feat: enable looking up values of static fields

gojni.h

@@ -7,6 +7,7 @@ __attribute__ ((visibility ("hidden"))) void _jni_ExceptionClear(JNIEnv *env);
 __attribute__ ((visibility ("hidden"))) jclass _jni_GetObjectClass(JNIEnv *env, jobject obj);
 __attribute__ ((visibility ("hidden"))) jmethodID _jni_GetMethodID(JNIEnv *env, jclass clazz, const char *name, const char *sig);
 __attribute__ ((visibility ("hidden"))) jmethodID _jni_GetStaticMethodID(JNIEnv *env, jclass clazz, const char *name, const char *sig);
+__attribute__ ((visibility ("hidden"))) jfieldID _jni_GetStaticFieldID(JNIEnv *env, jclass clazz, const char *name, const char *sig);
 __attribute__ ((visibility ("hidden"))) jsize _jni_GetStringLength(JNIEnv *env, jstring str);
 __attribute__ ((visibility ("hidden"))) const jchar *_jni_GetStringChars(JNIEnv *env, jstring str);
 __attribute__ ((visibility ("hidden"))) jstring _jni_NewString(JNIEnv *env, const jchar *unicodeChars, jsize len);
@@ -23,3 +24,12 @@ __attribute__ ((visibility ("hidden"))) jbyteArray _jni_NewByteArray(JNIEnv *env
 __attribute__ ((visibility ("hidden"))) jbyte *_jni_GetByteArrayElements(JNIEnv *env, jbyteArray arr);
 __attribute__ ((visibility ("hidden"))) void _jni_ReleaseByteArrayElements(JNIEnv *env, jbyteArray arr, jbyte *elems, jint mode);
 __attribute__ ((visibility ("hidden"))) jsize _jni_GetArrayLength(JNIEnv *env, jarray arr);
+__attribute__ ((visibility ("hidden"))) jobject _jni_GetStaticObjectField(JNIEnv *env, jclass clazz, jfieldID fieldID);
+__attribute__ ((visibility ("hidden"))) jboolean _jni_GetStaticBooleanField(JNIEnv *env, jclass clazz, jfieldID fieldID);
+__attribute__ ((visibility ("hidden"))) jbyte _jni_GetStaticByteField(JNIEnv *env, jclass clazz, jfieldID fieldID);
+__attribute__ ((visibility ("hidden"))) jchar _jni_GetStaticCharField(JNIEnv *env, jclass clazz, jfieldID fieldID);
+__attribute__ ((visibility ("hidden"))) jshort _jni_GetStaticShortField(JNIEnv *env, jclass clazz, jfieldID fieldID);
+__attribute__ ((visibility ("hidden"))) jint _jni_GetStaticIntField(JNIEnv *env, jclass clazz, jfieldID fieldID);
+__attribute__ ((visibility ("hidden"))) jlong _jni_GetStaticLongField(JNIEnv *env, jclass clazz, jfieldID fieldID);
+__attribute__ ((visibility ("hidden"))) jfloat _jni_GetStaticFloatField(JNIEnv *env, jclass clazz, jfieldID fieldID);
+__attribute__ ((visibility ("hidden"))) jdouble _jni_GetStaticDoubleField(JNIEnv *env, jclass clazz, jfieldID fieldID);

jni.c

@@ -36,6 +36,10 @@ jmethodID _jni_GetStaticMethodID(JNIEnv *env, jclass clazz, const char *name, co
 	return (*env)->GetStaticMethodID(env, clazz, name, sig);
 }
 
+jfieldID _jni_GetStaticFieldID(JNIEnv *env, jclass clazz, const char *name, const char *sig) {
+    return (*env)->GetStaticFieldID(env, clazz, name, sig);
+}
+
 jsize _jni_GetStringLength(JNIEnv *env, jstring str) {
 	return (*env)->GetStringLength(env, str);
 }
@@ -99,3 +103,40 @@ void _jni_ReleaseByteArrayElements(JNIEnv *env, jbyteArray arr, jbyte *elems, ji
 jsize _jni_GetArrayLength(JNIEnv *env, jarray arr) {
 	return (*env)->GetArrayLength(env, arr);
 }
+
+jobject _jni_GetStaticObjectField(JNIEnv *env, jclass clazz, jfieldID fieldID) {
+    return (*env)->GetStaticObjectField(env, clazz, fieldID);
+}
+
+jboolean _jni_GetStaticBooleanField(JNIEnv *env, jclass clazz, jfieldID fieldID) {
+    return (*env)->GetStaticBooleanField(env, clazz, fieldID);
+}
+
+jbyte _jni_GetStaticByteField(JNIEnv *env, jclass clazz, jfieldID fieldID) {
+    return (*env)->GetStaticByteField(env, clazz, fieldID);
+}
+
+jchar _jni_GetStaticCharField(JNIEnv *env, jclass clazz, jfieldID fieldID) {
+    return (*env)->GetStaticCharField(env, clazz, fieldID);
+}
+
+jshort _jni_GetStaticShortField(JNIEnv *env, jclass clazz, jfieldID fieldID) {
+    return (*env)->GetStaticShortField(env, clazz, fieldID);
+}
+
+jint _jni_GetStaticIntField(JNIEnv *env, jclass clazz, jfieldID fieldID) {
+    return (*env)->GetStaticIntField(env, clazz, fieldID);
+}
+
+jlong _jni_GetStaticLongField(JNIEnv *env, jclass clazz, jfieldID fieldID) {
+    return (*env)->GetStaticLongField(env, clazz, fieldID);
+}
+
+jfloat _jni_GetStaticFloatField(JNIEnv *env, jclass clazz, jfieldID fieldID) {
+    return (*env)->GetStaticFloatField(env, clazz, fieldID);
+}
+
+jdouble _jni_GetStaticDoubleField(JNIEnv *env, jclass clazz, jfieldID fieldID) {
+    return (*env)->GetStaticDoubleField(env, clazz, fieldID);
+}
+

jni.go

@@ -38,6 +38,7 @@ type (
 	Class     C.jclass
 	Object    C.jobject
 	MethodID  C.jmethodID
+	FieldID   C.jfieldID
 	String    C.jstring
 	ByteArray C.jbyteArray
 	Value     uint64 // All JNI types fit into 64-bits.
@@ -212,6 +213,20 @@ func GetStaticMethodID(e Env, cls Class, name, signature string) MethodID {
 	return MethodID(m)
 }
 
+// GetStaticFieldID returns the id for a static field. It panics if the field
+// wasn't found.
+func GetStaticFieldID(e Env, cls Class, name, signature string) FieldID {
+	mname := C.CString(name)
+	defer C.free(unsafe.Pointer(mname))
+	msig := C.CString(signature)
+	defer C.free(unsafe.Pointer(msig))
+	m := C._jni_GetStaticFieldID(e.env, C.jclass(cls), mname, msig)
+	if err := exception(e); err != nil {
+		panic(err)
+	}
+	return FieldID(m)
+}
+
 // GetMethodID returns the id for a method. It panics if the method
 // wasn't found.
 func GetMethodID(e Env, cls Class, name, signature string) MethodID {
@@ -259,3 +274,93 @@ func GoString(e Env, str String) string {
 	utf8 := utf16.Decode(utf16Chars)
 	return string(utf8)
 }
+
+// GetStaticObjectField looks up the value of a static field of type Object.
+// It panics if it is unable to find the field.
+func GetStaticObjectField(env Env, clazz Class, fieldID FieldID) Object {
+	value := C._jni_GetStaticObjectField(env.env, C.jclass(clazz), C.jfieldID(fieldID))
+	if err := exception(env); err != nil {
+		panic(err)
+	}
+	return Object(value)
+}
+
+// GetStaticBooleanField looks up the value of a static field of type boolean.
+// It panics if it is unable to find the field.
+func GetStaticBooleanField(env Env, clazz Class, fieldID FieldID) bool {
+	value := C._jni_GetStaticBooleanField(env.env, C.jclass(clazz), C.jfieldID(fieldID))
+	if err := exception(env); err != nil {
+		panic(err)
+	}
+	return value != 0
+}
+
+// GetStaticByteField looks up the value of a static field of type byte.
+// It panics if it is unable to find the field.
+func GetStaticByteField(env Env, clazz Class, fieldID FieldID) byte {
+	value := C._jni_GetStaticByteField(env.env, C.jclass(clazz), C.jfieldID(fieldID))
+	if err := exception(env); err != nil {
+		panic(err)
+	}
+	return byte(value)
+}
+
+// GetStaticCharField looks up the value of a static field of type char.
+// It panics if it is unable to find the field.
+func GetStaticCharField(env Env, clazz Class, fieldID FieldID) byte {
+	value := C._jni_GetStaticCharField(env.env, C.jclass(clazz), C.jfieldID(fieldID))
+	if err := exception(env); err != nil {
+		panic(err)
+	}
+	return byte(value)
+}
+
+// GetStaticShortField looks up the value of a static field of type short.
+// It panics if it is unable to find the field.
+func GetStaticShortField(env Env, clazz Class, fieldID FieldID) int16 {
+	value := C._jni_GetStaticShortField(env.env, C.jclass(clazz), C.jfieldID(fieldID))
+	if err := exception(env); err != nil {
+		panic(err)
+	}
+	return int16(value)
+}
+
+// GetStaticIntField looks up the value of a static field of type int.
+// It panics if it is unable to find the field.
+func GetStaticIntField(env Env, clazz Class, fieldID FieldID) int32 {
+	value := C._jni_GetStaticIntField(env.env, C.jclass(clazz), C.jfieldID(fieldID))
+	if err := exception(env); err != nil {
+		panic(err)
+	}
+	return int32(value)
+}
+
+// GetStaticLongField looks up the value of a static field of type long.
+// It panics if it is unable to find the field.
+func GetStaticLongField(env Env, clazz Class, fieldID FieldID) int64 {
+	value := C._jni_GetStaticLongField(env.env, C.jclass(clazz), C.jfieldID(fieldID))
+	if err := exception(env); err != nil {
+		panic(err)
+	}
+	return int64(value)
+}
+
+// GetStaticFloatField looks up the value of a static field of type float.
+// It panics if it is unable to find the field.
+func GetStaticFloatField(env Env, clazz Class, fieldID FieldID) float32 {
+	value := C._jni_GetStaticFloatField(env.env, C.jclass(clazz), C.jfieldID(fieldID))
+	if err := exception(env); err != nil {
+		panic(err)
+	}
+	return float32(value)
+}
+
+// GetStaticDoubleField looks up the value of a static field of type double.
+// It panics if it is unable to find the field.
+func GetStaticDoubleField(env Env, clazz Class, fieldID FieldID) float64 {
+	value := C._jni_GetStaticDoubleField(env.env, C.jclass(clazz), C.jfieldID(fieldID))
+	if err := exception(env); err != nil {
+		panic(err)
+	}
+	return float64(value)
+}