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下列程序用于连接数据库,请填写缺少的代码。 import ____java.sql.*;____ public class MySQLDb { ____private Connection conn=null;____ private Statement stmt =null; private ResultSet rs =null; public Connection ConnDB() { conn = null; try { String url="__3306 __://127.0.0.1:3306/test?useSSL=false&allowPublicKeyRetrieval=true&serverTimezone=UTC"; __Class.forName__("com.mysql.cj.jdbc.Driver"); conn=DriverManager.getConnection(__Url __,"root","root"); __return conn;__ } catch (Exception fe) { System.err.println("ConnDB(): "+ fe.getMessage()); return null; } } public Statement CreatStat() { stmt = null; try { if (conn == null) { conn = this.ConnDB(); } stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE); return stmt; } catch (Exception fe) { System.err.println("CreatStat(): "+ fe.getMessage()); return null; } } public PreparedStatement prepare(String sql, int autoGenereatedKeys) { PreparedStatement pstmt = null; __Try____{ if (conn == null){ conn = this.ConnDB(); } pstmt = conn.prepareStatement(sql, autoGenereatedKeys); } catch (SQLException e) { e.printStackTrace(); return null; } return pstmt; } public ResultSet getResult(String sql) { rs = null; try { stmt = this.CreatStat(); rs = stmt.executeQuery(sql); return rs; } catch (SQLException ex) { System.err.println("getResult: "+ ex.getMessage()); return null; } } public int executeSql(String sql) { int RowCount; try { stmt = this.CreatStat(); RowCount = __stmt.executeUpdate(sql);__ if (!conn.getAutoCommit()) { conn.commit(); } return RowCount; } catch (Exception e) { System.err.println("executeSql: "+ e.toString()); return 0; } } public void Release() throws SQLException { if (__rs != null _) {