Android Studio NDK编译protobuf库
1.在Android studio 里面有plugin 可以直接配置使用protobuf，但是如果想要在jni里面的c++上使用，就需要自己编译了。
2. 编译环境：Win10，Android studio 4.0.1
a.先去下载protobuf 源码：https://github.com/protocolbuffers/protobuf
b.将解压后的src下面的Google文件夹直接复制到jni下面去。
c.在Android.mk里面添加如下代码：
include $(CLEAR_VARS)
LOCAL_MODULE := protobuf
LOCAL_SRC_FILES := ../google/protobuf/stubs/bytestream.cc \
../google/protobuf/stubs/bytestream.h \
../google/protobuf/stubs/common.cc \
../google/protobuf/stubs/hash.h \
../google/protobuf/stubs/int128.cc \
../google/protobuf/stubs/int128.h \
../google/protobuf/io/io_win32.cc \
../google/protobuf/stubs/map_util.h \
../google/protobuf/stubs/mathutil.h \
../google/protobuf/stubs/status.cc \
../google/protobuf/stubs/status.h \
../google/protobuf/stubs/status_macros.h \
../google/protobuf/stubs/statusor.cc \
../google/protobuf/stubs/statusor.h \
../google/protobuf/stubs/stringpiece.cc \
../google/protobuf/stubs/stringpiece.h \
../google/protobuf/stubs/stringprintf.cc \
../google/protobuf/stubs/stringprintf.h \
../google/protobuf/stubs/structurally_valid.cc \
../google/protobuf/stubs/strutil.cc \
../google/protobuf/stubs/time.cc \
../google/protobuf/stubs/time.h \
../google/protobuf/any_lite.cc \
../google/protobuf/arena.cc \
../google/protobuf/arenastring.cc \
../google/protobuf/extension_set.cc \
../google/protobuf/generated_enum_util.cc \
../google/protobuf/generated_message_util.cc \
../google/protobuf/generated_message_table_driven_lite.h \
../google/protobuf/generated_message_table_driven_lite.cc \
../google/protobuf/implicit_weak_message.cc \
../google/protobuf/map.cc \
../google/protobuf/message_lite.cc \
../google/protobuf/parse_context.cc \
../google/protobuf/repeated_field.cc \
../google/protobuf/wire_format_lite.cc \
../google/protobuf/io/coded_stream.cc \
../google/protobuf/io/strtod.cc \
../google/protobuf/io/zero_copy_stream.cc \
../google/protobuf/io/zero_copy_stream_impl.cc \
../google/protobuf/io/zero_copy_stream_impl_lite.cc \
../google/protobuf/any.pb.cc \
../google/protobuf/api.pb.cc \
../google/protobuf/any.cc \
../google/protobuf/descriptor.cc \
../google/protobuf/descriptor_database.cc \
../google/protobuf/descriptor.pb.cc \
../google/protobuf/duration.pb.cc \
../google/protobuf/dynamic_message.cc \
../google/protobuf/empty.pb.cc \
../google/protobuf/extension_set_heavy.cc \
../google/protobuf/field_mask.pb.cc \
../google/protobuf/generated_message_reflection.cc \
../google/protobuf/generated_message_table_driven_lite.h \
../google/protobuf/generated_message_table_driven.cc \
../google/protobuf/map_field.cc \
../google/protobuf/message.cc \
../google/protobuf/reflection_internal.h \
../google/protobuf/reflection_ops.cc \
../google/protobuf/service.cc \
../google/protobuf/source_context.pb.cc \
../google/protobuf/struct.pb.cc \
../google/protobuf/stubs/substitute.cc \
../google/protobuf/stubs/substitute.h \
../google/protobuf/text_format.cc \
../google/protobuf/timestamp.pb.cc \
../google/protobuf/type.pb.cc \
../google/protobuf/unknown_field_set.cc \
../google/protobuf/wire_format.cc \
../google/protobuf/wrappers.pb.cc \
../google/protobuf/io/gzip_stream.cc \
../google/protobuf/io/printer.cc \
../google/protobuf/io/tokenizer.cc \
../google/protobuf/compiler/importer.cc \
../google/protobuf/compiler/parser.cc \
../google/protobuf/util/delimited_message_util.cc \
../google/protobuf/util/field_comparator.cc \
../google/protobuf/util/field_mask_util.cc \
../google/protobuf/util/internal/constants.h \
../google/protobuf/util/internal/datapiece.cc \
../google/protobuf/util/internal/datapiece.h \
../google/protobuf/util/internal/default_value_objectwriter.cc \
../google/protobuf/util/internal/default_value_objectwriter.h \
../google/protobuf/util/internal/error_listener.cc \
../google/protobuf/util/internal/error_listener.h \
../google/protobuf/util/internal/expecting_objectwriter.h \
../google/protobuf/util/internal/field_mask_utility.cc \
../google/protobuf/util/internal/field_mask_utility.h \
../google/protobuf/util/internal/json_escaping.cc \
../google/protobuf/util/internal/json_escaping.h \
../google/protobuf/util/internal/json_objectwriter.cc \
../google/protobuf/util/internal/json_objectwriter.h \
../google/protobuf/util/internal/json_stream_parser.cc \
../google/protobuf/util/internal/json_stream_parser.h \
../google/protobuf/util/internal/location_tracker.h \
../google/protobuf/util/internal/mock_error_listener.h \
../google/protobuf/util/internal/object_location_tracker.h \
../google/protobuf/util/internal/object_source.h \
../google/protobuf/util/internal/object_writer.cc \
../google/protobuf/util/internal/object_writer.h \
../google/protobuf/util/internal/protostream_objectsource.cc \
../google/protobuf/util/internal/protostream_objectsource.h \
../google/protobuf/util/internal/protostream_objectwriter.cc \
../google/protobuf/util/internal/protostream_objectwriter.h \
../google/protobuf/util/internal/proto_writer.cc \
../google/protobuf/util/internal/proto_writer.h \
../google/protobuf/util/internal/structured_objectwriter.h \
../google/protobuf/util/internal/type_info.cc \
../google/protobuf/util/internal/type_info.h \
../google/protobuf/util/internal/type_info_test_helper.cc \
../google/protobuf/util/internal/type_info_test_helper.h \
../google/protobuf/util/internal/utility.cc \
../google/protobuf/util/internal/utility.h \
../google/protobuf/util/json_util.cc \
../google/protobuf/util/message_differencer.cc \
../google/protobuf/util/time_util.cc \
../google/protobuf/util/type_resolver_util.cc
LOCAL_C_INCLUDES := 下载的目录/src
include $(BUILD_SHARED_LIBRARY)上面的../google是因为我的Android.mk不在jni目录下面，如果是在jni下面 就去掉前面的../ 路径这东西 大家应该都懂。
上面编译的是3.14.x版本
但如果用的是3.0.x版本的话 文件就要修改如下：
LOCAL_SRC_FILES := ../google/protobuf/stubs/atomicops_internals_x86_gcc.cc \
../google/protobuf/stubs/atomicops_internals_x86_msvc.cc \
../google/protobuf/stubs/bytestream.cc \
../google/protobuf/stubs/bytestream.h \
../google/protobuf/stubs/common.cc \
../google/protobuf/stubs/hash.h \
../google/protobuf/stubs/int128.cc \
../google/protobuf/stubs/int128.h \
../google/protobuf/stubs/mathutil.h \
../google/protobuf/stubs/once.cc \
../google/protobuf/stubs/shared_ptr.h \
../google/protobuf/stubs/status.cc \
../google/protobuf/stubs/status.h \
../google/protobuf/stubs/status_macros.h \
../google/protobuf/stubs/statusor.cc \
../google/protobuf/stubs/statusor.h \
../google/protobuf/stubs/stringpiece.cc \
../google/protobuf/stubs/stringpiece.h \
../google/protobuf/stubs/stringprintf.cc \
../google/protobuf/stubs/stringprintf.h \
../google/protobuf/stubs/structurally_valid.cc \
../google/protobuf/stubs/strutil.cc \
../google/protobuf/stubs/strutil.h \
../google/protobuf/stubs/time.cc \
../google/protobuf/stubs/time.h \
../google/protobuf/arena.cc \
../google/protobuf/arenastring.cc \
../google/protobuf/extension_set.cc \
../google/protobuf/generated_message_util.cc \
../google/protobuf/message_lite.cc \
../google/protobuf/repeated_field.cc \
../google/protobuf/wire_format_lite.cc \
../google/protobuf/io/coded_stream.cc \
../google/protobuf/io/coded_stream_inl.h \
../google/protobuf/io/zero_copy_stream.cc \
../google/protobuf/io/zero_copy_stream_impl_lite.cc