Blog do projektu Open Source JavaHotel

niedziela, 27 lutego 2011

DB2, Spring and GWT

I created simple GWT (2.2)  application trying to put together several different technologies :
DB2 (SAMPLE database), Spring JDBC as a layer between user interface and database (persistence) and GWT 2.2 as a user interface.
How to setup environment - read details from SampleGWT and source code.

I ended up with the following application:

Application displays one table (EMPLOYEE) from SAMPLE database. List box at the upper left of the screen allows data sorting - it is done by adding ORDER BY clause to SELECT * FROM EMPLOYEE statement. 'Incremental' check box does nothing with the statement - data are read incrementally by default. 'Decremental' check box adds 'DESC' clause to ORDER BY.
Of course - sorting can be done also by 'Column Sorting' - new feature added in GWT 2.2 to CellTable presentation widget.
It could be very interesting challenge which sorting method is more efficient. I dare say that more data are used than data sorting by database engine will be getting the upper hand.

I used Spring JDBC for data access layer. Of course - for such a small project (one statement) it is like to take a sledgehammer to crack a nut.
But I found it very useful - it is much more elegant to have in the main business stream something like:
  List mList = jdbc.query(query, new EmployeeRecordMapper());
and keep somewhere else :
private class EmployeeRecordMapper implements RowMapper {
        public EmployeeRecord mapRow(ResultSet res, int arg1)
                throws SQLException {
            String empno = res.getString(1);
            String firstname = res.getString(2);
            String midinit = res.getString(3);
            String lastname = res.getString(4);
            String workdept = res.getString(5);
            String phoneno = res.getString(6);
            Timestamp hiredate = res.getTimestamp(7);
            String job = res.getString(8);
            int edlevel = res.getInt(9);
            String sex = res.getString(10);
            Timestamp birthdate = res.getTimestamp(11);
            BigDecimal salary = res.getBigDecimal(12);
            BigDecimal bonus = res.getBigDecimal(13);
            BigDecimal comm = res.getBigDecimal(14);
            EmployeeRecord el = new EmployeeRecord();
            return el;

 then this terrible JDBC code :
 ResultSet res = ....
 while ( {
What is more important   EmployeeRecordMapper class is reusable component - can be utilized everywhere statement on EMPLOYEE table is performed.

Of course - every JDBC developer sooner or later creates his (her) own JDBC framework - during my professional life I created dozen of them. But for what purpose create next framework if Spring JDBC is already created and ready to use for free ?

wtorek, 15 lutego 2011

GWT 2.2

Finally I upgraded to GWT 2.2. But not without adventures.
Firstly, I had to download new version of GIN (snapshot), the current is not liked by GWT 2.2 compiler.
Secondly, this new version of GIN works only with the new version of GUICE (3.0) and some additional jars are necessary.
Thirdly, this way I was forced also to upgrade the server code to GUICE 3.0.
Fourthly, GUICE 3.0 lost from its internals @Nullable annotation. I spent several hours trying to guess what was going on. Finally I ended up with mysterious Guava project and jsr305.jar. I was told that is was my mistake to reference Nullable annotation from GUICE internal. Hm..., ok.
But finnaly I'm the happy consumer of GWT 2.2. GWT2.1 to GWT 2.2, one small step for a humble man like me, but giant leap for mankind.