feat(jni): use NewString to create jstring

Converting string from UTF-8 to UTF-16 before creating jstring could help us to avoid some exceptions.

Author: WhiredPlanck

app/src/main/jni/librime_jni/jni-utils.h

@@ -6,6 +6,7 @@
 #define TRIME_JNI_UTILS_H
 
 #include <jni.h>
+#include <utf8.h>
 
 #include <string>
 
@@ -61,9 +62,16 @@ class JString {
   JNIEnv *env_;
   jstring jstring_;
 
+  static inline jstring toJString(JNIEnv *env, const char *chars) {
+    if (chars == nullptr) return nullptr;
+    auto u16str = utf8::utf8to16(chars);
+    return env->NewString(reinterpret_cast<const jchar *>(u16str.data()),
+                          static_cast<int>(u16str.length()));
+  }
+
  public:
   JString(JNIEnv *env, const char *chars)
-      : env_(env), jstring_(env->NewStringUTF(chars)) {}
+      : env_(env), jstring_(toJString(env, chars)) {}
 
   JString(JNIEnv *env, const std::string &string)
       : JString(env, string.c_str()) {}

app/src/main/jni/librime_jni/objconv.h

@@ -20,7 +20,9 @@ inline jobject rimeContextToJObject(JNIEnv *env, const RimeContext &context) {
       env->NewObject(GlobalRef->RimeComposition, GlobalRef->RimeCompositionInit,
                      context.composition.length, context.composition.cursor_pos,
                      context.composition.sel_start, context.composition.sel_end,
-                     *JString(env, context.composition.preedit)));
+                     *JString(env, context.composition.preedit
+                                       ? context.composition.preedit
+                                       : "")));
 
   const auto &menu = context.menu;
 
@@ -50,7 +52,7 @@ inline jobject rimeContextToJObject(JNIEnv *env, const RimeContext &context) {
         env, env->NewObject(
                  GlobalRef->CandidateListItem, GlobalRef->CandidateListItemInit,
                  *JString(env, candidate.comment ? candidate.comment : ""),
-                 *JString(env, candidate.text ? candidate.text : "")));
+                 *JString(env, candidate.text)));
     env->SetObjectArrayElement(candidates, i, jcandidate);
   }
 
@@ -62,7 +64,9 @@ inline jobject rimeContextToJObject(JNIEnv *env, const RimeContext &context) {
 
   return env->NewObject(
       GlobalRef->RimeContext, GlobalRef->RimeContextInit, *jcomposition, *jmenu,
-      *JString(env, context.commit_text_preview), *selectLabels);
+      *JString(env,
+               context.commit_text_preview ? context.commit_text_preview : ""),
+      *selectLabels);
 }
 
 inline jobject rimeStatusToJObject(JNIEnv *env, const RimeStatus &status) {