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 Derby can be modified for a client/server implementation that uses the Derby Network Server.

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 $DERBY_HOME/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.
You will create a Derby 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 Derby 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.

  1. Create the WwdClient program using the following steps:
    1. Open a command window (Client-Shell).
    2. Change to the DERBYTUTOR directory.
    3. Make a copy of the WwdEmbedded.java program called WwdClient.java.
      Operating System Command

      UNIX
      (Korn Shell)

      cp WwdEmbedded.java WwdClient.java

      Windows

      copy WwdEmbedded.java WwdClient.java
    4. 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
      
    5. Edit the DEFINE VARIABLES SECTION of the program so that the driver variable contains the name of the Derby 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";
      
    6. 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.
  2. Set up the client/server environment using the following steps:
    1. Open a command window (Server-Shell).
    2. Change to the DERBYTUTOR directory.
    3. Start the Network Server:
      Operating System Command

      UNIX
      (Korn Shell)

      java -jar $DERBY_HOME/lib/derbyrun.jar server start
      Security manager installed using the Basic
       server security policy.
      Apache Derby Network Server - 10.4.2.0 -
       (689064) started and ready to accept
       connections on port 1527 at
       2008-09-17 14:18:59.653 GMT

      Windows

      java -jar %DERBY_HOME%\lib\derbyrun.jar server start
      Security manager installed using the Basic
       server security policy.
      Apache Derby Network Server - 10.4.2.0 -
       (689064) started and ready to accept
       connections on port 1527 at
       2008-09-17 14:18:59.653 GMT
  3. Run the client program using the following steps:
    1. Return to the Client-Shell window.
    2. If not already set, set the CLASSPATH environment variable to include the location of the file derbyclient.jar:
      Operating System Command

      UNIX
      (Korn Shell)

      export CLASSPATH=$DERBY_HOME/lib/derbyclient.jar:.

      Windows

      set CLASSPATH=%DERBY_HOME%\lib\derbyclient.jar;.
      Important: Include the dot (.) at the end of the command so that your current working directory is included in the classpath.
    3. 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 2008-09-17 10:11:28.235 I wished for a peppermint stick
      On 2008-09-17 10:11:38.555 I wished for a long vacation
      On 2008-09-17 10:22:19.249 I wished for a sunny day
        __________________________________________________________
      Enter wish-list item (enter exit to end):
      a new car
        __________________________________________________________
      On 2008-09-17 10:11:28.235 I wished for a peppermint stick
      On 2008-09-17 10:11:38.555 I wished for a long vacation
      On 2008-09-17 10:22:19.249 I wished for a sunny day
      On 2008-09-17 10:22:31.758 I wished for a new car
        __________________________________________________________
      Enter wish-list item (enter exit to end):
      exit
      Closed connection
      Working With Derby JDBC program ending.
  4. Shut down the Network Server:
    Operating System Command

    UNIX
    (Korn Shell)

    java -jar $DERBY_HOME/lib/derbyrun.jar server shutdown
    Apache Derby Network Server - 10.4.2.0 - (689064)
     shutdown at 2008-09-17 14:24:19.646 GMT
    

    Windows

    java -jar %DERBY_HOME%\lib\derbyrun.jar server shutdown
    Apache Derby Network Server - 10.4.2.0 - (689064)
     shutdown at 2008-09-17 14:24:19.646 GMT
    
    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 Derby Network Server defaults to accepting connections only from clients running on the local machine (localhost). Before this or any other Derby 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 "Network Server security" and "Running the Network Server under the security manager" sections of the Java DB Server and Administration Guide 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.

Derby's two architectures have caused confusion for some new Derby 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 Derby connections and then provide a means for multiple users to interact with the database on each connection. The Derby Network Server is an example of such an application.