JAVA JNI傳遞數據結構/類的例子

java通過JNI向C/C++傳遞基本數據類型比較簡單，但基本數據類型很難滿足應用程序開發的需要，心想要是能傳遞一個數據結構/類就好了。於是通過下面例子實驗了通過JNI傳遞數據結構/類也是OK的

1，定義一個用於測試的數據類（很簡單，沒有成員方法）

package com.rain.test;

public class testclass {
	public int iValue;
	public String strValue;
}

2，java主程序

package com.rain.test;

public class jniproject {

	public native String hello(testclass value);
	
	static
	{
		System.loadLibrary("jniproject");
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		testclass c = new testclass();
		c.iValue = 100;
		c.strValue = new String("HelloWorld");
		
		jniproject prj = new jniproject();
		String strResult = prj.hello(c);
		System.out.print(strResult);		
	}

}

3，工程中建立jni目錄，並利用javah編譯出c頭文件

javah -classpath bin -d jni com.rain.test.jniproject

4，新建jniproject.c文件實現native方法

#include "com_rain_test_jniproject.h"
#include <jni.h>

typedef struct
{
  int iValue;
  char* pStrValue;
}TestClass;

jstring Java_com_rain_test_jniproject_hello(JNIEnv* pEnv, jobject obj, jobject arg)
{
  jclass jcarg = (*pEnv)->GetObjectClass(pEnv, arg);

  TestClass input;
  jfieldID iid = (*pEnv)->GetFieldID(pEnv, jcarg, "iValue", "I");
  input.iValue = (*pEnv)->GetIntField(pEnv, arg, iid);

  jfieldID strid = (*pEnv)->GetFieldID(pEnv, jcarg, "strValue", "Ljava/lang/String;");
  jstring strValue = (*pEnv)->GetObjectField(pEnv, arg, strid);

  jsize strLen = (*pEnv)->GetStringUTFLength(pEnv, strValue);
  const char* pStrValue = (*pEnv)->GetStringUTFChars(pEnv, strValue, NULL);

  input.pStrValue = malloc(strLen + 1);
  strcpy(input.pStrValue, pStrValue);
  (*pEnv)->ReleaseStringUTFChars(pEnv, strValue, pStrValue);

  char buff[256] = {0};
  snprintf(buff, 255, "%d + %s", input.iValue, input.pStrValue);
  free(input.pStrValue);

  return (*pEnv)->NewStringUTF(pEnv, buff);
}

5，編譯動態庫

$ gcc -c -fPIC -I$JAVA_HOME/include -I$JAVA_HOME/include/linux jniproject.c

$ gcc -shared -fPIC -o libjniproject.so jniproject.o

6，爲了使java能夠找到so文件，避免程序運行時出現“java.library.path”相關的錯誤，需在eclipse中設置

select project, right click->properties, "java build path", "libraries" tab, select a jar, expand it, select "Native library location", click "edit...", folder chooser dialog will appear

7，運行