Figureout requirements by api and jdk and other dependecies

[romani]

Sonar 4.5.4 - jdk 1.6 munimum
Sonar 5.6 - jdk 1.8 minimum

Checkstyle 7.X - jdk 1.8 minimum

Checkstyle-sonar-plugin 3.1 is using 4.5.2 ( https://github.com/checkstyle/sonar-checkstyle/blob/master/pom.xml#L89 ) api but require jdk 1.8

What for we depend on sonar-java-plugin ?
https://github.com/checkstyle/sonar-checkstyle/blob/master/checkstyle-sonar-plugin/pom.xml#L52
This also need to be declared to user.

All test dependencies should be grouped at the end.

As we depend on sonar and checkstyle, we should depend on this two version. If some other dependencies have diffrent version that are provided by sonar, we should make comment on this.

http://www.sonarqube.org/sonar-ecosystem-upgrades-to-java-8/
http://checkstyle.sourceforge.net/releasenotes.html#Release_7.0
http://www.sonarqube.org/downloads/

[romani]

$ mvn clean package
$ unzip checkstyle-sonar-plugin/target/checkstyle-sonar-plugin-3.2-SNAPSHOT.jar -d checkstyle-sonar-plugin/target/
$ file checkstyle-sonar-plugin/target/org/sonar/plugins/checkstyle/CheckstyleExecutor.class 
checkstyle-sonar-plugin/target/org/sonar/plugins/checkstyle/CheckstyleExecutor.class: compiled Java class data, version 51.0 (Java 1.7)
$ javap -v checkstyle-sonar-plugin/target/org/sonar/plugins/checkstyle/CheckstyleExecutor.class | grep major
  major version: 51

but checkstyle is jdk 8 !!!

~/java/github/checkstyle/checkstyle
$ unzip target/checkstyle-7.4-SNAPSHOT.jar -d target
$ javap -v target/com/puppycrawl/tools/checkstyle/Checker.class | grep major
  major version: 52
$ file target/com/puppycrawl/tools/checkstyle/Checker.class
target/com/puppycrawl/tools/checkstyle/Checker.class: compiled Java class data, version 52.0 (Java 1.8)

shaded checkstyle is also jdk 8:

~/java/github/checkstyle/sonar-checkstyle
$ unzip checkstyle-all/target/checkstyle-all-3.2-SNAPSHOT-shaded.jar -d checkstyle-all/target/
$ file checkstyle-all/target/com/puppycrawl/tools/checkstyle/Checker.class 
checkstyle-all/target/com/puppycrawl/tools/checkstyle/Checker.class: compiled Java class data, version 52.0 (Java 1.8)

So we have mix of java versions in our plugin. We should upgrade to jdk8.

[romani]

What for we depend on sonar-java-plugin ?

moved to #40

[romani]

all required investigation was done.
README.md was updated with mapping to jdk.

All other dependencies are embedded to result plugin jar as inner jar dependencies, so they are not public dependencies:

META-INF/lib/checkstyle-all-3.2-SNAPSHOT-shaded.jar
META-INF/lib/jaxen-1.1.4.jar
META-INF/lib/sslr-core-1.20.jar
META-INF/lib/sslr-squid-bridge-2.6.1.jar
META-INF/lib/sslr-xpath-1.20.jar