Can I run a system native method?
(Sorry for the cross-posting. I put this in advanced-topics before I discovered this forum).
This method definition exists in ObjectInputStream.java:
private static native Object allocateNewObject(Class aclass, Class initclass)
throws InstantiationException, IllegalAccessException;
I want to use this same method. I can compile with the above definition in my source with no problem. When I try to run it I get a dll missing error.
I checked every occurance of loadLibrary in jdk1.3.1 source and found nothing that looks useful.
How do I call this native system method as ObjectInputStream.java does?
[658 byte] By [
mchahn] at [2007-9-26 1:35:14]
Ok, I think I have a solution for you using jni. You'll need a C/C++ compiler (I've used Visual C++).
I've tested it on Windows 2000 server, but should be more or less portable. Forgive me if I'm making an utmost fool of myself it there are much better/easier solutions, but I can't come up with a better one. At least my code works for me.
Also note that there might be extra code required (exception handling, ...).
Here it comes:
1) create a file named New.java:import java.lang.reflect.*;
public class New {
static {
System.loadLibrary("ObjectHandler");
}
public static void main (String[] args) {
try {
Object obj;
obj = allocNewObject (Class.forName ("java.awt.List"));
printMethods (obj);
}
catch (Exception ex) {
System.out.println ("Exception occurred: " + ex);
ex.printStackTrace();
}
}
// simple function to test reflection
static void printMethods(Object obj) {
Method[] methods = obj.getClass().getMethods();
for (int j=0; j < methods.length; j++) {
System.out.println("Method " + methods[j].getName() +
" returns " + methods[j].getReturnType().getName());
}
}
public static native Object allocNewObject (Class aClass);
}
2) create a file named New.h:#include <jni.h>
#ifndef _Included_New
#define _Included_New
#ifdef __cplusplus
extern "C" {
#endif
/*
* Class:New
* Method:allocNewObject
* Signature: (Ljava/lang/Class;Ljava/lang/Class;)Ljava/lang/Object;
*/
JNIEXPORT jobject JNICALL Java_New_allocNewObject
(JNIEnv *, jclass, jclass);
#ifdef __cplusplus }
#endif
#endif
3) create a file named ObjectHandlerFuncs.cpp:#include <stdio.h>
#include "New.h"
JNIEXPORT jobject JNICALL Java_New_allocNewObject
(JNIEnv *env, jclass cl, jclass aClass) {
jobject obj = env->AllocObject (aClass);
return obj;
}
4) Start Visual C++, and create a new project. Name it "ObjectHandler". Follow the instructions from the jdk or website to link your project to the right jni library and imports. Then, add the files New.h and ObjectHandlerFuncs.cpp to this project. Compile the project, resulting in a file named ObjectHandler.dll. Copy this file into the same directory as the previously created classfile.
5) Run the program. This is a part from the output for "java.awt.List":
Method add returns void
Method add returns void
Method remove returns void
Method remove returns void
Method clear returns void
Method removeAll returns void
Method addNotify returns void
Method removeNotify returns void
Method getSelectedIndexes returns [I
Method getItemCount returns int
Method countItems returns int
Method getItem returns java.lang.String
Method getItems returns [Ljava.lang.String;
Method addItem returns void
Method addItem returns void
Method replaceItem returns void
Method delItem returns void
Method delItems returns void
Method getSelectedIndex returns int
Method getSelectedItem returns java.lang.String
Method getSelectedItems returns [Ljava.lang.String;
Method getSelectedObjects returns [Ljava.lang.Object;
Good luck!
If you have any questions/compiler errors, please post them and I'll look for a solution.
Kurt.
