No dhtreader in java.library.path

Question

I try to get this maven projekt to run on the Raspberry Pi 3 but the DHT11 sensor gives me the following error:

sudo java -classpath '.:classes:*:classes:/opt/pi4j/lib/*' com.epam.llpd.greenhouse.web.ServerStarter

java.lang.UnsatisfiedLinkError: no dhtreader in java.library.path
    at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1864)
    at java.lang.Runtime.loadLibrary0(Runtime.java:870)
    at java.lang.System.loadLibrary(System.java:1122)
    at com.epam.llpd.greenhouse.sensor.Sensor.<clinit>(Sensor.java:16)
    at com.epam.llpd.greenhouse.PiHardwareController$1.run(PiHardwareController.java:132)

In the folder \\src\\main\\java\\com\\epam\\llpd\\greenhouse\\sensor there is the dhtreader.c file.

I did compile a binary objekt with the following command:

gcc -o dhtreader.so -lc -shared -I/usr/lib/jvm/jdk-7-oracle-arm-vfp-hflt/include -I/usr/lib/jvm/jdk-7-oracle-arm-vfp-hflt/include/linux dhtreader.c -l bcm2835

The dhtreader.so is placed in the same folder as the .jar .

The dhtreader.c file is a common C class specific for the Raspberry Pi to use the DHT11 and DHT22 sensor and it is used in many Raspberry Pi projects and has alot of sources like this one .

This C class (dhtreader.c) is used via. JNI/C but it just doesn't work because of the error above.

I allready tried to set the java.library.path with the following method in the java main:

System.setProperty("java.library.path", "./");

That didn't help. Instead i added -Djava.library.path=./ to the java command:

sudo java -classpath '.:classes:*:classes:/opt/pi4j/lib/*' com.epam.llpd.greenhouse.web.ServerStarter -Djava.library.path=./

But that didn't help neither.

Now i'm stuck and don't know how to add the dhtreader.so to the java.library.path .

How do i add the dhtreader.so to the java.library.path ?

I asked in the Raspberry Pi StackExchange first but they thought that it's off-topic.

Answer 1

Try to simply rename dhtreader.so to libdhtreader.so .

Indeed when we call System.loadLibrary("foo") in java the expected name of the library is:

• Windows: foo.dll
• Unix/Linux: libfoo.so
• Mac: libfoo.jnilib

Try to launch it as next:

sudo java -Djava.library.path=./lib -classpath '.:classes:*:classes:/opt/pi4j/lib/*' com.epam.llpd.greenhouse.web.ServerStarter

NB: The command above assumes that your lib is located in the lib directory that is itself located in the directory where the command has been launched.