JNI 数据类型转换、乱码解决方案

1：JNI 数据类型转换 

下面是 Test.c 

#include <jni.h>
#include "com_test_Test.h"
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>

//获取字符串
JNIEXPORT void JNICALL Java_com_test_Test_sayHello(JNIEnv * env, jobject obj,
  jstring s) {

 char * str = (char *) (*env)->GetStringUTFChars(env, s, 0);
 printf("\n c-string: hello - %s", str);

}

//获取，返回int
JNIEXPORT jint JNICALL Java_com_test_Test_add(JNIEnv * env, jobject obj,
  jint a, jint b) {
 int i = a;
 int j = b;
 printf("\n c-int: %d - %d", i, j);
 char str[256];
 sprintf(str, "%d", i + j);
 return (jint) i + j;
}

//获取，返回float
JNIEXPORT jfloat JNICALL Java_com_test_Test_getFloat(JNIEnv * env, jobject obj,
  jfloat f) {
 float fl = f;
 printf("\n c-float: %3f", fl);

 fl = 200.555;
 return (jfloat) fl;
}

//获取，返回 double
JNIEXPORT jdouble JNICALL Java_com_test_Test_getDouble(JNIEnv * env,
  jobject obj, jdouble dou) {
 double d = dou;
 printf("\n c-double: %3f", d);

 d = 800.88;
 return (jdouble) d;
}

//获取，返回boolean
JNIEXPORT jboolean JNICALL Java_com_test_Test_getBoolean(JNIEnv * env,
  jobject obj, jboolean bool) {

 unsigned char b = bool;
 printf("\n c-boolean: %lu  ", b);
 if (b) {
  printf("true");
 } else {
  printf("false");
 }

 b = 1;
 return (jboolean) b;
}

//获取，返回 string
JNIEXPORT jstring JNICALL Java_com_test_Test_getString(JNIEnv * env,
  jobject obj, jstring s) {
 char * st = (char *) (*env)->GetStringUTFChars(env, s, 0);
 printf("\n c-string:  %s", st);

 char * str = "hello wang wu!";
 jstring rtn;
 rtn = (*env)->NewStringUTF(env, str);
 return rtn;
}

//获取，返回 string []
JNIEXPORT jobjectArray JNICALL Java_com_test_Test_getStringArray(JNIEnv * env,
  jobject obj, jobjectArray arr) {
 int len = (*env)->GetArrayLength(env, arr);
 printf("\n c-stringArray :");
 int i = 0;
 for (i = 0; i < len; i++) {
  jobject obj = (*env)->GetObjectArrayElement(env, arr, i);
  jstring str = (jstring) obj;
  const char * szStr = (*env)->GetStringUTFChars(env, str, 0);
  printf(" %d-%s ", i, szStr);
  (*env)->ReleaseStringChars(env, str, szStr);
 }
 //-----返回----

 jstring str;
 jobjectArray args = 0;
 jsize size = 5;
 char* sa[] = { "Hello,", "world!", "zhang", "san", "yuang" };
 int j = 0;
 jclass objClass = (*env)->FindClass(env, "java/lang/String");
 args = (*env)->NewObjectArray(env, size, objClass, 0);
 for (j = 0; j < size; j++) {
  str = (*env)->NewStringUTF(env, sa[j]);
  (*env)->SetObjectArrayElement(env, args, j, str);
 }
 return args;
}

下面是Test.java 

package com.test;

public class Test {
 private native void sayHello(String str);

 private native int add(int a, int b);

 private native float getFloat(float f);

 private native double getDouble(double d);

 private native boolean getBoolean(boolean b);

 private native String getString(String str);

 private native String[] getStringArray(String[] sa);

 static {
  System.loadLibrary("Test");
 }

 public static void main(String[] args) {
  Test test = new Test();
  test.sayHello("zhang san");
  System.out.println("int     --> " + test.add(10, 20));
  System.out.println("float   --> " + test.getFloat((float) 20.123));
  System.out.println("double  --> " + test.getDouble(100.369));
  System.out.println("boolean --> " + test.getBoolean(true));
  System.out.println("string  --> " + test.getString("wang Wu"));

  String[] ss = { "hello", "-", "zhang", "san" };
  Object[] obj = test.getStringArray(ss);
  System.out.print("string[]-->  ");
  for (Object object : obj) {
   System.out.print(object + " ");
  }

 }

}

++++++++++++++++++++++++++++++++++++++++++++++++++ 
上面类型转换没有一个一个去试，应该都是可以的 
++++++++++++++++++++++++++++++++++++++++++++++++++ 



2：JNI 乱码解决方案 

顺便再转一个JNI相关的：jni乱码解决方案 
http://www.wangchao.net.cn/bbsdetail_57022.html 


Java代码： 

/*
* javactransfer.java
* By dpwu
* e-mail：[email protected]
*/
public class javactransfer
{
 public String hypotenuse(String send_buf,String recv_buf,int errno)
 {
 return hypotenuse0(send_buf,recv_buf,errno);
 }
 private native String hypotenuse0(String send_buf,String recv_buf,int errno);
 static
 {
 System.loadLibrary("javactransfer");//调用dll
 }
 public static void main( String[] args )
 {
 javactransfer obj= new javactransfer();
 System.out.println("");
 System.out.println("");
 System.out.println(" begin!");
 System.out.println("");
 System.out.println("");
 String javasend="发送中文chinese!";
 System.out.println(" java send:"+"["+javasend+"]");
String javarecv=obj.hypotenuse("teststr",javasend,1);
//javasend传含有中文字符串给C
//javarecv接受C含有中的文字符串
 System.out.println(" java recv:"+"["+javarecv+"]");
 System.out.println("");
 System.out.println("");
 System.out.println(" end!");
 }
}

C实现代码为： 

/*
　　* javactransfer.c
　　* By dpwu
　　* e-mail：[email protected]
　　*/
　　#include <windows.h>
　　#include "javactransfer.h"//通过javah –jni javactransfer 生成
　　#include <stdio.h>
　　#include "stdlib.h"
　　#include "string.h"
　　char* jstringToWindows( JNIEnv *env, jstring jstr );
　　jstring WindowsTojstring( JNIEnv* env, char* str );
　　JNIEXPORT jstring JNICALL
　　Java_javactransfer_hypotenuse0(JNIEnv *env,jobject obj,jstring send_buf,jstring recv_buf,jint errno)
　　{
　　 char * Buf_Return;
　　 Buf_Return = (char*)malloc(1024);

　　 const char * recvtest = jstringToWindows( env, recv_buf );
　　/*上句recvtest接收Java传过来的中文字符串正确,如果改为下句,则出现乱码:
　　const char * recvtest = (*env)->GetStringUTFChars( env,recv_buf,0);
　　*/
　　printf( " c recv :[%s]\n" , recvtest);

　　 sprintf(Buf_Return,"接收中文chinese!");
　　 printf( "\n\n\n c send :[%s]\n" , Buf_Return);
　　 recv_buf = WindowsTojstring(env ,Buf_Return);
　　/*上句recv_buf传windows本地C中含有中文字符串给Java正确;如果改为下句出现乱码:
　　recv_buf = (*env)->NewStringUTF( env, Buf_Return );
　　 */
　　 return recv_buf;
　　}
　　char* jstringToWindows( JNIEnv *env, jstring jstr )
　　{
　　 int length = (*env)->GetStringLength(env,jstr );
　　 const jchar* jcstr = (*env)->GetStringChars(env,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(env,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(env,str );
　　 else
　　 {
　　 int length = MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, NULL, 0 );
　　 buffer = malloc( length*2 + 1 );
　　 if( MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, (LPWSTR)buffer, length ) >0 )
　　 rtn = (*env)->NewString( env, (jchar*)buffer, length );
　　 }
　　 if( buffer )
　　 free( buffer );
　　 return rtn;
　　}

C++实现代码为: 

/*
* javactransfer.cpp
* By dpwu
* e-mail：[email protected]
*/
#include <windows.h>
#include "javactransfer.h"//通过javah –jni javactransfer 生成
#include <stdio.h>
#include "stdlib.h"
#include "string.h"
char* jstringToWindows( JNIEnv *env, jstring jstr );
jstring WindowsTojstring( JNIEnv* env, char* str );
JNIEXPORT jstring JNICALL
Java_javactransfer_hypotenuse0(JNIEnv *env,jobject obj,jstring send_buf,jstring recv_buf,jint _tperrno)
{
 char * Buf_Return;
 Buf_Return = (char*)malloc(1024);
 const char * ctest = jstringToWindows( env, recv_buf );
/*
 如果把上句改为下句，C接收Java字符串时将出现乱码：
 const char *ctest = (env)->GetStringUTFChars( recv_buf , 0);
*/
 printf( " c recv :[%s]\n" , ctest);

 sprintf(Buf_Return,"接收中文chinese!");
 printf( "\n\n\n c send :[%s]\n" , Buf_Return);
 recv_buf = WindowsTojstring(env ,Buf_Return);
/*上句执行正确,如果把上句换成下句,Java在接收C字符串时出现乱码
recv_buf = (env)->NewStringUTF(Buf_Return);
*/
 return recv_buf;
}
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;
}