将c++静态库实现二次封装供java调用-白红宇

工作中常常作为c++开发者，常常需要与java开发人员进行对接，或者他们看重了一些很好的c++库想借用，就需要将这些已有的开发可进行二次封装给java开发调用

首先需要从官网下载jdk并安装，例如本人的安装路径：C:\software\java\jdk1.8.0_45\

假如我们目前已有一组c++的头文件及库文件

[1]建立对应的java类及结构

c++头文件ReData.h里有一个结构数据：

///ReData.h

struct MSGItem

{

MSGItem() : chl_id(0), t_sec(0),t_usec(0),_direct(0),_msg("")

{

};

~MSGItem()

{

};

MSGItem& operator=(const MSGItem& rhs)

{

if(this!=&rhs){

this->chl_id = rhs.chl_id;

this->t_sec = rhs.t_sec;

this->t_usec = rhs.t_usec;

this->_direct = rhs._direct;

this->_msg = rhs._msg;

}

return *this;

};

unsigned int chl_id;

unsigned int t_sec; /* seconds */

unsigned int t_usec; /* and microseconds */

int _direct;

std::string _msg;

};

//ReData.h

假如有一个MSGRecive类，并该类引用了MSGItem结构，

//MSGRecive.h

class MSGRecive

{

public:

MSGRecive(void);

~MSGRecive(void);

public:

.......................................

//获取报文数据

bool getMsg(MSGItem &_item);

//取对应ip的设备id

int GetIDByIP(int _id);

//批量取对应ip的设备id

int GetIDByIPRange(int _startId, int _endId,std::map<int,int> &_idMaps);

.......................................................

};

//MSGRecive.h

现在建立java与c++结构数据对应的结构及类，例如

建立一个java工程，在src\lib_et1100目录下建立对应的java类

//JMSGItem.java

package lib_et1100;

public class JMSGItem {

public int chl_id;

public int t_sec; /* seconds */

public int t_usec; /* and microseconds */

public int _direct;

public String _msg;

}

//JMSGItem.java

//JMSGRecive.java

package lib_et1100;

import java.util.Map;

import lib_et1100.JMSGItem;

public class JMSGRecive {

static

{

System.loadLibrary("jk_dll");

}

public JMSGRecive()

{

mNativeMSGRecive = init();

}

........................................................

//获取报文数据

public boolean getMsg(JMSGItem _item)

{

return getMsg_c(mNativeMSGRecive,_item);

}

//取对应ip的设备id

public int GetIDByIP(int _id)

{

return GetIDByIP_c(mNativeMSGRecive,_id);

}

//批量取对应ip的设备id

public int GetIDByIPRange(int _startId, int _endId, Map _idMaps)

{

return GetIDByIPRange_c(mNativeMSGRecive,_startId,_endId,_idMaps);

}

........................................................................................

private native int init();

private native int GetIDByIP_c(int mMSGRecive,int _id);

private native boolean getMsg_c(int mMSGRecive,JMSGItem _item);

private native int GetIDByIPRange_c(int mMSGRecive,int _startId, int _endId, Map _idMaps);

private int mNativeMSGRecive;

}

//JMSGRecive.java

//LibJavaEt.java,主程序类

package lib_et1100;

public class LibJavaEt {

public static void main(String[] args) {

JMSGRecive msg = new JMSGRecive();

..............................................................

JMSGItem it = new JMSGItem();

boolean ret = msg.getMsg(it);

.....................................................................

}

//LibJavaEt.java

[2]使用javah命令（javah 类的全路径）

javah .classpath -jni

//.classpath conf///

<?xml version="1.0" encoding="UTF-8"?>

</attributes>

</classpathentry>

</classpath>

///

.classpath配置java源src及输出bin目录，

然后生成本地方法的C++头文件，例如lib_et1100_JMSGRecive.h到bin目录,并在bin下会生成一组对应的java的.class文件，

例如lib_et1100/JMSGItem.class, lib_et1100/JMSGRecive.class，

在lib_et1100_JMSGRecive.h文件中，lib_et1100_JMSGRecive对应lib_et1100/JMSGItem.class的输出

javah .classpath

//lib_et1100_JMSGRecive.h

#include <jni.h>

#ifdef __cplusplus

extern "C" {

#endif

..................................................................................................

* Class: lib_et1100_JMSGRecive

* Method: init

* Signature: ()I

JNIEXPORT jint JNICALL Java_lib_1et1100_JMSGRecive_init

(JNIEnv *, jobject)；

* Class: lib_et1100_JMSGRecive

* Method: getMsg_c

* Signature: (ILlib_et1100/JMSGItem;)Z

JNIEXPORT jboolean JNICALL Java_lib_1et1100_JMSGRecive_getMsg_1c

(JNIEnv *, jobject, jint, jobject);

* Class: lib_et1100_JMSGRecive

* Method: GetIPByID_c

* Signature: (II)I

JNIEXPORT jint JNICALL Java_lib_1et1100_JMSGRecive_GetIDByIP_1c

(JNIEnv *, jobject, jint obj, jint _id);

* Class: lib_et1100_JMSGRecive

* Method: GetIDByIPRange_c

* Signature: (IIILjava/util/Map;)I

JNIEXPORT jint JNICALL Java_lib_1et1100_JMSGRecive_GetIDByIPRange_1c

(JNIEnv *env, jobject, jint obj, jint startId, jint endId, jobject rmap);

........................................................................

#ifdef __cplusplus

}

#endif

//lib_et1100_JMSGRecive.h

[3]需要建立一个c++项目将这些库封装成java调用的动态库，

我们建立一个c++项目并设置jdk的头及库调用

C:\software\java\jdk1.8.0_45\include

C:\software\java\jdk1.8.0_45\include\win

C:\software\java\jdk1.8.0_45\lib

同时将需要java调用的c++的头及库文件加入项目

并将javah命令生成的头文件加入到项目中，

[4]c++数据结构转换Java数据结构

我们在StructDataTran.h将c++结构数据进行转换

//StructDataTran.h

#include <jni.h>//JNI是Java Native Interface的缩写，中文为JAVA本地调用。使用JNI可以很方便的用我们的Java程序调用C/C++程序。

#include <map>

#include "ReData.h"

void cp_msgitem(JNIEnv *env,MSGItem_item,jobject ritem)

{

jclass ritem_c = env->GetObjectClass(ritem);

if(NULL!=ritem_c)

{

//获取相关数据;

jfieldID _direct = env->GetFieldID(ritem_c,"_direct","I");

jfieldID chl_id = env->GetFieldID(ritem_c,"chl_id","I");

jfieldID t_sec = env->GetFieldID(ritem_c,"t_sec","I");

jfieldID t_usec = env->GetFieldID(ritem_c,"t_usec","I");

jfieldID _msg = env->GetFieldID(ritem_c,"_msg","Ljava/lang/String;");

//设置相关数据

env->SetIntField(ritem,_direct,_item._direct);

env->SetIntField(ritem,chl_id,_item.chl_id);

env->SetIntField(ritem,t_sec,_item.t_sec);

env->SetIntField(ritem,t_usec,_item.t_usec);

jstring str = env->NewStringUTF(_item._msg.c_str());

env->SetObjectField(ritem,_msg,str);

}

};

//还需要转换标准库的一些结构及容器类

void cp_map(JNIEnv *env,std::map<int,int> _idMaps,jobject rmap)

{

if(!_idMaps.empty()){

jclass ritem_c = env->GetObjectClass(rmap);

//jclass ritem_c = env->FindClass("java/util/HashMap");

if(NULL!=ritem_c)

{

jmethodID HashMap_put = env->GetMethodID(ritem_c, "put",

"(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;");

if (HashMap_put == NULL)

printf("method ID jput not valid\n\n");

else

{

for(std::map<int,int>::iterator it=_idMaps.begin();it!=_idMaps.end();it++)

{

char key[64]={0};

itoa(it->first,key,10);

char val[64]={0};

itoa(it->second,val,10);

env->CallVoidMethod(rmap,HashMap_put,env->NewStringUTF(key),env->NewStringUTF(val));

}

};

[5]实现javah命令生成的头文件的源代码

///lib_et1100_JMSGRecive.cpp

#include "lib_et1100_JMSGRecive.h"

#include "MSGRecive.h"

#include "StructDataTran.h"

..................................................................................................

JNIEXPORT jint JNICALL Java_lib_1et1100_JMSGRecive_init

(JNIEnv *, jobject)

{

MSGRecive* p = new MSGRecive();

return (jint)p;

};

JNIEXPORT jboolean JNICALL Java_lib_1et1100_JMSGRecive_getMsg_1c

(JNIEnv *, jobject, jint, jobject)

{

MSGRecive* p = (MSGRecive*)obj;

MSGItem _item;

jboolean ret = p->getMsg(_item);

if(!ret){

printf("getMsg error!\n");

}else{

cp_msgitem(env,_item,ritem);

}

return ret;

};

JNIEXPORT jint JNICALL Java_lib_1et1100_JMSGRecive_GetIDByIP_1c

(JNIEnv *, jobject, jint obj, jint _id)

{

MSGRecive* p = (MSGRecive*)obj;

return p->GetIDByIP(_id);

};

JNIEXPORT jint JNICALL Java_lib_1et1100_JMSGRecive_GetIDByIPRange_1c

(JNIEnv *env, jobject, jint obj, jint startId, jint endId, jobject rmap)

{

MSGRecive* p = (MSGRecive*)obj;

std::map<int,int> _idMaps;

jint ret = p->GetIDByIPRange(startId,endId,_idMaps);

cp_map(env,_idMaps,rmap);

return ret;

};

........................................................................

///lib_et1100_JMSGRecive.cpp

//最终项目生成一个dll文件，例如jk_dll.dll文件，将动态库输出到java工程的bin里，

[6]java调用

现在在java工程里，这些java的类及结构数据调用类似

注意JNI为JAVA本地调用，会丧失平台可移植性,工程结构如下

java工程：

jk_et1100_interface

bin

lib_et1100

JMSGItem.class

JMSGRecive.class

LibJavaEt.class

jk_dll.dll

lib_et1100_JMSGRecive.h

src

lib_et1100

JMSGItem.java

JMSGRecive.java

LibJavaEt.java

.classpath

.project

jk_dll库项目：

jk_dll

jk_et1100_interface

bin

lib_et1100_JMSGRecive.h

c++lib

ReData.h

MSGRecive.h

c++Lib.lib

src

lib_et1100_JMSGRecive.cpp

StructDataTran.h

StructDataTran.cpp

梳理一下，首先知道 c++lib的头文件及库需要调用，然后在java工程/src/lib_et1100建立对应的java类

通过javah命令生成java工程下，bin下的c++头文件及/bin/lib_et110的.class文件，

然后建立库工程jk_dll，将c++lib的头文件及库以及javah命令输出的头文件加载到项目，并实现javah命令输出的头文件的源代码，

jk_dll项目生成动态库到java工程bin下，供java项目使用