Android中的数据库操作（保证线程安全）
16lz
2021-01-26
类DbHelper：
import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;public class DbHelper extends SQLiteOpenHelper { //数据库名字 private static final String DATABASE_NAME = "lindb"; //数据库版本 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) { //创建学生表 db.execSQL("create table students(id integer primary key autoincrement,name text )"); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { //处理版本升级 //添加字段 //ALTER TABLE table_name ADD column_name datatype //ALTER TABLE table_name DROP COLUMN column_name }}类DbManager：
import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.util.Log;import java.util.concurrent.atomic.AtomicInteger;public class DbManager { //线程安全的i++或i--操作,初始值为0 private AtomicInteger openCounter = new AtomicInteger(0); //数据库管理单例 private static DbManager instance; //要管理的数据库 private static SQLiteDatabase database; private DbHelper dbHelper; private DbManager(Context context) { dbHelper = new DbHelper(context); } /** * 需要在Application * 初始化数据库单例 * * @param context */ public static void initDbManager(Context context) { if (instance == null) { instance = new DbManager(context); } } /** * 同步获取该数据库管理类单例 */ public static synchronized DbManager getInstance() { if (instance == null) { throw new IllegalStateException("DbManager is not init in application"); } return instance; } /** * 这个方法可能需要很长时间才能返回， * 所以你不应该从应用程序主线程调用它， * 包括from ContentProvider.onCreate() */ public SQLiteDatabase openDb() { Log.v("Lin2", "openDb:" + openCounter.get()); if (openCounter.incrementAndGet() == 1) { Log.v("Lin2", "打开了db"); database = dbHelper.getWritableDatabase(); } else { Log.v("Lin2", "返回打开的db"); } return database; } public void closeDb() { Log.v("Lin2", "closeDb:" + openCounter.get()); if (openCounter.decrementAndGet() == 0) { Log.v("Lin2", "关闭了db"); database.close(); } else { Log.v("Lin2", "还有其他线程操作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); // 模拟数据库操作 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); // 模拟数据库操作 Thread.sleep(1000); } DbManager.getInstance().closeDb(); } catch (InterruptedException e) { Log.v("Lin2", "Thread: Thread2" + ", " + " interrupted."); } Log.v("Lin2", "Thread: Thread2" + ", " + " exiting."); } }}打印的数据：
data.png数据库操作类
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 { /** * 添加名字 * * @param name * @return 是否添加成功 */ 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(); //关闭database DbManager.getInstance().closeDb(); return execSql != -1; } /** * 查找所有的名字 * * @return 名字列表 */ public static List getNameList() { List 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; } /** * 删除 * * @param name * @return 删除的行数 */ 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 修改后的 * @param oldName 要修改的 * @return 修改的行数 */ 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; } /** * 以上增删改查的方法查看源代码就会知道最终执行是拼接的sql语句，但这些方法有时候并不能为所欲为。 * 下面是直接运用sql语句来实现增删改查 */ //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插入失败原因:" + e.getMessage()); } finally { database.setTransactionSuccessful(); database.endTransaction(); DbManager.getInstance().closeDb(); } } //删 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删除失败原因:" + 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更新失败原因:" + e.getMessage()); } finally { database.setTransactionSuccessful(); database.endTransaction(); DbManager.getInstance().closeDb(); } } //查 select * from students public static List getListBySql() { List 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查询失败原因:" + e.getMessage()); }finally { DbManager.getInstance().closeDb(); } return list; } /** * 以上是都是简单的基础的sql */ 更多相关文章
- GreenDao 连接与关闭Sqlite数据库
- viewModel与recyclerView结合
- Android中Assets下文件操作
- Android(安卓)数据库的问题
- android > 获取当前位置
- Android(安卓)有时环信初始化失败，创建applocation失败
- android写入数据库、读取sqlite中的图片
- Android(安卓)使用Room 生成不了数据库文件
- 懒加载fragment基类