<< The WwdEmbedded program | Set up program to execute SQL >>

Define key variables and objects

Getting Started with Derby

within the program code and serve as cross-reference points between this section and
the Java program. The program uses methods from the

WwdUtils

class. The utility class

code is not described here but is available for review in the file

WwdUtils.java

Initialize the program

INITIALIZATION SECTION: The initial lines of code identify the Java packages used in
the program, then set up the Java class

WwdEmbedded

and the

main

method signature.

Refer to a Java programming guide for information on these program constructs.

import java.sql.*;

public class WwdEmbedded
{
public static void main(String[] args)
{

Define key variables and objects

DEFINE VARIABLES SECTION: The initial lines of the

main

method define the variables

and objects used in the program. This example uses variables to store the information
needed to connect to the Derby database. The use of variables for this information
makes it easy to adapt the program to other configurations and other databases.

driver

Stores the name of the Derby embedded driver.

dbName

Stores the name of the database.

connectionURL

Stores the Derby connection URL that is used to access the database.

createString

Stores the SQL

CREATE

statement for the

WISH_LIST

table.

String driver = "org.apache.derby.jdbc.EmbeddedDriver";
String dbName="jdbcDemoDB";
String connectionURL = "jdbc:derby:" + dbName + ";create=true";
...
String createString = "CREATE TABLE WISH_LIST "
+ "(WISH_ID INT NOT NULL GENERATED ALWAYS AS IDENTITY "
...
+ " WISH_ITEM VARCHAR(32) NOT NULL) " ;

Start the Derby engine

LOAD DRIVER SECTION: Loading the Derby embedded JDBC driver starts the Derby
database engine. The

try

and

catch

block (the Java error-handling construct) catches

the exceptions that may occur. A problem here is usually due to an incorrect classpath
setting.

String driver = "org.apache.derby.jdbc.EmbeddedDriver";
...
try {
Class.forName(driver);
} catch(java.lang.ClassNotFoundException e) {
...
}

Boot the database

BOOT DATABASE SECTION: The

DriverManager

class loads the database using

the Derby connection URL stored in the variable

connectionURL

. This URL includes

the parameter

;create=true

so that the database will be created if it does not already

exist. The primary

try

and

catch

block begins here. This construct handles errors for

the database access code.