Question

I am trying to run an application that reads and writes to the amazon dynamo DB. I downloaded the Eclipse toolkit and AWS SDK and if I run the application from my local PC it works perfectly. Next, I exported it to a jar file and uploaded it to my EC2 instance. However, when I run it there I get an error.

  /home/apps/java/database/bin$ java -jar myJar.jar
Exception in thread "main" java.lang.NoClassDefFoundError: com/amazonaws/auth/AW                                                                  SCredentials
Caused by: java.lang.ClassNotFoundException: com.amazonaws.auth.AWSCredentials
        at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: DynamoDB. Program will exit.

I assume it has to do with the classpath, but in /home/ubuntu/.bashrc I have set it as such:

CLASSPATH="./:/home/apps/java/database/bin/*:/home/apps/java/database/bin/aws-java-sdk-1.3.12.jar"
export CLASSPATH

/home/apps/java/database/bin contains all the .jar files that are in the AWS SDK:

• aspectjrt.jar
• aspectjweaver.jar
• aws-java-sdk-1.3.12.jar
• aws-java-sdk-1.3.12-javadoc.jar
• aws-java-sdk-1.3.12-sources.jar
• aws-java-sdk-flow-build-tools-1.3.12.jar
• commons-codec-1.3.jar
• commons-logging-1.1.1.jar
• freemarker-2.3.18.jar
• httpclient-4.1.1.jar
• httpcore-4.1.jar
• jackson-core-asl-1.8.7.jar
• jackson-mapper-asl-1.8.7.jar
• mail-1.4.3.jar
• myJar.jar
• spring-beans-3.0.7.jar
• spring-context-3.0.7.jar
• spring-core-3.0.7.jar
• stax-1.2.0.jar
• stax-api-1.0.1.jar

What am I missing?? I have been looking at this for a day and a half. Thank you in advance!!

Answer 1

The classpath entry of “/directory/*” may be messing things up. Classpaths are separated with colons, but asterisk expansion gives spaces. Try this little shell script to start it.

#!/bin/sh
JAVA_OPTS="-Xms256M -Xmx4G"
CP=`find /home/apps/java/database/bin/*jar -exec echo -n "{}:" \;`
java -cp ${CP%?} -jar yourjar.jar

A couple of notes:

• the JAVA_OPTS is only there as a reminder that you may need more memory than the default.
• the crazy syntax for CP on the final line strips the last character, since the “find” line is leaving a colon on the end.
• You may want to include your jar and launch the correct class if it isn’t an executable jar.

Hope this helps!