title: Cmake cannot recognize java while building OpenCv
body: <p>I'm trying to build <strong>OpenCv</strong> on <a href="https://www.khadas.com/vim#comp-jav7nz1x" rel="nofollow noreferrer">Khadas Vim2</a>, that has a pre-installed Ubuntu Mate with an <strong>arm 64 bit</strong> based cpu architecture, using CMake. However CMake is not recognizing Java (<code>where i already have both oracle-jdk-1.8 and openjdk-1.8</code>). I tried to reinstall Apache Ant, exporting <code>JAVA_HOME</code> and <code>ANT_HOME</code> into <code>PATH</code> through:</p>
  
  <pre><code>export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-arm64
  export PATH=$JAVA_HOME/bin:$PATH
  export ANT_HOME=/usr/local/ant
  export PATH=$ANT_HOME/bin:$PATH
  </code></pre>
  
  <p>I also tried to set the GCC and G++ compilers in the toolchain file as:</p>
  
  <pre><code>set( CMAKE_SYSTEM_PROCESSOR arm )
  set( CMAKE_C_COMPILER arm-linux-gnueabi-gcc )
  set( CMAKE_CXX_COMPILER arm-linux-gnueabi-g++ )
  
      if(COMMAND toolchain_save_config)
        return() # prevent recursive call
      endif()
  
      set(CMAKE_SYSTEM_NAME Linux)
      set(CMAKE_SYSTEM_VERSION 1)
      if(NOT DEFINED CMAKE_SYSTEM_PROCESSOR)
        set(CMAKE_SYSTEM_PROCESSOR arm)
      else()
        #message("CMAKE_SYSTEM_PROCESSOR=${CMAKE_SYSTEM_PROCESSOR}")
      endif()
  
      include("${CMAKE_CURRENT_LIST_DIR}/gnu.toolchain.cmake")
  
      if(CMAKE_SYSTEM_PROCESSOR STREQUAL arm AND NOT ARM_IGNORE_FP)
        set(FLOAT_ABI_SUFFIX "")
        if(NOT SOFTFP)
          set(FLOAT_ABI_SUFFIX "hf")
        endif()
      endif()
  
      if(NOT "x${GCC_COMPILER_VERSION}" STREQUAL "x")
        set(__GCC_VER_SUFFIX "-${GCC_COMPILER_VERSION}")
      endif()
  
      if(NOT DEFINED CMAKE_C_COMPILER)
        find_program(CMAKE_C_COMPILER NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-gcc${__GCC_VER_SUFFIX})
      else()
        #message(WARNING "CMAKE_C_COMPILER=${CMAKE_C_COMPILER} is defined")
      endif()
      if(NOT DEFINED CMAKE_CXX_COMPILER)
        find_program(CMAKE_CXX_COMPILER NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-g++${__GCC_VER_SUFFIX})
      else()
        #message(WARNING "CMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER} is defined")
      endif()
      if(NOT DEFINED CMAKE_LINKER)
        find_program(CMAKE_LINKER NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ld${__GCC_VER_SUFFIX} ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ld)
      else()
        #message(WARNING "CMAKE_LINKER=${CMAKE_LINKER} is defined")
      endif()
      if(NOT DEFINED CMAKE_AR)
        find_program(CMAKE_AR NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ar${__GCC_VER_SUFFIX} ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ar)
      else()
        #message(WARNING "CMAKE_AR=${CMAKE_AR} is defined")
      endif()
  
      if(NOT DEFINED ARM_LINUX_SYSROOT AND DEFINED GNU_MACHINE)
        set(ARM_LINUX_SYSROOT /usr/${GNU_MACHINE}${FLOAT_ABI_SUFFIX})
      endif()
  
      if(NOT DEFINED CMAKE_CXX_FLAGS)
        set(CMAKE_CXX_FLAGS           "" CACHE INTERNAL "")
        set(CMAKE_C_FLAGS             "" CACHE INTERNAL "")
        set(CMAKE_SHARED_LINKER_FLAGS "" CACHE INTERNAL "")
        set(CMAKE_MODULE_LINKER_FLAGS "" CACHE INTERNAL "")
        set(CMAKE_EXE_LINKER_FLAGS    "" CACHE INTERNAL "")
  
        set(CMAKE_CXX_FLAGS           "${CMAKE_CXX_FLAGS} -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi")
        set(CMAKE_C_FLAGS             "${CMAKE_C_FLAGS} -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi")
        if(CMAKE_SYSTEM_PROCESSOR STREQUAL arm)
          set(CMAKE_CXX_FLAGS           "-mthumb ${CMAKE_CXX_FLAGS}")
          set(CMAKE_C_FLAGS             "-mthumb ${CMAKE_C_FLAGS}")
          set(CMAKE_EXE_LINKER_FLAGS    "${CMAKE_EXE_LINKER_FLAGS} -Wl,-z,nocopyreloc")
        endif()
        if(CMAKE_SYSTEM_PROCESSOR STREQUAL arm)
          set(ARM_LINKER_FLAGS "-Wl,--fix-cortex-a8 -Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now")
        elseif(CMAKE_SYSTEM_PROCESSOR STREQUAL aarch64)
          set(ARM_LINKER_FLAGS "-Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now")
        endif()
        set(CMAKE_SHARED_LINKER_FLAGS "${ARM_LINKER_FLAGS} ${CMAKE_SHARED_LINKER_FLAGS}")
        set(CMAKE_MODULE_LINKER_FLAGS "${ARM_LINKER_FLAGS} ${CMAKE_MODULE_LINKER_FLAGS}")
        set(CMAKE_EXE_LINKER_FLAGS    "${ARM_LINKER_FLAGS} ${CMAKE_EXE_LINKER_FLAGS}")
      else()
        #message(WARNING "CMAKE_CXX_FLAGS='${CMAKE_CXX_FLAGS}' is defined")
      endif()
  
      if(USE_NEON)
        message(WARNING "You use obsolete variable USE_NEON to enable NEON instruction set. Use -DENABLE_NEON=ON instead." )
        set(ENABLE_NEON TRUE)
      elseif(USE_VFPV3)
        message(WARNING "You use obsolete variable USE_VFPV3 to enable VFPV3 instruction set. Use -DENABLE_VFPV3=ON instead." )
        set(ENABLE_VFPV3 TRUE)
      endif()
  
      set(CMAKE_FIND_ROOT_PATH ${CMAKE_FIND_ROOT_PATH} ${ARM_LINUX_SYSROOT})
  
      if(EXISTS ${CUDA_TOOLKIT_ROOT_DIR})
        set(CMAKE_FIND_ROOT_PATH ${CMAKE_FIND_ROOT_PATH} ${CUDA_TOOLKIT_ROOT_DIR})
      endif()
  
      set(TOOLCHAIN_CONFIG_VARS ${TOOLCHAIN_CONFIG_VARS}
          ARM_LINUX_SYSROOT
          ENABLE_NEON
          ENABLE_VFPV3
          CUDA_TOOLKIT_ROOT_DIR
      )
      toolchain_save_config()
  </code></pre>
  
  <p>but still having the following output after running the cmake command:</p>
  
  <p><strong>Command:</strong></p>
  
  <pre><code>khadas@Khadas:~/Downloads/opencv/platforms/linux/build_hardfp$ cmake -DBUILD_SHARED_LIBRARY=OFF -DLAPACK_LIBRARIES=/usr/lib/liblapack.a -DOPENCV_EXTRA_MODULES_PATH=/home/khadas/Downloads/opencv_contrib/modules -DCMAKE_TOOLCHAIN_FILE=../arm-gnueabi.toolchain.cmake ../../..
  </code></pre>
  
  <p><strong>Output:</strong></p>
  
  <pre><code>-- General configuration for OpenCV 4.0.0-pre =====================================
  --   Version control:               3.4.3-374-g475c775-dirty
  -- 
  --   Extra modules:
  --     Location (extra):            /home/khadas/Downloads/opencv_contrib/modules
  --     Version control (extra):     3.4.3-93-g3054618
  -- 
  --   Platform:
  --     Timestamp:                   2018-09-24T09:23:39Z
  --     Host:                        Linux 4.9.40 aarch64
  --     Target:                      Linux 1 arm
  --     CMake:                       3.5.1
  --     CMake generator:             Unix Makefiles
  --     CMake build tool:            /usr/bin/make
  --     Configuration:               Release
  -- 
  --   CPU/HW features:
  --     Baseline:
  --       requested:                 DETECT
  --       disabled:                  VFPV3 NEON
  -- 
  --   C/C++:
  --     Built as dynamic libs?:      YES
  --     C++ Compiler:                /usr/bin/arm-linux-gnueabi-g++  (ver 5.4.0)
  --     C++ flags (Release):         -mthumb  -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wsuggest-override -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections  -mfp16-format=ieee -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG  -DNDEBUG
  --     C++ flags (Debug):           -mthumb  -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wsuggest-override -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections  -mfp16-format=ieee -fvisibility=hidden -fvisibility-inlines-hidden -g  -O0 -DDEBUG -D_DEBUG
  --     C Compiler:                  /usr/bin/arm-linux-gnueabi-gcc
  --     C flags (Release):           -mthumb  -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-narrowing -Wno-comment -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections  -mfp16-format=ieee -fvisibility=hidden -O3 -DNDEBUG  -DNDEBUG
  --     C flags (Debug):             -mthumb  -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-narrowing -Wno-comment -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections  -mfp16-format=ieee -fvisibility=hidden -g  -O0 -DDEBUG -D_DEBUG
  --     Linker flags (Release):      -Wl,--fix-cortex-a8 -Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now    
  --     Linker flags (Debug):        -Wl,--fix-cortex-a8 -Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now    
  --     ccache:                      NO
  --     Precompiled headers:         NO
  --     Extra dependencies:          dl m pthread rt
  --     3rdparty dependencies:
  -- 
  --   OpenCV modules:
  --     To be built:                 aruco bgsegm bioinspired calib3d ccalib core datasets dnn dnn_objdetect dpm face features2d flann fuzzy hfs highgui img_hash imgcodecs imgproc java_bindings_generator line_descriptor ml objdetect optflow phase_unwrapping photo plot python_bindings_generator reg rgbd saliency shape stereo stitching structured_light superres surface_matching text tracking ts video videoio videostab xfeatures2d ximgproc xobjdetect xphoto
  --     Disabled:                    js world
  --     Disabled by dependency:      -
  --     Unavailable:                 cnn_3dobj cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev cvv freetype hdf java matlab ovis python2 python3 sfm viz
  --     Applications:                tests perf_tests apps
  --     Documentation:               NO
  --     Non-free algorithms:         NO
  -- 
  --   GUI: 
  --     GTK+:                        NO
  -- 
  --   Media I/O: 
  --     ZLib:                        build (ver 1.2.11)
  --     JPEG:                        libjpeg-turbo (ver 1.5.3-62)
  --     WEBP:                        build (ver encoder: 0x020e)
  --     PNG:                         build (ver 1.6.34)
  --     TIFF:                        build (ver 42 - 4.0.9)
  --     JPEG 2000:                   build (ver 1.900.1)
  --     OpenEXR:                     build (ver 1.7.1)
  --     HDR:                         YES
  --     SUNRASTER:                   YES
  --     PXM:                         YES
  --     PFM:                         YES
  -- 
  --   Video I/O:
  --     DC1394:                      NO
  --     FFMPEG:                      NO
  --       avcodec:                   NO
  --       avformat:                  NO
  --       avutil:                    NO
  --       swscale:                   NO
  --       avresample:                NO
  --     GStreamer:                   NO
  --     libv4l/libv4l2:              NO
  --     v4l/v4l2:                    linux/videodev2.h
  -- 
  --   Parallel framework:            pthreads
  -- 
  --   Trace:                         YES (built-in)
  -- 
  --   Other third-party libraries:
  --     Lapack:                      NO
  --     Custom HAL:                  YES (carotene (ver 0.0.1))
  --     Protobuf:                    build (3.5.1)
  -- 
  --   OpenCL:                        YES (no extra features)
  --     Include path:                /home/khadas/Downloads/opencv/3rdparty/include/opencl/1.2
  --     Link libraries:              Dynamic load
  -- 
  --   Python (for build):            /usr/bin/python2.7
  -- 
  --   Install to:                    /home/khadas/Downloads/opencv/platforms/linux/build_hardfp/install
  -- -----------------------------------------------------------------
  -- 
  -- Configuring done
  -- Generating done
  </code></pre>
  
  <p>Please consider the following line in the output under <strong>Opencv Models</strong>:</p>
  
  <pre><code>--     Unavailable:                 cnn_3dobj cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev cvv freetype hdf java matlab ovis python2 python3 sfm viz
  </code></pre>
  
  <p><strong><em>Thanks in advance!!</em></strong></p>