背景

在前面两篇文章中，我们总结了Java 调用 C/C++ SDK 的几种方案，分享了JNI在实践过程中的一些踩坑点，而在这篇文章将继续分享针对Java List类型及其嵌套类型，我们的JNI如何接收。

分析

如下，是我的的SDK的结构体定义：

struct CustomParam{std::string key;std::vector<std::string> values;
};

SDK的请求体入参定义如下：

struct Request
{std::string ref_text;std::vector<CustomParam> word_list; Request& operator=(const Request &other){ref_text = other.ref_text;word_list = other.word_list;return *this;}
};

解决

● 根据上面的SDK结构体的相关定义，我们在Java层可以有如下的 类型定义：

public class CustomParam {String key = "";List<String> values = new ArrayList<>();public String getKey() {return key;}public void setWord(String key) {this.key = key;}public List<String> getValues() {return values;}public void setValues(List<String> values) {this.values = values;}
}

● 关于native的方法申明如下：

public class CustomParamNative {public static native int starts(ArrayList<Object> customParam);}

● 根据native方法生成 头部文件

javac -encoding utf8 -h . XXX.java

● 如下为生成的native方法的头部文件

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_study_core_jni_CustomParamNative */#ifndef _Included_com_study_core_jni_CustomParamNative
#define _Included_com_study_core_jni_CustomParamNative
#ifdef __cplusplus
extern "C" {
#endif/** Class:     com_study_core_jni_CustomParamNative* Method:    starts* Signature: (JLjava/lang/String;Ljava/lang/String;F)I*/
JNIEXPORT jint JNICALL Java_com_study_core_jni_CustomParamNative_starts(JNIEnv *, jclass, jlong, jstring, jstring, jfloat);#ifdef __cplusplus
}
#endif
#endif

● 头部文件的具体实现

#include "com_study_core_jni_CustomParamNative.h"
#include <vector>
#undef __request
#define __request Request#include "stdio.h"
#include "stdlib.h"JNIEXPORT jint JNICALL Java_com_study_core_jni_CustomParamNative_starts(JNIEnv *env, jclass obj, jstring jni_ref, jobject customParamList)
{__request request;CopyString(env, thread->text_buff, jni_ref);request.ref_text = thread->text_buff.data();CopyString(env, thread->text_buff, jni_utt);request.audio_id = thread->text_buff.data();if (customParamList != NULL){// 获取ArrayList类和对应的方法IDjclass arrayListClass = env->FindClass("java/util/ArrayList");jmethodID getMethodID = env->GetMethodID(arrayListClass, "get", "(I)Ljava/lang/Object;");jmethodID sizeMethodID = env->GetMethodID(arrayListClass, "size", "()I");// 获取CustomParam类和对应的字段IDjclass customParamClass = env->FindClass("com/seewo/study/core/bo/CustomParam");jfieldID wordFieldID = env->GetFieldID(customParamClass, "key", "Ljava/lang/String;");jfieldID valuesFieldID = env->GetFieldID(customParamClass, "values", "Ljava/util/List;");// 获取ArrayList的大小jint size = env->CallIntMethod(customParamList, sizeMethodID);printf("size = %d\n", size);// 遍历ArrayList并解析CustomParam对象for (int i = 0; i < size; i++){// 获取CustomParam对象jobject customParamObj = env->CallObjectMethod(customParamList, getMethodID, i);// 获取key字段的值jstring wordString = (jstring)env->GetObjectField(customParamObj, wordFieldID);printf("字符 = %c\n", wordString);jboolean is_copy;const char *word = env->GetStringUTFChars(wordString, &is_copy);printf("字符 = %c\n", word);// 将word和values赋值给C++结构体// 创建CustomParam结构体对象CustomParam customParam;// 将word字段的值赋值给C++结构体customParam.word = word;// 获取values字段的值jobject valuesList = env->GetObjectField(customParamObj, valuesFieldID);jclass listClass = env->FindClass("java/util/List");jmethodID toArrayMethodID = env->GetMethodID(listClass, "toArray", "()[Ljava/lang/Object;");jobjectArray valuesArray = (jobjectArray)env->CallObjectMethod(valuesList, toArrayMethodID);jsize size = env->GetArrayLength(valuesArray);std::vector<std::string> values;for (int j = 0; j < size; j++){jstring valuesString = (jstring)env->GetObjectArrayElement(valuesArray, j);const char *pron = env->GetStringUTFChars(valuesString, &is_copy);values.push_back(pron);env->ReleaseStringUTFChars(valuesString, pron);env->DeleteLocalRef(valuesString);}customParam.values = values;request.word_list.push_back(customParam);// 释放资源env->DeleteLocalRef(customParamObj);env->ReleaseStringUTFChars(wordString, word);env->DeleteLocalRef(wordString);env->DeleteLocalRef(valuesList);env->DeleteLocalRef(valuesArray);}// 释放资源env->DeleteLocalRef(arrayListClass);env->DeleteLocalRef(customParamClass);return ThreadHandleStarts<__request>(request);}}