hello-jni

Beginner guide to Java Native Interface (JNI), is a framework that provides a bridge between Java and native applications

Steps

1. Simple c/cpp program

Create a "c" or "cpp" program file

• ex: MessagePrinter.cpp
• compile the program

gcc MessagePrinter.cpp -o printer
./printer

• This program will print "Hello World" as output

2. Simple java program (template)

Create a "java" program file

• ex: MessagePrinter.java
• compile the program

javac MessagePrinter.java

• generate c headers

javah MessagePrinter

• This will output MessagePrinter.h in the same directory

3. Create a shared lib

Create a new cpp program with jni header

• ex: MessagePrinter2.cpp
• Now we can create "shared lib"
• For linux:

gcc -fPIC -I/usr/lib/jvm/java-1.8.0-openjdk-amd64/include/ -I/usr/lib/jvm/java-1.8.0-openjdk-amd64/include/linux -shared -o libprinter.so MessagePrinter2.cpp

• This will output libprinter.so in the same directory

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• For MacOS

gcc -fPIC -I/Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/include/ -I/Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/include/darwin/ -shared -o libprinter.dylib MessagePrinter2.cpp

• This will output libprinter.dylib in the same directory

4. Access the shared lib inside java program (client)

Create a java program

• ex: TestClient.java
• compile the program

javac TestClient.java 

• run the program

java -Djava.library.path=. TestClient

• You will get the output as "HelloWorld!"

References

1. https://www3.ntu.edu.sg/home/ehchua/programming/java/JavaNativeInterface.html
2. https://stackoverflow.com/a/8459911/5739971