What Happens If Client JDBC DataSource JAR Is Missing?

This section describes what will happen if you try to retrieve a client DataSource object, but the client JAR file is missing.

When you retrieve the object back from the JNDI directory service, you need to cast it back to its original class type, DataSource object, like:

  DataSource ds = (DataSource) ctx.lookup("DerbyTestDB");

Of course, this statement requires the javax.sql.DataSource class. It does not explicitly require the client DataSource class provided by the JDBC driver. But the client DataSource class is required, because the object stored in the directory service was created by the client DataSource class.

You can test this by executing the following program without the Derby JDBC JAR file in the classpath:

/* DerbyJndiLookup.java
 - Copyright (c) 2007, HerongYang.com, All Rights Reserved.
 */
import java.util.*;
import java.sql.*;
import javax.sql.*;
import javax.naming.*;
public class DerbyJndiLookup {
  public static void main(String [] args) {
    Connection con = null;
    try {

// Starting the Directory service
      Hashtable env = new Hashtable();
      env.put(Context.INITIAL_CONTEXT_FACTORY, 
        "com.sun.jndi.fscontext.RefFSContextFactory");
      env.put(Context.PROVIDER_URL, "file:/local/fscontext");
      Context ctx = new InitialContext(env);

// Looking up the DataSource object
      DataSource ds = (DataSource) ctx.lookup("DerbyTestDB");

// Getting a connection object
      con = ds.getConnection();

// Running a query
      Statement sta = con.createStatement(); 
      ResultSet res = sta.executeQuery(
        "SELECT * FROM HY_Address");
      System.out.println("List of Addresses: "); 
      while (res.next()) {
         System.out.println(
           "  "+res.getInt("ID")
           + ", "+res.getString("StreetName")
           + ", "+res.getString("City"));
      }
      res.close();
      sta.close();

      con.close();

    } catch (Exception e) {
      System.err.println("Exception: "+e.getMessage());
      e.printStackTrace();
    }
  }
}

Here is the output of compilation and execution of the program:

C:\>javac DerbyJndiLookup.java
Note: DerbyJndiLookup.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

C:\>java -cp .;\local\lib\fscontext.jar;\local\lib\providerutil.jar
  DerbyJndiLookup
Exception: javax.naming.Reference cannot be cast to 
javax.sql.DataSource 
java.lang.ClassCastException: javax.naming.Reference cannot be 
cast to javax.sql.DataSource
        at DerbyJndiLookup.main(DerbyJndiLookup.java:22)

There was no compilation error. But the execution without Derby JDBC JAR resulted in an exception. It is interesting that the exception message is telling you directly what is wrong. The message just says that the object was failed to be cast to javax.sql.DataSource. The real reason was that the casting requires the object's original class, org.apache.derby.jdbc.ClientDataSource class, which is missing in the classpath, without the derbyclient.jar file.

Last update: 2007.

Table of Contents

 About This Book

 JDBC (Java Database Connectivity) Introduction

 JDK (Java SE) Installation

 Installing and Running Java DB - Derby

 Derby (Java DB) JDBC Driver

Derby (Java DB) JDBC DataSource Objects

 Derby - Connection with DataSource Objects

 Derby - Using ClientDataSource Directly

 Installing JNDI File System Service Provider

 Derby - Storing ClientDataSource Objects on File System

 Derby - Looking Up ClientDataSource Objects on File System

What Happens If Client JDBC DataSource JAR Is Missing?

 Java DB (Derby) - DML Statements

 Java DB (Derby) - ResultSet Objects of Queries

 Java DB (Derby) - PreparedStatement

 MySQL Installation on Windows

 MySQL JDBC Driver (MySQL Connector/J)

 MySQL - PreparedStatement

 MySQL - Reference Implementation of JdbcRowSet

 MySQL - JBDC CallableStatement

 MySQL CLOB (Character Large Object) - TEXT

 MySQL BLOB (Binary Large Object) - BLOB

 Oracle Express Edition Installation on Windows

 Oracle JDBC Drivers

 Oracle - Reference Implementation of JdbcRowSet

 Oracle - PreparedStatement

 Oracle - JBDC CallableStatement

 Oracle CLOB (Character Large Object) - TEXT

 Oracle BLOB (Binary Large Object) - BLOB

 Microsoft SQL Server 2005 Express Edition

 Microsoft JDBC Driver for SQL Server - sqljdbc42.jar

 Microsoft JDBC Driver - Query Statements and Result Sets

 Microsoft JDBC Driver - DatabaseMetaData Object

 Microsoft JDBC Driver - DDL Statements

 Microsoft JDBC Driver - DML Statements

 SQL Server - PreparedStatement

 SQL Server CLOB (Character Large Object) - TEXT

 SQL Server BLOB (Binary Large Object) - BLOB

 JDBC-ODBC Bridge Driver - sun.jdbc.odbc.JdbcOdbcDriver

 JDBC-ODBC Bridge Driver - Flat Text Files

 JDBC-ODBC Bridge Driver - MS Access

 JDBC-ODBC Bridge Driver - MS SQL Server

 Summary of JDBC Drivers and Database Servers

 Additional Tutorial Notes to Be Added

 Outdated Tutorials

 References

 PDF Printing Version