cumbersome, but when you consider the alternative of wrapping try…catch statements around each operation, this seems like a better solution. Note also that warnings can be chained together, just like SQLExceptions (for more information on chaining, see the JDBC Exception Types section earlier in this chapter). Two (Or More) For The Price Of One Some database systems allow SQL statements that return multiple results (columnar data or an update count) to be executed. If you are unfortunate enough to be developing a JDBC driver using one of these database systems, take heart. The JDBC specification does address this issue. The getMoreResults method is intended to move through the results. Figuring out when you have reached the end of the results, however, is a bit convoluted. To do so, you first call getMoreResults. If it returns true, there is another ResultSet present and you can use getResultSet to retrieve it. If getMoreResults returns false, you have either reached the end of the results, or an update count exists; you must call getUpdateCount to determine which situation exists. If getUpdateCount returns -1, you have reached the end of the results; otherwise, it will return the number of rows affected by the statement. The SimpleText driver does not support multiple result sets, so I don t have any example code to present to you. The only DBMS that I am aware of that supports this is Sybase. Because there are already multiple JDBC drivers available for Sybase (one of which I have developed), I doubt you will have to be concerned with getMoreResults. Consider yourself lucky. PreparedStatement The PreparedStatement is used for pre-compiling an SQL statement, typically in conjunction with parameters, and can be efficiently executed multiple times with just a change in a parameter value; the SQL statement does not have to be parsed and compiled each time. Because the PreparedStatement class extends the Statement class, you will have already implemented a majority of the methods. The executeQuery, executeUpdate, and execute methods are very similar to the Statement methods of the same name, but they do not take an SQL statement as a parameter. The SQL statement for the PreparedStatement was provided when the object was created with the prepareStatement method from the Connection object. One danger to note here: Because PreparedStatement is derived from the Statement class, all of the methods in Statement are also in PreparedStatement. The three execute methods from the Statement class that accept SQL statements are not valid for the PreparedStatement class. To prevent an application from invoking these methods, the driver should also implement them in PreparedStatement, as shown here: // The overloaded executeQuery on the Statement object (which we // extend) is not valid for PreparedStatement or CallableStatement // objects. public ResultSet executeQuery( String sql) throws SQLException { throw new SQLException(”Method is not valid”);
Do you want something as professional as you are? Well, we are, but our plans are even better, please check Web Hosting SSH and look why we are the best.