我尝试运行测试程序来证明 Apache Derby 的安装是可以的。
根据本教程安装 在 Ubuntu 上安装 Apache Derby
对于运行程序，必须从终端键入：
java -classpath driver_class_path:. TestDB database.properties
代码来自TestDB class:
public class TestDB
{
public static void main(String[] args) throws Exception
{
if (args.length == 0)
{
System.out.println(
"Usage: java -classpath driver_class_path"
+ File.pathSeparator
+ ". TestDB database.properties");
return;
}
else
SimpleDataSource.init(args[0]);
Connection conn = SimpleDataSource.getConnection();
try
{
Statement stat = conn.createStatement();
stat.execute("CREATE TABLE Test (Name CHAR(20))");
stat.execute("INSERT INTO Test VALUES ('Romeo')");
ResultSet result = stat.executeQuery("SELECT * FROM Test");
result.next();
System.out.println(result.getString("Name"));
stat.execute("DROP TABLE Test");
}
finally
{
conn.close();
}
}
}
从SimpleDataSource class:
public class SimpleDataSource
{
private static String url;
private static String username;
private static String password;
/**
Initializes the data source.
@param fileName the name of the property file that
contains the database driver, URL, username, and password
*/
public static void init(String fileName)
throws IOException, ClassNotFoundException
{
Properties props = new Properties();
FileInputStream in = new FileInputStream(fileName);
props.load(in);
String driver = props.getProperty("jdbc.driver");
url = props.getProperty("jdbc.url");
username = props.getProperty("jdbc.username");
if (username == null) username = "";
password = props.getProperty("jdbc.password");
if (password == null) password = "";
if (driver != null)
Class.forName(driver);
}
/**
Gets a connection to the database.
@return the database connection
*/
public static Connection getConnection() throws SQLException
{
return DriverManager.getConnection(url, username, password);
}
}
内容database.properties:
jdbc:oracle:thin:@larry.mathcs.sjsu.edu:1521:InvoiceDB
/usr/share/javadb
用于数据库用户名 和数据库密码的空行。
并在运行后输出：
nazar_art@nazar-desctop:~/Desktop/Big JAVA/bj4_code/ch22/test$ java -classpath /usr/share/javadb:. TestDB database.properties
Exception in thread "main" java.sql.SQLException: The url cannot be null
at java.sql.DriverManager.getConnection(DriverManager.java:556)
at java.sql.DriverManager.getConnection(DriverManager.java:215)
at SimpleDataSource.getConnection(SimpleDataSource.java:45)
at TestDB.main(TestDB.java:26)
更新：
我尝试使用 derby 嵌入式驱动程序。我database.properties改为
jdbc.driver=org.apache.derby.jdbc.EmbeddedDriver
jdbc.url=jdbc:derby:InvoiceDB;create=true;
user=me;
password=mine
但运行后我有下一个输出：
nazar_art@nazar-desctop:~/Desktop/Big JAVA/bj4_code/ch22/test$ java -classpath /usr/share/javadb:. TestDB database.properties
Exception in thread "main" java.lang.ClassNotFoundException: org.apache.derby.jdbc.EmbeddedDriver
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:190)
at SimpleDataSource.init(SimpleDataSource.java:36)
at TestDB.main(TestDB.java:24)
如何解决这个麻烦？