Thank you very much for your detailed illustration. But the compiler
complies that there is no such methods isNull() and wasNull()
???
On 6/21/07, Reinhardt Christiansen <[EMAIL PROTECTED]> wrote:
----- Original Message -----
From: "Mohammed Zabin" <[EMAIL PROTECTED]>
To: "Tomcat Users List" <users@tomcat.apache.org>
Sent: Thursday, June 21, 2007 6:45 AM
Subject: Null
> Hi All
>
> Anyone knows how to deal with null values in JDBC ResultSet??
>
> I am trying to render a table in jsp page that read its value from the
> database, sometimes, the database returns null values, and so, the whole
> table couldn't be rendered. Is there any way to deal with null values.
>
The correct way to detect nulls in a JDBC ResultSet is rather different
from
the replies you've had so far. You should detect the presence of nulls in
a
given result set row by using the ResultSet.isNull() method.
So, let's say that we have a result set called 'rs' (you will probably
have
used a Statement or PreparedStatement or some other technique to get your
result set from the database):
Statement stmt = ____________; //an arbitrary Statement object
ResultSet rs = stmt.executeQuery("select employee_number, last_name,
first_name, middle_initial from employee_table");
Now, on to the matter of nulls. Let's say that you are working your way
through your ResultSet. As you know, you get the rows of the ResultSet one
row at a time, using the next() method, as follows:
while (rs.next()) { //as long as there are rows in the result set
//handle one row of the result set
}
Within the while loop, each iteration of the loop will handle one complete
row of the result set.
Let's assume you don't know which columns of the result set are null and
you
want to display the values in each column of the result set exactly as
they
appear in the result set, except that when the value is null, you want to
display the word "unknown". Here's what you would need to do:
String empno = null;
String lastname = null;
String firstname = null;
String midinit = null;
while (rs.next()) {
empno = rs.getString("employee_number"); //get the employee number
from this row of the result set
if (rs.wasNull()) { //if the employee number is null
System.out.println("Employee Number is unknown");
}
else {
System.out.println("Employee Number is " + empno);
}
lastname = rs.getString("last_name"); //get the last name from this
row of the result set
if (rs.wasNull()) { //if the last name is null
System.out.println("Last Name is unknown");
}
else {
System.out.println("Last Name is " + lastname);
}
firstname = rs.getString("first_name"); //get the first name from
this row of the result set
if (rs.wasNull()) { //if the first name is null
System.out.println("First Name is unknown");
}
else {
System.out.println("First Name is " + firstname);
}
midinit = rs.getString("middle_initial"); //get the middle initial
from this row of the result set
if (rs.wasNull()) { //if the middle initial is null
System.out.println("Middle Initial is unknown");
}
else {
System.out.println("Middle Initial is " + midinit);
}
}
Although this example uses only result set columns that are being stored
in
Strings, the technique differs very little for non-text data. Let's say
that
we had a column called annual_salary in our result set, where the
annual_salary was an integer containing the number of dollars that the
person earned per year. Let's assume that some people are still
negotiating
their salaries so that the salary is stored as null for those people until
the salary has been fully agreed.. The technique to handle the salary
would
look like this:
int salary = null;
while (rs.next()) {
salary = getInt("annual_salary"); //get the salary from this row of
the result set
if (rs.isNull()) { //if the salary is null
System.out.println("Annual Salary is unknown");
}
else {
System.out.println("Annual Salary is " + salary);
}
I hope this helps you with your null handling!
--
Rhino
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