Prevent duplicate data

Question

I would like to make sure there are no duplicate data entries in my JSP that populates an Oracle database with a table called MainTable. MainTable has an Id field that is the primary key, ValData with a varchar data type, Fid and Fid2 are number data types. Fid and Fid2 are foreign key values that are taken from another table.
Id   ValData   Fid   Fid2
1    abc         34    2
2    efg          23    34
3    zeo         25    43Sometimes someone can enter duplicate data and the ValData, Fid and Fid2 will end up like this:
Id   ValData   Fid   Fid2
1    abc          34    2
2    efg           23    34
3    zeo          25    43
4    zeo          25    43Is there anything in Java I can implement to prevent duplicate data entry in the above example?

Answer 1

Thanks,
It now works after I added unique constraints to each of the fields.
Google results showed me that ORA-00001 is Oracle's Duplicate message and I added a condition in the SQLException Catch area and it catches all my Duplicate entry attempts and shows message to the user.
Here is what I have and would like to know if this is an efficient way I am doing this??
try
// db stuff
catch (SQLException sqle)
    String message = sqle.getMessage();  
    if (message.indexOf("ORA-00001") != -1)
        out.println("Duplicate Data entry.");  
    else
      out.println("some other ORA error");  
}