執行結果集中的訪問查詢Java

Question

我正在嘗試在MDB文件上執行計數查詢，並且希望將它存儲到本地變量中。

如果直接指定輸出，則會出現「類型不匹配：無法從布爾型轉換爲整型」錯誤。

試圖使用結果集我得到類似的錯誤，以及「類型不匹配：不能從布爾值轉換爲結果」

下面的代碼：

String connectionString ="jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)}; DBQ=C:\\test\\TestEJFolder\\BWC_Ejournal.mdb;"; 

     DriverManager.getConnection(connectionString, "", ""); 

     Connection conn = DriverManager.getConnection(connectionString, "", ""); 
     Connection conn1 = DriverManager.getConnection(connectionString, "", ""); 
     Connection conn2 = DriverManager.getConnection(connectionString, "", ""); 

     String sql = "SELECT * FROM Events"; 
     String dt = "SELECT TOP 1 [Date] FROM Events"; 
     String count = "SELECT COUNT(ID) FROM Events"; 

     Statement cmd = conn.createStatement(); 
     Statement cmd1 = conn1.createStatement(); 
     Statement cmd2 = conn2.createStatement(); 

     cmd.execute(sql); 
     cmd1.execute(dt); 
     cmd2.execute(count); 

     ResultSet rc = cmd2.execute(count); 

     int r_count = cmd2.execute(count); 

需要幫助解決這個問題。

Answer 1

錯誤代碼的方式太多。開始閱讀JDBC tutorial。

嘗試這樣：

ResultSet rc = cmd2.execute(count); 
int r_count = 0; 
while (rc.next()) { 
    r_count = rc.getInt(1); 
} 

您不關閉您的任何JDBC資源，這隻會飲恨的。

您應該外部化您的連接信息。

我會將更多的東西封裝成小的，孤立的方法，而不是像這樣混淆多個語句。

你應該考慮一個定義良好的基於​​接口的持久層。

進行那些SQL查詢private static final String。沒有必要讓他們成爲本地人。

我建議你嘗試更類似的東西。啓動與接口：

package persistence; 

import java.util.List; 
import java.util.Map; 

/** 
* EventDao 
* @author Michael 
* @link http://stackoverflow.com/questions/5016730/creating-a-dsn-less-connection-for-ms-access-within-java 
* @since 6/25/13 5:19 AM 
*/ 
public interface EventDao { 
    List<Map<String, Object>> findAllEvents(); 
} 

然後寫一個實現：

package persistence; 

import java.sql.*; 
import java.util.ArrayList; 
import java.util.HashMap; 
import java.util.List; 
import java.util.Map; 

/** 
* EventDaoImpl 
* @author Michael 
* @link http://stackoverflow.com/questions/17213307/execute-access-query-in-resultset-java/17213356?noredirect=1#comment25072519_17213356 
* @since 6/25/13 5:15 AM 
*/ 
public class EventDaoImpl implements EventDao { 

    private static final String DEFAULT_URL = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)}; DBQ=C:\\test\\TestEJFolder\\BWC_Ejournal.mdb;"; 
    private static final String SQL_FIND_ALL_EVENTS = "SELECT * FROM Events"; 

    private Connection connection; 

    public EventDaoImpl(Connection connection) { 
     this.connection = connection; 
    } 

    @Override 
    public List<Map<String, Object>> findAllEvents() { 
     List<Map<String, Object>> results = new ArrayList<Map<String, Object>>(); 
     Statement st = null; 
     ResultSet rs = null; 
     try { 
      st = this.connection.createStatement(); 
      rs = st.executeQuery(SQL_FIND_ALL_EVENTS); 
      results = map(rs); 
     } catch (SQLException e) { 
      e.printStackTrace(); 
      throw new RuntimeException(e); 
     } finally { 
      close(rs); 
      close(st); 
     } 
     return results; 
    } 

    public static Connection createConnection(String driver, String url, String username, String password) throws ClassNotFoundException, SQLException { 
     Class.forName(driver); 
     if ((username == null) || (password == null) || (username.trim().length() == 0) || (password.trim().length() == 0)) { 
      return DriverManager.getConnection(url); 
     } else { 
      return DriverManager.getConnection(url, username, password); 
     } 
    } 

    public static void close(Connection connection) { 
     try { 
      if (connection != null) { 
       connection.close(); 
      } 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 
    } 


    public static void close(Statement st) { 
     try { 
      if (st != null) { 
       st.close(); 
      } 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 
    } 

    public static void close(ResultSet rs) { 
     try { 
      if (rs != null) { 
       rs.close(); 
      } 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 
    } 

    public static void rollback(Connection connection) { 
     try { 
      if (connection != null) { 
       connection.rollback(); 
      } 
     } catch (SQLException e) { 
      e.printStackTrace(); 
     } 
    } 

    public static List<Map<String, Object>> map(ResultSet rs) throws SQLException { 
     List<Map<String, Object>> results = new ArrayList<Map<String, Object>>(); 
     try { 
      if (rs != null) { 
       ResultSetMetaData meta = rs.getMetaData(); 
       int numColumns = meta.getColumnCount(); 
       while (rs.next()) { 
        Map<String, Object> row = new HashMap<String, Object>(); 
        for (int i = 1; i <= numColumns; ++i) { 
         String name = meta.getColumnName(i); 
         Object value = rs.getObject(i); 
         row.put(name, value); 
        } 
        results.add(row); 
       } 
      } 
     } finally { 
      close(rs); 
     } 
     return results; 
    } 

    public static List<Map<String, Object>> query(Connection connection, String sql, List<Object> parameters) throws SQLException { 
     List<Map<String, Object>> results = null; 
     PreparedStatement ps = null; 
     ResultSet rs = null; 
     try { 
      ps = connection.prepareStatement(sql); 

      int i = 0; 
      for (Object parameter : parameters) { 
       ps.setObject(++i, parameter); 
      } 
      rs = ps.executeQuery(); 
      results = map(rs); 
     } finally { 
      close(rs); 
      close(ps); 
     } 
     return results; 
    } 
}