Methods in some interfaces generate an SQLWarning object if the methods cause a database access warning.
Methods in the following interfaces can generate an SQLWarning:
When a method generates an SQLWarning object, the caller is not informed that a data access warning has occurred. The getWarnings method must be called on the appropriate object to retrieve the SQLWarning object. However, the DataTruncation subclass of SQLWarning may be thrown in some circumstances. It should be noted that the native JDBC driver opts to ignore some database-generated warnings for increased efficiency. For example, a warning is generated by the system when you attempt to retrieve data beyond the end of a ResultSet through the ResultSet.next method. In this case, the next method is defined to return false instead of true, informing you of the error. It is unnecessary to create an object to restate this, so the warning is simply ignored.
If multiple data access warnings occur, they are chained to the first one and can be retrieved by calling the SQLWarning.getNextWarning method. If there are no more warnings in the chain, getNextWarning returns null.
Subsequent SQLWarning objects continue to be added to the chain until the next statement is processed or, in the case of a ResultSet object, when the cursor is repositioned. As a result, all SQLWarning objects in the chain are removed.
Using Connection, Statement, and ResultSet objects can cause SQLWarnings to be generated. SQLWarnings are informational messages indicating that while a particular operation has completed successfully, there might be other information of which you should be aware. SQLWarnings are an extension of the SQLException class, but they are not thrown. They are instead attached to the object that causes their generation. When an SQLWarning is generated, nothing happens to inform the application that the warning has been generated. Your application must actively request warning information.
Like SQLExceptions, SQLWarnings can be chained to one another. You can call the clearWarnings method on a Connection, Statement, or ResultSet object to clear the warnings for that object.
The JDBC driver clears SQLWarning objects at specific times if you do not clear them manually. SQLWarning objects are cleared when the following actions are taken: