Common helper functions for JNI

IntegerByReference.java

package com.generic.jni.byref;

/**
 * class to facilitate passing of integer values by reference. 
 * @author Naveed
 */
public class IntegerByReference {
    private int value;

    public IntegerByReference(int value) {
        this.value = value;
    }

    public IntegerByReference() {
    }

    public int getValue() {
        return value;
    }

    public void setValue(int value) {
        this.value = value;
    }
}

jni-common.h

/**
\file
\brief common functions for JNI
\author Naveed Quadri
\version 1.0
*/
#pragma once
#include <jni.h>


#define JNI_NO_CLASS_DEF "java/lang/NoClassDefFoundError"
#define JNI_NO_SUCH_METHOD "java/lang/NoSuchMethodError"

/**
\brief Throws Java exception 
\param env						Pointer to JNIEnv
\param name						[in] fully qualified exception class name [ eg. java/lang/NoSuchMethodError ]
\param message					[in] exception message
*/
void ThrowExceptionByClassName(JNIEnv *env, const char *name, const char *message)
{
	jclass clazz = env->FindClass(name);
	if (clazz != NULL) {
		env->ThrowNew(clazz, message);
		env->DeleteLocalRef(clazz);
	}
}

/**
\brief Throws Java exception
\param env						Pointer to JNIEnv
\param name						[in] fully qualified exception class name [ eg. java/lang/NoSuchMethodError ]
\param message					[in] exception message
*/
void CopyToCharPtr(JNIEnv *env, jstring string, char* dest, int size)
{
	const char *nativeString = env->GetStringUTFChars(string, 0);
	memcpy(dest, nativeString, size);
	env->ReleaseStringUTFChars(string, nativeString);
}

/**
\brief convenience method to get the class and method 
\param env					Pointer to JNIEnv
\param clazzObj				[int] class object
\param method_name			[in] method name
\param sig					[in] methid signature
\param clazz				[out] exception message
\param mid					[out] exception message
*/
bool GetClassAndMethodOrThrow(JNIEnv *env, jobject clazzObj,const char* method_name, const char* sig, jclass &clazz, jmethodID &mid)
{
	clazz = env->GetObjectClass(clazzObj);
	if (clazz == NULL)
	{
		ThrowExceptionByClassName(env, JNI_NO_CLASS_DEF, "");
		return false;
	}
	mid = env->GetMethodID(clazz, method_name, sig);
	if (mid == NULL)
	{
		ThrowExceptionByClassName(env, JNI_NO_SUCH_METHOD, method_name);
		return false;
	}
	return true;
}

/**
\brief Gets jint from the clazzObj
\param env				Pointer to JNIEnv
\param clazzObj			[in]  class object
\param method_name		[in]  method name
\param sig				[in]  method signature
\param value			[out] jint value to returned
\return true if succeful, false otherwise
*/
bool GetIntValue(JNIEnv *env, jobject clazzObj, const char* name, const char* sig, jint &value)
{
	jclass clazz;
	jmethodID mid;
	bool b = GetClassAndMethodOrThrow(env, clazzObj, name, sig, clazz, mid);
	if (!b) return false;
	value = env->CallIntMethod(clazzObj, mid);
	return true;
}

/**
\brief Gets jlong from the clazzObj
\param env				Pointer to JNIEnv
\param clazzObj			[in]  class object
\param method_name		[in]  method name
\param sig				[in]  method signature
\param value			[out] jlong value to returned
\return true if succeful, false otherwise
*/
bool GetLongValue(JNIEnv *env, jobject clazzObj, const char* name, const char* sig,jlong &value)
{
	jclass clazz;
	jmethodID mid;
	bool b = GetClassAndMethodOrThrow(env, clazzObj, name, sig, clazz, mid);
	if (!b) return false;
	value = env->CallLongMethod(clazzObj, mid);
	return true;
}

/**
\brief Gets jbyte from the clazzObj
\param env				Pointer to JNIEnv
\param clazzObj			[in]  class object
\param method_name		[in]  method name
\param sig				[in]  method signature
\param value			[out] jbyte value to returned
\return true if succeful, false otherwise
*/
bool GetByteValue(JNIEnv *env, jobject clazzObj, const char* name, const char* sig, jbyte &value)
{
	jclass clazz;
	jmethodID mid;
	bool b = GetClassAndMethodOrThrow(env, clazzObj, name, sig, clazz, mid);
	if (!b) return false;
	value = env->CallByteMethod(clazzObj, mid);
	return true;
}

/**
\brief Gets jboolean from the clazzObj
\param env				Pointer to JNIEnv
\param clazzObj			[in]  class object
\param method_name		[in]  method name
\param sig				[in]  method signature
\param value			[out] jboolean value to returned
\return true if succeful, false otherwise
*/
bool GetBoolValue(JNIEnv *env, jobject clazzObj, const char* name, const char* sig, jboolean &value)
{
	jclass clazz;
	jmethodID mid;
	bool b = GetClassAndMethodOrThrow(env, clazzObj, name, sig, clazz, mid);
	if (!b) return false;
	value = env->CallBooleanMethod(clazzObj, mid);
	return true;
}

/**
\brief Gets jobject from the clazzObj
\param env				Pointer to JNIEnv
\param clazzObj			[in]  class object
\param method_name		[in]  method name
\param sig				[in]  method signature
\param value			[out] jobject value to returned
\return true if succeful, false otherwise
*/
bool GetObjectValue(JNIEnv *env, jobject clazzObj, const char* name, const char* sig, jobject &value)
{
	jclass clazz;
	jmethodID mid;
	bool b = GetClassAndMethodOrThrow(env, clazzObj, name, sig, clazz, mid);
	if (!b) return false;
	value = env->CallObjectMethod(clazzObj, mid);
	return true;
}

/**
\brief Gets jstring from the clazzObj
\param env				Pointer to JNIEnv
\param clazzObj			[in]  class object
\param method_name		[in]  method name
\param sig				[in]  method signature
\param value			[out] jstring value to returned
\return true if succeful, false otherwise
*/
bool GetString(JNIEnv *env, jobject clazzObj, const char* method_name, const char* sig, jstring &value)
{
	jclass clazz;
	jmethodID mid;
	
	bool b = GetClassAndMethodOrThrow(env, clazzObj, method_name, sig, clazz, mid);
	if (!b) return false;
	jobject obj = env->CallObjectMethod(clazzObj, mid);
	value = (jstring)obj;
	return true;
}

/**
\brief Retrieves the jstring from the clazzObj and converts it to char*. Convenience method, same as calling ::GetString then ::CopyToCharPtr
\param env					Pointer to JNIEnv
\param clazzObj				[in]  class object
\param method_name			[in]  method name
\param sig					[in]  method signature
\param dest					[out] destination buffer
\param size					[in]  size of the destination buffer
\return true if succeful, false otherwise
*/
bool GetStringAsCharPtr(JNIEnv *env, jobject clazzObj, const char* name, const char* sig, char* dest,int size)
{
	jstring str;
	bool res = GetString(env, clazzObj, name, sig, str);
	if (!res) return false;

	CopyToCharPtr(env, str, dest, size);
	return true;
}


template <class Type>
/**
\brief A generic setter method
\param  env				Pointer to JNIEnv
\param  clazzObj		[in] class object
\param  method_name		[in] method name
\param  sig				[in] method signature [ \see http://docs.oracle.com/javase/1.5.0/docs/guide/jni/spec/types.html ]
\param  value			the <Type> value to set
\return true if succeful, false otherwise
*/
bool SetValue(JNIEnv *env, jobject clazzObj, const char* method_name, const char* sig, Type value)
{
	jclass clazz;
	jmethodID mid;
	bool res = GetClassAndMethodOrThrow(env, clazzObj, name, sig, clazz, mid);
	if (!res) return false;
	env->CallVoidMethod(clazzObj, mid, value);
	return true;
}

LongByReference.java

package com.generic.jni.byref;

/**
 * class to facilitate passing of long values by reference. 
 * @author Naveed
 */
public class LongByReference {
    private long value;

    public LongByReference() {
    }

    public LongByReference(long value) {
        this.value = value;
    }

    public long getValue() {
        return value;
    }

    public void setValue(long value) {
        this.value = value;
    }
}