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分类: Java

2011-03-31 22:52:17

 

JNI 的基本问题就是解决 Java 和 C++ 代码互相调用的通信问题,在 C++ 代码编写过程中最大的问题莫过于适应其中的代码编写规则,C++调用或是返回的内容必须遵守 JVM 和 C++ 代码的通信规则。

C++ 调用 Java 的一般步骤如下:

  • 获得类:
    • jclass cls          = env->FindClass("com/ldq/Student");
    • cls 可认为是类的句柄
    • "com/ldq/Student" 就是类文件,注意不能用 "com.ldq.Student"
  • 获得方法:
    • jmethodID mid = env->GetMethodID(cls,"","()V");
    • 以上为构造函数,参数是 "" "()V"
    • jmethodID mid = env->GetMethodID(cls,"getAge","()I");
    • 以上为类的方法,第一个参数是类句柄,第二个参数是方法名字,第三个参数是签名标识 

Java类型

符号
boolean Z 

byte

B 

char

 
short S 
int I 
long  
float  

double

D  

void

V 
objects对象 Lfully-qualified-class-name;        L类名;
Arrays数组 [array-type [数组类型 
methods方法                  (argument-types)return-type(参数类型)返回类型 
  • 获得对象:
    • jobject obj=env->NewObject(cls,mid);
    • 以上便获得了一个对象的句柄
  • 获得对象成员变量:
    • jfieldID fid=env->GetFieldID(cls,"age","I");
    • 以上和获得类方法差不多
  • 操作成员变量:
    • jint a=env->GetIntField(obj,mid);
    • age=age+10;
    • env->SetIntField(obj,fid,a);
  • 返回:
    • return obj;

下面是本人练习的例子

  • ExList.java

Java代码
  1. package com.ldq.list;   
  2.   
  3. import java.util.List;   
  4.   
  5. public class ExList {   
  6.   
  7.     /**  
  8.      * @param args  
  9.      */  
  10.     public static void main(String[] args) {   
  11.         // TODO Auto-generated method stub   
  12.         System.out.println("-------WifiManager.test()");   
  13.         System.out.println(WifiManager.test());   
  14.   
  15.         System.out.println("-------WifiManager.testArray()");   
  16.         String[] s1 = WifiManager.testArray();   
  17.         for (int i = 0; i < s1.length; i++) {   
  18.             System.out.println(s1[i]);   
  19.         }   
  20.   
  21.         System.out.println("-------WifiManager.testObject()");   
  22.         System.out.println(WifiManager.testObject().ssid);   
  23.         System.out.println(WifiManager.testObject().mac);   
  24.         System.out.println(WifiManager.testObject().level);   
  25.   
  26.         System.out.println("-------WifiManager.getScanResultsA()");   
  27.         ScanResult[] s2 = WifiManager.getScanResultsA();   
  28.         for (int i = 0; i < s2.length; i++) {   
  29.             System.out.println(s2[i].ssid);   
  30.             System.out.println(s2[i].mac);   
  31.             System.out.println(s2[i].level);   
  32.         }   
  33.   
  34.         System.out.println("-------WifiManager.getScanResults()");   
  35.         List list = WifiManager.getScanResults();   
  36.         System.out.println(list.get(0).ssid);   
  37.         System.out.println(list.get(0).mac);   
  38.         System.out.println(list.get(0).level);   
  39.   
  40.     }   
  41. }  
package com.ldq.list; import java.util.List; public class ExList { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub System.out.println("-------WifiManager.test()"); System.out.println(WifiManager.test()); System.out.println("-------WifiManager.testArray()"); String[] s1 = WifiManager.testArray(); for (int i = 0; i < s1.length; i++) { System.out.println(s1[i]); } System.out.println("-------WifiManager.testObject()"); System.out.println(WifiManager.testObject().ssid); System.out.println(WifiManager.testObject().mac); System.out.println(WifiManager.testObject().level); System.out.println("-------WifiManager.getScanResultsA()"); ScanResult[] s2 = WifiManager.getScanResultsA(); for (int i = 0; i < s2.length; i++) { System.out.println(s2[i].ssid); System.out.println(s2[i].mac); System.out.println(s2[i].level); } System.out.println("-------WifiManager.getScanResults()"); List list = WifiManager.getScanResults(); System.out.println(list.get(0).ssid); System.out.println(list.get(0).mac); System.out.println(list.get(0).level); } }

 

 

 

  • ScanResult.java

Java代码 复制代码 收藏代码
  1. package com.ldq.list;   
  2.   
  3. public class ScanResult {   
  4.     String ssid;   
  5.     String mac;   
  6.     int level;   
  7.   
  8.     public ScanResult() {   
  9.     }   
  10.   
  11.     public ScanResult(String ssid, String mac, int level) {   
  12.         this.ssid = ssid;   
  13.         this.mac = mac;   
  14.         this.level = level;   
  15.     }   
  16. }  
package com.ldq.list; public class ScanResult { String ssid; String mac; int level; public ScanResult() { } public ScanResult(String ssid, String mac, int level) { this.ssid = ssid; this.mac = mac; this.level = level; } }

 

 

 

  • WifiManager.java

Java代码 复制代码 收藏代码
  1. package com.ldq.list;   
  2.   
  3. import java.util.List;   
  4.   
  5. public class WifiManager {   
  6.   
  7.     static {   
  8.         System.loadLibrary("wifi");   
  9.     }   
  10.   
  11.     public native static String test();   
  12.   
  13.     public native static String[] testArray();   
  14.   
  15.     public native static ScanResult testObject();   
  16.   
  17.     public native static ScanResult[] getScanResultsA();   
  18.   
  19.     public native static List getScanResults();   
  20. }  
package com.ldq.list; import java.util.List; public class WifiManager { static { System.loadLibrary("wifi"); } public native static String test(); public native static String[] testArray(); public native static ScanResult testObject(); public native static ScanResult[] getScanResultsA(); public native static List getScanResults(); }

 

  • wifi.cpp
Cpp代码 复制代码 收藏代码
  1. #include    
  2. #include "com_ldq_list_WifiManager.h"   
  3.   
  4. /*  
  5.  * Class:     com_ldq_list_WifiManager  
  6.  * Method:    test  
  7.  * Signature: ()Ljava/lang/String;  
  8.  */  
  9. JNIEXPORT jstring JNICALL Java_com_ldq_list_WifiManager_test (JNIEnv *env, jclass cls)   
  10. {   
  11.     return env->NewStringUTF("hello");   
  12. }   
  13.   
  14. /*  
  15.  * Class:     com_ldq_list_WifiManager  
  16.  * Method:    testArray  
  17.  * Signature: ()[Ljava/lang/String;  
  18.  */  
  19. JNIEXPORT jobjectArray JNICALL Java_com_ldq_list_WifiManager_testArray (JNIEnv *env, jclass cls)   
  20. {   
  21.     jobjectArray ret;   
  22.     int i;   
  23.   
  24.     char *message[5]= {"first",    
  25.     "second",    
  26.     "third",    
  27.     "fourth",    
  28.     "fifth"};   
  29.   
  30.     ret= (jobjectArray)env->NewObjectArray(5,   
  31.          env->FindClass("java/lang/String"),   
  32.          env->NewStringUTF(""));   
  33.   
  34.     for(i=0;i<5;i++) {   
  35.         env->SetObjectArrayElement(   
  36.         ret,i,env->NewStringUTF(message[i]));   
  37.     }   
  38.     return(ret);   
  39.   
  40. }   
  41.   
  42. /*  
  43.  * Class:     com_ldq_list_WifiManager  
  44.  * Method:    testObject  
  45.  * Signature: ()Lcom/ldq/list/ScanResult;  
  46.  */  
  47. JNIEXPORT jobject JNICALL Java_com_ldq_list_WifiManager_testObject (JNIEnv *env, jclass cls)   
  48. {   
  49.     jclass m_cls  = env->FindClass("com/ldq/list/ScanResult");   
  50.     jmethodID mid = env->GetMethodID(m_cls,"","()V");   
  51.     jobject obj   = env->NewObject(m_cls,mid);   
  52.   
  53.     jfieldID fid_ssid  = env->GetFieldID(m_cls,"ssid","Ljava/lang/String;");   
  54.     jfieldID fid_mac   = env->GetFieldID(m_cls,"mac","Ljava/lang/String;");   
  55.     jfieldID fid_level = env->GetFieldID(m_cls,"level","I");   
  56.   
  57.                          env->SetObjectField(obj,fid_ssid,env->NewStringUTF("AP1"));   
  58.                          env->SetObjectField(obj,fid_mac,env->NewStringUTF("00-11-22-33-44-55"));   
  59.                          env->SetIntField(obj,fid_level,-66);   
  60.     return obj;   
  61. }   
  62.   
  63. /*  
  64.  * Class:     com_ldq_list_WifiManager  
  65.  * Method:    getScanResultsA  
  66.  * Signature: ()[Lcom/ldq/list/ScanResult;  
  67.  */  
  68. JNIEXPORT jobjectArray JNICALL Java_com_ldq_list_WifiManager_getScanResultsA (JNIEnv *env, jclass cls)   
  69. {   
  70.     jclass cls_array=env->FindClass("java/lang/Object");   
  71.     jobjectArray obj_array=env->NewObjectArray(2,cls_array,0);   
  72.   
  73.     jclass cls_obj = env->FindClass("com/ldq/list/ScanResult");   
  74.     jmethodID m    = env->GetMethodID(cls_obj,"","()V");   
  75.   
  76.     jfieldID fid_ssid  = env->GetFieldID(cls_obj,"ssid","Ljava/lang/String;");   
  77.     jfieldID fid_mac   = env->GetFieldID(cls_obj,"mac","Ljava/lang/String;");   
  78.     jfieldID fid_level = env->GetFieldID(cls_obj,"level","I");   
  79.   
  80.     for(int i=0;i<2;i++)   
  81.     {   
  82.         jobject obj=env->NewObject(cls_obj,m);   
  83.   
  84.         jobject o1=env->NewStringUTF("AP2");   
  85.         env->SetObjectField(obj,fid_ssid,o1);   
  86.   
  87.         jobject o2=env->NewStringUTF("22-22-22-22-22-22");   
  88.         env->SetObjectField(obj,fid_mac,o2);   
  89.   
  90.         env->SetIntField(obj,fid_level,-66);   
  91.   
  92.         env->SetObjectArrayElement(obj_array,i,obj);   
  93.     }   
  94.     return obj_array;   
  95. }   
  96.   
  97. /*  
  98.  * Class:     com_ldq_list_WifiManager  
  99.  * Method:    getScanResults  
  100.  * Signature: ()Ljava/util/List;  
  101.  */  
  102. JNIEXPORT jobject JNICALL Java_com_ldq_list_WifiManager_getScanResults (JNIEnv *env, jclass cls)   
  103. {   
  104.     jclass m_cls_list    = env->FindClass("java/util/ArrayList");   
  105.     jmethodID m_mid_list = env->GetMethodID(m_cls_list,"","()V");   
  106.     jobject m_obj_list   = env->NewObject(m_cls_list,m_mid_list);   
  107.   
  108.     jmethodID m_mid_add  = env->GetMethodID(m_cls_list,"add","(Ljava/lang/Object;)Z");   
  109.   
  110.     jclass m_cls_result    = env->FindClass("com/ldq/list/ScanResult");   
  111.     jmethodID m_mid_result = env->GetMethodID(m_cls_result,"","()V");   
  112.     jobject m_obj_result   = env->NewObject(m_cls_result,m_mid_result);   
  113.   
  114.     jfieldID m_fid_1 = env->GetFieldID(m_cls_result,"ssid","Ljava/lang/String;");   
  115.     jfieldID m_fid_2 = env->GetFieldID(m_cls_result,"mac","Ljava/lang/String;");   
  116.     jfieldID m_fid_3 = env->GetFieldID(m_cls_result,"level","I");   
  117.   
  118.     env->SetObjectField(m_obj_result,m_fid_1,env->NewStringUTF("AP6"));   
  119.     env->SetObjectField(m_obj_result,m_fid_2,env->NewStringUTF("66-66-66-66-66-66"));   
  120.     env->SetIntField(m_obj_result,m_fid_3,-66);   
  121.   
  122.     env->CallBooleanMethod(m_obj_list,m_mid_add,m_obj_result);   
  123.   
  124.     return m_obj_list;   
  125. }  
#include #include "com_ldq_list_WifiManager.h" /* * Class: com_ldq_list_WifiManager * Method: test * Signature: ()Ljava/lang/String; */ JNIEXPORT jstring JNICALL Java_com_ldq_list_WifiManager_test (JNIEnv *env, jclass cls) { return env->NewStringUTF("hello"); } /* * Class: com_ldq_list_WifiManager * Method: testArray * Signature: ()[Ljava/lang/String; */ JNIEXPORT jobjectArray JNICALL Java_com_ldq_list_WifiManager_testArray (JNIEnv *env, jclass cls) { jobjectArray ret; int i; char *message[5]= {"first", "second", "third", "fourth", "fifth"}; ret= (jobjectArray)env->NewObjectArray(5, env->FindClass("java/lang/String"), env->NewStringUTF("")); for(i=0;i<5;i++) { env->SetObjectArrayElement( ret,i,env->NewStringUTF(message[i])); } return(ret); } /* * Class: com_ldq_list_WifiManager * Method: testObject * Signature: ()Lcom/ldq/list/ScanResult; */ JNIEXPORT jobject JNICALL Java_com_ldq_list_WifiManager_testObject (JNIEnv *env, jclass cls) { jclass m_cls = env->FindClass("com/ldq/list/ScanResult"); jmethodID mid = env->GetMethodID(m_cls,"","()V"); jobject obj = env->NewObject(m_cls,mid); jfieldID fid_ssid = env->GetFieldID(m_cls,"ssid","Ljava/lang/String;"); jfieldID fid_mac = env->GetFieldID(m_cls,"mac","Ljava/lang/String;"); jfieldID fid_level = env->GetFieldID(m_cls,"level","I"); env->SetObjectField(obj,fid_ssid,env->NewStringUTF("AP1")); env->SetObjectField(obj,fid_mac,env->NewStringUTF("00-11-22-33-44-55")); env->SetIntField(obj,fid_level,-66); return obj; } /* * Class: com_ldq_list_WifiManager * Method: getScanResultsA * Signature: ()[Lcom/ldq/list/ScanResult; */ JNIEXPORT jobjectArray JNICALL Java_com_ldq_list_WifiManager_getScanResultsA (JNIEnv *env, jclass cls) { jclass cls_array=env->FindClass("java/lang/Object"); jobjectArray obj_array=env->NewObjectArray(2,cls_array,0); jclass cls_obj = env->FindClass("com/ldq/list/ScanResult"); jmethodID m = env->GetMethodID(cls_obj,"","()V"); jfieldID fid_ssid = env->GetFieldID(cls_obj,"ssid","Ljava/lang/String;"); jfieldID fid_mac = env->GetFieldID(cls_obj,"mac","Ljava/lang/String;"); jfieldID fid_level = env->GetFieldID(cls_obj,"level","I"); for(int i=0;i<2;i++) { jobject obj=env->NewObject(cls_obj,m); jobject o1=env->NewStringUTF("AP2"); env->SetObjectField(obj,fid_ssid,o1); jobject o2=env->NewStringUTF("22-22-22-22-22-22"); env->SetObjectField(obj,fid_mac,o2); env->SetIntField(obj,fid_level,-66); env->SetObjectArrayElement(obj_array,i,obj); } return obj_array; } /* * Class: com_ldq_list_WifiManager * Method: getScanResults * Signature: ()Ljava/util/List; */ JNIEXPORT jobject JNICALL Java_com_ldq_list_WifiManager_getScanResults (JNIEnv *env, jclass cls) { jclass m_cls_list = env->FindClass("java/util/ArrayList"); jmethodID m_mid_list = env->GetMethodID(m_cls_list,"","()V"); jobject m_obj_list = env->NewObject(m_cls_list,m_mid_list); jmethodID m_mid_add = env->GetMethodID(m_cls_list,"add","(Ljava/lang/Object;)Z"); jclass m_cls_result = env->FindClass("com/ldq/list/ScanResult"); jmethodID m_mid_result = env->GetMethodID(m_cls_result,"","()V"); jobject m_obj_result = env->NewObject(m_cls_result,m_mid_result); jfieldID m_fid_1 = env->GetFieldID(m_cls_result,"ssid","Ljava/lang/String;"); jfieldID m_fid_2 = env->GetFieldID(m_cls_result,"mac","Ljava/lang/String;"); jfieldID m_fid_3 = env->GetFieldID(m_cls_result,"level","I"); env->SetObjectField(m_obj_result,m_fid_1,env->NewStringUTF("AP6")); env->SetObjectField(m_obj_result,m_fid_2,env->NewStringUTF("66-66-66-66-66-66")); env->SetIntField(m_obj_result,m_fid_3,-66); env->CallBooleanMethod(m_obj_list,m_mid_add,m_obj_result); return m_obj_list; }

 

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