Android 数据库连通性

Android 中一个非常有用的特征就是存在本地关系数据库。保证您能在本地文件中存储您的数据，但通常更有用的是使用一个关系型数据库管理系统（Relational Database Management System，RDBMS）来存储。Android 提供给您常用的 SQLite 数据库来进行处理，因为对于像 Android 这类嵌入式系统它是高度优化的。它被 Android 上的核心应用程序所用。例如，用户地址簿是存储在一个 SQLite 数据库中。现在，对于给定的 Android 的 Java 实现，您可以使用 JDBC 来访问这些数据库。出人意料的是，Android 甚至包括构成主要部分 JDBC API 的 java.sql 和 javax.sql 包。然而，当涉及使用本地 Android 数据库进行处理时，这毫无用处。相反地，您想要使用 android.database 和 android.database.sqlite 包。清单 5 是一个使用这些类存储和检索数据的示例。

清单 5. 使用 Android 进行数据库访问

public class StocksDb {      private static final String DB_NAME = "stocks.db";      private static final int DB_VERSION = 1; private static final String TABLE_NAME = "stock";      private static final String CREATE_TABLE = "CREATE TABLE " + TABLE_NAME + " (id INTEGER PRIMARY KEY, symbol TEXT, max_price DECIMAL(8,2), " +              "min_price DECIMAL(8,2), price_paid DECIMAL(8,2), " +              "quantity INTEGER)";      private static final String INSERT_SQL = "INSERT INTO " + TABLE_NAME +              " (symbol, max_price, min_price, price_paid, quantity) " +              "VALUES (?,?,?,?,?)";      private static final String READ_SQL = "SELECT id, symbol, max_price, " +              "min_price, price_paid, quantity FROM " + TABLE_NAME;      private final Context context;      private final SQLiteOpenHelper helper;      private final SQLiteStatement stmt;      private final SQLiteDatabase db;      public StocksDb(Context context){          this.context = context;          helper = new SQLiteOpenHelper(context, DB_NAME, null,                   DB_VERSION){              @Override public void onCreate(SQLiteDatabase db) {                  db.execSQL(CREATE_TABLE);              }               @Override             public void onUpgrade(SQLiteDatabase db, int oldVersion,                       int newVersion) {        throw new UnsupportedOperationException();              }          };          db =helper.getWritableDatabase();   stmt = db.compileStatement(INSERT_SQL);      }      public Stock addStock(Stock stock){          stmt.bindString(1, stock.getSymbol());          stmt.bindDouble(2, stock.getMaxPrice());          stmt.bindDouble(3, stock.getMinPrice());       stmt.bindDouble(4, stock.getPricePaid());          stmt.bindLong(5, stock.getQuantity());          int id = (int) stmt.executeInsert();          return new Stock (stock, id);      }      public ArrayList<Stock> getStocks() {          Cursor results = db.rawQuery(READ_SQL, null);          ArrayList<Stock> stocks =                    new ArrayList<Stock>(results.getCount());          if (results.moveToFirst()){              int idCol = results.getColumnIndex("id");              int symbolCol = results.getColumnIndex("symbol");              int maxCol = results.getColumnIndex("max_price");             int minCol = results.getColumnIndex("min_price");              int priceCol = results.getColumnIndex("price_paid");           int quanitytCol = results.getColumnIndex("quantity");              do {                  Stock stock = new Stock(results.getString(symbolCol),                           results.getDouble(priceCol),                           results.getInt(quanitytCol),                                       results.getInt(idCol));                  stock.setMaxPrice(results.getDouble(maxCol));                  stock.setMinPrice(results.getDouble(minCol));                  stocks.add(stock);              } while (results.moveToNext());          }          if (!results.isClosed()){              results.close();          }          return stocks;      }      public void close(){          helper.close();      }      }

出处：CSDN
责任编辑：bluehearts

上一页 享受Android应用程序的Java技术盛宴 [3] 下一页 享受Android应用程序的Java技术盛宴 [5]

◎进入论坛网络编程版块参加讨论