try-catch块不能抑制java.lang.NullPointerException

Question

I am getting the java.lang.NullPointerException and i am not sure why. I am trying to use a try-catch block but it does not work. Can anyone explain what is wrong with this block?

public PriceDataAdder(Connection conn) {
        try {
            this.conn = conn;
            statement = conn.prepareStatement("INSERT INTO `blah` (a,b,c,d,e,f,g,h,`i`,j) VALUE( ?,?,?,?,?,?,?,?,?,? )");
        } catch (SQLException ex) {
            Logger.getLogger(PriceDataAdder.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

Answer 1

Try catching Exception instead of SQLException . It will work because Exception is the superclass of all exceptions, and by catching it you're catching all possible exceptions that might get generated inside the try block.

Anyway, the problem is probably caused because conn is null at the point where prepareStatement() is called, start by making sure that you're passing a correct instance of Connection where the PriceDataAdder method is called.

Also take a look at the log that's being generated, that Logger object should be put to good use.

Answer 2

You are only catching SQLException objects, and NullPointerException is not a subclass of SQLException . You can insert NullPointerException| to catch those also; see http://docs.oracle.com/javase/7/docs/technotes/guides/language/catch-multiple.html .

Answer 3

You should manage your exception like the below code

try {
    this.conn = conn;
    statement = conn.prepareStatement("INSERT INTO `blah` (a,b,c,d,e,f,g,h,`i`,j) VALUE( ?,?,?,?,?,?,?,?,?,? )");
} catch (SQLException ex) {
    Logger.getLogger(PriceDataAdder.class.getName()).log(Level.SEVERE, null, ex);
    } catch (NullPointerException ex) {
        Logger.getLogger(PriceDataAdder.class.getName()).log(Level.SEVERE, null, ex);
    } catch (Exception ex) {
        Logger.getLogger(PriceDataAdder.class.getName()).log(Level.SEVERE, null, ex);
    }