====================================对象处理====================================================
JNI 的基本问题就是解决 Java 和 C++ 代码互相调用的通信问题,在 C++ 代码编写过程中最大的问题莫过于适应其中的代码编写规则,C++调用或是返回的内容必须遵守 JVM 和 C++ 代码的通信规则。
C++ 调用 Java 的一般步骤如下:
Java类型 |
符号 |
boolean | Z |
byte |
B |
char |
C |
short | S |
int | I |
long | L |
float | F |
double |
D |
void |
V |
objects对象 | Lfully-qualified-class-name; L类名; |
Arrays数组 | [array-type [数组类型 |
methods方法 | (argument-types)return-type(参数类型)返回类型 |
下面是本人练习的例子
package com.ldq.list;import java.util.List;public class ExList { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub System.out.println("-------WifiManager.test()"); System.out.println(WifiManager.test()); System.out.println("-------WifiManager.testArray()"); String[] s1 = WifiManager.testArray(); for (int i = 0; i < s1.length; i++) { System.out.println(s1[i]); } System.out.println("-------WifiManager.testObject()"); System.out.println(WifiManager.testObject().ssid); System.out.println(WifiManager.testObject().mac); System.out.println(WifiManager.testObject().level); System.out.println("-------WifiManager.getScanResultsA()"); ScanResult[] s2 = WifiManager.getScanResultsA(); for (int i = 0; i < s2.length; i++) { System.out.println(s2[i].ssid); System.out.println(s2[i].mac); System.out.println(s2[i].level); } System.out.println("-------WifiManager.getScanResults()"); Listlist = WifiManager.getScanResults(); System.out.println(list.get(0).ssid); System.out.println(list.get(0).mac); System.out.println(list.get(0).level); }}
package com.ldq.list;public class ScanResult { String ssid; String mac; int level; public ScanResult() { } public ScanResult(String ssid, String mac, int level) { this.ssid = ssid; this.mac = mac; this.level = level; }}
package com.ldq.list;import java.util.List;public class WifiManager { static { System.loadLibrary("wifi"); } public native static String test(); public native static String[] testArray(); public native static ScanResult testObject(); public native static ScanResult[] getScanResultsA(); public native static ListgetScanResults();}
===============================================数据类型转换===================================================
作者:陈波 2011/10/30(转载请注明出处,From:http://blog.csdn.net/jinhill/article/details/6918821)
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
package com.jinhill.util;
public 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自定义结构体
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;
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
//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;
}
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) 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 { 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 { 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; } 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; } 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; } 4. 编写Java测试代码 public class TestInfo { /** * @param args */ public static void main(String[] args) { int i =0; String[] sArr = new String[2]; for(i=0; i<2; i++) { sArr[i] = "ID=" + i; } byte[] b = new byte[10]; for(i=0; i<10; i++) { b[i] = (byte)i; } MyInfo mi = new MyInfo(); mi.array = b; mi.b = false; mi.c = 'C'; mi.d = 2011.11; mi.i = 1752; mi.s = "Hello World!"; mi.rec = new Record(); mi.rec.id = 2012; mi.rec.name = "Record"; mi.rec.data = b; NativeModule nm = new NativeModule(); nm.testArg(mi.i, mi.b, mi.c, mi.d); byte[] b2 = nm.testByte(mi.array); String[] s = nm.testString(mi.s, sArr); nm.setInfo(mi); MyInfo mi2 = nm.getInfo(); System.out.println("finish"); } } 5. 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 //将windows类型转换成jstring类型 6. 源码下载
char* jstringToWindows( JNIEnv *env, jstring jstr )
{
int length = (env)->GetStringLength(jstr );
const jchar* jcstr = (env)->GetStringChars(jstr, 0 );
char* rtn = (char*)malloc( length*2+1 );
int size = 0;
size = WideCharToMultiByte( CP_ACP, 0, (LPCWSTR)jcstr, length,rtn,(length*2+1), NULL, NULL );
if( size <= 0 )
return NULL;
(env)->ReleaseStringChars(jstr, jcstr );
rtn[size] = 0;
return rtn;
}
jstring WindowsTojstring( JNIEnv* env, char* str )
{
jstring rtn = 0;
int slen = strlen(str);
unsigned short * buffer = 0;
if( slen == 0 )
rtn = (env)->NewStringUTF(str );
else
{
int length = MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, NULL, 0 );
buffer = (unsigned short *)malloc( length*2 + 1 );
if( MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, (LPWSTR)buffer, length )>0 )
rtn = (env)->NewString( (jchar*)buffer, length );
}
if( buffer )
free( buffer );
return rtn;
}