The git pre-receive hook for java checkstyle check based on http://bluec0re.blogspot.com/2012/05/git-pre-receive-hook-with-checkstyle.html. Set checkstyle jar and xml with "git config checkstyle.checkfile google_checks.xml" and "git config checkstyle.jar checkstyle-6.12.1-all.jar".

pre-receive-checkstyle-hook.py

#!/usr/bin/env python
 
import subprocess
import sys
import tempfile
import shutil
import os
import errno

# variables for checkstyle
CONFIG_CHECK_FILE = 'checkstyle.checkfile'
CONFIG_JAR = 'checkstyle.jar'

# implementing check_output for python < 2.7
if not hasattr(subprocess, 'check_output'):
    def check_output(*popenargs, **kwargs):
        if 'stdout' in kwargs:
            raise ValueError('stdout argument not allowed, it will be overridden.')
        process = subprocess.Popen(stdout=subprocess.PIPE, *popenargs, **kwargs)
        output, unused_err = process.communicate()
        retcode = process.poll()
        if retcode:
            cmd = kwargs.get("args")
            if cmd is None:
                cmd = popenargs[0]
            er = subprocess.CalledProcessError(retcode, cmd)
            er.output = output
            raise er
        return output
    subprocess.check_output = check_output
 
 
# helper for calling executables
def call(*args, **kwargs):
    return subprocess.check_output(*args, **kwargs).strip()
 
 
# helper for calling git
def call_git(cmd, *args, **kwargs):
    return call(['git'] + cmd, *args, **kwargs)
 
 
# get all new commits from stdin
def get_commits():
    commits = {}
    for line in sys.stdin:
        old, new, ref = line.strip().split(' ')
        if old == '0000000000000000000000000000000000000000':
            old = '4b825dc642cb6eb9a060e54bf8d69288fbee4904'
 
        if ref not in commits:
            commits[ref] = []
        commits[ref].append({
            'old': old,
            'new': new,
            'files': get_changed_files(old, new)
            })
 
    return commits
 
 
# get a list of changed files between to commits
def get_changed_files(old, new):
    return call_git(['diff', '--name-only', old, new]).split('\n')
 
 
# get filemode, object type (blob,tree,commit), hash for the given file at the
# given commit
def get_change_type(commit, filename):
    return call_git(['ls-tree', commit, filename]).split('\t')[0].split(' ')

# get the checkstyle jar and xml from git config.
checkstyle = call_git(['config', '--get', CONFIG_JAR])
checkstyle_config = call_git(['config', '--get', CONFIG_CHECK_FILE])

commits = get_commits()
 
# use the latest file commit only
print "Cleaning up file list..."
 
files = {}
count = 0
for ref, data in commits.iteritems():
    files[ref] = {}
    for commit in data:
        for filename in commit['files']:
            if not filename.lower().endswith('.java'):
                continue
            files[ref][filename] = get_change_type(commit['new'], filename)
    count += len(files[ref])
 
print "%d Files to check in %d branches" % (count, len(files))
 
# create temporary dir and save a copy of the new files
tempdir = tempfile.mkdtemp('git_hook')
for ref, files in files.iteritems():
    for filename, data in files.iteritems():
        dname = os.path.dirname(filename)
        bname = os.path.basename(filename)
        try:
            os.makedirs(os.path.join(tempdir, dname))
        except OSError, exc:
            if exc.errno == errno.EEXIST:  # directory exists already
                pass
            else:
                raise
 
        with open(os.path.join(tempdir, dname, bname), 'w') as fp:
            fp.write(call_git(['cat-file', data[1], data[2]]))
 
try:
    # call checkstyle and print output
    output = call(['java', '-jar', checkstyle, '-c', checkstyle_config, tempdir])
    print(output)
    if output.find('warning') >= 0 or output.find('error') >= 0:
        exit(2)
except subprocess.CalledProcessError, ex:
    print ex.output  # print checkstyle messages
    exit(1)
finally:
    # remove temporary directory
    shutil.rmtree(tempdir)