JNI层与Java层结构体传递

JNI层与Java层结构体传递

最近在做移动终端开发，需要把native层C++一些统计数据传递给java层使用，在做这部分功能的时候发现JNI层与Java层结构体以及内嵌结构体传递在网上的资料甚少，因此完成功能后做一下这方面的总结，方面后人学习。

• JNI函数返回一个结构体

1. 首先我们定义C层的结构体和函数  

   typedef struct _VoiceAPIStat {intnSLESRecOpenSucceedCnt;//open slel mic 创建成功次数intnSLESRecOpenFailedCnt;//open slel mic 创建失败次数intnSLESPlayOpenSucceedCnt;//open slel render 创建成功次数intnSLESPlayOpenFailedCnt;//open slel render 创建失败次数intnJAVARecOpenSucceedCnt;//java mic 创建成功次数intnJAVARecOpenFailedCnt;//java mic 创建失败次数intnJAVAPlayOpenSucceedCnt;//java  render 创建成功次数intnJAVAPlayOpenFailedCnt;//java  render 创建失败次数}VoiceAPIStat;// -------------------------------------------------------------------------------------------------//    系统关键指标数据统计// -------------------------------------------------------------------------------------------------typedef struct _EngRunInfoStat{boolbStatisticsEnable;  <span style="white-space:pre"></span>// 统计是否使能（为假，则不上报）intnStatisticsLevel;// 统计级别（为0，则不统计）intnRptIntervalInMs;// 上报周期（毫秒）intnSpeakMode;//说话模式intnJavaAPILevel;//java api 级别VoiceAPIStatstVoiceApiStat;//音频采集API信息统计}EngRunInfoStat;

   //定义C层获取结构体信息函数

   int  GetRunInfoStat(EngRunInfoStat *pAllStat);

   如代码所示，我们定义一个嵌套的结构体，定义C层提供给JNI层获取EngRunInfoStat结构体参数信息的函数，EngRunInfoStat是一个嵌套结构体，我们最终目的把该C层该结构体值传递到Java层。  
2. 定义Java层对应的函数和结构体类

   package com.test.eng;public class EngRunInfoStat {public booleanbStatisticsEnable;  // 统计是否使能（为假，则不上报）public intnStatisticsLevel;// 统计级别（为0，则不统计）public intnRptIntervalInMs;// 上报周期（毫秒）public intnSpeakMode;//说话模式public intnJavaAPILevel;//java api 级别public VoiceAPIStatstVoiceApiStat;//音频采集API信息统计public class VoiceAPIStat {public intnSLESRecOpenSucceedCnt;//open slel mic 创建成功次数public intnSLESRecOpenFailedCnt;//open slel mic 创建失败次数public intnSLESPlayOpenSucceedCnt;//open slel render 创建成功次数public intnSLESPlayOpenFailedCnt;//open slel render 创建失败次数public intnJAVARecOpenSucceedCnt;//java mic 创建成功次数public intnJAVARecOpenFailedCnt;//java mic 创建失败次数public intnJAVAPlayOpenSucceedCnt;//java  render 创建成功次数public intnJAVAPlayOpenFailedCnt;//java  render 创建失败次数};};

   //定义对应获取类函数 public final static native EngRunInfoStat GetRunInfoStat();

   如java代码定义对应C层EngRunInfoStat结构体对应的EngRunInfoStat java类，并且定义与jni层通信的native函数，native函数如果与JNI使用不是本节重点，不做额外描述，重点放在结构体传递上。
3. 通过JNI层实现C层与Java层结构体转换 JNI层的代码实现是最关键的，首先我们要获取对应Java层定义的EngRunInfoStat类，并且需要获取该类的构造函数，然后通过NewObject函数创建该类的一个实例，注意我们EngRunInfoStat类里面还包含一个内嵌类，通过NewObject创建EngRunInfoStat类并没有包含内嵌类的实例，内嵌类我们后面还需单独的创建，先看示例代码

   //获取Java实例jclass objectClass = (env)->FindClass("com/test/eng/EngRunInfoStat");//获取成员变量jmethodID objectClassInitID = (env)->GetMethodID(objectClass, "<init>", "()V");jobject  objectNewEng = (env)->NewObject(objectClass, objectClassInitID);

   objectNewEng即是我们新创建出来EngRunInfoStat实例，为了给类成员变量赋值，我们还需要将类中成员变量ID导出来，用于后续赋值操作

   jfieldID bStatisticsEnable = (env)->GetFieldID(objectClass, "bStatisticsEnable", "Z");jfieldID nStatisticsLevel = (env)->GetFieldID(objectClass, "nStatisticsLevel", "I");jfieldID nRptIntervalInMs = (env)->GetFieldID(objectClass, "nRptIntervalInMs", "I");jfieldID nSpeakMode = (env)->GetFieldID(objectClass, "nSpeakMode", "I");jfieldID nJavaAPILevel = (env)->GetFieldID(objectClass, "nJavaAPILevel", "I");jfieldID stVoiceApiStat = (env)->GetFieldID(objectClass, "stVoiceApiStat", "Lcom/test/eng/EngRunInfoStat$VoiceAPIStat;");

   如代码所示，普通成员变量jfiledID通过GetFieldID()，根据变量名称和类型签名导出即可，关键是成员中内嵌类导出比较特殊，stVoiceApiStat是一个内嵌类成员变量它是VoiceAPIStat内嵌类，内嵌类的签名比较特殊，首先是L开头代表类，然后包名，外部类与内部类签名之间用$隔开，即“Lcom/test/eng/EngRunInfoStat$VoiceAPIStat;”，获取到成员变量字段ID后，对于一般成员变量，我们就可以对其赋值了，示例如下：

   if(0 == GetRunInfoStat(&stEngInfoStat)){(env)->SetBooleanField(objectNewEng, bStatisticsEnable, (jboolean)stEngInfoStat.bStatisticsEnable);(env)->SetIntField(objectNewEng, nStatisticsLevel, stEngInfoStat.nStatisticsLevel);(env)->SetIntField(objectNewEng, nRptIntervalInMs, stEngInfoStat.nRptIntervalInMs);(env)->SetIntField(objectNewEng, nSpeakMode, stEngInfoStat.nSpeakMode);(env)->SetIntField(objectNewEng, nJavaAPILevel, stEngInfoStat.nJavaAPILevel);<span style="white-space:pre"></span>}

   GetRunInfoStat是C层获取C结构体变量的函数，stEngInfoStat是获取数据后保存的变量，获取数据成功后就可以将每个值设置到对应java类成员变量中，即通过SetIntField()函数设置，用法见示例代码，可以看到我们还没有对内嵌类stVoiceApiStat进行操作，这是因为对内嵌类的操作比较特殊，与普通成员变量需要区别对待，对于内嵌类我们首先要导出内嵌类对象，然后到处内嵌类构造函数，接着用NewObject创建内嵌类的实例，示例代码如下：

   jclass obVoiceAPI = (env)->FindClass("com/qq/qtx/EngRunInfoStat$VoiceAPIStat");jmethodID objectVoiceInitID = (env)->GetMethodID(obRecordMode, "<init>", "(Lcom/qq/qtx/EngRunInfoStat;)V");jobject objectVoice = (env)->NewObject(obVoiceAPI, objectVoiceInitID, objectNewEng);

   jfieldID nSLESRecOpenSucceedCnt = (env)->GetFieldID(obVoiceAPI, "nSLESRecOpenSucceedCnt", "I");jfieldID nSLESRecOpenFailedCnt = (env)->GetFieldID(obVoiceAPI, "nSLESRecOpenFailedCnt", "I");jfieldID nSLESPlayOpenSucceedCnt = (env)->GetFieldID(obVoiceAPI, "nSLESPlayOpenSucceedCnt", "I");jfieldID nSLESPlayOpenFailedCnt = (env)->GetFieldID(obVoiceAPI, "nSLESPlayOpenFailedCnt", "I");jfieldID nJAVARecOpenSucceedCnt = (env)->GetFieldID(obVoiceAPI, "nJAVARecOpenSucceedCnt", "I");jfieldID nJAVARecOpenFailedCnt = (env)->GetFieldID(obVoiceAPI, "nJAVARecOpenFailedCnt", "I");jfieldID nJAVAPlayOpenSucceedCnt = (env)->GetFieldID(obVoiceAPI, "nJAVAPlayOpenSucceedCnt", "I");jfieldID nJAVAPlayOpenFailedCnt = (env)->GetFieldID(obVoiceAPI, "nJAVAPlayOpenFailedCnt", "I");

   创建实例后，就可以给内嵌类的成员变量赋值操作了，示例代码如下：

   <span style="white-space:pre"></span>(env)->SetIntField(objectVoice, nSLESRecOpenSucceedCnt, stEngInfoStat.stVoiceApiStat.nSLESRecOpenSucceedCnt);(env)->SetIntField(objectVoice, nSLESRecOpenFailedCnt, stEngInfoStat.stVoiceApiStat.nSLESRecOpenFailedCnt);(env)->SetIntField(objectVoice, nSLESPlayOpenSucceedCnt, stEngInfoStat.stVoiceApiStat.nSLESPlayOpenSucceedCnt);(env)->SetIntField(objectVoice, nSLESPlayOpenFailedCnt, stEngInfoStat.stVoiceApiStat.nSLESPlayOpenFailedCnt);(env)->SetIntField(objectVoice, nJAVARecOpenSucceedCnt, stEngInfoStat.stVoiceApiStat.nJAVARecOpenSucceedCnt);(env)->SetIntField(objectVoice, nJAVARecOpenFailedCnt, stEngInfoStat.stVoiceApiStat.nJAVARecOpenFailedCnt);(env)->SetIntField(objectVoice, nJAVAPlayOpenSucceedCnt, stEngInfoStat.stVoiceApiStat.nJAVAPlayOpenSucceedCnt);(env)->SetIntField(objectVoice, nJAVAPlayOpenFailedCnt, stEngInfoStat.stVoiceApiStat.nJAVAPlayOpenFailedCnt);

   赋值完成后，我们还需要将创建内嵌类ObjectVoice用SetObjectField()函数设置到创建到外部类中，这样外部类中内嵌类才起作用是有效的，示例代码如下：

   (env)->SetObjectField(objectNewEng, stVoiceApiStat, objectVoice);

   至此JNI层函数里面对于Java结构体类就创建赋值完成了，最后通过函数返回给Java层就可以了，JNI函数完成代码示例如下：

   /* * Class:     com_test_eng_jni_NativeMethodJNI * Method:    GetRunInfoStat * Signature: ()Lcom/test/eng/EngRunInfoStat; */JNIEXPORT jobject JNICALL Java_com_test_eng_jni_NativeMethodJNI_GetRunInfoStat(JNIEnv *env, jclass obj){EngRunInfoStat  stEngInfoStat;memset(&stEngInfoStat, 0, sizeof(EngRunInfoStat));//获取Java实例jclass objectClass = (env)->FindClass("com/tess/eng/EngRunInfoStat");//获取成员变量jmethodID objectClassInitID = (env)->GetMethodID(objectClass, "<init>", "()V");jobject  objectNewEng = (env)->NewObject(objectClass, objectClassInitID);jfieldID bStatisticsEnable = (env)->GetFieldID(objectClass, "bStatisticsEnable", "Z");jfieldID nStatisticsLevel = (env)->GetFieldID(objectClass, "nStatisticsLevel", "I");jfieldID nRptIntervalInMs = (env)->GetFieldID(objectClass, "nRptIntervalInMs", "I");jfieldID nSpeakMode = (env)->GetFieldID(objectClass, "nSpeakMode", "I");jfieldID nJavaAPILevel = (env)->GetFieldID(objectClass, "nJavaAPILevel", "I");jfieldID stVoiceApiStat = (env)->GetFieldID(objectClass, "stVoiceApiStat", "Lcom/test/eng/EngRunInfoStat$VoiceAPIStat;");jclass obVoiceAPI = (env)->FindClass("com/qq/qtx/EngRunInfoStat$VoiceAPIStat");jmethodID objectVoiceInitID = (env)->GetMethodID(obRecordMode, "<init>", "(Lcom/test/eng/EngRunInfoStat;)V");jobject objectVoice = (env)->NewObject(obVoiceAPI, objectVoiceInitID, objectNewEng);jfieldID nSLESRecOpenSucceedCnt = (env)->GetFieldID(obVoiceAPI, "nSLESRecOpenSucceedCnt", "I");jfieldID nSLESRecOpenFailedCnt = (env)->GetFieldID(obVoiceAPI, "nSLESRecOpenFailedCnt", "I");jfieldID nSLESPlayOpenSucceedCnt = (env)->GetFieldID(obVoiceAPI, "nSLESPlayOpenSucceedCnt", "I");jfieldID nSLESPlayOpenFailedCnt = (env)->GetFieldID(obVoiceAPI, "nSLESPlayOpenFailedCnt", "I");jfieldID nJAVARecOpenSucceedCnt = (env)->GetFieldID(obVoiceAPI, "nJAVARecOpenSucceedCnt", "I");jfieldID nJAVARecOpenFailedCnt = (env)->GetFieldID(obVoiceAPI, "nJAVARecOpenFailedCnt", "I");jfieldID nJAVAPlayOpenSucceedCnt = (env)->GetFieldID(obVoiceAPI, "nJAVAPlayOpenSucceedCnt", "I");jfieldID nJAVAPlayOpenFailedCnt = (env)->GetFieldID(obVoiceAPI, "nJAVAPlayOpenFailedCnt", "I");if(0 == GetRunInfoStat(&stEngInfoStat)){(env)->SetBooleanField(objectNewEng, bStatisticsEnable, (jboolean)stEngInfoStat.bStatisticsEnable);(env)->SetIntField(objectNewEng, nStatisticsLevel, stEngInfoStat.nStatisticsLevel);(env)->SetIntField(objectNewEng, nRptIntervalInMs, stEngInfoStat.nRptIntervalInMs);(env)->SetIntField(objectNewEng, nSpeakMode, stEngInfoStat.nSpeakMode);(env)->SetIntField(objectNewEng, nJavaAPILevel, stEngInfoStat.nJavaAPILevel);(env)->SetIntField(objectVoice, nSLESRecOpenSucceedCnt, stEngInfoStat.stVoiceApiStat.nSLESRecOpenSucceedCnt);(env)->SetIntField(objectVoice, nSLESRecOpenFailedCnt, stEngInfoStat.stVoiceApiStat.nSLESRecOpenFailedCnt);(env)->SetIntField(objectVoice, nSLESPlayOpenSucceedCnt, stEngInfoStat.stVoiceApiStat.nSLESPlayOpenSucceedCnt);(env)->SetIntField(objectVoice, nSLESPlayOpenFailedCnt, stEngInfoStat.stVoiceApiStat.nSLESPlayOpenFailedCnt);(env)->SetIntField(objectVoice, nJAVARecOpenSucceedCnt, stEngInfoStat.stVoiceApiStat.nJAVARecOpenSucceedCnt);(env)->SetIntField(objectVoice, nJAVARecOpenFailedCnt, stEngInfoStat.stVoiceApiStat.nJAVARecOpenFailedCnt);(env)->SetIntField(objectVoice, nJAVAPlayOpenSucceedCnt, stEngInfoStat.stVoiceApiStat.nJAVAPlayOpenSucceedCnt);(env)->SetIntField(objectVoice, nJAVAPlayOpenFailedCnt, stEngInfoStat.stVoiceApiStat.nJAVAPlayOpenFailedCnt);}(env)->SetObjectField(objectNewEng, stVoiceApiStat, objectVoice);return objectNewEng;}

• Java函数传递结构体参数

参数为结构体传递和上面返回值类似，本次先介绍到这里，后面需要的时候在续写参数为结构体情况。