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：

package com.chnic.service;

import com.chnic.bean.Order;  

public class Business {  
    static{  
        System.loadLibrary("FruitFactory");  
    }  
      
    public Business(){  
          
    }  
      
    public native double getPrice(String name);  
    public native Order getOrder(String name, int amount);  
    public native Order getRamdomOrder();  
    public static native void analyzeOrder(Order order);  
    
    public native void showArray(int []nums);
    
    public native int[] getIntArray();
    
    public native String[] getStringArray(String[] ss);
    
    public native void test2DStringArray(String[][] ss);
      
    public void notification(){  
        System.out.println("Got a notification.");  
    }  
      
    public static void notificationByStatic(){  
        System.out.println("Got a notification in a static method.");  
    }  
    
    public static void main(String...args){
        Business bus = new Business();
        System.out.println("price:"+bus.getPrice("Apple"));
        System.out.println("-------------------------");
        
        System.out.println("price:"+bus.getPrice("Pear"));
        System.out.println("-------------------------");
        
        System.out.println(bus.getOrder("Apple",23));
        System.out.println("-------------------------");
        
        System.out.println(bus.getRamdomOrder());
        System.out.println("-------------------------");
        
        Order order = new Order();
        order.setName("orange");
        Business.analyzeOrder(order);
        System.out.println("-------------------------");
        
        int[]ia={1,2,3,4};
        bus.showArray(ia);
        System.out.println("-------------------------");
        
        int[] iaa = bus.getIntArray();
        for(int i:iaa){
            System.out.println(i);
        }
        System.out.println("-------------------------");
        
        String[]abc= {"aa","bb","cc","dd"};
        bus.getStringArray(abc);
        System.out.println("-------------------------");
        
        String []abcd = bus.getStringArray(abc);
        for(String s:abcd){
            System.out.println(s);
        }
        System.out.println("-------------------------");
        
        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"}};
        bus.test2DStringArray(test);
        System.out.println("-------------------------");
    }
}  

package com.chnic.bean;

public class Order {  
    
    private String name = "Fruit";  
    private double price;  
    private int amount = 30;  
      
    public Order(){  
          
    }  
  
    public int getAmount() {  
        return amount;  
    }  
   
    public void setAmount(int amount) {  
        this.amount = amount;  
    }  
  
    public String getName() {  
        return name;  
    }  
  
    public void setName(String name) {  
        this.name = name;  
    }  
  
    public double getPrice() {  
        return price;  
    }  
  
    public void setPrice(double price) {  
        this.price = price;  
    }  
    
    public String toString(){
        return "name is "+name+",price is "+price+",amount is "+amount+"."; 
    }
}  

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

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_chnic_service_Business */

#ifndef _Included_com_chnic_service_Business
#define _Included_com_chnic_service_Business
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_chnic_service_Business
 * Method:    getPrice
 * Signature: (Ljava/lang/String;)D
 */
JNIEXPORT jdouble JNICALL Java_com_chnic_service_Business_getPrice
  (JNIEnv *, jobject, jstring);

/*
 * Class:     com_chnic_service_Business
 * Method:    getOrder
 * Signature: (Ljava/lang/String;I)Lcom/chnic/bean/Order;
 */
JNIEXPORT jobject JNICALL Java_com_chnic_service_Business_getOrder
  (JNIEnv *, jobject, jstring, jint);

/*
 * Class:     com_chnic_service_Business
 * Method:    getRamdomOrder
 * Signature: ()Lcom/chnic/bean/Order;
 */
JNIEXPORT jobject JNICALL Java_com_chnic_service_Business_getRamdomOrder
  (JNIEnv *, jobject);

/*
 * Class:     com_chnic_service_Business
 * Method:    analyzeOrder
 * Signature: (Lcom/chnic/bean/Order;)V
 */
JNIEXPORT void JNICALL Java_com_chnic_service_Business_analyzeOrder
  (JNIEnv *, jclass, jobject);

/*
 * Class:     com_chnic_service_Business
 * Method:    showArray
 * Signature: ([I)V
 */
JNIEXPORT void JNICALL Java_com_chnic_service_Business_showArray
  (JNIEnv *, jobject, jintArray);

/*
 * Class:     com_chnic_service_Business
 * Method:    getIntArray
 * Signature: ()[I
 */
JNIEXPORT jintArray JNICALL Java_com_chnic_service_Business_getIntArray
  (JNIEnv *, jobject);

/*
 * Class:     com_chnic_service_Business
 * Method:    getStringArray
 * Signature: ([Ljava/lang/String;)[Ljava/lang/String;
 */
JNIEXPORT jobjectArray JNICALL Java_com_chnic_service_Business_getStringArray
  (JNIEnv *, jobject, jobjectArray);

/*
 * Class:     com_chnic_service_Business
 * Method:    test2DStringArray
 * Signature: ([[Ljava/lang/String;)V
 */
JNIEXPORT void JNICALL Java_com_chnic_service_Business_test2DStringArray
  (JNIEnv *, jobject, jobjectArray);

#ifdef __cplusplus
}
#endif
#endif

编写的CPP实现文件（文件名随意），内容如下：

#include <iostream.h>  
#include <string.h>  
#include "com_chnic_service_Business.h"  
  
jobject getInstance(JNIEnv* env, jclass obj_class);  
/*
 * Class:     com_chnic_service_Business
 * Method:    getPrice
 * Signature: (Ljava/lang/String;)D
 *  传递string参数，返回double值
 */
JNIEXPORT jdouble JNICALL Java_com_chnic_service_Business_getPrice(JNIEnv* env,   
                                                                   jobject obj,   
                                                                   jstring name)  
{  
    const char* pname = env->GetStringUTFChars(name, NULL);  
    cout << "Before release: "  << pname << endl;  
  
    if (strcmp(pname, "Apple") == 0)  
    {  
        env->ReleaseStringUTFChars(name, pname);  
        cout << "After release: " << pname << endl;  
        return 1.2;  
    }   
    else  
    {  
        env->ReleaseStringUTFChars(name, pname);  
        cout << "After release: " << pname << endl;  
        return 2.1;  
    }     
}  
  
/*
 * Class:     com_chnic_service_Business
 * Method:    getOrder
 * Signature: (Ljava/lang/String;I)Lcom/chnic/bean/Order;
 * 传递string、int参数，回调java类中的方法，并且返回一个java对象
 */  
JNIEXPORT jobject JNICALL Java_com_chnic_service_Business_getOrder(JNIEnv* env,   
                                                                   jobject obj,   
                                                                   jstring name,   
                                                                   jint amount)  
{  
    jclass order_class = env->FindClass("com/chnic/bean/Order");  
    jobject order = getInstance(env, order_class);  
      
    jmethodID setName_method = env->GetMethodID(order_class, "setName", "(Ljava/lang/String;)V");  
    env->CallVoidMethod(order, setName_method, name);  
  
    jmethodID setAmount_method = env->GetMethodID(order_class, "setAmount", "(I)V");  
    env->CallVoidMethod(order, setAmount_method, amount);  
  
    return order;  
}  
  
/*
 * Class:     com_chnic_service_Business
 * Method:    getRamdomOrder
 * Signature: ()Lcom/chnic/bean/Order;
 * 无参方法，在C++中构造一个java对象返回
 */
JNIEXPORT jobject JNICALL Java_com_chnic_service_Business_getRamdomOrder(JNIEnv* env,   
                                                                         jobject obj)  
{  
    jclass business_class = env->GetObjectClass(obj);  
    jobject business_obj = getInstance(env, business_class);  
  
    jmethodID notification_method = env->GetMethodID(business_class, "notification", "()V");  
    env->CallVoidMethod(obj, notification_method);  
  
    jclass order_class = env->FindClass("com/chnic/bean/Order");  
    jobject order = getInstance(env, order_class);  
    jfieldID amount_field = env->GetFieldID(order_class, "amount", "I");  
    jint amount = env->GetIntField(order, amount_field);  
    cout << "amount: " << amount << endl;  
    return order;  
}  
  

/*
 * Class:     com_chnic_service_Business
 * Method:    analyzeOrder
 * Signature: (Lcom/chnic/bean/Order;)V
 * 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
 */  
JNIEXPORT void JNICALL Java_com_chnic_service_Business_analyzeOrder (JNIEnv* env,   
                                                                     jclass cls,   
                                                                     jobject obj)  
{  
    jclass order_class = env->GetObjectClass(obj);  
    jmethodID getName_method = env->GetMethodID(order_class, "getName", "()Ljava/lang/String;");  
    jstring name_str = static_cast<jstring>(env->CallObjectMethod(obj, getName_method));  
    const char* pname = env->GetStringUTFChars(name_str, NULL);  
  
    cout << "Name in Java_com_chnic_service_Business_analyzeOrder: " << pname << endl;  


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

/*
 * 根据类，构造对应的对象返回
 */
jobject getInstance(JNIEnv* env, jclass obj_class)  
{  
    jmethodID construction_id = env->GetMethodID(obj_class, "<init>", "()V");  
    jobject obj = env->NewObject(obj_class, construction_id);  
    return obj;  
}  

/*
 * Class:     com_chnic_service_Business
 * Method:    showArray
 * Signature: ([I)V
 * 传递字符串数组，在C++中使用
 */
JNIEXPORT void JNICALL Java_com_chnic_service_Business_showArray
(JNIEnv* env, jobject job, jintArray jia)
{
    jint* nums;
    nums = env->GetIntArrayElements(jia,NULL); 

    jint length = env->GetArrayLength(jia);
    cout<<"length:"<<length<<endl;
    int i;
    for(i=0;i<length;i++)
    {
        cout<<nums[i]<<endl;
    }
}

/*
 * Class:     com_chnic_service_Business
 * Method:    getIntArray
 * Signature: ()[I
 * 返回整形数组
 */
JNIEXPORT jintArray JNICALL Java_com_chnic_service_Business_getIntArray
  (JNIEnv *env, jobject job)
{
    jsize col=10;
    jint temp[10]={1,2,3,4,5,6,7,8,9,10};
    
    jintArray iarr = env->NewIntArray(col);
    env->SetIntArrayRegion(iarr, 0, col, temp);
    return iarr;
}

/*
 * Class:     com_chnic_service_Business
 * Method:    getStringArray
 * Signature: ([Ljava/lang/String;)[Ljava/lang/String;
 * 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
 */
JNIEXPORT jobjectArray JNICALL Java_com_chnic_service_Business_getStringArray
(JNIEnv* env, jobject job, jobjectArray joa)
{
    //打印传递进来的字符串数组
    jsize si = env->GetArrayLength(joa);
    //cout<<si<<endl;
    int i;
    for(i=0;i<si;i++)
    {
        jstring str = (jstring)(env)->GetObjectArrayElement(joa, i);
        //cout<<str<<endl;
        const char* pname = env->GetStringUTFChars(str, NULL);  
        cout<<pname<<endl;
    }
    //构造新的字符串数组
    jstring s1=env->NewStringUTF("123");
    jstring s2=env->NewStringUTF("456");
    jstring s3=env->NewStringUTF("789");
    jstring ss[3]={s1,s2,s3};
    

jobjectArray swArray = env->NewObjectArray(3,env->FindClass("java/lang/String"), env->NewStringUTF(""));
//SetObjectArrayElement刷新数组元素内容  
  for(i = 0; i < 3; i++)
   env->SetObjectArrayElement(swArray, i, ss[i]) ;
    return swArray;
}

/**
 * java传递二维字符串
 *
 */
JNIEXPORT void JNICALL Java_com_chnic_service_Business_test2DStringArray
  (JNIEnv *env, jobject obj, jobjectArray array)
{
 int size = env->GetArrayLength(array);
 for (int i = 0; i < size; i++) {
  jobjectArray myarray =(jobjectArray) (env->GetObjectArrayElement(array, i));
  int length = env->GetArrayLength(myarray);
  cout<<"length:   "<<length<<endl;
  for (int j = 0; j < length; j++) {
   jstring string = (jstring)(env->GetObjectArrayElement(myarray, j));
   const char * chars =  env->GetStringUTFChars(string, 0);
   cout<<chars<<"  ";
    env->ReleaseStringUTFChars(string, chars);
  }
  cout<<endl;
 }
}

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。