本例采用jsoncpp-src-0.6.0-rc2-amalgamation.tar
java调用语句
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));
单写一个类来管理native函数如下
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（详见http://blog.csdn.net/pengchua/article/details/7582949
http://my.oschina.net/lifj/blog/177087）
在cywin控制窗口cd到自己的项目下，如 /cygdrive/d/jdk/work/mJson/
javah -classpath bin/classes -d jni com.mJson.system
生成.h接口文件
/* 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
本来对于JNIEXPORT jstring JNICALL Java_com_...这个函数需要entends
“c”{}包含，用于标识是c实现，便于编译成动态库，但是
由于我将函数的实现挪到了system.cpp中实现，所以此处去掉，将此加到system.cpp中，不然编译时会报冲突错误
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下新建Application
# it is needed for ndk-r5
#APP_STL := stlport_static
APP_STL :=
gnustl_static
在jni下新建Android.mk文件
在Makefile时注意路径
1、JsonCpp用到了stl的exception，所以如果你在android的编译系统的Application文件中指定STL库路径时，如果使用： APP_STL
:= stlport_static，那么就无法通过编译。需要改成：APP_STL := gnustl_static
2、jsoncpp的make
file。注意LOCAL_CPPFLAGS := -DJSON_IS_AMALGAMATION -fexceptions
这一行。宏定义JSON_IS_AMALGAMATION告诉jsoncpp是amalgamation版本，即是我们刚才下载的版本。-fexceptions则开启exception应用。
3、我们的测试程序的make
file。注意LOCAL_C_INCLUDES :=
$(LOCAL_PATH)/soncpp这一行，我们指定了头文件的地址为，当前路径（即$project/jni/test/)的上一级的jsoncpp文件夹，即$project/jni/jsoncpp/,这样在使用中我们需要inlcude的就是
"json/json.h"。
- LOCAL_LDLIBS := -L$(call host-path, $(LOCAL_PATH)/../../libs/armeabi) \
- -ljsoncpp -llog
这里则指定使用的库libjsoncpp和liblog
4、java端的接口，注意加载库的先后顺序：
[java] view
plaincopy
- System.loadLibrary("jsoncpp");
- 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)