接[轉]C++和JNI的數據轉換(一)
下面我們來看看，如果通過使用數組和對象，從C++中的獲取到Java中的DiskInfo 類對象，並返回一個DiskInfo數組:
//返回一個結構數組，返回一個硬盤信息的結構數組JNIEXPORT jobjectArray JNICALL Java_com_sundy_jnidemo_ChangeMethodFromJni_getStructArray(JNIEnv
*env, jobject _obj)
{
//申明一個object數組
jobjectArray args
= 0;
//數組大小 jsize len
= 5;
//獲取object所屬類,一般爲ava/lang/Object就可以了 jclass objClass
= (env)->FindClass("java/lang/Object");
//新建object數組 args
= (env)->NewObjectArray(len, objClass,
0);
/* 下面爲獲取到Java中對應的實例類中的變量*/
//獲取Java中的實例類 jclass objectClass
= (env)->FindClass("com/sundy/jnidemo/DiskInfo");
//獲取類中每一個變量的定義
//名字 jfieldID str
= (env)->GetFieldID(objectClass,"name","Ljava/lang/String;");
//序列號 jfieldID ival
= (env)->GetFieldID(objectClass,"serial","I");
//給每一個實例的變量付值，並且將實例作爲一個object，添加到objcet數組中
for(int i=0; i
< len; i++ )
{
//給每一個實例的變量付值 jstring jstr
= WindowsTojstring(env,"我的磁盤名字是 D:");
//(env)->SetObjectField(_obj,str,(env)->NewStringUTF("my name is D:")); (env)->SetObjectField(_obj,str,jstr); (env)->SetShortField(_obj,ival,10);
//添加到objcet數組中 (env)->SetObjectArrayElement(args, i, _obj);
}
//返回object數組
return args;
}全部的C/C++方法實現代碼如下:
/*** 一縷陽光(sundy)版權所有，保留所有權利。*//***
* TODO Jni 中一個從Java到C/C++參數傳遞測試類** @author 劉正偉(sundy)* @see
http://www.cnweblog.com/sundy* @see mailto:[email protected]* @version 1.0* @since 2005-4-30*
* 修改記錄：*
* 日期 修改人 描述* ----------------------------------------------------------------------------------------------****/// JniManage.cpp : 定義 DLL 應用程序的入口點。//package com.sundy.jnidemo;#include
"stdafx.h"#include
<stdio.h>#include
<math.h>#include
"jni.h"#include
"jni_md.h"#include
"./head/Base.h"#include
"head/wmi.h"#include
"head/com_sundy_jnidemo_ChangeMethodFromJni.h"
//通過javah –jni javactransfer 生成#include
<stdio.h>#include
"stdlib.h"#include
"string.h"#pragma comment (lib,"BaseInfo.lib")#pragma comment (lib,"jvm.lib")//硬盤信息struct
{
char name[256];
int serial;}DiskInfo;/*BOOL APIENTRY DllMain( HANDLE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved ){ LPTSTR strName = new CHAR[256] ; (*GetHostName)(strName); printf("%s\n",strName); delete [] strName; return TRUE;}*///將jstring類型轉換成windows類型char* jstringToWindows( JNIEnv
*env, jstring jstr );//將windows類型轉換成jstring類型jstring WindowsTojstring( JNIEnv* env,
char* str );//主函數BOOL WINAPI DllMain(HANDLE hHandle, DWORD dwReason, LPVOID lpReserved){
return TRUE;}//輸入常用的數值類型 Boolean,Byte,Char,Short,Int,Float,DoubleJNIEXPORT
void JNICALL Java_com_sundy_jnidemo_ChangeMethodFromJni_displayParms(JNIEnv
*env, jobject obj, jstring s, jint i, jboolean b){
const
char* szStr
= (env)->GetStringUTFChars(s,
0 ); printf(
"String = [%s]\n", szStr ); printf(
"int = %d\n", i ); printf(
"boolean = %s\n", (b==JNI_TRUE
? "true" :
"false") ); (env)->ReleaseStringUTFChars(s, szStr );}//調用一個靜態方法,只有一個簡單類型輸出JNIEXPORT jint JNICALL Java_com_sundy_jnidemo_ChangeMethodFromJni_add(JNIEnv
*env, jobject, jint a, jint b){
int rtn
= (int)(a
+ b);
return (jint)rtn;}////輸入一個數組,這裏輸入的是一個Boolean類型的數組JNIEXPORT
void JNICALL Java_com_sundy_jnidemo_ChangeMethodFromJni_setArray(JNIEnv
*env, jobject, jbooleanArray ba){ jboolean* pba
= (env)->GetBooleanArrayElements(ba,
0 ); jsize len
= (env)->GetArrayLength(ba);
int i=0;
// change even array elements
for( i=0; i
< len; i+=2 )
{ pba[i]
= JNI_FALSE; printf(
"boolean = %s\n", (pba[i]==JNI_TRUE
? "true" :
"false") ); } (env)->ReleaseBooleanArrayElements(ba, pba,
0 );}////返回一個字符串數組JNIEXPORT jobjectArray JNICALL Java_com_sundy_jnidemo_ChangeMethodFromJni_getStringArray(JNIEnv
*env, jobject){ jstring str; jobjectArray args
= 0; jsize len
= 5;
char* sa[]
= {
"Hello,",
"world!",
"JNI",
"is",
"fun" };
int i=0; args
= (env)->NewObjectArray(len,(env)->FindClass("java/lang/String"),0);
for( i=0; i
< len; i++ )
{ str
= (env)->NewStringUTF(sa[i] ); (env)->SetObjectArrayElement(args, i, str); }
return args;}//返回一個結構,這裏返回一個硬盤信息的簡單結構類型JNIEXPORT jobject JNICALL Java_com_sundy_jnidemo_ChangeMethodFromJni_getStruct(JNIEnv
*env, jobject obj){
/* 下面爲獲取到Java中對應的實例類中的變量*/
//獲取Java中的實例類 jclass objectClass
= (env)->FindClass("com/sundy/jnidemo/DiskInfo");
//獲取類中每一個變量的定義
//名字 jfieldID str
= (env)->GetFieldID(objectClass,"name","Ljava/lang/String;");
//序列號 jfieldID ival
= (env)->GetFieldID(objectClass,"serial","I");
//給每一個實例的變量付值 (env)->SetObjectField(obj,str,(env)->NewStringUTF("my
name is D:")); (env)->SetShortField(obj,ival,10);
return obj;}//返回一個結構數組，返回一個硬盤信息的結構數組JNIEXPORT jobjectArray JNICALL Java_com_sundy_jnidemo_ChangeMethodFromJni_getStructArray(JNIEnv
*env, jobject _obj){
//申明一個object數組
jobjectArray args
= 0;
//數組大小 jsize len
= 5;
//獲取object所屬類,一般爲ava/lang/Object就可以了 jclass objClass
= (env)->FindClass("java/lang/Object");
//新建object數組 args
= (env)->NewObjectArray(len, objClass,
0);
/* 下面爲獲取到Java中對應的實例類中的變量*/
//獲取Java中的實例類 jclass objectClass
= (env)->FindClass("com/sundy/jnidemo/DiskInfo");
//獲取類中每一個變量的定義
//名字 jfieldID str
= (env)->GetFieldID(objectClass,"name","Ljava/lang/String;");
//序列號 jfieldID ival
= (env)->GetFieldID(objectClass,"serial","I");
//給每一個實例的變量付值，並且將實例作爲一個object，添加到objcet數組中
for(int i=0; i
< len; i++ )
{
//給每一個實例的變量付值 jstring jstr
= WindowsTojstring(env,"我的磁盤名字是 D:");
//(env)->SetObjectField(_obj,str,(env)->NewStringUTF("my name is D:")); (env)->SetObjectField(_obj,str,jstr); (env)->SetShortField(_obj,ival,10);
//添加到objcet數組中 (env)->SetObjectArrayElement(args, i, _obj); }
//返回object數組
return args; }//將jstring類型轉換成windows類型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;}color: #000