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IBM contributed a copy of IBM Cloudscape 10.0 to the Apache Software Foundation in August 2004, which the ASF accepted into the incubator as Derby. Moving forward, Derby is the base relational database management system (RDBMS) engine, and IBM Cloudscape is the commercial product that distributes Derby with additional features for developers, such as the sample databases, examples, and scripts mentioned in this technical article.
The Java class path tells the
java interpreter
and the javac compiler
where to find the classes they need to execute or import.
Classes
(those *.class files you might have noticed)
can be stored in directories or in jar files,
or in a combination of both,
but the Java compiler or interpreter won't be able to find them unless
they are somewhere in your class path.
Multiple entries in the class path are separated by
a semicolon on Windows® (;) and by a colon on UNIX® (:).
In the example below, the class path includes two Derby jar files
(derby.jar and derbytools.jar),
and a directory location
(myDevDir) that stores
*.class files:
Windows class path: C:\Derby\lib\derby.jar;C:\Derby\lib\derbytools.jar;C:\myPath\myDevDir UNIX class path: /Derby/lib/derby.jar:/Derby/lib/derbytools.jar:/myPath/myDevDir |
The rest of the examples in this technical article use Windows syntax. So, if you are on a UNIX machine, please adjust the syntax accordingly.
The Derby class path lets you store jar files in the database itself.
In Derby,
the sqlj.install_jar() procedure
installs a jar file into the database and the
SYSCS_UTIL.SYSCS_SET_DATABASE_PROPERTY procedure
sets the
derby.database.classpath property.
Derby first looks in your Java class path for a class,
then it looks in the database class path.
We mention Derby class path to make you aware of the capability, but the rest of this article focuses on the Java class path.
There are three ways to set the Java class path:
- Permanently by setting the
CLASSPATHenvironment variable at the system level. - Temporarily by setting the
CLASSPATHenvironment variable in a command window or shell. - At runtime by specifying the class path each time you start your Java application and the JVM.
Examples for setting class path each way are in the sections below
and assume you have installed the IBM Cloudscape 10.0 distribution and set
the CLOUDSCAPE_INSTALL environment variable
to the root location for that installation; for example:
C:\>set CLOUDSCAPE_INSTALL=C:\Derby |
If you have installed just the base Derby software, not the IBM Cloudscape 10.0 distribution, this technical article will still have good tips for you, but you won't have the sample programs that are referenced. For readability in this technical article, commands are often broken across several lines. Also, remember that the Java class path is composed of one or more entries, separated by a semicolon on Windows (;) and by a colon on UNIX (:). The examples show Windows syntax, which you must adjust for UNIX.
Setting class path permanently
Figure 1 sets the Windows environment variable permanently,
using the Control Panel's System Settings to add a new variable called
CLASSPATH.
Figure 1. Setting the CLASSPATH environment variable permanently in Windows via System Settings
A UNIX user can set the class path permanently by adding the
CLASSPATH variable to his or her
.profile or
.cshrc file.
Setting class path temporarily
The SimpleApp client class is included in
the IBM Cloudscape 10.0 software distribution in
%CLOUDSCAPE_INSTALL%\demo\programs\simple.
The %CLOUDSCAPE%\lib\derby.jar
file is required to run this class in embedded mode.
Listing 1 shows how to temporarily set
CLASSPATH
in a Windows command window to include
derby.jar and the current working directory
before running
SimpleApp.
Listing 1. Set Java CLASSPATH temporarily
C:\>set CLASSPATH=%CLOUDSCAPE_INSTALL%\lib\derby.jar;. C:\>cd %CLOUDSCAPE_INSTALL%\demo\programs\simple C:\Derby\demo\programs\simple>java SimpleApp SimpleApp starting in embedded mode. Loaded the appropriate driver. Connected to and created database derbyDB Created table derbyDB Inserted 1956 Webster Inserted 1910 Union Updated 1956 Webster to 180 Grand Updated 180 Grand to 300 Lakeshore Verified the rows Dropped table derbyDB Closed result set and statement Committed transaction and closed connection Database shut down normally SimpleApp finished |
If you set the class path temporarily, each time you open a new command window you need to set it again.
Listing 2 shows how to use the -cp option
to specify the class path at runtime,
which is when the application is launched and the JVM is started.
Listing 2. Set Java class path at runtime with the -cp option
C:\Derby\demo\programs\simple>java -cp
%CLOUDSCAPE_INSTALL%\lib\derby.jar; SimpleApp
SimpleApp starting in embedded mode.
Loaded the appropriate driver.
Connected to and created database derbyDB
Created table derbyDB
Inserted 1956 Webster
Inserted 1910 Union
Updated 1956 Webster to 180 Grand
Updated 180 Grand to 300 Lakeshore
Verified the rows
Dropped table derbyDB
Closed result set and statement
Committed transaction and closed connection
Database shut down normally
SimpleApp finished |
Now let's look at a complete example that shows how to set your class path to
run ij, the Derby SQL scripting tool.
Listing 3 sets the
CLASSPATH environment variable
to the bare minimum required by Derby to run
ij.
Listing 3. Set Java CLASSPATH
C:\>set CLOUDSCAPE_INSTALL=C:\Derby
C:\>set CLASSPATH=%CLOUDSCAPE_INSTALL%\lib\derby.jar;
%CLOUDSCAPE_INSTALL%\lib\derbytools.jar
C:\>echo %CLASSPATH%
C:\Derby\lib\derby.jar;C:\Derby\lib\derbytools.jar |
If CLASSPATH is set correctly and the software
really is installed in
C:\Derby,
the command shown in Listing 4 reports useful version information:
Listing 4. Output Derby version information
C:\>java org.apache.derby.tools.sysinfo ------------------ Java Information ------------------ Java Version: 1.4.2_05 Java Vendor: Sun Microsystems Inc. Java home: C:\Program Files\Java\j2re1.4.2_05 Java classpath: C:\Derby\lib\derby.jar;C:\Derby\lib\derbytools.jar OS name: Windows XP OS architecture: x86 OS version: 5.1 Java user name: jander Java user home: C:\Documents and Settings\Administrator Java user dir: C:\ --------- Derby Information -------- [C:\Derby\lib\derby.jar] 10.0.2.0 - (30301) [C:\Derby\lib\derbytools.jar] 10.0.2.0 - (30301) ------------------------------------------------------ ----------------- Locale Information ----------------- ------------------------------------------------------ |
And with the Java class path set correctly,
we should be able to successfully start
ij, as shown below:
C:\>java org.apache.derby.tools.ij ij version 10.0 (C) Copyright IBM Corp. 1997, 2004. ij> |
However, if the class path is set incorrectly,
the command that should output version information instead
outputs a frustrating
NoClassDefFoundError
error:
C:\>java org.apache.derby.tools.sysinfo
Exception in thread "main" java.lang.NoClassDefFoundError:
org/apache/derby/tools/sysinfo |
The
ClassNotFoundException
and
NoClassDefFoundError
errors are common
when the class path is not set properly.
The first means the class itself can't be found.
The second means the class was found,
but a class that it imports wasn't.
For more information, see the section titled
Common Class Path Errors.
Derby / Cloudscape library and package names
The names of various objects -- such as libraries, packages, drivers, and tools -- change between product releases. Table 1 below summarizes Derby and Cloudscape names for several versions. For complete information about names, consult the documentation in your software distribution.
Table 1. Derby/Cloudscape libraries and packages
| Name | Derby & Cloudscape 10.0 | Cloudscape 10.0 Beta | 5.1 | 4.0 |
|---|---|---|---|---|
| RDBMS engine : embedded databases | derby.jar | cs.jar | db2j.jar | cloudscape.jar |
| Tools | derbytools.jar | cstools.jar | db2jtools.jar | cloudutil.jar |
| Cview | - | - | db2jcview.jar | cloudview.jar |
| Cview's help system | - | - | jh.jar | jh.jar |
| Network Server functions | derbynet.jar | csnet.jar | db2jnet.jar | - |
| DB2 JDBC Universal Driver (no name change) | db2jcc.jar | db2jcc.jar | db2jcc.jar | - |
| License Files | db2jcc_license_c.jar | db2jcc_license_c.jar | db2jcc_license_c.jar, db2jcc_license_cu.jar, or db2jcc_license_cisuz.jar | - |
| Package name | org.apache.derby | com.ihost.cs | com.ibm.db2j | COM.cloudscape |
Listings 1 and 2
showed how to run the
%CLOUDSCAPE_INSTALL%\demo\programs\simple\SimpleApp
in embedded mode.
Embedded mode is very simple and only requires including
derby.jar in the class path.
You can also run the SimpleApp
example in network server mode.
To start the network server,
include the libraries listed below in your class path:
-
derby.jar -
derbynet.jar
Next, to run SimpleApp in network server mode,
include the libraries listed below in your class path:
-
derbytools.jar(optional, for example to use 'ij') -
db2jcc.jar -
db2jcc_license_c.jar
There are two major types of class path problems.
The first occurs when a Java class you are trying
to use is not found in the class path, so it throws a
java.lang.ClassNotFoundException
exception.
The second problem occurs when the class you are trying to use is found,
but one of the classes it imports is not found.
In this case, at compile time the imported classes were present, but at run time
the imported class was not part of the class path.
This will throw a
java.lang.NoClassDefFoundError
exception.
Another way to think of the
NoClassDefFoundError is to say that the
searched-for class definition existed when the currently executing class was compiled,
but the definition can no longer be found at runtime.
How can you fix this? Check your class path and verify that the libraries really are where you think they are. For example, on Windows use this command to output your class path:
C:\>echo %CLASSPATH% C:\Derby\lib\derby.jar;C:\Derby\lib\derbytools.jar |
Look at each entry in the
CLASSPATH variable and check with the
dir (Windows) or
ls (UNIX) command
to see if those files exist.
If you don't know which jar file the class is in you can check with this command:
jar -tvf cs.jar | more |
That produces a lot of output.
If you are using Linux or Unix, or UNIX utilities on Windows,
you can use grep to filter out for the class
you're looking for.
For example, the command below looks
for the org.apache.derby.tools.sysinfo class:
C:\Derby\lib>jar tvf derby.jar | grep -i org.apache.derby.tools.sysinfo 1550 Thu Aug 12 14:04:16 PDT 2004 org/apache/derby/tools/sysinfo.class |
Another way to search for a class using the
sysinfo utility is described in the next section.
Verify you have everything you really need
Derby includes a
sysinfo tool with
a -cp option that verifies the class path.
For complete information, see the Tools and Utilities Guide in your
software distribution.
Used without additional arguments, the
-cp option tests for all Derby libraries,
outputting the libraries it can find as well as the ones it cannot,
as shown below:
C:\>java org.apache.derby.tools.sysinfo -cp
Testing for presence of all Derby-related libraries; typically,
only some are needed. For a list of possible arguments, type
java org.apache.derby.tools.sysinfo -cp args
FOUND IN CLASS PATH:
Derby embedded engine library (derby.jar)
Derby tools library (derbytools.jar)
NOT FOUND IN CLASS PATH:
Derby Network Server library (derbynet.jar)
(org.apache.derby.drda.NetworkServerControl not found.)
Cloudscape Client libraries (db2jcc.jar)
(com.ibm.db2.jcc.DB2Driver not found.)
|
Optional arguments to the -cp option include:
- embedded
- tools
- sampleApp
- anyClass.class
The example below looks for the SimpleApp
class in the class path:
C:\Derby\demo\programs\simple>java org.apache.derby.tools.sysinfo
-cp SimpleApp.class
FOUND IN CLASS PATH:
NOT FOUND IN CLASS PATH:
user-specified class (SimpleApp)
(SimpleApp not found.)
|
Remember to include your current working directory in your path if you want to run a class in it:
C:\Derby\demo\programs\simple>set CLASSPATH=%CLASSPATH%;.
C:\Derby\demo\programs\simple>echo %CLASSPATH%
C:\Derby\lib\derby.jar;C:\Derby\lib\derbytools.jar;.
C:\Derby\demo\programs\simple>java org.apache.derby.tools.sysinfo
-cp SimpleApp.class
FOUND IN CLASS PATH:
user-specified class (SimpleApp)
SUCCESS: All Derby related classes found in class path.
|
Finally, to test your class path for Cloudscape 5.1, use the 5.1 package name instead, for example:
java com.ibm.db2j.tools.sysinfo -cp |
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