Why ClassPath parameter does not work when I run a JAR?!

Posted on 2010-08-28
Medium Priority
Last Modified: 2012-06-27

I have created a JAR file in Eclipse (Eclipse Java EE IDE for Web Developers. Version: Helios Release. Build id: 20100617-1415).

Then I'm starting it using a bat file (see enclosed code # 1) but I'm getting the following error:
ERROR(java.lang.ClassNotFoundException): COM.ibm.db2.jdbc.app.DB2Driver

So, I think that means that java.exe ignored my -cp "%JdbcRef%" parameter because db2java.zip is exactly the file which contains the required class.

Question are:
1) Why java ignoring ClassPath I have specified?
How to make it working?

2) Is it possible to override (or add more pathes to) the CLASSPATH specified inside a JAR in the ".classpath" file?

3) Why it hang at the Class.forName("COM.ibm.db2.jdbc.app.DB2Driver") if code in my JAR starts another copy of java.exe and run the same JAR with different parameters?

a) I know for sure - database parameters are correct - when I'm running it under debugger in Eclipse it works fine. So, problems exists only when I run a JAR.

b) Eclipse configured to use the same JRE (see the %JavaHome% in a bat file example). So, it cannot be because of different JRE.

@echo off

set JavaDir=C:\Program Files (x86)\IBM\SQLLIB\java
set JavaHome=%JavaDir%\jdk\jre
set JdbcRef=%JavaDir%\db2java.zip

echo "%JavaHome%\bin\java.exe" -cp "%JdbcRef%" -jar JavaCslMon.jar TxMonitor -mode=test -test=database

"%JavaHome%\bin\java.exe" -cp "%JdbcRef%" -jar JavaCslMon.jar TxMonitor -mode=test -test=database

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private string dbDriverName = "COM.ibm.db2.jdbc.app.DB2Driver";
private string dbName = "PT2010A";
private string dbUser = "uzver";
private string dbPassword = "pazzw0rd";

public Connection getConnection() throws Exception
	if (this.dbConn != null) return this.dbConn;
	MiscUtils.toLogger(Level.WARNING, String.format("Trying db driver (%1$s) ...", this.dbDriverName));
		Class c = Class.forName(this.dbDriverName, false, this.getClass().getClassLoader());
		this.dbDriver = (Driver)c.newInstance();
		MiscUtils.toLogger(Level.WARNING, String.format("* Db driver (%1$s): found", this.dbDriverName));
	catch (ClassNotFoundException exc)
		MiscUtils.toLogger(Level.WARNING, String.format("! Db driver (%1$s).ERROR(%2$s): %3$s", this.dbDriverName,
				exc.getClass().getName(), exc.getMessage()));
	MiscUtils.toLogger(Level.WARNING, String.format("Trying to connect db (%1$s) as (%2$s) ...", this.dbName, this.dbUser));
		//this.dbConn = DriverManager.getConnection(this.dbName, this.dbUser, this.dbPassword);
		Properties props = new Properties();
		props.setProperty("user", this.dbUser);
		props.setProperty("password", this.dbPassword);
		this.dbConn = this.dbDriver.connect(this.dbName, props);
		MiscUtils.toLogger(Level.WARNING, String.format("* Db successfully connected."));
	catch (SQLException exc)
		MiscUtils.toLogger(Level.WARNING, String.format("! Fail to connect database (%1$s)! ERROR(%2$s): %3$s", this.dbName,
				exc.getClass().getName(), exc.getMessage()));
	MiscUtils.toLogger(Level.WARNING, String.format("Trying to configure db connection..."));
	catch (SQLException exc)
		MiscUtils.toLogger(Level.WARNING, String.format("! Fail to configure database connection! ERROR(%1$s): %2$s", 
				exc.getClass().getName(), exc.getMessage()));
	return this.dbConn;

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Question by:Dmitry_Bond
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LVL 86

Accepted Solution

CEHJ earned 1000 total points
ID: 33550576
When using the -jar argument. the classpath is ignored. The Class-Path attribute inside the jar is used instead. You need to do
"%JavaHome%\bin\java.exe" -cp "%JdbcRef%";JavaCslMon.jar TxMonitor -mode=test -test=database

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Author Comment

ID: 33550645
Waw, super! Yes, true, this works:

"%JavaHome%\bin\java.exe" -cp "JavaCslMon.jar;%JdbcRef%" TxMonitor -mode=test -test=database

BUT(!) next part of problem - why java.exe ignoring the CLASSPATH?
For example if I change command to

"%JavaHome%\bin\java.exe" -cp "JavaCslMon.jar" TxMonitor -mode=test -test=database

Then it stops to work with the "java.lang.ClassNotFoundException: COM.ibm.db2.jdbc.app.DB2Driver" error. BUT WHY?!
I clearly see that the CLASSPATH environment variable contains the required path. So, if I add the "echo CP: [%CLASSPATH%]" command to a bat file I see following output:

CP: [.;C:\Program Files (x86)\Java\jre6\lib\ext\QTJava.zip;C:\PROGRA~2\IBM\SQLLIB\java\db2java.zip;C:\PROGRA~2\IBM\SQLLIB\java\db2jcc.jar;C:\PROGRA~2\IBM\SQLLIB\java\sqlj.zip;C:\PROGRA~2\IBM\SQLLIB\java\db2jcc_license_cu.jar;C:\PROGRA~2\IBM\SQLLIB\bin;C:\PROGRA~2\IBM\SQLLIB\java\common.jar]

And there is I can see the required ZIP file - C:\PROGRA~2\IBM\SQLLIB\java\db2java.zip.
Question is - why java.exe cannot find it?
Is there any option to make java.exe use %CLASSPATH% + the pathes in "-cp" command line parameter?
LVL 92

Expert Comment

ID: 33550712
you can use this:

"%JavaHome%\bin\java.exe" -cp "JavaCslMon.jar";%CLASSPATH% TxMonitor -mode=test -test=database
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LVL 92

Assisted Solution

objects earned 1000 total points
ID: 33550722

Author Comment

ID: 33550755
Ok, thanks.
Seems I have solved my problems with CLASSPATH.
So, now my solution is:

use the following code in a bat file:

    set CLASSPATH=.\JavaCslMon.jar;%CLASSPATH%
    "%JavaHome%\bin\java.exe" TxMonitor

So, later when it starts another java.exe from application code it will re-use environment of existing process and should works fine.
LVL 86

Expert Comment

ID: 33552345

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