应用程序嵌入JVM使用

有时候我们会想jvm和程序在同一进程中，和jvm交互或者做一些定制工作，需要把jvm嵌入到程序中。简单来说过程可以分为三步：初始化jvm/执行java字节码/退出jvm

初始化jvm

加载libjvm.so到进程中并且调用JNI_CreateJavaVm

    JNI_CreateJavaVM(JavaVM **vm, void **penv, JavaVMOption* options)

options我们按照launcher中的设置就好，包含了classpath/command/pid

    pid_t pid = getpid();
    char *op_pid = NEW_STRING(256);
    sprintf(op_pid,"-Dsun.java.launcher.pid=%d",pid);

    options[op_count++].optionString = "-Djava.class.path=.";
    if(class_path != nullptr && strcmp(class_path,".") != 0){
        char *op_class_path = NEW_STRING(strlen(class_path)+50);
        sprintf(op_class_path,"-Djava.class.path=%s",class_path);
        options[op_count++].optionString = op_class_path;
    }
    options[op_count++].optionString = "-Dsun.java.command=test_jvm";
    options[op_count++].optionString = "-Dsun.java.launcher=SUN_STANDARD";
    options[op_count++].optionString = op_pid;

退出jvm

 if(vm->DetachCurrentThread() != JNI_OK || vm->DestroyJavaVM() != JNI_OK){
        return -1;
 }

执行java字节码

    JavaVM *vm = init_jvm(".:shen.jar");
    JNIEnv *env = get_jni_env();
    if(vm == nullptr || env == nullptr)
        return -1;

    jclass cla = env->FindClass("test");

    jmethodID method = env->GetStaticMethodID(cla,"main","([Ljava/lang/String;)V");

    jclass cla_string = env->FindClass("java/lang/String");

    jobjectArray args = env->NewObjectArray(1,cla_string, nullptr);

    char *cwd = NEW_STRING(256);
    getcwd(cwd,256);
    env->SetObjectArrayElement(args,0,env->NewStringUTF(cwd));

    env->CallStaticObjectMethod(cla,method,args);


    destroy_jvm();

本文代码

jvm_helper.cpp