此Java错误的含义是什么

Question

I am trying to retrieve data from my database here this is my code, followed by the error. What's going wrong? Any help appreciated in figuring out why it returns the error message it does.

My code:

String query = "SELECT * FROM ebloodfinder.tempids";

try {
    int a = db.updateResult(query).getInt("did");
    int b = db.updateResult(query).getInt("bid");
    dor.setDid(++a);
    dor.setBid(++b);
} catch (ClassNotFoundException | SQLException ex) {
    Logger.getLogger(testForm.class.getName()).log(Level.SEVERE, null, ex);
}

jtxt_Did.setText(dor.getDid()+"");
jtxt_Did_DR.setText(dor.getBid()+"");

This exception occurs:

/*  Dec 12, 2014 2:22:37 PM extra.testForm <init>
SEVERE: null
java.sql.SQLException: Before start of result set*/

Answer 1

You need to move the cursor to the first row and then request for the data.

int a = 0, b = 0;

try {
    ResultSet rs = db.updateResult(query)

    if (rs.next()) { 
        a = rs.getInt("did");
        b = rs.getInt("bid");
    }
} 
catch (ClassNotFoundException | SQLException ex) {
    //blah blah
}

Answer 2

When you get the results in the ResultSet its cursor is at the position Before First .

Some Hint

Say if the data starts from 1st row then the cursor will be at 0.

What you need to do is move the cursor to the First position to read data.

To do this you need to call rs.next() method and this method returns boolean . If it moves to next position then true, if no more further positions are there then false.

The same method can be used to iterate through all the rows fetched from the server.

while(rs.next()){
    //get data
}