# 通过 JAVA_HOME环境变量定位 jni.h和jni_md.h
if(NOT DEFINED ENV{JAVA_HOME})
    # 没有找到JAVA_HOME环境变量，输出错误信息退出
    message(FATAL_ERROR "not defined environment variable:JAVA_HOME")  
endif()
set(JNI_INCLUDE "$ENV{JAVA_HOME}/include")
# jni.h的位置加入搜索路径
include_directories(${JNI_INCLUDE})
# 判断操作系统,添加jni_md.h搜索路径
if(WIN32)
    #win32系统下`jni_md.h`位于`<jni_h_dir>/win32`下
    include_directories("${JNI_INCLUDE}/win32")
elseif(CMAKE_SYSTEM_NAME MATCHES "Linux")
    #linux系统下`jni_md.h`位于`<jni_h_dir>/linux`下
    include_directories("${JNI_INCLUDE}/linux")
else()
    # 不支持的操作系统报错退出
    message(FATAL_ERROR "other unsupported platform: ${CMAKE_SYSTEM_NAME}")  
endif(CMAKE_SYSTEM_NAME MATCHES "Windows")

FindJNI
Find JNI java libraries.

This module finds if Java is installed and determines where the include files and libraries are. It also determines what the name of the library is. The caller may set variable JAVA_HOME to specify a Java installation prefix explicitly.

This module sets the following result variables:

JNI_INCLUDE_DIRS      = the include dirs to use
JNI_LIBRARIES         = the libraries to use
JNI_FOUND             = TRUE if JNI headers and libraries were found.
JAVA_AWT_LIBRARY      = the path to the jawt library
JAVA_JVM_LIBRARY      = the path to the jvm library
JAVA_INCLUDE_PATH     = the include path to jni.h
JAVA_INCLUDE_PATH2    = the include path to jni_md.h
JAVA_AWT_INCLUDE_PATH = the include path to jawt.h

# 加入REQUIRED 参数,如果找不到JNI,就报错退出
find_package(JNI REQUIRED)
# 加入jni支持
include_directories(${JAVA_INCLUDE_PATH})
include_directories(${JAVA_INCLUDE_PATH2})