[rosjava bootstrap warning]What I should do to solve this warning?

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I installed ROS on Raspberry Pi 3. http://wiki.ros.org/rosjava/Tutorials... I did this tutorial [3.1]. When I do [catkin_make],

[ 90%] Built target rosjava_test_msgs_generate_messages_eus
Could not find metadata org.ros.rosjava_bootstrap:gradle_plugins/maven-metadata.xml in remote (file:/home/ubuntu/rosjava/devel/share/maven/)
warning: [options] bootstrap class path not set in conjunction with -source 1.6
Note: /home/ubuntu/rosjava/src/rosjava_bootstrap/message_generation/src/main/java/org/ros/internal/message/MessageImpl.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
1 warning
warning: [options] bootstrap class path not set in conjunction with -source 1.7
Could not find metadata org.ros.rosjava_bootstrap:message_generation/maven-metadata.xml in remote (file:/home/ubuntu/rosjava/devel/share/maven/)
1 warning
Uploading: org/ros/rosjava_messages/std_msgs/0.5.11/std_msgs-0.5.11.jar to repository remote at file:/home/ubuntu/rosjava/devel/share/maven/
Transferring 15K from remote
Uploaded 15K
[ 90%] Built target gradle-rosjava_bootstrap
Scanning dependencies of target gradle-zeroconf_jmdns_suite
Scanning dependencies of target rosjava_test_msgs_generate_messages_java_gradle
[ 92%] Gradling tasks for zeroconf_jmdns_suite
[ 94%] Compiling Java code for rosjava_test_msgs
warning: [options] bootstrap class path not set in conjunction with -source 1.7
1 warning
Uploading: org/ros/rosjava_messages/actionlib_msgs/1.12.5/actionlib_msgs-1.12.5.jar to repository remote at file:/home/ubuntu/rosjava/devel/share/maven/
Transferring 3K from remote
Uploaded 3K
warning: [options] bootstrap class path not set in conjunction with -source 1.7
1 warning
Uploading: org/ros/rosjava_messages/diagnostic_msgs/1.12.5/diagnostic_msgs-1.12.5.jar to repository remote at file:/home/ubuntu/rosjava/devel/share/maven/
Transferring 6K from remote
Uploaded 6K
warning: [options] bootstrap class path not set in conjunction with -source 1.7
warning: [options] bootstrap class path not set in conjunction with -source 1.7
1 warning
1 warning
Uploading: org/ros/rosjava_messages/gateway_msgs/0.9.0/gateway_msgs-0.9.0.jar to repository remote at file:/home/ubuntu/rosjava/devel/share/maven/
Transferring 18K from remote
Uploaded 18K
warning: [options] bootstrap class path not set in conjunction with -source 1.7
Uploading: org/ros/rosjava_messages/rosjava_test_msgs/0.3.0/rosjava_test_msgs-0.3.0.jar to repository remote at file:/home/ubuntu/rosjava/devel/share/maven/
Transferring 6K from remote
Uploaded 6K
[ 96%] Built target rosjava_test_msgs_generate_messages_java_gradle
Scanning dependencies of target rosjava_test_msgs_generate_messages
[ 96%] Built target rosjava_test_msgs_generate_messages
Scanning dependencies of target gradle-rosjava_core
[ 98%] Gradling tasks for rosjava_core
warning: [options] bootstrap class path not set in conjunction with -source 1.7
1 warning
Uploading: org/ros/rosjava_messages/geometry_msgs/1.12.5/geometry_msgs-1.12.5.jar to repository remote at file:/home/ubuntu/rosjava/devel/share/maven/
Transferring 15K from remote
Uploaded 15K
1 warning
warning: [options] bootstrap class path not set in conjunction with -source 1.7
1 warning
Could not find metadata com.github.rosjava.zeroconf_jmdns_suite:jmdns/maven-metadata.xml in remote (file:/home/ubuntu/rosjava/devel/share/maven/)
Uploading: org/ros/rosjava_messages/ar_track_alvar_msgs/0.7.1/ar_track_alvar_msgs-0.7.1.jar to ...