Activity 4: Create and run a JDBC program using the client driver and Network Server This activity demonstrates the ease with which a program that embeds can be modified for a client/server implementation that uses the Network Server. WwdClient.java programorg.apache.derby.jdbc.ClientDriver This activity assumes you have performed the preceding activities and have a working directory called DERBYTUTOR, and have copies of the program files from the $/demo/programs/workingwithderby/ directory. A basic knowledge of the WwdEmbedded.java program and experience starting and connecting to the Network Server are helpful. You will need to use a text editor to create the WwdClient.java program. As a convenience, the workingwithderby directory contains a program, WwdClientExample.java, which has already been edited in the appropriate manner. You can use this program directly as it is, or you can compare the contents of this program to the WwdClient.java program that you will construct in this activity, to see how the changes are made. You will create a client program, WwdClient.java, by changing a few lines of the WwdEmbedded.java program. You can run the client program in multiple command shells, allowing simultaneous update from two or more sources.

You use two command windows (Server-Shell and Client-Shell) in this activity. You use the Server-Shell to start the Network Server and display Network Server messages. You use the Client-Shell to edit, compile and run the newly created WwdClient.java program. You set the CLASSPATH environment variable in the Client-Shell to support the client JDBC program.

 Create the WwdClient program using the following steps: Open a command window (Client-Shell). Change to the DERBYTUTOR directory. Make a copy of the WwdEmbedded.java program called WwdClient.java, as shown in the following table. Command to copy the programThis table lists the commands to copy the WwdEmbedded.java program on UNIX and Windows systems. Operating System Command UNIX (Korn Shell) cp WwdEmbedded.java WwdClient.java Windows copy WwdEmbedded.java WwdClient.java
Open the WwdClient.java file in a text editor and update the class name to reflect the new file name:Original declaration public class WwdEmbedded New declaration public class WwdClient Edit the DEFINE VARIABLES SECTION of the program so that the driver variable contains the name of the client driver class and the connectionURL variable contains the hostname and port number of the Network Server.Original definitions String driver = "org.apache.derby.jdbc.EmbeddedDriver"; String dbName="jdbcDemoDB"; String connectionURL = "jdbc:derby:" + dbName + ";create=true"; New definitions String driver = "org.apache.derby.jdbc.ClientDriver"; ... String connectionURL = "jdbc:derby://localhost:1527/" + dbName + ";create=true"; Compile the application.javac WwdClient.java A command prompt appears if the compilation is successful. The binary file WwdClient.class is created. If an error message appears, modify the line indicated so that it is identical to the example. (As noted above, you can compare the contents of your WwdClient.java against the WwdClientExample.java program provided in the workingwithderby directory to verify that your editing was performed successfully.) Set up the client/server environment using the following steps: Open a command window (Server-Shell). Change to the DERBYTUTOR directory. Start the Network Server, as shown in the following table. Command to start the Network ServerThis table lists the commands to start the Network Server on UNIX and Windows systems. Operating System Command UNIX (Korn Shell) java -jar $DERBY_HOME/lib/derbyrun.jar server start Fri Sep 14 09:55:23 EDT 2012 : Security manager installed using the Basic server security policy. Fri Sep 14 09:55:24 EDT 2012 : Apache Derby Network Server - 10.10.0.0 - (1384314) started and ready to accept connections on port 1527 Windows java -jar %DERBY_HOME%\lib\derbyrun.jar server start Fri Sep 14 09:55:23 EDT 2012 : Security manager installed using the Basic server security policy. Fri Sep 14 09:55:24 EDT 2012 : Apache Derby Network Server - 10.10.0.0 - (1384314) started and ready to accept connections on port 1527
Run the client program using the following steps: Return to the Client-Shell window. Set the CLASSPATH environment variable to include the location of the file derbyclient.jar (not derby.jar as in the embedded example), as shown in the following table. Command to set the <codeph>CLASSPATH</codeph> environment variableThis table lists the commands to set the CLASSPATH environment variable on UNIX and Windows systems. Operating System Command UNIX (Korn Shell) export CLASSPATH=$DERBY_HOME/lib/derbyclient.jar:. Windows set CLASSPATH=%DERBY_HOME%\lib\derbyclient.jar;.
Include the dot (.) at the end of the command so that your current working directory is included in the classpath. Run the program: java WwdClient org.apache.derby.jdbc.ClientDriver loaded. Connected to database jdbcDemoDB Enter wish-list item (enter exit to end): a sunny day __________________________________________________ On 2012-09-14 09:46:37.77 I wished for a peppermint stick On 2012-09-14 09:46:51.654 I wished for a long vacation On 2012-09-14 09:56:36.6 I wished for a sunny day __________________________________________________ Enter wish-list item (enter exit to end): a new car __________________________________________________ On 2012-09-14 09:46:37.77 I wished for a peppermint stick On 2012-09-14 09:46:51.654 I wished for a long vacation On 2012-09-14 09:56:36.6 I wished for a sunny day On 2012-09-14 09:56:48.367 I wished for a new car __________________________________________________ Enter wish-list item (enter exit to end): exit Closed connection Getting Started With Derby JDBC program ending. Shut down the Network Server, as shown in the following table. Command to shut down the Network ServerThis table lists the commands to shut down the Network Server on UNIX and Windows systems. Operating System Command UNIX (Korn Shell) java -jar $DERBY_HOME/lib/derbyrun.jar server shutdown Fri Sep 14 09:58:12 EDT 2012 : Apache Derby Network Server - 10.10.0.0 - (1384314) shutdown Windows java -jar %DERBY_HOME%\lib\derbyrun.jar server shutdown Fri Sep 14 09:58:12 EDT 2012 : Apache Derby Network Server - 10.10.0.0 - (1384314) shutdown
The server shutdown confirmation appears in both command windows. Activity notes

In a client/server environment, the client program is often used from other computers on the network. Whenever a system accepts connections from other computers, there is a chance of abuse. To maintain security, the Network Server defaults to accepting connections only from clients running on the local machine (localhost). Before this or any other client program can access the Network Server from another machine, additional steps should be taken to secure the Network Server environment. Once secured, the Network Server can be safely configured to accept connections from other machines. Refer to the for important information on securing the Network Server and enabling network connections.

With the Network Server started, you can run the client program simultaneously in multiple windows. To demonstrate this, open two command windows and perform the substeps of the "Run the client program" step in each window. Both clients will operate without a problem. In contrast, it would not be possible for a program that uses the embedded driver (for example, WwdEmbedded.java) to access the database until the database or the Network Server is shut down.

You may have noticed that the client program does not shut down the database. This is because the database is a shared resource in a client/server environment and, in most cases, should be shut down only when the Network Server is shut down. If multiple clients are accessing the database and one client shuts down the database, the remaining clients will encounter a failure the next time they attempt an SQL command.

's two architectures have caused confusion for some new users, who mistakenly think that embedded is a single-user configuration. This is not true. The embedded driver supports multiple simultaneous connections, performs locking, and provides performance, integrity, and recoverability. Any application that uses the embedded driver can open multiple connections and then provide a means for multiple users to interact with the database on each connection. The Network Server is an example of such an application.