zoukankan      html  css  js  c++  java
  • JNI高级教程之数据类型转换


    最近做Android开发的人越来越多,Android开发难免会遇到调用本地库,这就需要采用JNI技术,JNI本身并不复杂,但大多数开发者在类型转换上遇到麻烦,今天特地将几种常用类型转换写成一个实例来告诉大家如何转换,尤其是Java的类和C的结构的转换,结构体中嵌套结构体如何处理,这部分网上的资料也比较少。

    1. 编写Java类

    点击(此处)折叠或打开

    1. package com.jinhill.util;
    2. public class NativeModule
    3. {
    4.     public native int testArg(int i, boolean b, char c, double d);
    5.     public native byte[] testByte(byte[] b);
    6.     public native String[] testString(String s, String[] sarr);
    7.     public native int setInfo(MyInfo info);
    8.     public native MyInfo getInfo();

    9.     static
    10.     {
    11.         System.loadLibrary("NativeModule");
    12.     }
    13. }

    其中MyInfo类定义如下:

    点击(此处)折叠或打开

    1. public class Record
    2. {
    3.     int id;
    4.     String name;
    5.     byte[] data;
    6. }

    7. public class MyInfo
    8. {
    9.     public boolean b;
    10.     public char c;
    11.     public double d;
    12.     public int i;
    13.     public byte[] array;
    14.     public String s;
    15.     public Record rec;
    16. }

    C自定义结构体 

    点击(此处)折叠或打开

    1. typedef struct
    2. {
    3.     int id;
    4.     char name[255];
    5.     char data[255];
    6. } Record;

    7. typedef struct
    8. {
    9.     BOOL b;
    10.     char c;
    11.     double d;
    12.     int i;
    13.     char arr[255];
    14.     char sz[255];
    15.     Record rec;
    16. }MyInfo;

    2. 生成jni头文件

    1) 编译javac com/jinhill/util/NativeModule.java

    2) javah –jni com.jinhill.util.NativeModule

    这样com_jinhill_util_NativeModule.h文件就生成好了。

    3. 编写C库

    1) Java与C不同类型参数转换实例

    点击(此处)折叠或打开

    1. //不同类型参数处理

    2. JNIEXPORT jintJNICALL Java_com_jinhill_util_NativeModule_testArg
    3. (JNIEnv *env, jobject jo, jint ji, jbooleanjb, jchar jc, jdouble jd)
    4. {
    5.     //获取jint型值
    6.     int i = ji;

    7.     //获取jboolean型值
    8.     BOOL b = jb;

    9.     //获取jdouble型值
    10.     double d = jd;

    11.     //获取jchar型值,Java的char两字节
    12.     char ch[5] = {0};

    13.     int size = 0;

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

    15.     if(size <= 0)
    16.     {
    17.         return -1;
    18.     }

    19.     Trace("ji=%d,jb=%d,jc=%s,jd=%lf",i, b, ch, d);
    20.     return 0;
    21. }

    2) Java byte与C char数组类型数组转换实例

    点击(此处)折叠或打开

    1. //btye数组处理,形参作为输入或输出,返回btye数组

    2. JNIEXPORTjbyteArray JNICALL Java_com_jinhill_util_NativeModule_testByte
    3. (JNIEnv *env, jobject jo, jbyteArray jbArr)
    4. {
    5.     char chTmp[] = "Hello JNI!";
    6.     int nTmpLen = strlen(chTmp);

    7.     //获取jbyteArray
    8.     char *chArr = (char*)env->GetByteArrayElements(jbArr,0);

    9.     //获取jbyteArray长度
    10.     int nArrLen = env->GetArrayLength(jbArr);
    11.     char *szStrBuf =(char*)malloc(nArrLen*2+10);
    12.     memset(szStrBuf, 0, nArrLen*2+10);
    13.     Bytes2String(chArr, nArrLen, szStrBuf,nArrLen*2+10);
    14.     Trace("jbArr=%s", szStrBuf);
    15.     //将jbArr作为输出形参
    16.     memset(chArr, 0, nArrLen);
    17.     memcpy(chArr, chTmp, nTmpLen);

    18.     //返回jbyteArray
    19.     jbyteArray jarrRV =env->NewByteArray(nTmpLen);
    20.     jbyte *jby =env->GetByteArrayElements(jarrRV, 0);
    21.     memcpy(jby, chTmp, strlen(chTmp));
    22.     env->SetByteArrayRegion(jarrRV, 0,nTmpLen, jby);
    23.     return jarrRV;
    24. }
    3) Java String与C char数组类型转换实例

    点击(此处)折叠或打开

    1. //String 和String[]处理
    2. JNIEXPORTjobjectArray JNICALL Java_com_jinhill_util_NativeModule_testString
    3. (JNIEnv *env, jobject jo, jstring jstr,jobjectArray joarr)
    4. {
    5.     int i = 0;
    6.     char chTmp[50] = {0};

    7.     //获取jstring值
    8.     const char* pszStr = (char*)env->GetStringUTFChars(jstr, 0);
    9.     Trace("jstr=%s", pszStr);

    10.     //获取jobjectArray值
    11.     int nArrLen =env->GetArrayLength(joarr);
    12.     Trace("joarr len=%d",nArrLen);
    13.     for(i=0; i<nArrLen; i++)
    14.     {
    15.         jstring js =(jstring)env->GetObjectArrayElement(joarr, i);
    16.         const char* psz = (char*)env->GetStringUTFChars(js, 0);
    17.         Trace("joarr[%d]=%s",i, psz);
    18.     }
    19.     
    20.     //将joarr作为输出形参
    21.     jstring jstrTmp = NULL;
    22.     for(i=0; i<nArrLen; i++)
    23.     {
    24.         sprintf(chTmp, "No.%dHello JNI!", i);
    25.         jstrTmp =env->NewStringUTF(chTmp);
    26.         env->SetObjectArrayElement(joarr,i, jstrTmp);
    27.         env->DeleteLocalRef(jstrTmp);
    28.     }

    29.     //返回jobjectArray
    30.     jclass jstrCls =env->FindClass("Ljava/lang/String;");
    31.     jobjectArray jstrArray =env->NewObjectArray(2, jstrCls, NULL);

    32.     for(i=0; i<2; i++)
    33.     {
    34.         sprintf(chTmp, "No. %dReturn JNI!", i);
    35.         jstrTmp =env->NewStringUTF(chTmp);
    36.         env->SetObjectArrayElement(jstrArray,i, jstrTmp);
    37.         env->DeleteLocalRef(jstrTmp);
    38.     }
    39.     return jstrArray;
    40. }

    4) Java 类与C结构体类型转换实例

    点击(此处)折叠或打开

    1. JNIEXPORT jint JNICALL Java_com_jinhill_util_NativeModule_setInfo
    2. (JNIEnv *env, jobject jo, jobject jobj)
    3. {
    4.     char chHexTmp[512] = {0};
    5.     //将Java类转换成C结构体
    6.     MyInfo mi;

    7.     //获取Java中的实例类Record
    8.     jclass jcRec = env->FindClass("com/jinhill/util/Record");
    9.     //int id

    10.     jfieldID jfid = env->GetFieldID(jcRec, "id", "I");
    11.     //String name

    12.     jfieldID jfname = env->GetFieldID(jcRec, "name", "Ljava/lang/String;");
    13.     //byte[] data;

    14.     jfieldID jfdata = env->GetFieldID(jcRec, "data", "[B");
    15.     //获取Java中的实例类MyInfo

    16.     jclass jcInfo = env->FindClass("com/jinhill/util/MyInfo");
    17.     //获取类中每一个变量的定义

    18.     //boolean b
    19.     jfieldID jfb = env->GetFieldID(jcInfo, "b", "Z");

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

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

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

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

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

    30.     //Record rec;
    31.     jfieldID jfrec = env->GetFieldID(jcInfo, "rec", "Lcom/jinhill/util/Record;");
    32.     //获取实例的变量b的值
    33.     mi.b = env->GetBooleanField(jobj, jfb);
    34.     
    35.     //获取实例的变量c的值
    36.     jchar jc = env->GetCharField(jobj, jfc);
    37.     char ch[5] = {0};
    38.     int size = 0;
    39.     size = WideCharToMultiByte(CP_ACP, NULL, (LPCWSTR)&jc, -1, ch, 5, NULL, FALSE);
    40.     mi.c = ch[0];
    41.     
    42.     //获取实例的变量d的值
    43.     mi.d = env->GetDoubleField(jobj, jfd);
    44.     
    45.     //获取实例的变量i的值
    46.     mi.i = env->GetIntField(jobj, jfi);
    47.     
    48.     //获取实例的变量array的值
    49.     jbyteArray ja = (jbyteArray)env->GetObjectField(jobj, jfa);
    50.     int nArrLen = env->GetArrayLength(ja);
    51.     char *chArr = (char*)env->GetByteArrayElements(ja, 0);
    52.     memcpy(mi.arr, chArr, nArrLen);
    53.     
    54.     //获取实例的变量s的值
    55.     jstring jstr = (jstring)env->GetObjectField(jobj, jfs);
    56.     const char* pszStr = (char*)env->GetStringUTFChars(jstr, 0);
    57.     strcpy(mi.sz, pszStr);

    58.     //获取Record对象
    59.     jobject joRec = env->GetObjectField(jobj, jfrec);
    60.     
    61.     //获取Record对象id值
    62.     mi.rec.id = env->GetIntField(joRec, jfid);
    63.     Trace("mi.rec.id=%d",mi.rec.id);
    64.     
    65.     //获取Record对象name值
    66.     jstring jstrn = (jstring)env->GetObjectField(joRec, jfname);
    67.     pszStr = (char*)env->GetStringUTFChars(jstrn, 0);
    68.     strcpy(mi.rec.name, pszStr);
    69.     
    70.     //获取Record对象data值
    71.     jbyteArray jbd = (jbyteArray)env->GetObjectField(joRec, jfdata);
    72.     nArrLen = env->GetArrayLength(jbd);
    73.     chArr = (char*)env->GetByteArrayElements(jbd, 0);
    74.     memcpy(mi.rec.data, chArr, nArrLen);
    75.     
    76.     //日志输出
    77.     Bytes2String(mi.arr, nArrLen, chHexTmp, sizeof(chHexTmp));
    78.     Trace("mi.arr=%s, mi.b=%d, mi.c=%c, mi.d=%lf, mi.i=%d, mi.sz=%s 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);
    79.     return 0;
    80. }

    5) C结构体类型与Java 类转换实例

    点击(此处)折叠或打开

    1. JNIEXPORT jobject JNICALL Java_com_jinhill_util_NativeModule_getInfo
    2.   (JNIEnv *env, jobject jo)
    3. {
    4.     wchar_t wStr[255] = {0};
    5.     char chTmp[] = "Hello JNI";
    6.     int nTmpLen = strlen(chTmp);
    7.     //将C结构体转换成Java类

    8.     MyInfo mi;
    9.     memcpy(mi.arr, chTmp, strlen(chTmp));
    10.     mi.b = TRUE;
    11.     mi.c = 'B';
    12.     mi.d = 2000.9;
    13.     mi.i = 8;
    14.     strcpy(mi.sz, "Hello World!");
    15.     mi.rec.id = 2011;
    16.     memcpy(mi.rec.data, "x01x02x03x04x05x06", 6);
    17.     strcpy(mi.rec.name, "My JNI");

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

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

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

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


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

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

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

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

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

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

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

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

    43.     //创建新的对象
    44.     jobject joRec = env->AllocObject(jcRec);
    45.     env->SetIntField(joRec, jfid, mi.rec.id);
    46.     jstring jstrn = env->NewStringUTF(mi.rec.name);
    47.     env->SetObjectField(joRec, jfname, jstrn);
    48.     jbyteArray jbarr = env->NewByteArray(6);
    49.     jbyte *jb = env->GetByteArrayElements(jbarr, 0);
    50.     memcpy(jb, mi.rec.data, 6);
    51.     env->SetByteArrayRegion(jbarr, 0, 6, jb);
    52.     env->SetObjectField(joRec, jfdata, jbarr);
    53.     //创建新的对象
    54.     jobject joInfo = env->AllocObject(jcInfo);
    55.     //给类成员赋值
    56.     env->SetBooleanField(joInfo, jfb, mi.b);
    57.     // MultiByteToWideChar (CP_ACP, 0, mi.c, -1, wStr, 255);

    58.     // env->SetCharField(joInfo, jfc, (jchar)wStr);
    59.     env->SetCharField(joInfo, jfc, (jchar)mi.c);
    60.     env->SetDoubleField(joInfo, jfd, mi.d);
    61.     env->SetIntField(joInfo, jfi, mi.i);
    62.     jbyteArray jarr = env->NewByteArray(nTmpLen);
    63.     jbyte *jby = env->GetByteArrayElements(jarr, 0);
    64.     memcpy(jby, mi.arr, nTmpLen);
    65.     env->SetByteArrayRegion(jarr, 0, nTmpLen, jby);
    66.     env->SetObjectField(joInfo, jfa, jarr);
    67.     jstring jstrTmp = env->NewStringUTF(chTmp);
    68.     env->SetObjectField(joInfo, jfs, jstrTmp);
    69.     env->SetObjectField(joInfo, jfrec, joRec);
    70.     return joInfo;
    71. }
    4. 编写Java测试代码

    点击(此处)折叠或打开

    1. public class TestInfo {

    2.     public static void main(String[] args)
    3.     {
    4.         int i =0;
    5.         String[] sArr = new String[2];
    6.         for(i=0; i<2; i++)
    7.         {
    8.             sArr[i] = "ID=" + i;
    9.         }

    10.         byte[] b = new byte[10];
    11.         for(i=0; i<10; i++)
    12.         {
    13.             b[i] = (byte)i;
    14.         }

    15.         MyInfo mi = new MyInfo();
    16.         mi.array = b;
    17.         mi.b = false;
    18.         mi.c = 'C';
    19.         mi.d = 2011.11;
    20.         mi.i = 1752;
    21.         mi.s = "Hello World!";
    22.         mi.rec = new Record();
    23.         mi.rec.id = 2012;
    24.         mi.rec.name = "Record";
    25.         mi.rec.data = b;
    26.         NativeModule nm = new NativeModule();
    27.         nm.testArg(mi.i, mi.b, mi.c, mi.d);
    28.         byte[] b2 = nm.testByte(mi.array);
    29.         String[] s = nm.testString(mi.s, sArr);
    30.         nm.setInfo(mi);
    31.         MyInfo mi2 = nm.getInfo();
    32.         System.out.println("finish");
    33.     }
    34. }
    5. Java String与 C char数组转换时的中文问题

    点击(此处)折叠或打开

    1. //将jstring类型转换成windows类型
    2. char* jstringToWindows( JNIEnv *env, jstring jstr )
    3. {
    4.     int length = (env)->GetStringLength(jstr );
    5.     const jchar* jcstr = (env)->GetStringChars(jstr, 0 );
    6.     char* rtn = (char*)malloc( length*2+1 );
    7.     int size = 0;
    8.     size = WideCharToMultiByte( CP_ACP, 0, (LPCWSTR)jcstr, length,rtn,(length*2+1), NULL, NULL );
    9.     if( size <= 0 )
    10.         return NULL;
    11.     (env)->ReleaseStringChars(jstr, jcstr );
    12.     rtn[size] = 0;
    13.     return rtn;
    14. }

    15. //将windows类型转换成jstring类型
    16. jstring WindowsTojstring( JNIEnv* env, char* str )
    17. {
    18.     jstring rtn = 0;
    19.     int slen = strlen(str);
    20.     unsigned short * buffer = 0;
    21.     if( slen == 0 )
    22.         rtn = (env)->NewStringUTF(str );
    23.     else
    24.     {
    25.         int length = MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, NULL, 0 );
    26.         buffer = (unsigned short *)malloc( length*2 + 1 );
    27.         if( MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, (LPWSTR)buffer, length )>0 )
    28.         rtn = (env)->NewString( (jchar*)buffer, length );
    29.     }
    30.     if( buffer )
    31.         free( buffer );
    32.     return rtn;
    33. }

    阅读(1977) | 评论(0) | 转发(3) |
    给主人留下些什么吧!~~
    评论热议
  • 相关阅读:
    码农如何通过编程赚更多的钱
    理解 OAuth 2.0 认证流程
    把同事的代码重写得干净又整洁,老板却让我做回滚?
    精读《如何做好 CodeReview》
    互联网行业的软件与人员的代际更迭随想
    十大最佳自动化测试工具
    使用 docker 高效部署你的前端应用
    在Linux 命令行中转换大小写
    Python批量检测服务器端口可用性与Socket函数使用
    基于华为云CSE微服务接口兼容常见问题
  • 原文地址:https://www.cnblogs.com/black/p/5171788.html
Copyright © 2011-2022 走看看