Do not use custom FindJNI.cmake, do not require JDK_11 env variable

Author: VladRassokhin

CMakeLists.txt

@@ -14,8 +14,10 @@ if (WIN32 AND (NOT MINGW) AND (NOT CYGWIN))
     set(CMAKE_CXX_FLAGS_MINSIZEREL "/MT")
 endif ()
 
-list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
-find_package(JNI11)
+find_package(Java 11 REQUIRED COMPONENTS Development)
+include(${CMAKE_CURRENT_LIST_DIR}/SetJavaHomeFromJavaExecutable.cmake)
+find_package(JNI REQUIRED)
+
 include_directories(${JNI_INCLUDE_DIRS})
 
 add_library(memory_agent SHARED

CONTRIBUTING.md

@@ -1,8 +1,10 @@
 # Contributing guide for debugger memory agent
+
+## Prerequisites
+To build the project you should have CMake 3.1 or higher installed, and JDK 11 or higher is installed.
+
 ## Building
-To build the project you should have Cmake 3.1 or higher installed, and `JDK_11` 
-environmental variable should be set to jdk 11 or higher. Once you've downloaded the project, 
-you can build it using the following commands in the root project directory:
+Once you've downloaded the project, you can build it using the following commands in the root project directory:
 ```
 cmake .
 cmake --build .

FindJNI11.cmake

@@ -0,0 +1,20 @@
+if(NOT Java_JAVA_EXECUTABLE)
+    message(FATAL_ERROR "java executable not found")
+endif()
+execute_process(COMMAND "${Java_JAVA_EXECUTABLE}" -XshowSettings:properties -version
+        RESULT_VARIABLE res
+        OUTPUT_VARIABLE var
+        ERROR_VARIABLE var
+        OUTPUT_STRIP_TRAILING_WHITESPACE
+        ERROR_STRIP_TRAILING_WHITESPACE)
+if(res)
+    message(FATAL_ERROR "Error executing java -version")
+else()
+    set(_java_version_regex "java\\.home = ([^\n]+)")
+    if(var MATCHES "${_java_version_regex}")
+        set(JAVA_HOME "${CMAKE_MATCH_1}")
+    else()
+        string(REPLACE "\n" "\n  " ver_msg "\n${var}")
+        message(FATAL_ERROR "Java output not recognized:${ver_msg}\nPlease report.")
+    endif()
+endif()