Golang에서 JVM 메서드 호출 프로세스의 속도를 높이기 위해 캐시를 사용하는 방법입니다.

package jvm

/*
#cgo CFLAGS: -I/usr/local/java/include -I/usr/local/java/include/linux
#cgo LDFLAGS: -L/usr/local/java/jre/lib/amd64/server -ljvm
#include <stdlib.h>
#include <jni.h>
*/
import "C"
import (
    "sync"
)

// 缓存C语言对象
var cache = &sync.Map{}

// 获取class对象
func getClass(className string, jvm JavaVM) (jclass, error) {
    cName := C.CString(className)
    defer C.free(unsafe.Pointer(cName))

    // 先从缓存中获取
    if cClass, ok := cache.Load(cName); ok {
        return cClass.(jclass), nil
    }

    // 调用JNI创建class对象
    jniEnv, err := jvm.GetEnv()
    if err != nil {
        return nil, err
    }
    cClass, err := jniEnv.FindClass(cName)
    if err != nil {
        return nil, err
    }

    // 将对象放入缓存
    cache.Store(cName, cClass)

    return cClass, nil
}

// 调用实例方法
func InvokeMethod(jvm JavaVM, className string, methodName string, methodSignature string, objObj ObjObject, args ...interface{}) (interface{}, error) {
    // 获取class对象和method id
    cClass, err := getClass(className, jvm)
    if err != nil {
        return nil, err
    }
    cMethodName := C.CString(methodName)
    defer C.free(unsafe.Pointer(cMethodName))
    cMethodSignature := C.CString(methodSignature)
    defer C.free(unsafe.Pointer(cMethodSignature))
    jniEnv, err := jvm.GetEnv()
    if err != nil {
        return nil, err
    }
    methodID, err := jniEnv.GetMethodID(cClass, cMethodName, cMethodSignature)
    if err != nil {
        return nil, err
    }

    // 将参数转化为jvalue结构体
    jValue, err := convertArgs(jniEnv, args...)
    if err != nil {
        return nil, err
    }

    // 调用JNI方法
    result, err := jniEnv.CallObjectMethodV(objObj, methodID, jValue)
    if err != nil {
        return nil, err
    }

    // 将结果转化为interface{}类型
    return convertResult(jniEnv, result), nil
}

// 转换参数
func convertArgs(env *C.JNIEnv, args ...interface{}) ([]C.jvalue, error) {
    jValues := make([]C.jvalue, len(args))
    for i, arg := range args {
        switch arg.(type) {
        case int:
            jValues[i].i = C.jint(arg.(int))
        case int64:
            jValues[i].j = C.jlong(arg.(int64))
        case float64:
            jValues[i].d = C.jdouble(arg.(float64))
        case bool:
            jValues[i].z = C.jboolean(arg.(bool))
        case string:
            cStr := C.CString(arg.(string))
            defer C.free(unsafe.Pointer(cStr))
            jValues[i].l = C.jobject(unsafe.Pointer(env.NewStringUTF(cStr)))
        default:
            return nil, fmt.Errorf("Unsupported arg type: %T", arg)
        }
    }
    return jValues, nil
}

// 转换结果
func convertResult(env *C.JNIEnv, result jobject) interface{} {
    className, err := jni.GetObjectClassName(env, result)
    if err != nil {
        return nil
    }

    switch className {
    case "java/lang/String":
        return convertToString(env, result)
    case "java/lang/Integer":
        return convertToInt(env, result)
    case "java/lang/Long":
        return convertToLong(env, result)
    case "java/lang/Double":
        return convertToDouble(env, result)
    case "java/lang/Boolean":
        return convertToBool(env, result)
    case "java/lang/Object":
        return convertToObject(env, result)
    default:
        return result
    }
}

// 将结果转化为string
func convertToString(env *C.JNIEnv, result jobject) string {
    cStr := env.GetStringUTFChars((*C.jstring)(unsafe.Pointer(result)), nil)
    defer env.ReleaseStringUTFChars((*C.jstring)(unsafe.Pointer(result)), cStr)
    return C.GoString(cStr)
}

// 将结果转化为int
func convertToInt(env *C.JNIEnv, result jobject) int {
    return int(env.CallIntMethod(result, env.GetMethodID(env.FindClass("java/lang/Integer"), "intValue", "()I")))
}

// 将结果转化为long
func convertToLong(env *C.JNIEnv, result jobject) int64 {
    return int64(env.CallLongMethod(result, env.GetMethodID(env.FindClass("java/lang/Long"), "longValue", "()J")))
}

// 将结果转化为double
func convertToDouble(env *C.JNIEnv, result jobject) float64 {
    return float64(env.CallDoubleMethod(result, env.GetMethodID(env.FindClass("java/lang/Double"), "doubleValue", "()D")))
}

// 将结果转化为bool
func convertToBool(env *C.JNIEnv, result jobject) bool {
    return env.CallBooleanMethod(result, env.GetMethodID(env.FindClass("java/lang/Boolean"), "booleanValue", "()Z"))
}

// 将结果转化为object
func convertToObject(env *C.JNIEnv, result jobject) interface{} {
    return result
}