Java Enterprise in a Nutshell, Second Edition

Results

When an SQL query executes, the results form a pseudo-table that contains all rows that fit the query criteria. For instance, here’s a textual representation of the results of the query string “SELECT NAME, CUSTOMER_ID, PHONE FROM CUSTOMERS”:

NAME                             CUSTOMER_ID  PHONE
-------------------------------- ----------- -------------------
Jane Markham                      1           617 555-1212
Louis Smith                       2           617 555-1213
Woodrow Lang                      3           508 555-7171
Dr. John Smith                    4           (011) 42 323-1239

This kind of textual representation is not very useful for Java programs. Instead, JDBC uses the java.sql.ResultSet interface to encapsulate the query results as Java primitive types and objects. You can think of a ResultSet as an object that represents an underlying table of query results, where you use method calls to navigate between rows and retrieve particular column values.

A Java program might handle the previous query as follows:

Statement stmt = con.createStatement(  );
ResultSet rs = stmt.executeQuery(
 "SELECT NAME, CUSTOMER_ID, PHONE FROM CUSTOMERS");

while(rs.next(  )) {
 System.out.print("Customer #" + rs.getString("CUSTOMER_ID"));
 System.out.print(", " + rs.getString("NAME"));
 System.out.println(", is at " + rs.getString("PHONE");
}
rs.close(  );
stmt.close(  );

Here’s the resulting output:

Customer #1, Jane Markham, is at 617 555-1212
Customer #2, Louis Smith, is at 617 555-1213
Customer #3, Woodrow Lang, is at 508 555-7171
Customer #4, Dr. John Smith, is at (011) 42 323-1239

The code loops through each row of the ResultSet ...