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
*/