JNI C ++为什么也需要.class和.jar？

Question

I have a very straight-forward code to call JAVA Functions through JNI from C++, however it only works if I provide the compiled .class files and the bundled .jar file(s) also. If I remove either of them my application stops working. Example code:

void JniProvider::CreateVM(const QString compiledSource, const QString jar) throw(std::runtime_error) {
    QString     classpath   = QString("-Djava.class.path=%1;%2").arg(compiledSource).arg(jar);
    QByteArray  cpbytes     = classpath.toLocal8Bit();
    char*       chrpath     = cpbytes.data();
    // VM Arguments size:
    const int optionsSize = 2;
    // jvm options:
    JavaVMOption options[optionsSize];
                 options[0].optionString = "-Djava.compiler=NONE";
                 options[1].optionString = chrpath;
    // jvm args
    JavaVMInitArgs vm_args;
                   vm_args.version             = JNI_VERSION_1_6;
                   vm_args.nOptions            = optionsSize;
                   vm_args.options             = options;
                   vm_args.ignoreUnrecognized  = JNI_TRUE;
    // startup jvm
    jint responseCode = JNI_CreateJavaVM(&virtualMachine, reinterpret_cast<void**>(&environment), &vm_args);
    if (responseCode < 0) {
        virtualMachine->DestroyJavaVM();
        throw std::runtime_error("Failed to create Java virtual machine.");
    }
}

Notice the classpath line. If I remove the jar I can't call any functions at all through jni. When I set it again it all works fine. Is it intended functionality that I need the compiled sources and the bunbled jar(s - with dependency jars) too?

@Edit: Thank you for your responses. Allow me to clarify some of the popped up questions in one place. So, the Java Project has the following structure within Netbeans 7.4:

Core
 Source Packages
  core
   Core.java
  model
   model.java
 Test Packages
 Libraries
  enttoolkit.jar
  mail.jar
  wm-isclient.jar

As you can see I have three dependencies as external jar files. Whether I like it or not sadly, the java app uses these. After compilation the following structure appears in the dist folder of the project:

lib
 enttoolkit.jar
 mail.jar
 wm-isclient.jar
Core.jar
 core
  core.class
 META-INF
  MANIFEST.MF
 model
  model.class

I have the Core.jar with the compiled classes inside and a lib folder with the external jar files in it.

Now to the actual problematic part. If I remove either the .class or .jar file from the classpath in CreateVM function later on env->Findclass fails. It just won't find the any classes, where if I provide both the class files and the jar files it succeeds and I can call any method from the class, static or not.

MANIFEST.MF contents:

Manifest-Version: 1.0
Ant-Version: Apache Ant 1.9.1
Created-By: 1.7.0_25-b17 (Oracle Corporation)
Class-Path: lib/enttoolkit.jar lib/mail.jar lib/wm-isclient.jar
X-COMMENT: Main-Class will be added automatically by build
Main-Class: core.Core

@Edit (10:30): The error is NoClassDefFoundError. The value of compiledSource is the path to the .class file including the class file itself while the jar is the same with the jar file. for example:

"-Djava.class.path=C:/Users/johorvat/AppData/Local/Temp/resource.class" <- The upper NoClassDefFoundError
"-Djava.class.path=C:/Users/johorvat/AppData/Local/Temp/resource.class;C:/Users/johorvat/AppData/Local/Temp/resource.jar" <- Works flawlessly without any errors and produces Java method return values on C++ side.

The same happens if I leave out the class file and use the only the jar. It only works if I have both of them, or get the NoClassDefFoundError. Kind of strange for me...

Answer 1

No. You only have to provide a correctly constructed JAR file or a hierarchy of .class files. I suggest something is missing from your jar file, or present under the wrong name or directory.

And note that NoClassDefError isn't the same as ClassNotFoundException. It means the file was found but it didn't contain the class expected, eg wrong case or wrong package.