Convert StringBuffer to char*

Question

Hi,
I try to convert a StringBuffer field to a char* in C++.
But it doesn't work at all.
I try to get the String of the StringBuffer and then convert this String with UTF.
I post my code. If anyone can help, please ....
     jfieldID fidLoN = env->GetFieldID(cls, "pszLogicalName", "Ljava/lang/StringBuffer;");
     jobject strBuff = (jobject) env->GetObjectField(pModelInfo, fidLoN);          
     jclass jclsStrBuf = env->FindClass("Ljava/lang/StringBuffer;");
     jmethodID jmethToStr = env->GetMethodID(jclsStrBuf, "toString", "()Ljava/lang/String;");
     jstring str1 = NULL;
     env->CallObjectMethod(str, jmethToStr, str1);
     const char *buf1 = env->GetStringUTFChars(str1,0);
     strcpy(BUF1, buf1);
// C++ structure
     modInf.pszLogicalName = (char*) BUF1;
Thanks a lot
Zauz

Answer 1

void testmethod(char *s) {
  if(s != NULL) {
    printf("Received: %s\n", s);
    sprintf(s, "hello world");
#ifdef __cplusplus
extern "C" {
#endif
JNIEXPORT void JNICALL Java_exampleJNI_testmethod(JNIEnv *jenv, jclass jcls, jobject jarg1) {
    char *arg1 ;
    (void)jenv;
    (void)jcls;
        arg1 = NULL;
        if(jarg1 != NULL) {
            /* Get the String from the StringBuffer */
            jmethodID setLengthID;
            jclass sbufClass = (*jenv)->GetObjectClass(jenv, jarg1);
            jmethodID toStringID = (*jenv)->GetMethodID(jenv, sbufClass, "toString", "()Ljava/lang/String;");
            jstring js = (jstring) (*jenv)->CallObjectMethod(jenv, jarg1, toStringID);
            /* Convert the String to a C string */
            const char *pCharStr = (*jenv)->GetStringUTFChars(jenv, js, 0);
            /* Take a copy of the C string as the typemap is for a non const C string */
            jmethodID capacityID = (*jenv)->GetMethodID(jenv, sbufClass, "capacity", "()I");
            jint capacity = (*jenv)->CallIntMethod(jenv, jarg1, capacityID);
            arg1 = (char *) malloc(capacity+1);
            strcpy(arg1, pCharStr);
            /* Release the UTF string we obtained with GetStringUTFChars */
            (*jenv)->ReleaseStringUTFChars(jenv,  js, pCharStr);
            /* Zero the original StringBuffer, so we can replace it with the result */
            setLengthID = (*jenv)->GetMethodID(jenv, sbufClass, "setLength", "(I)V");
            (*jenv)->CallVoidMethod(jenv, jarg1, setLengthID, (jint) 0);
    testmethod(arg1);
        if(arg1 != NULL) {
            /* Append the result to the empty StringBuffer */
            jstring newString = (*jenv)->NewStringUTF(jenv, arg1);
            jclass sbufClass = (*jenv)->GetObjectClass(jenv, jarg1);
            jmethodID appendStringID = (*jenv)->GetMethodID(jenv, sbufClass, "append", "(Ljava/lang/String;)Ljava/lang/StringBuffer;");
            (*jenv)->CallObjectMethod(jenv, jarg1, appendStringID, newString);
            /* Clean up the string object, no longer needed */
            free(arg1);
            arg1 = NULL;
#ifdef __cplusplus
#endifJava code:
class exampleJNI {
  public final static native void testmethod(StringBuffer jarg1);
public class example {
  public static void testmethod(StringBuffer SBUF) {
    exampleJNI.testmethod(SBUF);
public class main {
  public static void main(String argv[]) {
    System.loadLibrary("example");
    StringBuffer sb = new StringBuffer(20);
    sb.append( "Java message" );
    example.testmethod(sb);
    System.out.println("returned: " + sb);
}Run main and you should get:
Received: Java message
returned: hello world
Code adapted from one of the SWIG examples.