SQLite Database判断是否存在、新建、删除...

1、SQLite Database判断是否存在、新建、删除.Android SQLite Database本打算封装SQLite的，但是，发现实际上Android已经封装了一层，尤其是数据的增、删、查、改上，更是如此，所以，我后来只封装了一个连接层，负责打开、建立数据库，并返回一个SQLite的实例用来完成增、删、插、改等操作。/- DBHelper -package utility.db;import java.io.FileNotFoundException;import android.content.Context;import android.database.sqlite.SQLite

2、Database;import android.database.sqlite.SQLiteDatabase.CursorFactory;public class DBHelperprivate SQLiteDatabase db = null;private Context ctx = null;public DBHelper( Context ctx )this.ctx = ctx;/* 判断数据库是否存在* param dbName* 数据库名称* return true存在 false不存在*/public boolean exist( String dbName )Log.log(&

3、quot;called fun : exist()");boolean flag = false;trydb = ctx.openDatabase(dbName, null);Log.log("database/"+dbName+" exist");flag = true;catch (FileNotFoundException e)flag = false;Log.log("database/"+dbName+" not exist");finallyif (db != null)db.close();

4、db = null;return flag;/* 打开数据库* param dbName* 数据库名称* return true 打开成功 false打开失败*/public boolean openDatabase( String dbName , boolean created )return openDatabase(dbName, null, created);/* 打开数据库* param dbName* 数据库名称* param factory* return true 打开成功 false打开失败*/public boolean openDatabase( String dbNa

5、me , CursorFactory factory ,boolean created )Log.log("called fun : openDatabase()");Log.log("called fun : if not exist then created "+dbName+" ? : "+created);boolean flag = false;if(exist(dbName)trydb = ctx.openDatabase(dbName, factory);Log.log("database/"+dbN

6、ame+" is opened");flag = true;catch (FileNotFoundException e)Log.log("database/"+dbName+" is not opened");flag = false;elseif(created)flag = createDatabase(dbName, 1, 0, factory);elseflag = false;return flag;/* 创建数据库* param dbName* 数据库名称* param version* 数据库版本* param mod

7、e* 模式* param factory* return true 建立成功 false 建立失败*/public boolean createDatabase( String dbName , int version , int mode ,CursorFactory factory )Log.log("called fun : createDatabase()");boolean flag = false;trydb = ctx.createDatabase(dbName, version, mode, factory);Log.log("database/&

8、quot;+dbName+" is created successfully!");flag = true;catch (FileNotFoundException e)Log.log("database/"+dbName+" can't be created");flag = true;return flag;/* 建立数据库* param dbName* 数据库名称* return true 打开成功 false 打开失败*/public boolean createDatabase( String dbName )ret

9、urn createDatabase(dbName);/* 关闭数据库*/public void closeDatabase()Log.log("close database");if (db != null)db.close();db = null;ctx = null;/* 删除表* param tableName 表名* return 成功则返回 表名 失败则返回null*/public String dropTable( String tableName )Log.log("called fun dropTable()");if (tableNa

10、me = null)Log.log("table name is error! "+tableName+" is null !");return null;String DROP_TABLE = "DROP TABLE IF EXISTS " + tableName;db.execSQL(DROP_TABLE);Log.log("table/"+tableName+" is dropped successfully");return tableName;/* 取得数据库实例* return 返回数据库实例*/public SQLiteDatabase getDBInstance()return db;public boolean execSQL(String SQL)boolean flag = false;Log.log("called fun execSQL()");Log.log("SQL:"+SQL)