Once we’ve converted native types we face the task of converting arbitrary classes and types. Another thing we’ll need is extract the C++ type of a Java object (jobject<\/tt> in JNI).<\/p>\n
For that task, we will follow the convention of calling the native pointers in Java classes _ptr<\/tt>. With that, we can define the following templates:<\/p>\n This should really be doing more error checking, but it is good enough for ilustrating how nice are things when using proper tools (both languages and libraries).<\/p>\n Converting arbitrary types also uses some template magic:<\/p>\n Now we need specializations for each type we want to convert, for instance, converting a paludis’ FSEntry<\/tt> into a java.io.File<\/tt> looks like the following:<\/p>\n Neat and clean.<\/p>\n For containers, a java.util.LinkedList<\/tt> would be used for paludis’ Sequence<\/tt>; and java.util.TreeSet<\/tt> for paludis’ Set<\/tt>:<\/p>\n And now defining NativeToJavaTypeMapper<\/tt> specializations for containers is quite easy:<\/p>\n I’ve spent a fair amount of the time fighting with make and the build system. It looks mostly sane now, though.<\/p>\n Dealing with exceptions has been a bit tricky, however, I think I have a good system<\/i> to deal with it now, even though Ciaran tagged it as icky<\/i> and ugly<\/i> \ud83d\ude42<\/tt>. That’d be the topic of the next part of the series.<\/p>\n The documentation is currently at http:\/\/dev.gentoo.org\/~ferdy\/paludis-jni\/ . All of that has been accomplished in:<\/p>\n Which is not a lot of code for what’s exposed.<\/p>\n — ferdy<\/p>\n","protected":false},"excerpt":{"rendered":" Once we’ve converted native types we face the task of converting arbitrary classes and types. Another thing we’ll need is extract the C++ type of a Java object (jobject in JNI). For that task, we will follow the convention of calling the native pointers in Java classes _ptr. With that, we can define the following … Continue reading Paludis meets Java, part III<\/span><\/a><\/p>\n","protected":false},"author":14,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[3,6],"tags":[],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/blogs.gentoo.org\/ferdy\/wp-json\/wp\/v2\/posts\/18"}],"collection":[{"href":"https:\/\/blogs.gentoo.org\/ferdy\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.gentoo.org\/ferdy\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.gentoo.org\/ferdy\/wp-json\/wp\/v2\/users\/14"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.gentoo.org\/ferdy\/wp-json\/wp\/v2\/comments?post=18"}],"version-history":[{"count":1,"href":"https:\/\/blogs.gentoo.org\/ferdy\/wp-json\/wp\/v2\/posts\/18\/revisions"}],"predecessor-version":[{"id":37,"href":"https:\/\/blogs.gentoo.org\/ferdy\/wp-json\/wp\/v2\/posts\/18\/revisions\/37"}],"wp:attachment":[{"href":"https:\/\/blogs.gentoo.org\/ferdy\/wp-json\/wp\/v2\/media?parent=18"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.gentoo.org\/ferdy\/wp-json\/wp\/v2\/categories?post=18"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.gentoo.org\/ferdy\/wp-json\/wp\/v2\/tags?post=18"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}template <typename T_>\r\ninline T_ * get_native_ptr(JNIEnv * env, const char * const class_name, jobject obj)\r\n{\r\n jclass cls(env->FindClass(class_name));\r\n jfieldID ptr_field(env->GetFieldID(cls, \"_ptr\", \"J\"));\r\n jlong ptr(env->GetLongField(obj, ptr_field));\r\n env->DeleteLocalRef(cls);\r\n return from_java_ptr<T_>(ptr);\r\n}\r\n\r\ntemplate <typename T_>\r\ninline tr1::shared_ptr<T_> get_native_sptr(JNIEnv * env, const char * const class_name, jobject obj)\r\n{\r\n jclass cls(env->FindClass(class_name));\r\n jfieldID ptr_field(env->GetFieldID(cls, \"_ptr\", \"J\"));\r\n jlong ptr(env->GetLongField(obj, ptr_field));\r\n env->DeleteLocalRef(cls);\r\n return from_java_ptr_sptr<T_>(ptr);\r\n}<\/pre>\ntemplate <typename T_>\r\nstruct NativeToJavaTypeMapper\r\n{\r\n jobject operator() (JNIEnv *, const T_ &);\r\n};<\/pre>\ntemplate<>\r\nstruct NativeToJavaTypeMapper<FSEntry>\r\n{\r\n jobject operator() (JNIEnv * env, const FSEntry & f)\r\n {\r\n jclass cls(env->FindClass(\"java\/io\/File\"));\r\n jmethodID constructor(env->GetMethodID(cls, \"<init>\", \"(Ljava\/lang\/String;)V\"));\r\n jobject ret(env->NewObject(cls, constructor, to_java_string(env, stringify(f))));\r\n env->DeleteLocalRef(cls);\r\n return ret;\r\n }\r\n};<\/pre>\ntemplate <typename T_, typename It_>\r\njobject range_to_list(JNIEnv * env, It_ begin, It_ end)\r\n{\r\n jclass list_class(env->FindClass(\"java\/util\/LinkedList\"));\r\n jmethodID constructor(env->GetMethodID(list_class, \"<init>\", \"()V\"));\r\n jobject our_list(env->NewObject(list_class, constructor));\r\n jmethodID add_method(env->GetMethodID(list_class, \"add\", \"(Ljava\/lang\/Object;)Z\"));\r\n\r\n for (It_ i(begin) ; i != end ; ++i)\r\n env->CallBooleanMethod(our_list, add_method, NativeToJavaTypeMapper<T_>()(env, *i));\r\n\r\n env->DeleteLocalRef(list_class);\r\n\r\n return our_list;\r\n}\r\n\r\ntemplate <typename T_, typename It_>\r\njobject range_to_set(JNIEnv * env, It_ begin, It_ end)\r\n{\r\n jclass set_class(env->FindClass(\"java\/util\/TreeSet\"));\r\n jmethodID constructor(env->GetMethodID(set_class, \"<init>\", \"()V\"));\r\n jobject our_set(env->NewObject(set_class, constructor));\r\n jmethodID add_method(env->GetMethodID(set_class, \"add\", \"(Ljava\/lang\/Object;)Z\"));\r\n\r\n for (It_ i(begin) ; i != end ; ++i)\r\n env->CallBooleanMethod(our_set, add_method, NativeToJavaTypeMapper<T_>()(env, *i));\r\n\r\n env->DeleteLocalRef(set_class);\r\n\r\n return our_set;\r\n}<\/pre>\ntemplate<>\r\ntemplate <typename T_>\r\nstruct NativeToJavaTypeMapper<tr1::shared_ptr<const Sequence<T_> > >\r\n{\r\n jobject operator() (JNIEnv * env, const tr1::shared_ptr<const Sequence<T_> > & s)\r\n {\r\n return range_to_list<T_>(env, s->begin(), s->end());\r\n }\r\n};\r\n\r\ntemplate<>\r\ntemplate <typename T_>\r\nstruct NativeToJavaTypeMapper<tr1::shared_ptr<const Set<T_> > >\r\n{\r\n jobject operator() (JNIEnv * env, const tr1::shared_ptr<const Set<T_> > & s)\r\n {\r\n return range_to_set<T_>(env, s->begin(), s->end());\r\n }\r\n};<\/pre>\n[ $ ~\/git\/paludis\/jni(jni) ] git diff --shortstat trunk..\r\n 65 files changed, 4371 insertions(+), 0 deletions(-)<\/pre>\n