JNI小记

本文参考《较详细的介绍JNI》一文，并添加了一些方法，代码已经过测试，留待日后工作使用。关于JNI的HelloWorld的例子，就不赘述了。

java代码：

 1 package com.chnic.service;

 2

 3 import com.chnic.bean.Order;

 4

 5 public class Business {

 6     static{

 7         System.loadLibrary("FruitFactory");

 8     }

 9

10     public Business(){

11

12     }

13

14     public native double getPrice(String name);

15     public native Order getOrder(String name, int amount);

16     public native Order getRamdomOrder();

17     public static native void analyzeOrder(Order order);

18

19     public native void showArray(int []nums);

20

21     public native int[] getIntArray();

22

23     public native String[] getStringArray(String[] ss);

24

25     public native void test2DStringArray(String[][] ss);

26

27     public void notification(){

28         System.out.println("Got a notification.");

29     }

30

31     public static void notificationByStatic(){

32         System.out.println("Got a notification in a static method.");

33     }

34

35     public static void main(String...args){

36         Business bus = new Business();

37         System.out.println("price:"+bus.getPrice("Apple"));

38         System.out.println("-------------------------");

39

40         System.out.println("price:"+bus.getPrice("Pear"));

41         System.out.println("-------------------------");

42

43         System.out.println(bus.getOrder("Apple",23));

44         System.out.println("-------------------------");

45

46         System.out.println(bus.getRamdomOrder());

47         System.out.println("-------------------------");

48

49         Order order = new Order();

50         order.setName("orange");

51         Business.analyzeOrder(order);

52         System.out.println("-------------------------");

53

54         int[]ia={1,2,3,4};

55         bus.showArray(ia);

56         System.out.println("-------------------------");

57

58         int[] iaa = bus.getIntArray();

59         for(int i:iaa){

60             System.out.println(i);

61         }

62         System.out.println("-------------------------");

63

64         String[]abc= {"aa","bb","cc","dd"};

65         bus.getStringArray(abc);

66         System.out.println("-------------------------");

67

68         String []abcd = bus.getStringArray(abc);

69         for(String s:abcd){

70             System.out.println(s);

71         }

72         System.out.println("-------------------------");

73

74         String[][]test = {{"一行1号","一行二号","一行三号"},{"二行一号","二行二号","二行三号"}};

75         bus.test2DStringArray(test);

76         System.out.println("-------------------------");

77     }

78 }

 1 package com.chnic.bean;

 2

 3 public class Order {

 4

 5     private String name = "Fruit";

 6     private double price;

 7     private int amount = 30;

 8

 9     public Order(){

10

11     }

12

13     public int getAmount() {

14         return amount;

15     }

16

17     public void setAmount(int amount) {

18         this.amount = amount;

19     }

20

21     public String getName() {

22         return name;

23     }

24

25     public void setName(String name) {

26         this.name = name;

27     }

28

29     public double getPrice() {

30         return price;

31     }

32

33     public void setPrice(double price) {

34         this.price = price;

35     }

36

37     public String toString(){

38         return "name is "+name+",price is "+price+",amount is "+amount+".";

39     }

40 }

生成的com_chnic_service_Business.h头文件内容如下：

 1 /* DO NOT EDIT THIS FILE - it is machine generated */

 2 #include <jni.h>

 3 /* Header for class com_chnic_service_Business */

 4

 5 #ifndef _Included_com_chnic_service_Business

 6 #define _Included_com_chnic_service_Business

 7 #ifdef __cplusplus

 8 extern "C" {

 9 #endif

10 /*

11  * Class:     com_chnic_service_Business

12  * Method:    getPrice

13  * Signature: (Ljava/lang/String;)D

14  */

15 JNIEXPORT jdouble JNICALL Java_com_chnic_service_Business_getPrice

16   (JNIEnv *, jobject, jstring);

17

18 /*

19  * Class:     com_chnic_service_Business

20  * Method:    getOrder

21  * Signature: (Ljava/lang/String;I)Lcom/chnic/bean/Order;

22  */

23 JNIEXPORT jobject JNICALL Java_com_chnic_service_Business_getOrder

24   (JNIEnv *, jobject, jstring, jint);

25

26 /*

27  * Class:     com_chnic_service_Business

28  * Method:    getRamdomOrder

29  * Signature: ()Lcom/chnic/bean/Order;

30  */

31 JNIEXPORT jobject JNICALL Java_com_chnic_service_Business_getRamdomOrder

32   (JNIEnv *, jobject);

33

34 /*

35  * Class:     com_chnic_service_Business

36  * Method:    analyzeOrder

37  * Signature: (Lcom/chnic/bean/Order;)V

38  */

39 JNIEXPORT void JNICALL Java_com_chnic_service_Business_analyzeOrder

40   (JNIEnv *, jclass, jobject);

41

42 /*

43  * Class:     com_chnic_service_Business

44  * Method:    showArray

45  * Signature: ([I)V

46  */

47 JNIEXPORT void JNICALL Java_com_chnic_service_Business_showArray

48   (JNIEnv *, jobject, jintArray);

49

50 /*

51  * Class:     com_chnic_service_Business

52  * Method:    getIntArray

53  * Signature: ()[I

54  */

55 JNIEXPORT jintArray JNICALL Java_com_chnic_service_Business_getIntArray

56   (JNIEnv *, jobject);

57

58 /*

59  * Class:     com_chnic_service_Business

60  * Method:    getStringArray

61  * Signature: ([Ljava/lang/String;)[Ljava/lang/String;

62  */

63 JNIEXPORT jobjectArray JNICALL Java_com_chnic_service_Business_getStringArray

64   (JNIEnv *, jobject, jobjectArray);

65

66 /*

67  * Class:     com_chnic_service_Business

68  * Method:    test2DStringArray

69  * Signature: ([[Ljava/lang/String;)V

70  */

71 JNIEXPORT void JNICALL Java_com_chnic_service_Business_test2DStringArray

72   (JNIEnv *, jobject, jobjectArray);

73

74 #ifdef __cplusplus

75 }

76 #endif

77 #endif

编写的CPP实现文件（文件名随意），内容如下：

  1 #include <iostream.h>

  2 #include <string.h>

  3 #include "com_chnic_service_Business.h"

  4

  5 jobject getInstance(JNIEnv* env, jclass obj_class);

  6 /*

  7  * Class:     com_chnic_service_Business

  8  * Method:    getPrice

  9  * Signature: (Ljava/lang/String;)D

 10  *  传递string参数，返回double值

 11  */

 12 JNIEXPORT jdouble JNICALL Java_com_chnic_service_Business_getPrice(JNIEnv* env,

 13                                                                    jobject obj,

 14                                                                    jstring name)

 15 {

 16     const char* pname = env->GetStringUTFChars(name, NULL);

 17     cout << "Before release: "  << pname << endl;

 18

 19     if (strcmp(pname, "Apple") == 0)

 20     {

 21         env->ReleaseStringUTFChars(name, pname);

 22         cout << "After release: " << pname << endl;

 23         return 1.2;

 24     }

 25     else

 26     {

 27         env->ReleaseStringUTFChars(name, pname);

 28         cout << "After release: " << pname << endl;

 29         return 2.1;

 30     }

 31 }

 32

 33 /*

 34  * Class:     com_chnic_service_Business

 35  * Method:    getOrder

 36  * Signature: (Ljava/lang/String;I)Lcom/chnic/bean/Order;

 37  * 传递string、int参数，回调java类中的方法，并且返回一个java对象

 38  */

 39 JNIEXPORT jobject JNICALL Java_com_chnic_service_Business_getOrder(JNIEnv* env,

 40                                                                    jobject obj,

 41                                                                    jstring name,

 42                                                                    jint amount)

 43 {

 44     jclass order_class = env->FindClass("com/chnic/bean/Order");

 45     jobject order = getInstance(env, order_class);

 46

 47     jmethodID setName_method = env->GetMethodID(order_class, "setName", "(Ljava/lang/String;)V");

 48     env->CallVoidMethod(order, setName_method, name);

 49

 50     jmethodID setAmount_method = env->GetMethodID(order_class, "setAmount", "(I)V");

 51     env->CallVoidMethod(order, setAmount_method, amount);

 52

 53     return order;

 54 }

 55

 56 /*

 57  * Class:     com_chnic_service_Business

 58  * Method:    getRamdomOrder

 59  * Signature: ()Lcom/chnic/bean/Order;

 60  * 无参方法，在C++中构造一个java对象返回

 61  */

 62 JNIEXPORT jobject JNICALL Java_com_chnic_service_Business_getRamdomOrder(JNIEnv* env,

 63                                                                          jobject obj)

 64 {

 65     jclass business_class = env->GetObjectClass(obj);

 66     jobject business_obj = getInstance(env, business_class);

 67

 68     jmethodID notification_method = env->GetMethodID(business_class, "notification", "()V");

 69     env->CallVoidMethod(obj, notification_method);

 70

 71     jclass order_class = env->FindClass("com/chnic/bean/Order");

 72     jobject order = getInstance(env, order_class);

 73     jfieldID amount_field = env->GetFieldID(order_class, "amount", "I");

 74     jint amount = env->GetIntField(order, amount_field);

 75     cout << "amount: " << amount << endl;

 76     return order;

 77 }

 78

 79

 80 /*

 81  * Class:     com_chnic_service_Business

 82  * Method:    analyzeOrder

 83  * Signature: (Lcom/chnic/bean/Order;)V

 84  * java中的静态方法，在C++中的实现，传递的参数是java对象，无返回值

 85  */

 86 JNIEXPORT void JNICALL Java_com_chnic_service_Business_analyzeOrder (JNIEnv* env,

 87                                                                      jclass cls,

 88                                                                      jobject obj)

 89 {

 90     jclass order_class = env->GetObjectClass(obj);

 91     jmethodID getName_method = env->GetMethodID(order_class, "getName", "()Ljava/lang/String;");

 92     jstring name_str = static_cast<jstring>(env->CallObjectMethod(obj, getName_method));

 93     const char* pname = env->GetStringUTFChars(name_str, NULL);

 94

 95     cout << "Name in Java_com_chnic_service_Business_analyzeOrder: " << pname << endl;

 96

 97

 98     jmethodID notification_method_static = env->GetStaticMethodID(cls, "notificationByStatic", "()V");

 99     env->CallStaticVoidMethod(cls, notification_method_static);

100

101 }

102

103 /*

104  * 根据类，构造对应的对象返回

105  */

106 jobject getInstance(JNIEnv* env, jclass obj_class)

107 {

108     jmethodID construction_id = env->GetMethodID(obj_class, "<init>", "()V");

109     jobject obj = env->NewObject(obj_class, construction_id);

110     return obj;

111 }

112

113 /*

114  * Class:     com_chnic_service_Business

115  * Method:    showArray

116  * Signature: ([I)V

117  * 传递字符串数组，在C++中使用

118  */

119 JNIEXPORT void JNICALL Java_com_chnic_service_Business_showArray

120 (JNIEnv* env, jobject job, jintArray jia)

121 {

122     jint* nums;

123     nums = env->GetIntArrayElements(jia,NULL);

124

125     jint length = env->GetArrayLength(jia);

126     cout<<"length:"<<length<<endl;

127     int i;

128     for(i=0;i<length;i++)

129     {

130         cout<<nums[i]<<endl;

131     }

132 }

133

134 /*

135  * Class:     com_chnic_service_Business

136  * Method:    getIntArray

137  * Signature: ()[I

138  * 返回整形数组

139  */

140 JNIEXPORT jintArray JNICALL Java_com_chnic_service_Business_getIntArray

141   (JNIEnv *env, jobject job)

142 {

143     jsize col=10;

144     jint temp[10]={1,2,3,4,5,6,7,8,9,10};

145

146     jintArray iarr = env->NewIntArray(col);

147     env->SetIntArrayRegion(iarr, 0, col, temp);

148     return iarr;

149 }

150

151 /*

152  * Class:     com_chnic_service_Business

153  * Method:    getStringArray

154  * Signature: ([Ljava/lang/String;)[Ljava/lang/String;

155  * 传递一个字符串数组，并且重新构造一个字符串数组，并返回

156  */

157 JNIEXPORT jobjectArray JNICALL Java_com_chnic_service_Business_getStringArray

158 (JNIEnv* env, jobject job, jobjectArray joa)

159 {

160     //打印传递进来的字符串数组

161     jsize si = env->GetArrayLength(joa);

162     //cout<<si<<endl;

163     int i;

164     for(i=0;i<si;i++)

165     {

166         jstring str = (jstring)(env)->GetObjectArrayElement(joa, i);

167         //cout<<str<<endl;

168         const char* pname = env->GetStringUTFChars(str, NULL);

169         cout<<pname<<endl;

170     }

171     //构造新的字符串数组

172     jstring s1=env->NewStringUTF("123");

173     jstring s2=env->NewStringUTF("456");

174     jstring s3=env->NewStringUTF("789");

175     jstring ss[3]={s1,s2,s3};

176

177

178 jobjectArray swArray = env->NewObjectArray(3,env->FindClass("java/lang/String"), env->NewStringUTF(""));

179 //SetObjectArrayElement刷新数组元素内容

180   for(i = 0; i < 3; i++)

181    env->SetObjectArrayElement(swArray, i, ss[i]) ;

182     return swArray;

183 }

184

185 /**

186  * java传递二维字符串

187  *

188  */

189 JNIEXPORT void JNICALL Java_com_chnic_service_Business_test2DStringArray

190   (JNIEnv *env, jobject obj, jobjectArray array)

191 {

192  int size = env->GetArrayLength(array);

193  for (int i = 0; i < size; i++) {

194   jobjectArray myarray =(jobjectArray) (env->GetObjectArrayElement(array, i));

195   int length = env->GetArrayLength(myarray);

196   cout<<"length:   "<<length<<endl;

197   for (int j = 0; j < length; j++) {

198    jstring string = (jstring)(env->GetObjectArrayElement(myarray, j));

199    const char * chars =  env->GetStringUTFChars(string, 0);

200    cout<<chars<<"  ";

201     env->ReleaseStringUTFChars(string, chars);

202   }

203   cout<<endl;

204  }

205 }

生成动态链接库后，运行java的main方法，控制台打印信息如下：

Before release: Apple
After release: V
price:1.2
-------------------------
Before release: Pear
After release: X
price:2.1
-------------------------
name is Apple,price is 0.0,amount is 23.
-------------------------
Got a notification.
amount: 30
name is Fruit,price is 0.0,amount is 30.
-------------------------
Name in Java_com_chnic_service_Business_analyzeOrder: orange
Got a notification in a static method.
-------------------------
length:4
1
2
3
4
-------------------------
1
2
3
4
5
6
7
8
9
10
-------------------------
aa
bb
cc
dd
-------------------------
aa
bb
cc
dd
123
456
789
-------------------------
length: 3
一行1号一行二号一行三号
length: 3
二行一号二行二号二行三号
-------------------------

备注：1、使用Win7+eclipse+VC++6.0开发

　　　2、VC++创建Win32 Dynamic-Link Library工程

　　　3、在java调用native方法传递中文字符串时，若java工程或java文件格式不是UTF格式，会有乱码。

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