Java example source code file (launcher.c)

This example Java source code file (launcher.c) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

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Java - Java tags/keywords

can't, cp_prop, java, javavminitargs, javavmoption, jni_createjavavm\\n, jni_true, jnienv, jnu_findcreatejavavm, null, rtld_lazy, usage, vm\n

The launcher.c Java example source code

/*
 * Copyright (c) 2006, 2007, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * A minature launcher for use by CustomLauncherTest.sh.  It sets
 * up the absolute minimal execution environment.
 */
#include <stdlib.h>
#include <strings.h>
#include <dlfcn.h>

#include "jni.h"

typedef jint (*create_vm_func)(JavaVM **, void**, void*);

void *JNU_FindCreateJavaVM(char *vmlibpath) {
    void *libVM = dlopen(vmlibpath, RTLD_LAZY);
    if (libVM == NULL) {
        return NULL;
    }
    return dlsym(libVM, "JNI_CreateJavaVM");
}

#define CP_PROP  "-Djava.class.path="

int main(int argc, char**argv) {
     JNIEnv *env;
     JavaVM *jvm;
     jint res;
     jclass cls;
     jmethodID mid;
     jstring jstr;
     jclass stringClass;
     jobjectArray args;
     create_vm_func create_vm;
     JavaVMInitArgs vm_args;
     char* cp_prop;
     JavaVMOption options[1];

     if (argc < 4) {
        fprintf(stderr, "Usage: %s jvm-path classpath class\n", argv[0]);
        return -1;
     }
     cp_prop = (char*)malloc(strlen(CP_PROP)+strlen(argv[2]) +1);
     sprintf(cp_prop, "%s%s", CP_PROP, argv[2]);

     options[0].optionString = cp_prop;
     vm_args.version = 0x00010002;
     vm_args.options = options;
     vm_args.nOptions = 1;
     vm_args.ignoreUnrecognized = JNI_TRUE;

     create_vm = (create_vm_func)JNU_FindCreateJavaVM(argv[1]);
     if (create_vm == NULL) {
        fprintf(stderr, "can't get address of JNI_CreateJavaVM\n");
        return -1;
     }

     res = (*create_vm)(&jvm, (void**)&env, &vm_args);
     if (res < 0) {
         fprintf(stderr, "Can't create Java VM\n");
         return -1;
     }
     cls = (*env)->FindClass(env, argv[3]);
     if (cls == NULL) {
         goto destroy;
     }

     mid = (*env)->GetStaticMethodID(env, cls, "main",
                                     "([Ljava/lang/String;)V");
     if (mid == NULL) {
         goto destroy;
     }
     jstr = (*env)->NewStringUTF(env, " from C!");
     if (jstr == NULL) {
         goto destroy;
     }
     stringClass = (*env)->FindClass(env, "java/lang/String");
     args = (*env)->NewObjectArray(env, 1, stringClass, jstr);
     if (args == NULL) {
         goto destroy;
     }
     (*env)->CallStaticVoidMethod(env, cls, mid, args);

 destroy:
     if ((*env)->ExceptionOccurred(env)) {
         (*env)->ExceptionDescribe(env);
     }
     (*jvm)->DestroyJavaVM(jvm);

     return 0;
 }