GWT 1.5.3 + Gears 1.1 Library で作る PropertiesManager

GWTのプロジェクトに'Gears 1.1 Library'をclass pathに追加して利用した．
(Gears 1.1 Library はGoogle Gearsを利用するためのライブラリ．）

もっとまともなSQLがかける人のを参考にするべきかもしれませんよ♪．

PropertiesManager.java

import java.util.HashMap;

import com.google.gwt.gears.client.Factory;
import com.google.gwt.gears.client.database.Database;
import com.google.gwt.gears.client.database.DatabaseException;
import com.google.gwt.gears.client.database.ResultSet;

public class PropertiesManager {
 private Database _database = null;

 private String _tableName = null;

 private HashMap<String, String> _hash = new HashMap<String, String>();

 public PropertiesManager(String dbName, String tableName) {
  if (dbName != null && dbName.length() > 0) {
   _database = PropertiesManager.checkDatabase(dbName);
   if (_database != null) {
    if (tableName != null && tableName.length() > 0) {
     _tableName = tableName;
     if (PropertiesManager.checkTable(_database, _tableName) == false) {
      PropertiesManager.createTable(_database, _tableName);
     }
    }
   }
  }
 }

 public Database get_database() {
  return _database;
 }

 public String getProperty(String key) {
  String ret = null;
  if (_database != null)
   ret = PropertiesManager.selectProp(_database, _tableName, key);
  else
   ret = _hash.get(key);
  return ret;
 }

 public void setProperty(String key, String value) {
  if (_database != null) {
   String oldValue = PropertiesManager
     .selectProp(_database, _tableName, key);
   if (oldValue == null) {
    PropertiesManager.insertProp(_database, _tableName, key, value);
   } else {
    PropertiesManager.updateProp(_database, _tableName, key, value);
   }
  }
  _hash.put(key, value);
 }

 public static Database checkDatabase(String dbName) {
  Database db = null;
  try {
   Factory factory = Factory.getInstance();
   if (factory != null) {
    db = factory.createDatabase();
    db.open(dbName);
   }
  } catch (Exception e) {
  }
  return db;
 }

 public static boolean createTable(Database db, String tableName) {
  if (db == null || tableName == null || tableName.length() == 0) {
   return false;
  }
  boolean ret = false;
  try {
   db.execute("CREATE TABLE IF NOT EXISTS " + tableName
     + " (id INTEGER PRIMARY KEY AUTOINCREMENT,"
     + " key TEXT, value TEXT)", new String[] {});
   ret = true;
  } catch (DatabaseException e) {
  }
  return ret;
 }

 public static boolean checkTable(Database db, String tableName) {
  if (db == null || tableName == null || tableName.length() == 0) {
   return false;
  }
  boolean ret = false;
  try {
   ResultSet rs = db.execute("SELECT COUNT(*) FROM " + tableName,
     new String[] {});
   if (rs != null) {
    ret = true;
   }
  } catch (DatabaseException e) {
  }
  return ret;
 }

 public static boolean removeProp(Database db, String tableName, String key) {
  if (db == null || tableName == null || tableName.length() == 0) {
   return false;
  }
  boolean ret = false;
  try {
   db.execute("DELETE FROM " + tableName + " WHERE key = ?",
     new String[] { key });
   ret = true;
  } catch (DatabaseException e) {
  }
  return ret;
 }

 public static boolean insertProp(Database db, String tableName, String key,
   String value) {
  if (db == null || tableName == null || tableName.length() == 0) {
   return false;
  }
  boolean ret = false;
  try {
   db.execute("INSERT INTO " + tableName + " VALUES(NULL, ?, ?)",
     new String[] { key, value });
   ret = true;
  } catch (DatabaseException e) {
  }
  return ret;
 }

 public static boolean updateProp(Database db, String tableName, String key,
   String value) {
  if (db == null || tableName == null || tableName.length() == 0) {
   return false;
  }
  boolean ret = false;
  try {
   db.execute("UPDATE " + tableName + " SET value=? WHERE key = ?",
     new String[] { value, key });

   ret = true;
  } catch (DatabaseException e) {
  }
  return ret;
 }

 public static String selectProp(Database db, String tableName, String key) {
  String ret = null;
  if (db == null || tableName == null || tableName.length() == 0) {
   return null;
  }
  try {
   ResultSet rs = db.execute("SELECT value FROM " + tableName
     + " WHERE key = ?", new String[] { key });
   if (rs != null && rs.isValidRow()) {
    ret = rs.getFieldAsString(0);
    //
    rs.next();
    if (rs.isValidRow()) {
     PropertiesManager.removeProp(db, tableName, key);
     PropertiesManager.insertProp(db, tableName, key, ret);
    }
   }
  } catch (DatabaseException e) {
  }
  return ret;
 }
}

• Factory.getInstance();の戻り値がからの場合はGearsが入っていない（んだと思う）．
  
• 結果を参照する時は以下のようにする作法（？）らしい？．
  

      ResultSet rs = db.execute("SELECT 句", new String[] { ... });
      for(;rs.isValidRow();rs.next())
      {
       ...
      }

db, table, hashの用意

PropertiesManager _propMgr = new PropertiesManager("DBNAME", "TABLENAME");

getter(dbが無かった時はhashからget)

String PROPERTY_VALUE = _propMgr.getProperty("PROPERTY_KEY");

setter(dbが無かった時はhashにset)

_propMgr.setProperty("PROPERTY_KEY", "PROPERTY_VALUE");

繰り返しますが，もっとまともなSQLがかける人のを参考にするべきかもしれませんよ♪．

一応，GWTFusenで利用中.