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Java JNI由淺入深(包括：Java和C++互傳ArrayList泛型對象參數(shù))

2010-11-25 09:57?1694人閱讀?評論(1)?收藏?舉報

?? ? ? ? 我們知道Java是一個運(yùn)行在虛擬機(jī)里面的高級的編程語言，如果要調(diào)用系統(tǒng)的動態(tài)鏈接庫的話，就要先聲明native修飾的方法(類似接口里面的方法)，再由C/C++程序來實現(xiàn)(類似實現(xiàn)接口里的方法)。這樣Java調(diào)用這些native方法就相當(dāng)于調(diào)用了C/C++里面實現(xiàn)了的方法。通常我們把這種機(jī)制叫做JNI(Java NativeInterfac)，即Java?本地編程接口

? ?? ?? ? Android也同理，要學(xué)會在Android上進(jìn)行NDK開發(fā)，首先我們到打好java JNI的基礎(chǔ)。現(xiàn)在我們暫時把Android開發(fā)丟到一邊先，試試在Java之下編譯一個C動態(tài)鏈接庫，再用Java程序調(diào)用。

1)先來個最簡單的打印HelloWorld例子：

Java代碼(HelloJni.java)：

[java]?view plaincopy

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

生成頭文件(HelloJni.h)：

先javac HelloJni.java編譯你的Java源碼，再javah–jni HelloJni生成所需的頭文件

頭文件內(nèi)容是這樣的：

[java]?view plaincopy

/*?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);??
#ifdef?__cplusplus??
}??
#endif??
#endif??

實現(xiàn)頭文件聲明的方法(HelloJni.cpp)

[c-sharp]?view plaincopy

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

編譯命令:?g++ -I$JAVA_HOME/include-I$JAVA_HOME/include/linux HelloJni.cpp -shared -o libhello.so

命令參數(shù)解析：-I?是指引入java虛擬機(jī)的庫的路徑，-shared?是指編譯成動態(tài)鏈接庫(共享庫) –o?輸出文件名(注意，在Linux平臺下的動態(tài)鏈接庫有一個命名格式：“l(fā)ib+庫名+.so”在java代碼里面loadLibrary的時候不要加lib前綴和.so后綴)

由于我這里把這個動態(tài)鏈接庫編譯放在當(dāng)前目錄下，所以還要設(shè)置環(huán)境變量LD_LIBRARY_PATH=該so動態(tài)鏈接庫所在的目錄，才能正常運(yùn)行

#############################+++華麗的分割線+++###########################

2)好了，可以打印HelloWorld出來后，我們再深入一點(diǎn)點(diǎn)，傳入一個int的數(shù)，在C/C++代碼里面加1后返回。

Java代碼(HelloJni.java)：

[java]?view plaincopy

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());??
????????}??
}??

生成頭文件(HelloJni.h)：

[c-sharp]?view plaincopy

/*?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??

實現(xiàn)頭文件聲明的方法(HelloJni.cpp)

[java]?view plaincopy

#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;??
}??

運(yùn)行結(jié)果：打印2

3)只是傳入簡單的數(shù)據(jù)類型不爽，這次讓C/C++生成個Java對象返回

Java代碼：pojo實體類(User.java)

[c-sharp]?view plaincopy

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代碼(HelloJni.java)：

[java]?view plaincopy

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());??
????????}??
}??

生成頭文件(HelloJni.h)：

[c-sharp]?view plaincopy

#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??

實現(xiàn)頭文件聲明的方法(HelloJni.cpp)

[c-sharp]?view plaincopy

#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)有些同學(xué)可能會說：“返回個Java對象算什么啊，C/C++和Java之間互傳復(fù)雜對象才好玩呢！”正所謂“不怕做不到，就怕想不到”，我們接著重構(gòu)一下上面那個例子!

這次我們傳包含有User對象的List到C/C++程序里面

Java代碼(User.java)

同上。

Java代碼(HelloJni.java)

[java]?view plaincopy

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頭文件(HelloJni.h)

[java]?view plaincopy

#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);??

頭文件的實現(xiàn)(HelloJni.cpp)

[java]?view plaincopy

#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;??
}??

運(yùn)行結(jié)果：

轉(zhuǎn)載于:https://www.cnblogs.com/qinjunni/archive/2012/02/20/2359181.html

總結(jié)

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