1.建立连接：
Class.forName = ("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(DB_URL,USER,PASSWD);
2.进行交互：
JDBC Statement, CallableStatement 和 PreparedStatement 接口定义的方法和属性，使可以发送SQL或PL/SQL命令和从数据库接收数据。
2.1 Statement
创建对象
Statement stmt = null; try { stmt = conn.createStatement( ); . . . } catch (SQLException e) { . . . } finally { . . . }
boolean execute(String SQL) : 如果ResultSet对象可以被检索返回布尔值true，否则返回false。使用这个方法来执行SQL DDL语句，或当需要使用真正的动态SQL。 int executeUpdate(String SQL) : 返回受影响的SQL语句执行的行的数目。使用此方法来执行，而希望得到一些受影响的行的SQL语句 - 例如，INSERT，UPDATE或DELETE语句。 ResultSet executeQuery(String SQL) : 返回ResultSet对象。当希望得到一个结果集使用此方法，就像使用一个SELECT语句。
2.2 PreparedStatement
创建对象
PreparedStatement pstmt = null; try { String SQL = "Update Employees SET age = ? WHERE id = ?"; pstmt = conn.prepareStatement(SQL); . . . } catch (SQLException e) { . . . } finally { . . . } 执行 String sql = "UPDATE Employees set age=? WHERE id=?"; stmt = conn.prepareStatement(sql); //Bind values into the parameters. stmt.setInt(1, 35); // This would set age stmt.setInt(2, 102); // This would set ID // Let us update age of the record with ID = 102; int rows = stmt.executeUpdate(); System.out.println("Rows impacted : " + rows ); // Let us select all the records and display them. sql = "SELECT id, first, last, age FROM Employees"; ResultSet rs = stmt.executeQuery(sql); //STEP 5: Extract data from result set while(rs.next()){ //Retrieve by column name int id = rs.getInt("id"); int age = rs.getInt("age"); String first = rs.getString("first"); String last = rs.getString("last"); //Display values System.out.print("ID: " + id); System.out.print(", Age: " + age); System.out.print(", First: " + first); System.out.println(", Last: " + last); }
