Why doesn't java respect the classpath when executing a jar file with the -jar switch?
It works:
$ java -cp ".:/PATH/TO/RXTXcomm.jar:./jobexftp.jar" -Djava.library.path=/usr/lib/jni com.lhf.jobexftp.StandAloneApp
JObexFTP 2.0 beta (15/10/2010)
Java Obex File Transfer Protocol application and library
Developed under/using 100% free software.
For more information access: http://www.lhf.ind.br/jobexftp/
Usage: jobexftp <serialPort> [<commands>] [<options>]
...
It does not mean:
$ java -cp ".:/PATH/TO/RXTXcomm.jar" -Djava.library.path=/usr/lib/jni -jar jobexftp.jar
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.NoClassDefFoundError: gnu/io/NoSuchPortException
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
I found the name of the class to execute (for the first example) in the META-INF / MANIFEST.MF file inside the jar:
Main-Class: com.lhf.jobexftp.StandAloneApp
Why does executing the jar file using the -jar switch seem to cause Java to ignore the classpath and cannot find the class gnu/io/NoSuchPortException
in RXTXcomm.jar?
On an older machine running Java 1.6, I can execute the jar file without requiring the classpath. How it works?
$ env | grep CLASS
$ env | grep JAVA
$ java -jar jobexftp.jar
JObexFTP 2.0 beta (15/10/2010)
Java Obex File Transfer Protocol application and library
Developed under/using 100% free software.
For more information access: http://www.lhf.ind.br/jobexftp/
Usage: jobexftp <serialPort> [<commands>] [<options>]
...
The reason it worked on the old machine is because it had a copy of RXTXcomm.jar in / usr / lib / jvm / java -6-sun-1.6.0.21 / jre / lib / ext /.
$ ls -lA /usr/lib/jvm/java-6-sun-1.6.0.21/jre/lib/ext/RXTXcomm.jar
-rwxr-xr-x 1 root root 137764 2011-02-17 16:58 /usr/lib/jvm/java-6-sun-1.6.0.21/jre/lib/ext/RXTXcomm.jar
Creating a new directory ext
in / usr / lib / jvm / java -8-oracle / jre and copying RXTXcomm.jar
to it will not get rid of the error in Java 1.8.
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The switch is -jar
designed to run the bank as an independent program. As stated in the man page java
:
When you use the parameter
-jar
, the specified JAR file is the source of all custom classes, and other classpath parameters are ignored.
To provide a classpath, use an entry Class-Path
in your manifest file.
Further Reading: The Java ™ Tutorials: Adding Classes to the JAR Classpath
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