Dependency for add_jar cmake - cmake

Question

I am actually generating java source files dynamically through code generators. I want to create jar file containing the java files created through this code generator.
add_custom_target(lang ALL)
add_custom_command(
TARGET lang
COMMAND ${Protobuf_PROTOC_EXECUTABLE} ${CMD_PRG_LNG} --proto_path=${PROTO_FILES} ${COMMONS}/*.proto")
If I run my cmake without add_jar command, it successfully run and generate java files in the respective folders. But, if I add add_jar
add_jar(${JAR_NAME} ${JAVA_SOURCES})
The above instruction fails with the following error message.
Scanning dependencies of target ProtoJava
make[2]: *** No rule to make target '../protoJava/Data.java', needed by 'CMakeFiles/ProtoJava.dir/java_compiled_ProtoJava'. Stop.
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/ProtoJava.dir/all' failed
make[1]: *** [CMakeFiles/ProtoJava.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
How to get the jar file created? I tried putting add_jar inside add_custom_command under the same target as java file creation.
add_custom_command(
TARGET lang_java
COMMAND add_jar(${JAR_NAME} ${JAVA_SOURCES}))
but it errors out with message
/bin/sh: 1: Syntax error: word unexpected (expecting ")")
CMakeFiles/lang_java.dir/build.make:57: recipe for target 'lang_java' failed
make[2]: *** [lang_java] Error 2
CMakeFiles/Makefile2:104: recipe for target 'CMakeFiles/lang_java.dir/all' failed
make[1]: *** [CMakeFiles/lang_java.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
How to fix this one?