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18.1 Basic Steps in Using JDBC

465

Create a Statement

A 

Statement

 object is used to send queries and commands to the database

and is created from the 

Connection

 as follows:

Statement statement = connection.createStatement();

Execute a Query

Once you have a 

Statement

 object, you can use it to send SQL queries by

using the 

executeQuery

 method, which returns an object of type 

Result 

Set

. Here is an example:

String query = "SELECT col1, col2, col3 FROM sometable";

ResultSet resultSet = statement.executeQuery(query);

To modify the database, use 

executeUpdate

 instead of 

executeQuery

,

and supply a string that uses 

UPDATE

, 

INSERT

, or 

DELETE

. Other useful meth 

ods in the 

Statement

 class include 

execute

 (execute an arbitrary command)

and 

setQueryTimeout

 (set a maximum delay to wait for results). You can

also create parameterized queries where values are supplied to a precom 

piled fixed format query. See Section 18.6 for details.

Process the Results

The simplest way to handle the results is to process them one row at a time,

using the 

ResultSet

's 

next

 method to move through the table a row at a

time. Within a row, 

ResultSet

 provides various 

get

Xxx methods that take a

column index or column name as an argument and return the result as a vari 

ety of different Java types. For instance, use 

getInt

 if the value should be an

integer, 

getString

 for a 

String

, and so on for most other data types. If you

just want to display the results, you can use 

getString

 regardless of the

actual column type. However, if you use the version that takes a column

index, note that columns are indexed starting at 1 (following the SQL conven 

tion), not at 0 as with arrays, vectors, and most other data structures in the

Java programming language.

Core Warning

The first column in a 

ResultSet

 row has index 1, not 0.

Here is an example that prints the values of the first three columns in all

rows of a 

ResultSet

.

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