Calling java APIs from a c program

From:

"ramasubramanian.rahul@gmail.com" <ramasubramanian.rahul@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

22 Nov 2006 21:13:27 -0800

Message-ID:

<1164258807.723963.114850@l12g2000cwl.googlegroups.com>

hi
i am trying to call some java APIs from c . i use the standatd JNI
calls to load the JVM from a c program and call all java functions by
using a pointer to the jvm which was returned by the JNI call
the source code is given below and also the errors ..
Plz help in resolving these.

This is a code being (slightly modified ) which was downloaded from SUN
website :

#include <jni.h>
#include <errno.h>
#define PATH_SEPARATOR ';'
#define USER_CLASSPATH "."

JavaVM *jvm; /* Pointer to a Java VM */
JNIEnv *env; /* Pointer to native method interface */
JDK1_1InitArgs vm_args; /* JDK 1.1 VM initialization requirements */
int verbose = 1;/* Debugging flag */
/*******************************************************hasExceptionOccurred
* Check to see if there is an exception. If there is one
* return the string with the value.
* Returns the following:
* > 0 Exception raised
* null no exception
* Exits for fatal errors such as
*
* unable to find object class for java.lang.Throwable
* unable to find method id getMessage in java.lang.Throwable
* unable to call method getMessage in java.lang.Throwable
* unable to UTF charchaters from String object returned from
getMessage
*/
char *hasExceptionOccurred( JNIEnv *env) {
    jthrowable jthr;
    jclass jThrowableClass;
    jmethodID mid;
    jstring errorString;
    const jbyte *errorInCString;
    jthr = (*env)->ExceptionOccurred ( env );

    printf("Is there an exception?" );
    /* If there was an exception, extract the message from the object */
    if ( jthr != (jthrowable)0 ) {
        printf (" Yes." );
        jThrowableClass = (*env)->GetObjectClass(env,jthr);
        if ( verbose )
            printf("The class for java.lang.Throwable is %x\n",jThrowableClass);
        if ( jThrowableClass == 0 )
            exit(-1);
        mid = (*env)->GetMethodID( env, jThrowableClass, "getMessage",
"()Ljava/lang/String;" );
        if ( verbose )
            printf("The method id for the ThrowableClass is %x\n", mid);
        if ( mid == 0 )
            exit(-1);
        errorString = (*env)->CallObjectMethod(env, jthr, mid);
        if ( verbose )
            printf("The java string object with the message is %x\n",
errorString);
        if ( errorString == 0 )
            exit(-1);
        errorInCString = (*env)->GetStringUTFChars(env,errorString,0);
        if ( errorInCString == 0 ) {
            exit(-1);
        /* N.B. The following is not valid for all UTF strings */
            printf ( "UTF stirng error");
            }
        if ( verbose )
            printf("The error from Java is \"%s\".\n", errorInCString );
        (*env)->ReleaseStringUTFChars(env,errorString,errorInCString);
    } else
        if ( verbose )
            printf (" No." );

    return ( (char *) 0 );
}
/***********************************************************************Mai=
n*/
/*
* Get the default initialization arguments and set the class path
* Call a method in java without raising an exception
* Call a mewthod in Java expecting to have an exception raised
*/
main(int argc, char **argv ) {

    jclass cls;
    jclass testcls;
    jmethodID mid;
    jthrowable jthr;
    jint res;
    char classpath[1024];
    JavaVMInitArgs vm_args;
    JavaVMOption options[5];

    options[0].optionString = "-Xms4M";
    options[1].optionString = "-Xmx64M";
    options[2].optionString = "-Xss512K";
    options[3].optionString = "-Xoss400K";
    options[4].optionString = "-Djava.class.path=.";

    //vm_args.version = JNI_VERSION_1_4;
    vm_args.version = 0x00010004;
    vm_args.options = options;
    vm_args.nOptions = 5;
    vm_args.ignoreUnrecognized = JNI_FALSE;
    printf("Reached Here1");
    fflush(stdout);

    //vm_args.ignoreUnrecognized = JNI_TRUE;
    res = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);

/*
    JDK1_1InitArgs vm_args;
    vm_args.version = 0x00010001;
    JNI_GetDefaultJavaVMInitArgs(&vm_args);
    // Append USER_CLASSPATH to the default system class path
    sprintf(classpath, "%s%c%s", vm_args.classpath, PATH_SEPARATOR,
USER_CLASSPATH);
    vm_args.classpath = classpath;
    // Create the Java VM
    res = JNI_CreateJavaVM(&jvm, &env, &vm_args);

    vm_args.classpath = ".;/users8/e43636/JNI";
    printf("\n Now Classpath [%s]\n", vm_args.classpath);
    fflush(stdout);
    */
    printf("Reached Here");
    fflush(stdout);
    if (res < 0 )
    {
            printf("JVM Could not be loaded [%d] and errorno[%d]\n", res,errno);
            exit(1);
    }
    /* Find the class we want to load */
    testcls = (*env)->FindClass(env , "java/lang/String");
        printf ( "Class: %x" , testcls );

    cls = (*env)->FindClass( env, "InstantiatedFromC" );
    if ( verbose )
        printf ( "Class: %x" , cls );
    fflush(stdout);

    /* Find the method we want to use */
    mid = (*env)->GetMethodID( env, cls, "test", "(I)I" );
    if ( verbose )
        printf ( "Method: %x" , mid );
    fflush(stdout);
    /* Call the method we want to use */
    printf("First call to Java returns:%d\n",
(*env)->CallStaticIntMethod(env, cls, mid, 1) );
    fflush(stdout);
    getchar();
    /* Check for an exception */
// if ( hasExceptionOccurred ( env ) != (char *)0 ) {
// printf("Exception has occurred.\n");
// }
    /* Call the method we want to use and raise an exception */
// printf("Second call to Java returns:%d\n",
// (*env)->CallStaticIntMethod(env, cls, mid, 2) );
    /* Check for an exception */
// if ( hasExceptionOccurred ( env ) != (char *)0 ) {
// printf("Exception has occurred.\n");
// }
    /*jvm->DestroyJavaVM( );*/
}

***************************************************************************=
***********************************

Java Class whose method is being called

public class InstantiatedFromC {

    public int test(int number) throws Exception {
        System.out.println("Number from C: " + number);
        if ( number == 2 )
            throw new Exception("Exception raised in java seen in C");
        return ( number + 1 );
    }
    //public static void main(String args[]) {
    //}
}

***************************************************************************=
****************************************8
THe C Code above is compiled as follows::
SHLIB_PATH=/opt/java1.4/jre/lib/PA_RISC:/opt/java1.4/jre/lib/PA_RISC/serv=
er:$SHLIB_PATH
export SHLIB_PATH
gcc -g tcl2JavaVM.c -I/opt/java1.4/include
-I/opt/java1.4/include/hp-ux
-L/opt/java1.4/jre/lib/PA_RISC/native_threads
-L/opt/java1.4/jre/lib/PA_RISC -L/opt/java1.4/jre/lib/PA_RISC/server
-ljvm -lpthread -llwp

on HP-UX machine...

***************************************************************************=
***********************************8

THe error stack being generated :

Reached Here1Reached HereClass: 4000c7a0Class: 4000c7c4Method: 4013fd78
Unexpected Signal : 4 occurred at PC=0x680A9F28
Function=[Unknown.]
Library=/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl

NOTE: We are unable to locate the function name symbol for the error
      just occurred. Please refer to release documentation for possible
      reason and solutions.

Current Java thread:
"main" prio=7 tid=4000bca8 nid=1 lwp_id=6600282 runnable
[0x680f9000..0x680f9628]
Stack_Trace: error while unwinding stack
( 0) 0x9139d884 report_error__FbPCciN22e + 0x6c
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 1) 0x9139d680 report_should_not_reach_here__FPCci + 0x3c
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 2) 0x913e1ecc sender__5frameCFP11RegisterMapP8CodeBlob + 0x1ac
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 3) 0x913de8bc real_sender__5frameCFP11RegisterMap + 0x20
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 4) 0x91779430 sender__6vframeCFv + 0x6c
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 5) 0x91744760 last_java_vframe__10JavaThreadFP11RegisterMap +
0x128 [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 6) 0x9174432c print_stack__10JavaThreadFv + 0x8c
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 7) 0x91649524 report_fatal_error__2osSFP12outputStreamPUci + 0x584
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 8) 0x9164a3c0 handle_unexpected_exception__2osSFP6ThreadiPUcPv +
0x680 [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 9) 0x91655398
JVM_handle_hpux_signal__Q2_2os4HpuxSFiP9__siginfoPvT1 + 0xa10
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
(10) 0x91651bbc signalHandler__Q2_2os4HpuxSFiP9__siginfoPv + 0x14
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
(11) 0xc020d138 _sigreturn [/usr/lib/libc.2]
[error occured during error reporting]
Stack_Trace: error while unwinding stack
( 0) 0x9139d884 report_error__FbPCciN22e + 0x6c
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 1) 0x9139d680 report_should_not_reach_here__FPCci + 0x3c
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 2) 0x913e1ecc sender__5frameCFP11RegisterMapP8CodeBlob + 0x1ac
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 3) 0x913de8bc real_sender__5frameCFP11RegisterMap + 0x20
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 4) 0x91779430 sender__6vframeCFv + 0x6c
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 5) 0x91744760 last_java_vframe__10JavaThreadFP11RegisterMap +
0x128 [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 6) 0x9174432c print_stack__10JavaThreadFv + 0x8c
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 7) 0x91649524 report_fatal_error__2osSFP12outputStreamPUci + 0x584
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 8) 0x9164a3c0 handle_unexpected_exception__2osSFP6ThreadiPUcPv +
0x680 [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
( 9) 0x91655398
JVM_handle_hpux_signal__Q2_2os4HpuxSFiP9__siginfoPvT1 + 0xa10
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
(10) 0x91651bbc signalHandler__Q2_2os4HpuxSFiP9__siginfoPv + 0x14
[/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]
(11) 0xc020d138 _sigreturn [/usr/lib/libc.2]
    4 Reached Here1Reached HereClass: 4000c7a0Class: 4000c7c4Method:
4013fd78^
M
    5 Unexpected Signal : 4 occurred at PC=0x680A9F28^M
    6 Function=[Unknown.]^M
    7 Library=/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl^M
    8 ^M
9 NOTE: We are unable to locate the function name symbol for the
error^M
    10 just occurred. Please refer to release documentation for
possible^
M
   11 reason and solutions.^M
    12 ^M
    13 ^M
    14 Current Java thread:^M
    15 "main" prio=7 tid=4000bca8 nid=1 lwp_id=6600282 runnable
[0x680f9000..0x
680f9628]^M
    16 Stack_Trace: error while unwinding stack^M
    17 ( 0) 0x9139d884 report_error__FbPCciN22e + 0x6c
[/opt/java1.4/jre/li
b/PA_RISC/server/libjvm.sl]^M
@[H [24;1H"resu" [Incomplete last line] 44 lines, 3596 characters[H

    18 ( 1) 0x9139d680 report_should_not_reach_here__FPCci + 0x3c
[/opt/jav
[KD[Aa1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H19 ( 2) 0x913e1ecc sender__5frameCFP11RegisterMapP8CodeBlob
+ 0x1ac [/o
D[Apt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H20 ( 3) 0x913de8bc real_sender__5frameCFP11RegisterMap +
0x20 [/opt/jav
D[Aa1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H21 ( 4) 0x91779430 sender__6vframeCFv + 0x6c
[/opt/java1.4/jre/lib/PA_R
D[AISC/server/libjvm.sl]^M
[A

D[23;5H22 ( 5) 0x91744760
last_java_vframe__10JavaThreadFP11RegisterMap + 0x128
D[A [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H23 ( 6) 0x9174432c print_stack__10JavaThreadFv + 0x8c
[/opt/java1.4/jre
D[A/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H24 ( 7) 0x91649524
report_fatal_error__2osSFP12outputStreamPUci + 0x584
D
[A [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H25 ( 8) 0x9164a3c0
handle_unexpected_exception__2osSFP6ThreadiPUcPv + 0x
D[A680 [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H26 ( 9) 0x91655398
JVM_handle_hpux_signal__Q2_2os4HpuxSFiP9__siginfoPvT1
D[A + 0xa10 [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H27 (10) 0x91651bbc
signalHandler__Q2_2os4HpuxSFiP9__siginfoPv + 0x14 [/
D[Aopt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H28 (11) 0xc020d138 _sigreturn [/usr/lib/libc.2]^M

D[23;5H29 [error occured during error reporting]^M

D[23;5H30 Stack_Trace: error while unwinding stack^M

D[23;5H31 ( 0) 0x9139d884 report_error__FbPCciN22e + 0x6c
[/opt/java1.4/jre/li
D[Ab/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H32 ( 1) 0x9139d680 report_should_not_reach_here__FPCci +
0x3c [/opt/jav
D[Aa1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H33 ( 2) 0x913e1ecc sender__5frameCFP11RegisterMapP8CodeBlob
+ 0x1ac [/o
D[Apt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H34 ( 3) 0x913de8bc real_sender__5frameCFP11RegisterMap +
0x20 [/opt/jav
D[Aa1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H35 ( 4) 0x91779430 sender__6vframeCFv + 0x6c
[/opt/java1.4/jre/lib/PA_R
D[AISC/server/libjvm.sl]^M
[A

D[23;5H36 ( 5) 0x91744760
last_java_vframe__10JavaThreadFP11RegisterMap + 0x128
D[A [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H37 ( 6) 0x9174432c print_stack__10JavaThreadFv + 0x8c
[/opt/java1.4/jre
D[A/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H38 ( 7) 0x91649524
report_fatal_error__2osSFP12outputStreamPUci + 0x584
D
[A [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H39 ( 8) 0x9164a3c0
handle_unexpected_exception__2osSFP6ThreadiPUcPv + 0x
D[A680 [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H40 ( 9) 0x91655398
JVM_handle_hpux_signal__Q2_2os4HpuxSFiP9__siginfoPvT1
D[A + 0xa10 [/opt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H41 (10) 0x91651bbc
signalHandler__Q2_2os4HpuxSFiP9__siginfoPv + 0x14 [/
D[Aopt/java1.4/jre/lib/PA_RISC/server/libjvm.sl]^M
[A

D[23;5H42 (11) 0xc020d138 _sigreturn [/usr/lib/libc.2]^M

***************************************************************************=
*********************************

any help in this regard will be gtreatly appriciated

Thanks in advance
rahul