CheckStyle, 强制你遵循编码规范

如今代码静态检查越来越重要，已经成为构建高质量软件的不可或缺的一个验证步骤。如果你使用的是java语言，那么CheckStyle则是一个利器。 CheckStyle能够帮助程序员检查代码是否符合制定的规范。通过将CheckStyle的检查引入到项目构建中，可以强制让项目中的所有的开发者遵循制定规范，而不是仅仅停留在纸面上。如果发现代码违反了标准，比如类名未以大写开头、单个方法超过了指定行数、甚至单个方法抛出了3个以上的异常等。这些检查由于是基于源码的，所以不需要编译，执行速度快。

CheckStyle有针对不同IDE和构建工具的各种插件，方便开发者随时随地对代码进行静态检查。下面就讲解下如何将CheckStyle引入到maven构建中。

配置CheckStyle插件

在maven中一个名为maven-checkstyle-plugin的插件，用于执行CheckStyle task。下面是一个简单的配置。

    org.apache.maven.plugins
    maven-checkstyle-plugin
    2.10
    
            checkstyle
            validate
            
                check
            
                true

我们定义了在maven lifecycle的validate阶段执行check task，并且如果发现有违反标准的情况就会fail当前的build。

maven-checkstyle-plugin内置了4种规范.

config/sun_checks.xml
config/maven_checks.xml
config/turbine_checks.xml
config/avalon_checks.xml

其中sun_checks.xml为默认值。如果想要使用其他三种规范，则只需配置configuration。下面是使用maven_checks.xml的示例。

    org.apache.maven.plugins
    maven-checkstyle-plugin
    2.10
    
        config/maven_checks.xml
    
            checkstyle
            validate
            
                check
            
                true

自定义规范文件

我们可以使用默认的规范未见，当然也支持自定义。下面是google的一个checkstyle规范文件。

        "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
        "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">

 name="Checker">

     name="RegexpSingleline">
        
         name="format"
                  value="^(//| \*) Copyright (\([cC]\) )?[\d]{4}(\-[\d]{4})? (Google Inc\.).*$" />
         name="minimum" value="1" />
         name="maximum" value="10" />
         name="message" value="Google copyright is missing or malformed." />
         name="severity" value="error" />
    
     name="FileTabCharacter">
        
     name="NewlineAtEndOfFile"/>

     name="RegexpSingleline">
        
         name="format" value="((//.*)|(\*.*))FIXME" />
         name="message" value='TODO is preferred to FIXME.  e.g. "TODO(johndoe): Refactor when v2 is released."' />
    
     name="RegexpSingleline">
        
         name="format" value="((//.*)|(\*.*))TODO[^(]" />
         name="message" value='All TODOs should be named.  e.g. "TODO(johndoe): Refactor when v2 is released."' />
    
     name="TreeWalker">

         name="RedundantImport">
            
             name="severity" value="error"/>
        
         name="ImportOrder">
            
             name="severity" value="warning"/>
             name="groups" value="com.google,android,junit,net,org,java,javax"/>
            
             name="option" value="top"/>
             name="tokens" value="STATIC_IMPORT, IMPORT"/>
        
         name="JavadocMethod">
             name="scope" value="protected"/>
             name="severity" value="warning"/>
             name="allowMissingJavadoc" value="true"/>
             name="allowMissingParamTags" value="true"/>
             name="allowMissingReturnTag" value="true"/>
             name="allowMissingThrowsTags" value="true"/>
             name="allowThrowsTagsForSubclasses" value="true"/>
             name="allowUndeclaredRTE" value="true"/>
        
         name="JavadocType">
             name="scope" value="protected"/>
             name="severity" value="error"/>
        
         name="JavadocStyle">
             name="severity" value="warning"/>
        
         name="PackageName">
            
             name="format" value="^[a-z]+(\.[a-z][a-z0-9]{1,})*$"/>
             name="severity" value="warning"/>
        
         name="TypeNameCheck">
            
             name="altname" value="TypeName"/>
             name="severity" value="warning"/>
        
         name="ConstantNameCheck">
            
             name="altname" value="ConstantName"/>
             name="applyToPublic" value="true"/>
             name="applyToProtected" value="true"/>
             name="applyToPackage" value="true"/>
             name="applyToPrivate" value="false"/>
             name="format" value="^([A-Z][A-Z0-9]*(_[A-Z0-9]+)*|FLAG_.*)$"/>
             key="name.invalidPattern"
                     value="Variable ''{0}'' should be in ALL_CAPS (if it is a constant) or be private (otherwise)."/>
             name="severity" value="warning"/>
        
         name="StaticVariableNameCheck">
            
             name="altname" value="StaticVariableName"/>
             name="applyToPublic" value="true"/>
             name="applyToProtected" value="true"/>
             name="applyToPackage" value="true"/>
             name="applyToPrivate" value="true"/>
             name="format" value="^[a-z][a-zA-Z0-9]*_?$"/>
             name="severity" value="warning"/>
        
         name="MemberNameCheck">
            
             name="altname" value="MemberName"/>
             name="applyToPublic" value="true"/>
             name="applyToProtected" value="true"/>
             name="applyToPackage" value="true"/>
             name="applyToPrivate" value="true"/>
             name="format" value="^[a-z][a-zA-Z0-9]*$"/>
             name="severity" value="warning"/>
        
         name="MethodNameCheck">
            
             name="altname" value="MethodName"/>
             name="format" value="^[a-z][a-zA-Z0-9]*(_[a-zA-Z0-9]+)*$"/>
             name="severity" value="warning"/>
        
         name="ParameterName">
            
             name="severity" value="warning"/>
        
         name="LocalFinalVariableName">
            
             name="severity" value="warning"/>
        
         name="LocalVariableName">
            
             name="severity" value="warning"/>
        
         name="LineLength">
            
             name="max" value="${com.puppycrawl.tools.checkstyle.checks.sizes.LineLength.max}" default="100"/>
             name="severity" value="error"/>

             name="ignorePattern"
                      value="${com.puppycrawl.tools.checkstyle.checks.sizes.LineLength.ignorePattern}"
                      default="^(package .*;\s*)|(import .*;\s*)|( *\* *https?://.*)$"/>
        
         name="LeftCurly">
            
             name="severity" value="warning"/>
        
         name="RightCurly">
            
             name="option" value="same"/>
             name="severity" value="warning"/>
        
         name="NeedBraces">
             name="severity" value="warning"/>
             name="tokens" value="LITERAL_IF, LITERAL_ELSE, LITERAL_FOR, LITERAL_WHILE, LITERAL_DO"/>
        
         name="UpperEll">
            
             name="severity" value="error"/>
        
         name="FallThrough">
            
             name="reliefPattern"
                      value="fall through|Fall through|fallthru|Fallthru|falls through|Falls through|fallthrough|Fallthrough|No break|NO break|no break|continue on"/>
             name="severity" value="error"/>
        
         name="ModifierOrder">
            
         name="WhitespaceAround">
            
             name="tokens" value="ASSIGN, BAND, BAND_ASSIGN, BOR,
        BOR_ASSIGN, BSR, BSR_ASSIGN, BXOR, BXOR_ASSIGN, COLON, DIV, DIV_ASSIGN,
        EQUAL, GE, GT, LAND, LE, LITERAL_CATCH, LITERAL_DO, LITERAL_ELSE,
        LITERAL_FINALLY, LITERAL_FOR, LITERAL_IF, LITERAL_RETURN,
        LITERAL_SYNCHRONIZED, LITERAL_TRY, LITERAL_WHILE, LOR, LT, MINUS,
        MINUS_ASSIGN, MOD, MOD_ASSIGN, NOT_EQUAL, PLUS, PLUS_ASSIGN, QUESTION,
        SL, SL_ASSIGN, SR_ASSIGN, STAR, STAR_ASSIGN"/>
             name="severity" value="error"/>
        
         name="WhitespaceAfter">
            
             name="tokens" value="COMMA, SEMI, TYPECAST"/>
        
         name="NoWhitespaceAfter">
            
             name="tokens" value="BNOT, DEC, DOT, INC, LNOT, UNARY_MINUS,
        UNARY_PLUS"/>
             name="allowLineBreaks" value="true"/>
             name="severity" value="error"/>
        
         name="NoWhitespaceBefore">
            
             name="tokens" value="SEMI, DOT, POST_DEC, POST_INC"/>
             name="allowLineBreaks" value="true"/>
             name="severity" value="error"/>
        
         name="ParenPad">
            
             name="severity" value="warning"/>

如果想启用自定义的规范文件，则依旧是修改configuration，指向你的文件地址。

        
            org.apache.maven.plugins
            maven-checkstyle-plugin
            2.10
            
                ${basedir}/src/config/custom_checkstyle.xml
            
                    checkstyle
                    validate
                    
                        check
                    
                        true

运行checkstyle检查

mvn checkstyle:checkstyle

查看checkstyle结果

运行maven命令后可以在console里查看checkstyle运行结果。

[INFO]
[INFO] There are 11 checkstyle errors.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.135s
[INFO] Finished at: Fri Jun 21 13:39:24 CST 2013
[INFO] Final Memory: 6M/81M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:2.10:check (checkstyle) on project SpringMessageSpike: You have 11 Checkstyle violations. -> [Help 1]

checkstye的详细结果信息被存放在target/checkstyle-result.xml中。下面是一个示例。

 version="5.6">
 name="/Users/twer/sourcecode/SpringMessageSpike/src/main/java/com/thoughtworks/config/SessionMessageSource.java">
 line="0" severity="error" message="Google copyright is missing or malformed." source="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineCheck"/>
 line="21" severity="warning" message="Wrong order for 'org.slf4j.LoggerFactory.getLogger' import." source="com.puppycrawl.tools.checkstyle.checks.imports.ImportOrderCheck"/>
 line="27" severity="error" message="Missing a Javadoc comment." source="com.puppycrawl.tools.checkstyle.checks.javadoc.JavadocTypeCheck"/>
 line="35" severity="error" message="Line is longer than 100 characters (found 115)." source="com.puppycrawl.tools.checkstyle.checks.sizes.LineLengthCheck"/>

跳过对指定文件的某些检查

如果对于指定文件检查出了一些问题，但是你想忽略它，则可以使用suppression。

例如在上述例子中有一个checkstyle error是说某行超过了100字符。如果我们不想修复这个错误怎么办那？可以将其suppress掉。

方法是建立一个checkstyle-suppressions.xml文件。其中加入下述内容

checkstyle-suppressions.xml

        "-//Puppy Crawl//DTD Suppressions 1.0//EN"
        "http://www.puppycrawl.com/dtds/suppressions_1_0.dtd">


     checks="LineLengthCheck"
              files="SessionMessageSource.java"
              />

然后配置maven-checkstyel-plugin设置suppressionsLocation。

    org.apache.maven.plugins
    maven-checkstyle-plugin
    2.10
    
        ${basedir}/src/config/custom_checkstyle.xml
        ${basedir}/src/config/checkstyle-suppressions.xml
    
            checkstyle
            validate
            
                check
            
                true