Why doesn't jrunscript honor my classpath?

Question

I'm trying to do some JDBC access from JavaScript using the Rhino included in Java 6. But I cannot make the DriverManager find the Driver I want to use.

These two examples should be equivalent:

Java:

public class DbTest {
    public static void main(String[] argv) {
        java.sql.Connection c = null;
        try {
            java.lang.Class.forName("net.sourceforge.jtds.jdbc.Driver");
            c = java.sql.DriverManager.getConnection(
                "jdbc:jtds:sqlserver://myserver/mydb", "user", "password");
        }
        catch (Exception e) {
            c = null;
            System.out.println(e);
        };

        if(c != null) {
           System.out.println("yay, got c!");
           try {
               c.close();
           }
           catch(Exception e) {}
        } else {
           System.out.println("awww.");
        }
    }
}

JavaScript:

importPackage(Packages.net.sourceforge.jtds.jdbc);
java.lang.Class.forName('net.sourceforge.jtds.jdbc.Driver');
var c = null;
try {
    c = java.sql.DriverManager.getConnection(
        'jdbc:jtds:sqlserver://myserver/mydb', 'user', 'password');
}
catch (e) {
    c = null;
    println(e);
};

if(c) {
   println('yay, got c!');
   c.close();
} else {
   println('awww.');
}

... but when I run them I get this behaviour:

Java:

> java -cp .;jtds-1.2.5.jar DbTest
java.sql.SQLException: Unknown server host name 'myserver'.
awww.

That's great, it managed to load the driver and tried to resolve the server.

JavaScript:

> jrunscript -cp .;jtds-1.2.5.jar dbtest.js
script error in file dbtest.js :
sun.org.mozilla.javascript.internal.WrappedException: 
Wrapped java.lang.ClassNotFoundException: 
net.sourceforge.jtds.jdbc.Driver (dbtest.js#2) in dbtest.js at line number 2

Why doesn't it find the class? I have tried with and without importPackage() and importClass(), with and without the Packages prefix. If I comment out forName, then DriverManager doesn't find a suitable driver.

Answer 1

According to an IBM DeveloperWorks forum post, "the jrunscript -classpath value is used by a separate "scripting" classloader that parallels the usual application classloader and that is used to resolve classes that have been mentioned in importClass() and importPackage()".

And according to this SO answer, "... DriverManager performs "tasks using the immediate caller's class loader instance" ".

So, unless you put the driver jar into the bootclasspath or find a way to modify how jrunscript (and Ant <script />) set the system classloader of the script environment, the only way to get this to work seems to be to skip DriverManager entirely:

var c = null;
try {
    var p = new java.util.Properties();
    p.setProperty('user', 'user');
    p.setProperty('password', 'password');
    c = (new net.sourceforge.jtds.jdbc.Driver()).connect(
             'jdbc:jtds:sqlserver://myserver/mydb', p);
}
catch (e) {
    c = null;
    println(e);
};

if(c) {
   println('yay, got c!');
   c.close();
} else {
   println('awww.');
}

It removes one layer of indirection, which may or may not be ones cup of tea, but it works (with real server/user/passwd inserted):

$ jrunscript -cp jtds-1.2.5.jar dbtest_realparams.js 
yay, got c!