# FindJNI

Finds the Java Native Interface (JNI) include directories and libraries.

JNI enables Java code running in a Java Virtual Machine (JVM) or Dalvik Virtual Machine (DVM) on Android to call and be called by native applications and libraries written in other languages such as C and C++.

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.

Added in version 3.24: Imported targets, components, and Android NDK support.

When using Android NDK, the corresponding package version is reported and a specific release can be requested. At Android API level 31 and above, the additional `NativeHelper` component can be requested. `NativeHelper` is also exposed as an implicit dependency of the `JVM` component (only if this does not cause a conflict) which provides a uniform access to JVM functions.

## Components

This module supports optional components, which can be specified with the `find_package()` command:

    find_package(JNI [COMPONENTS <components>...])

Supported components include:

`AWT`

  Added in version 3.24.

  Finds the Java Abstract Window Toolkit (AWT).

`JVM`

  Added in version 3.24.

  Finds the Java Virtual Machine (JVM).

`NativeHelper`

  Added in version 3.24.

  Finds the NativeHelper library on Android (`libnativehelper.so`), which exposes JVM functions such as `JNI_CreateJavaVM()`.

If no components are specified, the module defaults are:

- When targeting Android with API level 31 and above: module looks for the `NativeHelper` component. For other Android API levels, components are by default not set.

- When targeting other systems: module looks for `AWT` and `JVM` components.

## Imported Targets

This module provides the following Imported Targets:

`JNI::JNI`

  Added in version 3.24.

  Main target encapsulating all JNI usage requirements, available if `jni.h` is found.

`JNI::AWT`

  Added in version 3.24.

  Target encapsulating the Java AWT Native Interface (JAWT) library usage requirements, available if the `AWT` component is found.

`JNI::JVM`

  Added in version 3.24.

  Target encapsulating the Java Virtual Machine (JVM) library usage requirements, available if component `JVM` is found.

`JNI::NativeHelper`

  Added in version 3.24.

  Target encapsulating the NativeHelper library usage requirements, available when targeting Android API level 31 and above, and the library is found.

## Result Variables

This module defines the following variables:

`JNI_FOUND`

  Boolean indicating whether the JNI is found.

`JNI_<component>_FOUND`

  Added in version 3.24.

  Boolean indicating whether the `<component>` is found.

`JNI_VERSION`

  Full Android NDK package version (including suffixes such as `-beta3` and `-rc1`) or undefined otherwise.

`JNI_VERSION_MAJOR`

  Added in version 3.24.

  Android NDK major version or undefined otherwise.

`JNI_VERSION_MINOR`

  Added in version 3.24.

  Android NDK minor version or undefined otherwise.

`JNI_VERSION_PATCH`

  Added in version 3.24.

  Android NDK patch version or undefined otherwise.

`JNI_INCLUDE_DIRS`

  The include directories needed to use the JNI.

`JNI_LIBRARIES`

  The libraries (JAWT and JVM) needed to link against to use JNI.

## Cache Variables

The following cache variables are also available to set or use:

`JAVA_INCLUDE_PATH`

  The directory containing the `jni.h` header.

`JAVA_INCLUDE_PATH2`

  The directory containing machine-dependent headers `jni_md.h` and `jniport.h`. This variable is defined only if `jni.h` depends on one of these headers. In contrast, Android NDK `jni.h` can be typically used standalone.

`JAVA_AWT_INCLUDE_PATH`

  The directory containing the `jawt.h` header.

`JAVA_AWT_LIBRARY`

  The path to the Java AWT Native Interface (JAWT) library.

`JAVA_JVM_LIBRARY`

  The path to the Java Virtual Machine (JVM) library.

## Hints

This module accepts the following variables:

`JAVA_HOME`

  The caller can set this variable to specify the installation directory of Java explicitly.

## Examples

Finding JNI and linking it to a project target:

    find_package(JNI)
    target_link_libraries(project_target PRIVATE JNI::JNI)

Finding JNI with AWT component specified and linking them to a project target:

    find_package(JNI COMPONENTS AWT)
    target_link_libraries(project_target PRIVATE JNI::JNI JNI::AWT)

A more common way to use Java and JNI in CMake is to use a dedicated `UseJava` module:

    find_package(Java)
    find_package(JNI)
    include(UseJava)

## See Also

- The `FindJava` module to find Java runtime tools and development components.

- The `UseJava` module to use Java in CMake.