Add javadoc plugin.

Author: caojie09

pom.xml

@@ -245,6 +245,19 @@
 			<id>release</id>
 			<build>
 				<plugins>
+					<plugin>
+						<groupId>org.apache.maven.plugins</groupId>
+						<artifactId>maven-javadoc-plugin</artifactId>
+						<version>2.9.1</version>
+						<executions>
+							<execution>
+								<id>attach-javadocs</id>
+								<goals>
+									<goal>jar</goal>
+								</goals>
+							</execution>
+						</executions>
+					</plugin>
 					<plugin>
 						<groupId>org.sonatype.plugins</groupId>
 						<artifactId>nexus-staging-maven-plugin</artifactId>