Re: java to native code and Sun JVM alternatives

[wagde <wagde at checkpoint dot com>]

Hi

Thanx Andrew for the quick reply.

I'm trying to link my c code and I get:
undefined reference to `JNI_CreateJavaVM'
Although I have -lgcj in my ld command and it's the only undefined symbol in
my code.
Why is that?
I still don't understand how JNI_CreateJavaVM will create a gij VM and not
sun JAVA VM. can you explain this to me.

Thanx
Wagde


Andrew Haley wrote:
> 
> On 03/11/2010 11:45 AM, wagde wrote:
>> 
>> I'm working on a project which have java code (and c++), and until ow I
>> used
>> javac to compile the code and java to run the classes and JNI to call
>> java
>> from c++ code.
>> 
>> I don't want to use javac, javah, and java, ...(sun stuff) because of
>> royalties issues...
> 
> OpenJDK is free software, but let's press on...
> 
>> I'm looking for alternatives.
>> 
>> What I see right now are two alternatives:
>> 1. compile my java code to native code using gcj, and link it with the
>> c++
>> code.
>> 2. keep the classes and use the gij instead of java.
>> 
>> I start working on the two approaches in parallel and I'm having too many
>> problems in both them. So I need some REAL help here.
>> 
>> Problem with 1.
>> 1. I succeeded to compile my java code (after chaning the syntax) using
>> gcj
>> to linux "c" object files. But in the linkage to the binary, I got too
>> many
>> "undefined reference to", ... because I use external "jars" (like axis)
>> which are not compiled to native. I try to compile the axis jar to c and
>> get
>> too many compilation errors.
> 
> Compiling Java code with -findirect-dispatch is probably your best
> plan to solve this.  When an undefined class is discoveed, gcj's
> runtime will try to load its class files.
> 
>> Problem with 2.
>> I compiled all my classes with gcj. and the C code uses JNI to call it.
>> But
>> the JNI creates a JVM (JNI_CreateJavaVM)!!! which I don't want to use.
> 
> Why not?  This is fully supported by gcj, and doesn't hurt anything.
> 
>> I want to use gij instead. So I wanted to know if there is anyway to
>> let my JNI code to ceate a gij VM and and java VM. is there anything
>> like this ?!  If not, how can I use the classes I compiled with gcj
>> from the c code without using the JAVA VM?  CNI? does that mean that
>> I should convert my jni code to cni?
> 
> No, there's no need to do that.  JNI code should work with gcj just
> fine.  
> 
> Andrew.
> 
> 

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