JNI _10_jni Comprehensive Development

1. If you cannot find a class when using Ndk-build, you can use the following two methods to resolve it:

1, 1 into the SRC directory

D:\project3\jniandroid\src>set CLASSPATH=D:\PROJECT3\JNIANDROID\SRC

1, 2 set Classpath
Classpath.; %java_home%\lib\dt.jar;%java_home%\tools.jar; E:\developLib\android\platforms\android-8\android.jar

2. Basic class

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");}    }

Where the MyInfo class is defined as follows: 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 struct Definition

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. Write C library

3.1) Examples of different types of Java and C parameter conversions

Different types of parameter handling Jniexport jintjnicall java_com_jinhill_util_nativemodule_testarg  (jnienv *env, Jobject Jo, Jint ji, JBOOLEANJB,  Jchar JC, jdouble JD) {         //Get Jint type value         int i = ji;         Get Jboolean Type value         BOOL b = JB;         Gets the jdouble type value         double d = JD;         Gets the Jchar type value, Java of char two byte         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 and C char array type array conversion instance

Btye array processing, parameter as input or output, return Btye array Jniexportjbytearray jnicall java_com_jinhill_util_nativemodule_testbyte (JNIEnv *env,         Jobject Jo, Jbytearray jbarr) {char chtmp[] = "Hello jni!";         int ntmplen = strlen (chtmp);         Get Jbytearray char *charr = (char*) env->getbytearrayelements (jbarr,0);         Get jbytearray length 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);         The Jbarr is used as the output parameter memset (charr, 0, Narrlen);         memcpy (Charr, chtmp, Ntmplen);     Return to 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 and C char array type conversion instance  

String and string[] handle Jniexportjobjectarray jnicall java_com_jinhill_util_nativemodule_teststring (JNIEnv *env,         Jobject Jo, jstring jstr,jobjectarray joarr) {int i = 0;         Char chtmp[50] = {0};         Get jstring value const char* PSZSTR = (char*) env->getstringutfchars (jstr, 0);         Trace ("jstr=%s", pszstr);         Gets the Jobjectarray value 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);         }//Joarr as the output parameter 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->D Eletelocalref (jstrtmp);         }//Return to 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 class and C struct type conversion instance

Jniexport jint jnicall java_com_jinhill_util_nativemodule_setinfo (jnienv *env, Jobject Jo, Jobject jobj) {char ChHexT    MP[512] = {0};    Convert Java class to C structure MyInfo mi;    Gets the instance class in Java 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");    Gets the instance class in Java myinfo jclass jcinfo = Env->findclass ("Com/jinhill/util/myinfo");    Gets the definition of each variable in the class//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-&GT    Getfieldid (Jcinfo, "s", "ljava/lang/string;");    Record Rec;     Jfieldid Jfrec = Env->getfieldid (Jcinfo, "Rec", "lcom/jinhill/util/record;");    Gets the value of the variable B of the instance mi.b = Env->getbooleanfield (Jobj, JFB);    Gets the value of the variable C of the instance 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];    Gets the value of the variable d of the instance MI.D = Env->getdoublefield (Jobj, JFD);    Gets the value of the variable I for the instance mi.i = Env->getintfield (Jobj, JFI);    Gets the value of the instance variable array jbytearray ja = (jbytearray) Env->getobjectfield (Jobj, JFA);    int narrlen = env->getarraylength (JA);    Char *charr = (char*) env->getbytearrayelements (ja, 0);    memcpy (Mi.arr, Charr, Narrlen);    Gets the value of the instance's variable s jstring jstr = (jstring) Env->getobjectfield (Jobj, JFS);    Const char* PSZSTR = (char*) env->getstringutfchars (jstr, 0);     strcpy (MI.SZ, PSZSTR); Gets the Record object Jobject Jorec = Env->getobjectfield (Jobj, JFREC);    Gets the Record object id value mi.rec.id = Env->getintfield (Jorec, Jfid);    Trace ("mi.rec.id=%d", mi.rec.id);    Gets the Record object name value jstring jstrn = (jstring) Env->getobjectfield (Jorec, jfname);    Pszstr = (char*) env->getstringutfchars (jstrn, 0);    strcpy (Mi.rec.name, PSZSTR);    Gets the Record object data value Jbytearray JBD = (jbytearray) Env->getobjectfield (Jorec, jfdata);    Narrlen = Env->getarraylength (JBD);    Charr = (char*) env->getbytearrayelements (JBD, 0);    memcpy (Mi.rec.data, Charr, Narrlen);    Log Output 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 struct type and Java Class conversion example   

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);    Convert c structure to Java class 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");    Gets the instance class in Java 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");    Gets the instance class in Java Jclass jcinfo = Env->findclass ("Com/jinhill/util/myinfo");    Gets the definition of each variable in the class//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;");     Create a new object 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);     Create a new object Jobject joinfo = Env->allocobject (Jcinfo); Assigns a value to a class member 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) Chinese problem when converting Java string to C char array

Convert jstring type to Windows type 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;} Convert Windows type to jstring type 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 "&GT;&LT;/SPAN&GT;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); &L T;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" &GT;&LT;/SPAN&GT;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;}

JNI _10_jni Comprehensive Development