list.add(cursor.getString(cursor.getColumnIndex("name")));
}
cursor.close();
}
}catch (Exception e){
Log.e("Lin2", "students查詢失敗原因:" + e.getMessage());
}finally {
DbManager.getInstance().closeDb();
}

return list;
}

/**
* 以上是都是簡單的基礎的sql 
*/