JNI学习笔记 C++传递结构体、String、数组对象给JavaC++传递结构体、String、数组对象给Java
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有时候我们需要传递结构体给Java,而Java中没有与结构体,我们可以用一个类来接受结构数据,下面用一个Demo来说明如果传递。
关于如何通过Jni建立c++和Java通信,请看上篇博文JNI学习笔记(一)
Java代码:
创建2个类,一个类用来测试,一个类用来接收结构体参数。
测试类
- package test;
-
- public class MyJNI {
-
-
- public native void displayParms(String showText, int i, boolean bl);
-
- public native int add(int a, int b);
-
- public native void setArray(boolean[] blList);
-
- public native String[] getStringArray();
-
- public native DiskInfo getStruct();
-
- public native DiskInfo[] getStructArray();
-
- static {
-
- System.load("E:\\Workspaces\\CodeBlocks\\myJNI\\bin\\Debug\\myJNI.dll");
- }
-
-
- public static void main(String[] args) {
- MyJNI changeJni = new MyJNI();
-
-
- System.out.println("-----输入常用的数值类型(string int boolean)------");
- changeJni.displayParms("Hello World!", 100, true);
-
-
- System.out.println("------------------调用一个静态方法-----------");
- int ret = changeJni.add(12, 20);
- System.out.println("The result is: " + String.valueOf(ret));
-
-
- System.out.println("------------------输入一个数组-----------");
- boolean[] blList = new boolean[] { true, false, true };
- changeJni.setArray(blList);
-
-
- System.out.println("-------------返回一个字符串数组-----------");
- String[] strList = changeJni.getStringArray();
- for (int i = 0; i < strList.length; i++) {
- System.out.print(strList[i]);
- }
- System.out.println();
-
- System.out.println("--------------返回一个结构-----------");
-
-
- DiskInfo disk = changeJni.getStruct();
- System.out.println("name:" + disk.name);
- System.out.println("Serial:" + disk.serial);
-
-
- System.out.println("-----------返回一个结构数组 -----------");
- DiskInfo[] diskList = changeJni.getStructArray();
- for (int i = 0; i < diskList.length; i++) {
- System.out.println("name:" + diskList[i].name);
- System.out.println("Serial:" + diskList[i].serial);
- }
- }
- }
接收结构体类:
- package test;
-
- class DiskInfo {
-
- public String name;
-
-
- public int serial;
- }
C++代码(本人用的CodeBlocks生成的dll)- #include <stdio.h>
- #include "test_MyJNI.h"
- #include <windows.h>
-
-
- struct DiskInfo
- {
- char name[256];
- int serial;
- };
-
-
- char* jstringToWindows(JNIEnv *env, jstring jstr);
-
- jstring WindowsTojstring(JNIEnv* env, char* str);
-
-
-
-
-
-
- BOOL WINAPI DllMain(HANDLE hHandle, DWORD dwReason, LPVOID lpReserved)
- {
- return TRUE;
- }
-
-
- JNIEXPORT void JNICALL Java_test_MyJNI_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", (int)i);
- printf("boolean = %s\n", (b == JNI_TRUE ? "true" : "false"));
- (env)->ReleaseStringUTFChars(s, szStr);
- }
-
-
- JNIEXPORT jint JNICALL Java_test_MyJNI_add(JNIEnv *env, jobject, jint a, jint b)
- {
- int rtn = (int)(a + b);
- return (jint)rtn;
- }
-
-
- JNIEXPORT void JNICALL Java_test_MyJNI_setArray(JNIEnv *env, jobject, jbooleanArray ba)
- {
- jboolean* pba = (env)->GetBooleanArrayElements(ba, 0);
- jsize len = (env)->GetArrayLength(ba);
-
- for(int 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);
- }
-
-
- JNIEXPORT jobjectArray JNICALL Java_test_MyJNI_getStringArray(JNIEnv *env, jobject)
- {
- jstring str;
- jobjectArray args = 0;
- jsize len = 5;
- const char* sa[] = { "Hello,", "world!", " JNI", " is", " fun" };
-
- args = (env)->NewObjectArray(len, (env)->FindClass("java/lang/String"), 0);
- for(int i = 0; i < len; i++)
- {
- str = (env)->NewStringUTF(sa[i]);
- (env)->SetObjectArrayElement(args, i, str);
- }
- return args;
- }
-
-
- JNIEXPORT jobject JNICALL Java_test_MyJNI_getStruct(JNIEnv *env, jobject obj)
- {
-
-
-
- jclass objectClass = (env)->FindClass("test/DiskInfo");
-
-
- jfieldID str = (env)->GetFieldID(objectClass, "name", "Ljava/lang/String;");
-
- jfieldID ival = (env)->GetFieldID(objectClass, "serial", "I");
-
-
- (env)->SetObjectField(obj, str, (env)->NewStringUTF("my name is D:"));
- (env)->SetShortField(obj, ival, 10);
-
- return obj;
- }
-
-
- JNIEXPORT jobjectArray JNICALL Java_test_MyJNI_getStructArray(JNIEnv *env, jobject _obj)
- {
-
- jobjectArray args = 0;
-
- jsize len = 5;
-
- jclass objClass = (env)->FindClass("java/lang/Object");
-
- args = (env)->NewObjectArray(len, objClass, 0);
-
-
-
- jclass objectClass = (env)->FindClass("test/DiskInfo");
-
-
- jfieldID str = (env)->GetFieldID(objectClass, "name", "Ljava/lang/String;");
-
- jfieldID ival = (env)->GetFieldID(objectClass, "serial", "I");
-
- for(int i = 0; i < len; i++)
- {
-
- jstring jstr = WindowsTojstring(env, (char*)"我的磁盘名字是 D:");
-
- (env)->SetObjectField(_obj, str, jstr);
- (env)->SetShortField(_obj, ival, 10);
-
-
- (env)->SetObjectArrayElement(args, i, _obj);
- }
-
- return args;
- }
-
-
-
- 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;
- }
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