Re: loading jdbc Driver in servlet - Mailing list pgsql-general

On Mon, 17 Dec 2018 at 02:28, Thomas Kellerer <spam_eater@gmx.net> wrote:

Rob Sargent schrieb am 14.12.2018 um 19:28:
> Using java 1.8, postgresql-42.1.4.jar, embedded tomcat 9
>
> It appears to me that I need to make the call
> "Class.forName("org.postgresql.Driver)" when the entry is in a
> servlet.  Is this expected, within a servlet, or is this just /post
> hoc ergo propter hoc /at it finest and I changed something else
> (wittingly or not).  Same code outside of servlet does not need the
> forced loading of the class and the manual claims it's not need after
> java 1.6

Class.forName() is definitely not needed if the driver's JAR file is
included in the classloader of the class requesting a connection.

Where exactly did you put the JDBC driver's jar file?
And what exactly is your main() method doing?

If you look at Tomcat's startup script (catalina.sh or catalina.bat), it's
obvious that setting up the claspath isn't that straightforward.
My guess is, that that your main() method does something different
and does not properly include the driver's jar in the classpath.

Servlet classpath issues are legendary. As Thomas points out setting up the classpath for a servlet engine is not trivial.

As I've manage to get down the road using "forName()" this becomes largely academic.

The classpath of the main does have postgres.

Using this

    System.out.println("main classpath: \n" + getClasspathString());

    private String getClasspathString() {
        StringBuffer classpath = new StringBuffer();
        ClassLoader applicationClassLoader = this.getClass().getClassLoader();
        if (applicationClassLoader == null) {
            applicationClassLoader = ClassLoader.getSystemClassLoader();
        }
        java.net.URL[] urls = ((java.net.URLClassLoader)applicationClassLoader).getURLs();
        for(int i=0; i < urls.length; i++) {
            classpath.append(urls[i].getFile()).append("\n");
        }   
        return classpath.toString();
    }

I get:

main classpath:
/home/u0138544/gits/java/gitlab/gtdb/tport/build/libs/tport.jar
/home/u0138544/gits/java/gitlab/gtdb/tools/build/libs/tools.jar
/home/u0138544/gits/java/gitlab/gtdb/sgs/build/libs/sgs.jar
/home/u0138544/.m2/repository/org/slf4j/slf4j-api/1.7.7/slf4j-api-1.7.7.jar
/home/u0138544/.gradle/caches/modules-2/files-2.1/org.postgresql/postgresql/42.1.4/1c7788d16b67d51f2f38ae99e474ece968bf715a/postgresql-42.1.4.jar
/home/u0138544/.gradle/caches/modules-2/files-2.1/net.sf.jopt-simple/jopt-simple/4.9/ee9e9eaa0a35360dcfeac129ff4923215fd65904/jopt-simple-4.9.jar
/home/u0138544/.gradle/caches/modules-2/files-2.1/javax.servlet/javax.servlet-api/3.1.0/3cd63d075497751784b2fa84be59432f4905bf7c/javax.servlet-api-3.1.0.jar
/home/u0138544/.gradle/caches/modules-2/files-2.1/javax.servlet/javax.servlet-api/3.1.0/3cd63d075497751784b2fa84be59432f4905bf7c/javax.servlet-api-3.1.0.jar
/home/u0138544/.gradle/caches/modules-2/files-2.1/javax.xml.bind/jaxb-api/2.2.12/4c83805595b15acf41d71d49e3add7c0e85baaed/jaxb-api-2.2.12.jar
/home/u0138544/.gradle/caches/modules-2/files-2.1/org.apache.tomcat.embed/tomcat-embed-core/9.0.12/136c8dc5c84e82bf2d68bb10648d4fa8b402184/tomcat-embed-core-9.0.12.jar
/home/u0138544/.gradle/caches/modules-2/files-2.1/org.apache.tomcat.embed/tomcat-embed-el/9.0.12/8ee44bee76043321860cde871cf6343de1483ff5/tomcat-embed-el-9.0.12.jar
/home/u0138544/.gradle/caches/modules-2/files-2.1/org.apache.tomcat.embed/tomcat-embed-jasper/9.0.12/f81c352450b9695b73b90b3e5ef78d6f7fcb1a96/tomcat-embed-jasper-9.0.12.jar
/home/u0138544/.gradle/caches/modules-2/files-2.1/org.apache.tomcat.embed/tomcat-embed-logging-juli/9.0.0.M6/2b083aa89d92ce10356158da1e643f8a8e890b49/tomcat-embed-logging-juli-9.0.0.M6.jar
/home/u0138544/.gradle/caches/modules-2/files-2.1/org.apache.tomcat/tomcat-annotations-api/9.0.12/dfda698ec20b257a6801a2df25c76554658f6005/tomcat-annotations-api-9.0.12.jar
/home/u0138544/work/test/gtdb/

That is generated inside the run() method, as my main() is a Runnable (perhaps unnecessarily so, I'm in the midst of a migration from handling sockets myself to letting Tomcat do that work.  I'm embedding Tomcat to make the footprint just a little more streamlined (or maybe obfuscated).

Inside the servlet the classpath is:

Servlet classpath: file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/classes/
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/groovy-all-2.4.7.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/jaxb-api-2.2.12.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/tomcat-embed-logging-juli-9.0.0.M6.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/jpsgcs-3.1.1-2.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/jackson-annotations-2.9.8.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/tools.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/logback-classic-1.1.2.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/logback-access-1.1.2.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/jackson-core-2.9.8.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/jooq-3.11.7.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/logback-core-1.1.2.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/jooq-codegen-3.11.7.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/tomcat-embed-core-9.0.12.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/jackson-databind-2.9.8.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/tomcat-annotations-api-9.0.12.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/postgresql-42.1.4.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/jooq.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/sgs.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/jopt-simple-4.9.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/longpowerset-1.0.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/slf4j-api-1.7.7.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/anno.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/javax.servlet-api-3.1.0.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/tport.jar
file:/home/u0138544/work/test/crashpad/monitor/webapp.war*/WEB-INF/lib/jooq-meta-3.11.7.jar

Happy to let this be part of the servlet classpath legend!