checkStyle.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
  ~ Copyright 2017, OpenSkywalking Organization All rights reserved.
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~     http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License.
  ~
  ~ Project repository: https://github.com/OpenSkywalking/skywalking
  -->

<!DOCTYPE module PUBLIC
    "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
    "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
<!--Refer http://checkstyle.sourceforge.net/reports/google-java-style.html#s2.2-file-encoding -->
<module name="Checker">

    <property name="localeLanguage" value="en"/>

    <!--To configure the check to report on the first instance in each file-->
    <module name="FileTabCharacter"/>

    <!-- header -->
    <module name="Header">
        <property name="headerFile" value="${checkstyle.header.file}"/>
    </module>

    <module name="RegexpSingleline">
        <property name="format" value="System\.out\.println"/>
        <property name="message" value="Prohibit invoking System.out.println in source code !"/>
    </module>

    <module name="RegexpSingleline">
        <property name="format"
                  value=".*[\u3400-\u4DB5\u4E00-\u9FA5\u9FA6-\u9FBB\uF900-\uFA2D\uFA30-\uFA6A\uFA70-\uFAD9\uFF00-\uFFEF\u2E80-\u2EFF\u3000-\u303F\u31C0-\u31EF]+.*"/>
        <property name="message" value="Not allow chinese character !"/>
    </module>

    <module name="FileLength">
        <property name="max" value="3000"/>
    </module>

    <module name="TreeWalker">

        <module name="UnusedImports">
            <property name="processJavadoc" value="true"/>
        </module>
        <module name="RedundantImport"/>

        <!--Checks that classes that override equals() also override hashCode()-->
        <module name="EqualsHashCode"/>
        <!--Checks for over-complicated boolean expressions. Currently finds code like if (topic == true), topic || true, !false, etc.-->
        <module name="SimplifyBooleanExpression"/>
        <module name="OneStatementPerLine"/>
        <module name="UnnecessaryParentheses"/>
        <!--Checks for over-complicated boolean return statements. For example the following code-->
        <module name="SimplifyBooleanReturn"/>

        <!--Check that the default is after all the cases in producerGroup switch statement-->
        <module name="DefaultComesLast"/>
        <!--Detects empty statements (standalone ";" semicolon)-->
        <module name="EmptyStatement"/>
        <!--Checks that long constants are defined with an upper ell-->
        <module name="UpperEll"/>
        <module name="ConstantName">
            <property name="format" value="(^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$)|(^logger)"/>
        </module>
        <!--Checks that local, non-final variable names conform to producerGroup format specified by the format property-->
        <module name="LocalVariableName"/>
        <!--Validates identifiers for local, final variables, including catch parameters-->
        <module name="LocalFinalVariableName"/>
        <!--Validates identifiers for non-static fields-->
        <module name="MemberName"/>
        <!--Validates identifiers for class type parameters-->
        <module name="ClassTypeParameterName">
            <property name="format" value="(^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$)"/>
        </module>
        <!--Validates identifiers for method type parameters-->
        <module name="MethodTypeParameterName">
            <property name="format" value="(^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$)"/>
        </module>
        <module name="PackageName"/>
        <module name="ParameterName"/>
        <module name="StaticVariableName">
            <property name="format" value="(^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$)"/>
        </module>
        <module name="TypeName">
            <property name="format" value="(^[A-Z][a-zA-Z0-9]*$)|(^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$)"/>
        </module>

        <!--whitespace-->
        <module name="GenericWhitespace"/>
        <module name="NoWhitespaceBefore"/>
        <module name="NoWhitespaceAfter"/>
        <module name="WhitespaceAround">
            <property name="allowEmptyConstructors" value="true"/>
            <property name="allowEmptyMethods" value="true"/>
        </module>
        <module name="Indentation"/>
        <module name="MethodParamPad"/>
        <module name="ParenPad"/>
        <module name="TypecastParenPad"/>
        <module name="TypecastParenPad"/>
    </module>
</module>