JNI 返回对象

ScanResult.java 文件

package com.ldq;

public class ScanResult {

    String ssid;
    String mac;
    int level;

    ScanResult() {
    }

}

package com.ldq; public class ScanResult { String ssid; String mac; int level; ScanResult() { } }

WifiManager.java 文件

package com.ldq;

public class WifiManager {
    static {
        System.loadLibrary("wifi");
    }

    public native static String test();

    public native static ScanResult getScanResult();

}

package com.ldq; public class WifiManager { static { System.loadLibrary("wifi"); } public native static String test(); public native static ScanResult getScanResult(); }

 Test.java 文件

package com.ldq;

public class Test {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        System.out.println(WifiManager.test());
        System.out.println(WifiManager.getScanResult().ssid);
        System.out.println(WifiManager.getScanResult().mac);
        System.out.println(WifiManager.getScanResult().level);
    }

}

package com.ldq; public class Test { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub System.out.println(WifiManager.test()); System.out.println(WifiManager.getScanResult().ssid); System.out.println(WifiManager.getScanResult().mac); System.out.println(WifiManager.getScanResult().level); } }

• javah -jni com.ldq.WifiManager 生成头文件 com_ldq_WifiManager.h

com_ldq_WifiManager.h 文件

/* DO NOT EDIT THIS FILE - it is machine generated */
#include
/* Header for class com_ldq_WifiManager */

#ifndef _Included_com_ldq_WifiManager
#define _Included_com_ldq_WifiManager
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_ldq_WifiManager
 * Method:    test
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_ldq_WifiManager_test
  (JNIEnv *, jclass);

/*
 * Class:     com_ldq_WifiManager
 * Method:    getScanResult
 * Signature: ()Lcom/ldq/ScanResult;
 */
JNIEXPORT jobject JNICALL Java_com_ldq_WifiManager_getScanResult
  (JNIEnv *, jclass);

#ifdef __cplusplus
}
#endif
#endif

/* DO NOT EDIT THIS FILE - it is machine generated */ #include /* Header for class com_ldq_WifiManager */ #ifndef _Included_com_ldq_WifiManager #define _Included_com_ldq_WifiManager #ifdef __cplusplus extern "C" { #endif /* * Class: com_ldq_WifiManager * Method: test * Signature: ()Ljava/lang/String; */ JNIEXPORT jstring JNICALL Java_com_ldq_WifiManager_test (JNIEnv *, jclass); /* * Class: com_ldq_WifiManager * Method: getScanResult * Signature: ()Lcom/ldq/ScanResult; */ JNIEXPORT jobject JNICALL Java_com_ldq_WifiManager_getScanResult (JNIEnv *, jclass); #ifdef __cplusplus } #endif #endif

• VC++6.0中新建工程 wifi ，选 Win32 Dynamic-Link Library 方式
• Tools - Options - Directories - Include files 加入 jni.h 和 jni_md.h 的路径，此处为
  • C:\Program Files\Java\jdk1.6.0_13\include
  • C:\Program Files\Java\jdk1.6.0_13\include\win32
• 新建 wifi.cpp 文件

wifi.cpp 文件

#include "com_ldq_WifiManager.h"

/*
 * Class:     com_ldq_WifiManager
 * Method:    test
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_com_ldq_WifiManager_test (JNIEnv *env, jclass cls)
{
    return env->NewStringUTF("Hello");
}

/*
 * Class:     com_ldq_WifiManager
 * Method:    getScanResult
 * Signature: ()Lcom/ldq/ScanResult;
 */
JNIEXPORT jobject JNICALL Java_com_ldq_WifiManager_getScanResult (JNIEnv *env, jclass cls)
{
    jclass    m_cls   = env->FindClass("com/ldq/ScanResult");

    jmethodID m_mid   = env->GetMethodID(m_cls,"","()V");

    jfieldID  m_fid_1 = env->GetFieldID(m_cls,"ssid","Ljava/lang/String;");
    jfieldID  m_fid_2 = env->GetFieldID(m_cls,"mac","Ljava/lang/String;");
    jfieldID  m_fid_3 = env->GetFieldID(m_cls,"level","I");

    jobject   m_obj   = env->NewObject(m_cls,m_mid);

                        env->SetObjectField(m_obj,m_fid_1,env->NewStringUTF("AP1"));
                        env->SetObjectField(m_obj,m_fid_2,env->NewStringUTF("00-11-22-33-44-55"));
                        env->SetIntField(m_obj,m_fid_3,-50);
    return m_obj;
}

#include "com_ldq_WifiManager.h" /* * Class: com_ldq_WifiManager * Method: test * Signature: ()Ljava/lang/String; */ JNIEXPORT jstring JNICALL Java_com_ldq_WifiManager_test (JNIEnv *env, jclass cls) { return env->NewStringUTF("Hello"); } /* * Class: com_ldq_WifiManager * Method: getScanResult * Signature: ()Lcom/ldq/ScanResult; */ JNIEXPORT jobject JNICALL Java_com_ldq_WifiManager_getScanResult (JNIEnv *env, jclass cls) { jclass m_cls = env->FindClass("com/ldq/ScanResult"); jmethodID m_mid = env->GetMethodID(m_cls,"","()V"); jfieldID m_fid_1 = env->GetFieldID(m_cls,"ssid","Ljava/lang/String;"); jfieldID m_fid_2 = env->GetFieldID(m_cls,"mac","Ljava/lang/String;"); jfieldID m_fid_3 = env->GetFieldID(m_cls,"level","I"); jobject m_obj = env->NewObject(m_cls,m_mid); env->SetObjectField(m_obj,m_fid_1,env->NewStringUTF("AP1")); env->SetObjectField(m_obj,m_fid_2,env->NewStringUTF("00-11-22-33-44-55")); env->SetIntField(m_obj,m_fid_3,-50); return m_obj; }

• 上述文件中的代码是重点
  • 首先获得类文件，名字为 "com/ldq/ScanResult" ，不同于Java自身的文件，如 "Ljava/lang/String"，前面多了个 "L" ，个人理解为 Local 的意思，意为本地库
  • 再获得构造函数，注意格式，和一般的引用类的方法不同，名字为 "" 类型为 "()V" ，本人在此处耗费了很长时间
  • 获得类的各个成员变量域，方便后续引用
  • 生成对象，由于参数为空，所以 NewObject 函数只有两个参数
  • 设定对象的各个成员变量
  • 返回对象
• 编译，将生成的 wifi.dll 文件拷贝到 Eclipse 对应的工程文件根目录下，此处为
  • D:\workspace_java\ExWifi
• Eclipse 下运行，结果为

运行结果

Hello
AP1
00-11-22-33-44-55
-50

 

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