ndk編譯jsoncpp

標籤：des   android   style   blog   class   c   

本例採用jsoncpp-src-0.6.0-rc2-amalgamation.tar

java調用語句

        int id = 1001; 
        String name = "Kevin"; 
        String result = system.toBuildJson(id, name); 
        Log.i(TAG,String.format("Id:%1$d,Name:%2$s,The json formated string:%3$s", id,name,result));

 

單寫一個類來管理native函數如下

package com.mjson;

public class system {    

static {         

  System.loadLibrary("jsoncpp");        

  System.loadLibrary("system");     

}    

public static native String toBuildJson(int id,String name);

}

 

配置好ndk和cywin（詳見http://blog.csdn.net/pengchua/article/details/7582949
http://my.oschina.net/lifj/blog/177087）

在cywin控制視窗cd到自己的項目下，如 /cygdrive/d/jdk/work/mJson/

javah -classpath bin/classes -d jni com.mJson.system

產生.h介面檔案

/* DO NOT EDIT THIS FILE - it is machine generated */

#include <jni.h>

#include <android/log.h>

#include "json/json.h"

#define  LOG_TAG    "system"

#define  LOGD(...)  __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG,__VA_ARGS__)

/* Header for class com_mjson_system */

#ifndef _Included_com_mjson_system

#define _Included_com_mjson_system #ifdef __cplusplus

#endif

/*  * Class:     com_mjson_system  * Method:    toBuildJson  * Signature: (ILjava/lang/String;)Ljava/lang/String;  */

JNIEXPORT jstring JNICALL Java_com_mjson_system_toBuildJson   (JNIEnv *, jclass, jint, jstring);

#ifdef __cplusplus

#endif #endif

本來對於JNIEXPORT jstring JNICALL Java_com_...這個函數需要entends “c”{}包含，用於標識是c實現，便於編譯成動態庫，但是

由於我將函數的實現挪到了system.cpp中實現，所以此處去掉，將此加到system.cpp中，不然編譯時間會報衝突錯誤

systm.cpp如下

 

#include "com_mjson_system.h"

extern "C" {  

JNIEXPORT jstring JNICALL Java_com_mjson_system_toBuildJson

(JNIEnv*  env, jobject thiz,jint id,jstring name){  

jboolean isCopy = 0;  

const char* c_name = env->GetStringUTFChars(name, &isCopy);  

LOGD("on calling,id:%d,name:%s",id,c_name);  

// to build a json object with id and name  

Json::Value user;  

user["id"] = id;  

user["name"] = c_name;  

const char* json_str = user.toStyledString().c_str();  

jstring result = env->NewStringUTF(json_str);  

env->ReleaseStringUTFChars(name,c_name);  

return result;

  }

}

在jni下建立Application

# it is needed for ndk-r5
#APP_STL := stlport_static
APP_STL := gnustl_static

在jni下建立Android.mk檔案

在Makefile時注意路徑

1、JsonCpp用到了stl的exception，所以如果你在android的編譯系統的Application檔案中指定STL庫路徑時，如果使用： APP_STL := stlport_static，那麼就無法通過編譯。需要改成：APP_STL := gnustl_static

2、jsoncpp的make file。注意LOCAL_CPPFLAGS := -DJSON_IS_AMALGAMATION -fexceptions 這一行。宏定義JSON_IS_AMALGAMATION告訴jsoncpp是amalgamation版本，即是我們剛才下載的版本。-fexceptions則開啟exception應用。

3、我們的測試程式的make file。注意LOCAL_C_INCLUDES := $(LOCAL_PATH)/soncpp這一行，我們指定了標頭檔的地址為，當前路徑（即$project/jni/test/)的上一級的jsoncpp檔案夾，即$project/jni/jsoncpp/,這樣在使用中我們需要inlcude的就是 "json/json.h"。

 

1. LOCAL_LDLIBS := -L$(call host-path, $(LOCAL_PATH)/../../libs/armeabi) \  
2.                 -ljsoncpp -llog  

這裡則指定使用的庫libjsoncpp和liblog

4、java端的介面，注意載入庫的先後順序：

[java] view plaincopy

1. System.loadLibrary("jsoncpp");  
2. System.loadLibrary("main");  

 

 

 

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE := jsoncpp

LOCAL_CPPFLAGS := -DJSON_IS_AMALGAMATION -fexceptions

LOCAL_SRC_FILES := $(LOCAL_PATH)/jsoncpp/jsoncpp.cpp

LOCAL_C_INCLUDES := $(LOCAL_PATH)/jsoncpp/json

# it is used for ndk-r5

# if you build with ndk-r4, comment it

# because the new Windows toolchain doesn‘t support Cygwin‘s drive

# mapping (i.e /cygdrive/c/ instead of C:/)

#LOCAL_LDLIBS := -L$(call host-path, $(LOCAL_PATH)/../libs/armeabi)

include $(BUILD_SHARED_LIBRARY)

include $(CLEAR_VARS) LOCAL_MODULE := system

# for jsoncpp LOCAL_CPPFLAGS := -DJSON_IS_AMALGAMATION

LOCAL_SRC_FILES := system.cpp LOCAL_C_INCLUDES := $(LOCAL_PATH)/jsoncpp

# it is used for ndk-r5

# if you build with ndk-r4, comment it

# because the new Windows toolchain doesn‘t support Cygwin‘s drive

# mapping (i.e /cygdrive/c/ instead of C:/)

LOCAL_LDLIBS := -L$(call host-path, $(LOCAL_PATH)/../libs/armeabi) \                 -ljsoncpp -llog

include $(BUILD_SHARED_LIBRARY)