[BUILD] Check java formatting in Travis CI

* Introduced Formatting stage in travis
* Created script for downloading and executing
  the google java formatter

.travis.yml

@@ -43,7 +43,13 @@ jobs:
   allow_failures:
     - env: J_TYPE=STF_TEST
   include:
-    - if: type in (push, pull_request)
+    - stage: formatting
+      if: type in (push, pull_request)
+      script:
+        - $PWD/travis/script/format/check_java.sh $PWD
+
+    - stage: build
+      if: type in (push, pull_request)
       before_script: docker pull saros/ci_build:0.2
       script:
         - docker run -td --name build -v $PWD:/home/ci/saros_src saros/ci_build:0.2 bash

travis/script/format/check_java.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+
+shopt -s globstar
+
+project_root_dir=$1
+formatter_jar_name=formatter.jar
+
+function download_formatter() {
+  local jar_name=$1
+  local url="https://repo.maven.apache.org/maven2/com/google/googlejavaformat/google-java-format/1.6/google-java-format-1.6-all-deps.jar"
+  echo "Downloading formatter from $url"
+  curl -Lo "$jar_name" "$url"
+}
+
+function check_formatting() {
+  local jar_name=$1
+
+  echo 'Checking format'
+  java -jar "$jar_name" --dry-run --set-exit-if-changed **/*.java
+
+  local rc=$?
+  [ "$rc" == "0" ] &&
+    echo 'All files are well formatted' ||
+    printf "\nERROR: Some files are not well formatted. The file list above shows all files containing a wrong formatting.\n"
+
+  return "$rc"
+}
+
+cd $project_root_dir
+
+download_formatter $formatter_jar_name
+check_formatting $formatter_jar_name
+
+exit $?