Java JNI由浅入深(包括：Java和C++互传ArrayList泛型对象参数)，jniarraylist

来源： javaer 分享于 2019-10-18 点击 220 次点评：132

Java JNI由浅入深(包括：Java和C++互传ArrayList泛型对象参数)，jniarraylist

我们知道Java是一个运行在虚拟机里面的高级的编程语言，如果要调用系统的动态链接库的话，就要先声明native修饰的方法(类似接口里面的方法)，再由C/C++程序来实现(类似实现接口里的方法)。这样Java调用这些native方法就相当于调用了C/C++里面实现了的方法。通常我们把这种机制叫做JNI(Java NativeInterfac)，即Java 本地编程接口

Android也同理，要学会在Android上进行NDK开发，首先我们到打好java JNI的基础。现在我们暂时把Android开发丢到一边先，试试在Java之下编译一个C动态链接库，再用Java程序调用。

1)先来个最简单的打印HelloWorld例子：

Java代码(HelloJni.java)：

import java.util.*; public class HelloJni{ static{ System.loadLibrary("hello"); } public native static void sayHello(); public static void main(String [] args) { HelloJni.sayHello(); } }

生成头文件(HelloJni.h)：

先javac HelloJni.java编译你的Java源码，再javah–jni HelloJni生成所需的头文件

头文件内容是这样的：

实现头文件声明的方法(HelloJni.cpp)

#include "HelloJni.h" JNIEXPORT void JNICALL Java_HelloJni_sayHello(JNIEnv *env, jclass cls) { printf("HelloWorld"); }

编译命令: g++ -I$JAVA_HOME/include-I$JAVA_HOME/include/linux HelloJni.cpp -shared -o libhello.so

命令参数解析：-I 是指引入java虚拟机的库的路径，-shared 是指编译成动态链接库(共享库) –o 输出文件名(注意，在Linux平台下的动态链接库有一个命名格式：“lib+库名+.so”在java代码里面loadLibrary的时候不要加lib前缀和.so后缀)

由于我这里把这个动态链接库编译放在当前目录下，所以还要设置环境变量LD_LIBRARY_PATH=该so动态链接库所在的目录，才能正常运行

#############################+++华丽的分割线+++###########################

2)好了，可以打印HelloWorld出来后，我们再深入一点点，传入一个int的数，在C/C++代码里面加1后返回。

Java代码(HelloJni.java)：

public class HelloJni{ static{ System.loadLibrary("hello"); } public static native void sayHello(); public native int getInt(); public native void setInt(int i); public static void main(String args[]){ // HelloJni.sayHello(); HelloJni hello = new HelloJni(); hello.setInt(2); System.out.println(hello.getInt()); } }

生成头文件(HelloJni.h)：

/* DO NOT EDIT THIS FILE - it is machine generated */ #include <jni.h> /* Header for class HelloJni */ #ifndef _Included_HelloJni #define _Included_HelloJni #ifdef __cplusplus extern "C" { #endif JNIEXPORT void JNICALL Java_HelloJni_sayHello (JNIEnv *, jclass); JNIEXPORT jint JNICALL Java_HelloJni_getInt (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_HelloJni_setInt (JNIEnv *, jobject, jint); #ifdef __cplusplus } #endif #endif

实现头文件声明的方法(HelloJni.cpp)

#include "HelloJni.h" int i=1; JNIEXPORT void JNICALL Java_HelloJni_sayHello (JNIEnv *env, jclass cls){ printf("HelloWorld/n"); } JNIEXPORT jint JNICALL Java_HelloJni_getInt (JNIEnv *env, jobject thiz){ return i; } JNIEXPORT void JNICALL Java_HelloJni_setInt (JNIEnv *env, jobject thiz,jint ji){ i = ji+1; }

运行结果：打印2

3)只是传入简单的数据类型不爽，这次让C/C++生成个Java对象返回

Java代码：pojo实体类(User.java)

public class User{ private long id; private String userName; private boolean isMan; private int age; public User(){} public User(long id, String userName, boolean isMan, int age) { super(); this.id = id; this.userName = userName; this.isMan = isMan; this.age = age; } public long getId() { return id; } public void setId(long id) { this.id = id; } public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public boolean isMan() { return isMan; } public void setMan(boolean isMan) { this.isMan = isMan; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }

Java代码(HelloJni.java)：

public class HelloJni{ static{ System.loadLibrary("userbean"); } public static native void sayHello(); public native int getInt(); public native void setInt(int i); public native void setUser(String userName); public native User getUser(); public static void main(String args[]){ // HelloJni.sayHello(); HelloJni hello = new HelloJni(); // hello.setInt(2); // System.out.println(hello.getInt()); hello.setUser("LiangYaotian"); User user = hello.getUser(); System.out.println("user from c/c++"); System.out.println("name:"+user.getUserName()); System.out.println("isMan?:"+user.isMan()); System.out.println("age:"+user.getAge()); } }

生成头文件(HelloJni.h)：

#include <jni.h> /* Header for class HelloJni */ #ifndef _Included_HelloJni #define _Included_HelloJni #ifdef __cplusplus extern "C" { #endif JNIEXPORT void JNICALL Java_HelloJni_sayHello (JNIEnv *, jclass); JNIEXPORT jint JNICALL Java_HelloJni_getInt (JNIEnv *, jobject); JNIEXPORT void JNICALL Java_HelloJni_setInt (JNIEnv *, jobject, jint); JNIEXPORT void JNICALL Java_HelloJni_setUser (JNIEnv *, jobject, jstring); JNIEXPORT jobject JNICALL Java_HelloJni_getUser (JNIEnv *, jobject); #ifdef __cplusplus } #endif #endif

实现头文件声明的方法(HelloJni.cpp)

#include <iostream> #include <stdio.h> using namespace std; int i=1; jobject user; JNIEXPORT void JNICALL Java_HelloJni_sayHello (JNIEnv *env, jclass cls){ printf("HelloWorld/n"); } JNIEXPORT jint JNICALL Java_HelloJni_getInt (JNIEnv *env, jobject thiz){ return i; } JNIEXPORT void JNICALL Java_HelloJni_setInt (JNIEnv *env, jobject thiz,jint ji){ i = ji+1; } JNIEXPORT void JNICALL Java_HelloJni_setUser (JNIEnv *env, jobject thiz, jstring name){ jclass userClass = env->FindClass("User"); jmethodID userMethod = env->GetMethodID(userClass,"<init>","()V"); jfieldID mId = env->GetFieldID(userClass,"id","J"); jfieldID mUserName = env->GetFieldID(userClass,"userName","Ljava/lang/String;"); jfieldID mIsMan = env->GetFieldID(userClass,"isMan","Z"); jfieldID mAge = env->GetFieldID(userClass,"age","I"); jobject userObject = env->NewObject(userClass,userMethod); env->SetObjectField(userObject,mUserName,name); env->SetLongField(userObject,mId,1001); env->SetBooleanField(userObject,mIsMan,1); env->SetIntField(userObject,mAge,21); user = userObject; }

4)有些同学可能会说：“返回个Java对象算什么啊，C/C++和Java之间互传复杂对象才好玩呢！”正所谓“不怕做不到，就怕想不到”，我们接着重构一下上面那个例子!

这次我们传包含有User对象的List到C/C++程序里面

Java代码(User.java)

同上。

Java代码(HelloJni.java)

import java.util.*; public class HelloJni{ static{ System.loadLibrary("userbean"); } public native int get(); public native void set(int i); public native void setUser(String userName); public native User getUser(); public native void setUserList(ArrayList<User> userList); public native ArrayList<User> getUserList(); public static void main(String [] args) { HelloJni hello = new HelloJni(); // hello.set(2); // System.out.println(hello.get()); /* hello.setUser("LiangYaotian"); User user = hello.getUser(); System.out.println("user from c/c++"); System.out.println("name:"+user.getUserName()); System.out.println("isMan?:"+user.isMan()); System.out.println("age:"+user.getAge()); */ ArrayList<User> userList = new ArrayList<User>(); for(int i=0;i<10;i++){ User u = new User((long)(1000+i),"LiangYaotian"+i,true,21); userList.add(u); } hello.setUserList(userList); userList = null; userList = hello.getUserList(); System.out.println("ArrayList<User> construct from C++,then Java print it....."); for(User u : userList){ System.out.println("id:"+u.getId()+"; name:"+u.getUserName()); } } }

C头文件(HelloJni.h)

头文件的实现(HelloJni.cpp)

#include "HelloJni.h" int i=1; jobject user; JNIEXPORT jint JNICALL Java_HelloJni_get (JNIEnv *env, jobject jthiz){ printf("HelloWorld/n"); } JNIEXPORT void JNICALL Java_HelloJni_set (JNIEnv *env, jobject jthiz, jint ji){ i = ji+1; } JNIEXPORT void JNICALL Java_HelloJni_setUser (JNIEnv *env, jobject jthiz, jstring name){ jclass userClass = env->FindClass("User"); jmethodID userMethod = env->GetMethodID(userClass,"<init>","()V"); jfieldID mId = env->GetFieldID(userClass,"id","J"); jfieldID mUserName = env->GetFieldID(userClass,"userName","Ljava/lang/String;"); jfieldID mIsMan = env->GetFieldID(userClass,"isMan","Z"); jfieldID mAge = env->GetFieldID(userClass,"age","I"); jobject userObject = env->NewObject(userClass,userMethod); env->SetObjectField(userObject,mUserName,name); env->SetLongField(userObject,mId,1001); env->SetBooleanField(userObject,mIsMan,1); env->SetIntField(userObject,mAge,21); user = userObject; } JNIEXPORT jobject JNICALL Java_HelloJni_getUser (JNIEnv *env, jobject jthiz){ return user; } JNIEXPORT void JNICALL Java_HelloJni_setUserList (JNIEnv *env, jobject jthiz, jobject userList){ int i; //class ArrayList jclass cls_arraylist = env->GetObjectClass(userList); //method in class ArrayList jmethodID arraylist_get = env->GetMethodID(cls_arraylist,"get","(I)Ljava/lang/Object;"); jmethodID arraylist_size = env->GetMethodID(cls_arraylist,"size","()I"); jint len = env->CallIntMethod(userList,arraylist_size); printf("get java ArrayList<User> object by C++ , then print it...../n"); for(i=0;i<len;i++){ jobject obj_user = env->CallObjectMethod(userList,arraylist_get,i); jclass cls_user = env->GetObjectClass(obj_user); jmethodID user_getId = env->GetMethodID(cls_user,"getId","()J"); jmethodID user_getUserName = env->GetMethodID(cls_user,"getUserName","()Ljava/lang/String;"); jmethodID user_isMan = env->GetMethodID(cls_user,"isMan","()Z"); jmethodID user_getAge = env->GetMethodID(cls_user,"getAge","()I"); jstring name = (jstring)env->CallObjectMethod(obj_user,user_getUserName); jboolean b = true; const char *namePtr = env->GetStringUTFChars(name,&b); jlong id = env->CallLongMethod(obj_user,user_getId); jboolean sex = env->CallBooleanMethod(obj_user,user_isMan); jint age = env->CallIntMethod(obj_user,user_getAge); printf("Id:%d; ",id); printf("Name:%s; ",namePtr); printf("isMan? %d; ",sex); printf("Age:%d /n ",age); } } JNIEXPORT jobject JNICALL Java_HelloJni_getUserList (JNIEnv *env, jobject jthiz){ //ArrayList Object jclass cls_ArrayList = env->FindClass("java/util/ArrayList"); jmethodID construct = env->GetMethodID(cls_ArrayList,"<init>","()V"); jobject obj_ArrayList = env->NewObject(cls_ArrayList,construct,""); jmethodID arrayList_add = env->GetMethodID(cls_ArrayList,"add","(Ljava/lang/Object;)Z"); //User Object jclass cls_user = env->FindClass("User"); //none argument construct function jmethodID construct_user = env->GetMethodID(cls_user,"<init>","()V"); //new a object jobject obj_user = env->NewObject(cls_user,construct_user,""); //get method id /* jmethodID user_setId = env->GetMethodID(cls_user,"setId","(J)V"); jmethodID user_setUserName = env->GetMethodID(cls_user,"setUserName","(Ljava/lang/String;)V"); jmethodID user_setMan = env->GetMethodID(cls_user,"setMan","(Z)V"); jmethodID user_setAge = env->GetMethodID(cls_user,"setAge","(I)V"); */ int i; for(i=0;i<10;i++){ //new a object jobject obj_user = env->NewObject(cls_user,construct_user,""); //get field id jfieldID user_id = env->GetFieldID(cls_user,"id","J"); jfieldID user_name = env->GetFieldID(cls_user,"userName","Ljava/lang/String;"); jfieldID user_isMan = env->GetFieldID(cls_user,"isMan","Z"); jfieldID user_age = env->GetFieldID(cls_user,"age","I"); env->SetLongField(obj_user,user_id,i); env->SetObjectField(obj_user,user_name,env->NewStringUTF("LiangYaoTian")); env->SetBooleanField(obj_user,user_isMan,1); env->SetIntField(obj_user,user_age,21); env->CallObjectMethod(obj_ArrayList,arrayList_add,obj_user); } return obj_ArrayList; }

运行结果：

源码：E-Mail我：u_xtian@qq.com

原创作品，转载需注明出处...http://blog.csdn.net/u_xtian/archive/2010/11/25/6033963.aspx

Java JNI由浅入深(包括：Java和C++互传ArrayList泛型对象参数)，jniarraylist

Java JNI由浅入深(包括：Java和C++互传ArrayList泛型对象参数)，jniarraylist

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