JNI由浅入深_10_JNI 综合开发

于 2015-01-15 18:21:47 发布
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分类专栏： JNI 文章标签： jni 对象 结构体 对象转换
本文详细解析了如何在C++和Java之间进行互调用，包括使用NDK构建C++库，实现不同数据类型的转换，以及类与结构体之间的互操作。涵盖了从设置classpath到编写C库的全过程。

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1、使用ndk-build时如果找不到某个类，可以使用下面两种方法解决：

1、1 进入src目录

D:\project3\JNIAndroid\src>set classpath=D:\project3\JNIAndroid\src

1、2 设置classpath
classpath    .;%JAVA_HOME%\lib\dt.jar;%JAVA_HOME%\tools.jar;E:\developLib\android\platforms\android-8\android.jar

2、基础类

ublic class NativeModule {

    public native int testArg(int i, boolean b, char c, double d);

    public native byte[] testByte(byte[] b);

    public native String[] testString(String s, String[] sarr);

    public native int setInfo(MyInfo info);

    public native MyInfo getInfo();

    static {

       System.loadLibrary("NativeModule");

    }

}


//其中MyInfo类定义如下：

public class Record {

    int id;

    String name;

    byte[] data;

}

public class MyInfo {

    public boolean b;

    public char c;

    public double d;

    public int i;

    public byte[] array;

    public String s;

    public Record rec;

}

c 结构体定义 

typedef struct{

    int id;

    char name[255];

    char data[255];

}Record;

 

typedef struct{

    BOOL b;

    char c;

    double d;

    int i;

    char arr[255];

    char sz[255];

    Record rec;

}MyInfo;

3、编写C库

 3.1) Java与C不同类型参数转换实例

//不同类型参数处理

JNIEXPORT jintJNICALL Java_com_jinhill_util_NativeModule_testArg

  (JNIEnv *env, jobject jo, jint ji, jbooleanjb,  jchar jc, jdouble jd){
         //获取jint型值
         int i = ji;
         //获取jboolean型值
         BOOL b = jb;
         //获取jdouble型值
         double d = jd;
         //获取jchar型值,Java的char两字节
         char ch[5] = {0};
         int size = 0;
         size = WideCharToMultiByte(CP_ACP,NULL, (LPCWSTR)&jc, -1, ch, 5, NULL, FALSE);
         if(size <= 0) {
                   return -1;
         }
         Trace("ji=%d,jb=%d,jc=%s,jd=%lf",i, b, ch, d);
         return 0;

}

 3.2) Java byte与C char数组类型数组转换实例

//btye数组处理，形参作为输入或输出，返回btye数组

JNIEXPORTjbyteArray JNICALL Java_com_jinhill_util_NativeModule_testByte

  (JNIEnv *env, jobject jo, jbyteArray jbArr){
         char chTmp[] = "Hello JNI!";
         int nTmpLen = strlen(chTmp);
         //获取jbyteArray
         char *chArr = (char*)env->GetByteArrayElements(jbArr,0);
         //获取jbyteArray长度
         int nArrLen = env->GetArrayLength(jbArr);
         char *szStrBuf =(char*)malloc(nArrLen*2+10);
         memset(szStrBuf, 0, nArrLen*2+10);
         Bytes2String(chArr, nArrLen, szStrBuf,nArrLen*2+10);
         Trace("jbArr=%s", szStrBuf);
         //将jbArr作为输出形参
         memset(chArr, 0, nArrLen);
         memcpy(chArr, chTmp, nTmpLen);
         //返回jbyteArray
         jbyteArray jarrRV =env->NewByteArray(nTmpLen); 
    jbyte *jby =env->GetByteArrayElements(jarrRV, 0);
         memcpy(jby, chTmp, strlen(chTmp));
    env->SetByteArrayRegion(jarrRV, 0,nTmpLen, jby); 
         return jarrRV;
}

 3.3)   Java String与C char数组类型转换实例

 
//String 和String[]处理

JNIEXPORTjobjectArray JNICALL Java_com_jinhill_util_NativeModule_testString

  (JNIEnv *env, jobject jo, jstring jstr,jobjectArray joarr){
         int i = 0;

         char chTmp[50] = {0};

         //获取jstring值

         const char* pszStr = (char*)env->GetStringUTFChars(jstr, 0);

         Trace("jstr=%s", pszStr);

         //获取jobjectArray值

         int nArrLen =env->GetArrayLength(joarr);

         Trace("joarr len=%d",nArrLen);

         for(i=0; i<nArrLen; i++) {
                   jstring js =(jstring)env->GetObjectArrayElement(joarr, i);
                   const char* psz = (char*)env->GetStringUTFChars(js, 0);
                   Trace("joarr[%d]=%s",i, psz);
         }

         //将joarr作为输出形参

         jstring jstrTmp = NULL;

         for(i=0; i<nArrLen; i++) {
                   sprintf(chTmp, "No.%dHello JNI!", i);
                   jstrTmp =env->NewStringUTF(chTmp);

                   env->SetObjectArrayElement(joarr,i, jstrTmp);
                   env->DeleteLocalRef(jstrTmp);
         }

         //返回jobjectArray

         jclass jstrCls =env->FindClass("Ljava/lang/String;");

         jobjectArray jstrArray =env->NewObjectArray(2, jstrCls, NULL);

         for(i=0; i<2; i++) {
                   sprintf(chTmp, "No. %dReturn JNI!", i);
                   jstrTmp =env->NewStringUTF(chTmp);
                   env->SetObjectArrayElement(jstrArray,i, jstrTmp);
                   env->DeleteLocalRef(jstrTmp);
         }

         return jstrArray;

}

 3.4)   Java 类与C结构体类型转换实例

JNIEXPORT jint JNICALL Java_com_jinhill_util_NativeModule_setInfo

  (JNIEnv *env, jobject jo, jobject jobj){

    char chHexTmp[512] = {0};

    //将Java类转换成C结构体

    MyInfo mi;

    //获取Java中的实例类Record

    jclass jcRec = env->FindClass("com/jinhill/util/Record");

    //int id

    jfieldID jfid = env->GetFieldID(jcRec, "id", "I");

    //String name

    jfieldID jfname = env->GetFieldID(jcRec, "name", "Ljava/lang/String;");

    //byte[] data;

    jfieldID jfdata = env->GetFieldID(jcRec, "data", "[B");

    //获取Java中的实例类MyInfo
    jclass jcInfo = env->FindClass("com/jinhill/util/MyInfo");

    //获取类中每一个变量的定义
    //boolean b
    jfieldID jfb = env->GetFieldID(jcInfo, "b", "Z");

    //char c
    jfieldID jfc = env->GetFieldID(jcInfo, "c", "C");

    //double d
    jfieldID jfd = env->GetFieldID(jcInfo, "d", "D");

    //int i
    jfieldID jfi = env->GetFieldID(jcInfo, "i", "I");

    //byte[] array
    jfieldID jfa = env->GetFieldID(jcInfo, "array", "[B");

    //String s
    jfieldID jfs = env->GetFieldID(jcInfo, "s", "Ljava/lang/String;");

    //Record rec;
    jfieldID jfrec = env->GetFieldID(jcInfo, "rec", "Lcom/jinhill/util/Record;");

 

    //获取实例的变量b的值
    mi.b = env->GetBooleanField(jobj, jfb);

    //获取实例的变量c的值
    jchar jc = env->GetCharField(jobj, jfc);

    char ch[5] = {0};

    int size = 0;

    size = WideCharToMultiByte(CP_ACP, NULL, (LPCWSTR)&jc, -1, ch, 5, NULL, FALSE);

    mi.c = ch[0];

    //获取实例的变量d的值
    mi.d = env->GetDoubleField(jobj, jfd);

    //获取实例的变量i的值
    mi.i = env->GetIntField(jobj, jfi);

    //获取实例的变量array的值
    jbyteArray ja = (jbyteArray)env->GetObjectField(jobj, jfa);

    int  nArrLen = env->GetArrayLength(ja);

    char *chArr = (char*)env->GetByteArrayElements(ja, 0);

    memcpy(mi.arr, chArr, nArrLen);

    //获取实例的变量s的值
    jstring jstr = (jstring)env->GetObjectField(jobj, jfs);

    const char* pszStr = (char*)env->GetStringUTFChars(jstr, 0);

    strcpy(mi.sz, pszStr);

 

    //获取Record对象

    jobject joRec = env->GetObjectField(jobj, jfrec);

    //获取Record对象id值
    mi.rec.id = env->GetIntField(joRec, jfid);

    Trace("mi.rec.id=%d",mi.rec.id);

    //获取Record对象name值
    jstring jstrn = (jstring)env->GetObjectField(joRec, jfname);

    pszStr = (char*)env->GetStringUTFChars(jstrn, 0);

    strcpy(mi.rec.name, pszStr);

    //获取Record对象data值
    jbyteArray jbd = (jbyteArray)env->GetObjectField(joRec, jfdata);
    nArrLen = env->GetArrayLength(jbd);
    chArr = (char*)env->GetByteArrayElements(jbd, 0);
    memcpy(mi.rec.data, chArr, nArrLen);

    //日志输出

    Bytes2String(mi.arr, nArrLen, chHexTmp, sizeof(chHexTmp)); 
   Trace("mi.arr=%s, mi.b=%d, mi.c=%c, mi.d=%lf, mi.i=%d, \n mi.sz=%s\n mi.rec.id=%d, mi.rec.name=%s", chHexTmp, mi.b, mi.c, mi.d, mi.i, mi.sz, mi.rec.id, mi.rec.name);
     return 0;

}

 3.5)   C结构体类型与Java 类转换实例 

 
JNIEXPORT jobject JNICALL Java_com_jinhill_util_NativeModule_getInfo

  (JNIEnv *env, jobject jo){
   wchar_t wStr[255] = {0};
    char chTmp[] = "Hello JNI";
    int nTmpLen = strlen(chTmp);
    //将C结构体转换成Java类
    MyInfo mi;
    memcpy(mi.arr, chTmp, strlen(chTmp));
    mi.b = TRUE;
    mi.c = 'B';
    mi.d = 2000.9;
    mi.i = 8;

    strcpy(mi.sz, "Hello World!");
    mi.rec.id = 2011;
    memcpy(mi.rec.data, "\x01\x02\x03\x04\x05\x06", 6);
    strcpy(mi.rec.name, "My JNI");

    //获取Java中的实例类Record
    jclass jcRec = env->FindClass("com/jinhill/util/Record");

    //int id
    jfieldID jfid = env->GetFieldID(jcRec, "id", "I");

    //String name
    jfieldID jfname = env->GetFieldID(jcRec, "name", "Ljava/lang/String;");

    //byte[] data;
    jfieldID jfdata = env->GetFieldID(jcRec, "data", "[B");
 

    //获取Java中的实例类
    jclass jcInfo = env->FindClass("com/jinhill/util/MyInfo");

    //获取类中每一个变量的定义
    //boolean b
    jfieldID jfb = env->GetFieldID(jcInfo, "b", "Z");

    //char c
    jfieldID jfc = env->GetFieldID(jcInfo, "c", "C");

    //double d
    jfieldID jfd = env->GetFieldID(jcInfo, "d", "D");

    //int i
    jfieldID jfi = env->GetFieldID(jcInfo, "i", "I");

    //byte[] array
    jfieldID jfa = env->GetFieldID(jcInfo, "array", "[B");

    //String s
    jfieldID jfs = env->GetFieldID(jcInfo, "s", "Ljava/lang/String;");

    //Record rec;
    jfieldID jfrec = env->GetFieldID(jcInfo, "rec", "Lcom/jinhill/util/Record;");

 

    //创建新的对象
    jobject joRec = env->AllocObject(jcRec);

 

    env->SetIntField(joRec, jfid, mi.rec.id);

 

    jstring jstrn = env->NewStringUTF(mi.rec.name);

    env->SetObjectField(joRec, jfname, jstrn);

 

    jbyteArray jbarr = env->NewByteArray(6); 

    jbyte *jb = env->GetByteArrayElements(jbarr, 0);

    memcpy(jb, mi.rec.data, 6);

    env->SetByteArrayRegion(jbarr, 0, 6, jb);

    env->SetObjectField(joRec, jfdata, jbarr);

    //创建新的对象
    jobject joInfo = env->AllocObject(jcInfo);

     //给类成员赋值
    env->SetBooleanField(joInfo, jfb, mi.b);


//  MultiByteToWideChar (CP_ACP, 0, mi.c, -1, wStr, 255);
//  env->SetCharField(joInfo, jfc, (jchar)wStr);

    env->SetCharField(joInfo, jfc, (jchar)mi.c);

    env->SetDoubleField(joInfo, jfd, mi.d);

    env->SetIntField(joInfo, jfi, mi.i);

    jbyteArray jarr = env->NewByteArray(nTmpLen); 

    jbyte *jby = env->GetByteArrayElements(jarr, 0);
    memcpy(jby, mi.arr, nTmpLen);

    env->SetByteArrayRegion(jarr, 0, nTmpLen, jby);
    env->SetObjectField(joInfo, jfa, jarr);
    jstring jstrTmp = env->NewStringUTF(chTmp);
    env->SetObjectField(joInfo, jfs, jstrTmp);

    env->SetObjectField(joInfo, jfrec, joRec);
    return joInfo;

}

 3.6)   Java String与 C char数组转换时的中文问题

//将jstring类型转换成windows类型
char* jstringToWindows( JNIEnv *env, jstring jstr )
{
<span style="white-space:pre">	</span>int length = (env)->GetStringLength(jstr );
<span style="white-space:pre">	</span>const jchar* jcstr = (env)->GetStringChars(jstr, 0 );
<span style="white-space:pre">	</span>char* rtn = (char*)malloc( length*2+1 );
<span style="white-space:pre">	</span>int size = 0;
<span style="white-space:pre">	</span>size = WideCharToMultiByte( CP_ACP, 0, (LPCWSTR)jcstr, length,rtn,(length*2+1), NULL, NULL );
<span style="white-space:pre">	</span>if( size <= 0 )
<span style="white-space:pre">		</span>return NULL;
<span style="white-space:pre">	</span>(env)->ReleaseStringChars(jstr, jcstr );
<span style="white-space:pre">	</span>rtn[size] = 0;
<span style="white-space:pre">	</span>return rtn;
}

//将windows类型转换成jstring类型
jstring WindowsTojstring( JNIEnv* env, char* str )
{
<span style="white-space:pre">	</span>jstring rtn = 0;
<span style="white-space:pre">	</span>int slen = strlen(str);
<span style="white-space:pre">	</span>unsigned short * buffer = 0;
<span style="white-space:pre">	</span>if( slen == 0 )
<span style="white-space:pre">		</span>rtn = (env)->NewStringUTF(str );
<span style="white-space:pre">	</span>else
<span style="white-space:pre">	</span>{
<span style="white-space:pre">		</span>int length = MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, NULL, 0 );
<span style="white-space:pre">		</span>buffer = (unsigned short *)malloc( length*2 + 1 );
<span style="white-space:pre">		</span>if( MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, (LPWSTR)buffer, length )>0 )
<span style="white-space:pre">			</span>rtn = (env)->NewString( (jchar*)buffer, length );
<span style="white-space:pre">	</span>}
<span style="white-space:pre">	</span>if( buffer )
<span style="white-space:pre">		</span>free( buffer );
<span style="white-space:pre">	</span>return rtn;
}


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