Revert apacheGH-43378 and upgrade maven-site-plugin

ci/scripts/java_build.sh

@@ -72,6 +72,9 @@ if [ $ARROW_JAVA_SKIP_GIT_PLUGIN ]; then
  mvn="${mvn} -Dmaven.gitcommitid.skip=true"
 fi
 
+# Use `2 * ncores` threads
+mvn="${mvn} -T 2C"
+
 # https://github.com/apache/arrow/issues/41429
 # TODO: We want to out-of-source build. This is a workaround. We copy
 # all needed files to the build directory from the source directory
@@ -95,12 +98,10 @@ if [ "${ARROW_JAVA_JNI}" = "ON" ]; then
  mvn="${mvn} -Darrow.cpp.build.dir=${java_jni_dist_dir} -Parrow-jni"
 fi
 
-# Use `2 * ncores` threads
-${mvn} -T 2C clean install
+${mvn} clean install
 
 if [ "${BUILD_DOCS_JAVA}" == "ON" ]; then
  # HTTP pooling is turned of to avoid download issues https://issues.apache.org/jira/browse/ARROW-11633
- # GH-43378: Maven site plugins not compatible with multithreading
  mkdir -p ${build_dir}/docs/java/reference
  ${mvn} -Dcheckstyle.skip=true -Dhttp.keepAlive=false -Dmaven.wagon.http.pool=false clean install site
  rsync -a target/site/apidocs/ ${build_dir}/docs/java/reference

java/pom.xml

@@ -125,6 +125,7 @@ under the License.
  is addressed
  -->
  <version.maven-jar-plugin>3.2.2</version.maven-jar-plugin>
+ <version.maven-site-plugin>4.0.0-M16</version.maven-site-plugin>
  </properties>
 
  <dependencyManagement>