JVM Initialization for C++ examples

The source code

This procedure checks an evironment variable called RUNOPTIONS and interprets its value as the name of a file which contains the configuration information for the JMS C++ example. In addition to JVM initialization settings like classpath, etc., this file is expected to contain some property definitions for JNDI lookup names. This scheme makes a lot of sense for our examples, because we need to be able to demonstrate JMS vendor independence. For you, a less flexible and more easily maintained scheme might make more sense. You could for example hardcode all configuration information.

Don't be confused by constants like XMOG_FILE_SEPARATOR_STR. This is simply a platform-dependent value that you may use at your convenience to write platform-portable code. You could just as easily use your own macros or write platform-specific source code if portability is not important to you.

#include "java_lang_pkg.h"
#include "xmog_util.h"
#include <stdio.h>


///
/// @brief An example JVM initialization method.
///
/// You can use different schemes for the loading of the JVM.  Please
/// take a look at the rtconfig examples that illustrate several different
/// ways (XML config file, etc.)
///
/// This function first checks the environment variable 'RUNOPTIONS' for
/// the name of a configuration file.  If that variable is undefined or
/// the specified file cannot be found, we check the installation hierarchy
/// for the default file 'runoptions.xml'.
///
/// The RUNOPTIONS design makes sense for us because we want to support many
/// different JMS implementations with one set of examples, without requiring
/// you to rebuild with different configuration settings or lookup names.
///
/// For your own (JMS provider targeted) project, you might hardcode the 
/// configuration settings and you would certainly know the lookup names for
/// your queues and topics, so you would not have to make them configurable.
///
void    init_jvm( int argc, char * argv[] )
{
    // try to get the RUNOPTIONS config file from an environment variable
    char *    RUNOPTIONS = getenv( "RUNOPTIONS" );

    // do a sanity check on the value and reset the variable if we can't find our
    // configuration file
    if( RUNOPTIONS != NULL )
    {
        if( 0 != xmog_util::hasFileAccess( RUNOPTIONS, Read ) )
            RUNOPTIONS = NULL;
    }

    // if it is not available, use a relative path and (assuming we're in the 
    // install hierarchy)
    if( RUNOPTIONS == NULL )
    {
        RUNOPTIONS = ".." XMOG_FILE_SEPARATOR_STR ".." XMOG_FILE_SEPARATOR_STR "runoptions.xml";

        // do a sanity check on the value and reset it if we can't find our
        // configuration file
        if( 0 != xmog_util::hasFileAccess( RUNOPTIONS, Read ) )
            RUNOPTIONS = NULL;
    }

    // if it is not available, use another relative path (assuming we're in the 
    // install hierarchy)
    if( RUNOPTIONS == NULL )
    {
        RUNOPTIONS = ".." XMOG_FILE_SEPARATOR_STR "runoptions.xml";

        // do a sanity check on the value and reset it if we can't find our
        // configuration file
        if( 0 != xmog_util::hasFileAccess( RUNOPTIONS, Read ) )
            RUNOPTIONS = NULL;
    }

    xmog_jvm_loader &    loader = 
                           xmog_jvm_loader::get_jvm_loader( RUNOPTIONS, 
                                                            true, 
                                                            true, 
                                                            TraceAll, 
                                                            TraceErrors );

    // throw an exception if we couldn't identify a valid distribution
    // you can make this test as foolproof as you wish
    if( RUNOPTIONS == NULL )
        xmog_error_handler( &loader ).handleFrameworkException( 
                                           -2000, 
                                           "Couldn't locate configuration file (examples/runoptions.xml)" );

    // this will print out the required LD_LIBRARY_PATH for Unix-style platforms
    // the pattern here is a double invocation:
    // 1) get the configured JVM, derive the required runtime path from it, and exit
    // 2) invoke again with the required runtime path and load the JVM
    if( argc > 1 && !strcmp( argv[ 1 ], "-info" ) )
        loader.printLdLibraryPathAndExit();
    // this will throw an 'xmog_exception' typed framework exception 
    // if something goes wrong
    // potentially, it might also throw a Java proxy exception if you
    // haven't granted the privileges required for the framework to
    // initialize itself
    else
        loader.load();

    // try to find some classes that should be present to quickly diagnose 
    // configuration problems
    Class::forName( "javax.jms.Message" );
}