问题：
checkstyle插件报错

详情：
我在研究docker-maven-plugin插件源码，执行
mvn clean package
报错：
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:2.17:check (validate) on project docker-maven-plugin: Failed during checkstyle configuration: cannot initialize module SuppressionFilter - Cannot set property 'file' to 'checkstyle-suppressions.xml' in module SuppressionFilter: InvocationTargetException: Unable to find: checkstyle-suppressions.xml: http://www.puppycrawl.com/dtds/suppressions_1_0.dtd -> [Help 1]

配置：

  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-checkstyle-plugin</artifactId>
    <version>2.17</version>
    <executions>
      <execution>
        <id>validate</id>
        <phase>validate</phase>
        <configuration>
          <configLocation>checkstyle.xml</configLocation>
          <encoding>UTF-8</encoding>
          <consoleOutput>true</consoleOutput>
          <failsOnError>true</failsOnError>
          <includeTestSourceDirectory>true</includeTestSourceDirectory>
        </configuration>
        <goals>
          <goal>check</goal>
        </goals>
      </execution>
    </executions>
    <configuration>
      <linkXRef>false</linkXRef>
    </configuration>
  </plugin>

排查：
添加参数再次执行
mvn clean package -e -X
有如下
Caused by: com.puppycrawl.tools.checkstyle.api.CheckstyleException: Cannot set property 'file' to 'checkstyle-suppressions.xml' in module SuppressionFilter

    at com.puppycrawl.tools.checkstyle.api.AutomaticBean.tryCopyProperty(AutomaticBean.java:178)
    at com.puppycrawl.tools.checkstyle.api.AutomaticBean.configure(AutomaticBean.java:130)
    at com.puppycrawl.tools.checkstyle.Checker.setupChild(Checker.java:163)
    ... 25 more

Caused by: java.lang.reflect.InvocationTargetException

    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.commons.beanutils.PropertyUtilsBean.invokeMethod(PropertyUtilsBean.java:2116)
    at org.apache.commons.beanutils.PropertyUtilsBean.setSimpleProperty(PropertyUtilsBean.java:2097)
    at org.apache.commons.beanutils.BeanUtilsBean.copyProperty(BeanUtilsBean.java:435)
    at com.puppycrawl.tools.checkstyle.api.AutomaticBean.tryCopyProperty(AutomaticBean.java:168)
    ... 27 more

Caused by: com.puppycrawl.tools.checkstyle.api.CheckstyleException: Unable to find: checkstyle-suppressions.xml

    at com.puppycrawl.tools.checkstyle.filters.SuppressionsLoader.loadSuppressions(SuppressionsLoader.java:147)
    at com.puppycrawl.tools.checkstyle.filters.SuppressionsLoader.loadSuppressions(SuppressionsLoader.java:127)
    at com.puppycrawl.tools.checkstyle.filters.SuppressionFilter.setFile(SuppressionFilter.java:50)
    ... 35 more

Caused by: java.io.FileNotFoundException: http://www.puppycrawl.com/dtds/suppressions_1_0.dtd

    at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1872)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1474)
    at org.apache.xerces.impl.XMLEntityManager.setupCurrentEntity(Unknown Source)
    at org.apache.xerces.impl.XMLEntityManager.startEntity(Unknown Source)
    at org.apache.xerces.impl.XMLEntityManager.startDTDEntity(Unknown Source)
    at org.apache.xerces.impl.XMLDTDScannerImpl.setInputSource(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentScannerImpl$DTDDispatcher.dispatch(Unknown Source)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
    at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)

文件http://www.puppycrawl.com/dtds/suppressions_1_0.dtd未找到
网站：http://www.puppycrawl.com

解决方式：
1.找Oliver Bum要一个suppressions_1_0.dtd
2.删除checkstyle-suppressions.xml文件（会报错）
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:2.17:check (validate) on project docker-maven-plugin: Failed during checkstyle configuration: cannot initialize module SuppressionFilter - Cannot set property 'file' to 'checkstyle-suppressions.xml' in module SuppressionFilter: InvocationTargetException: Unable to find: checkstyle-suppressions.xml -> [Help 1]
3.自己写一个，如果知道内容可以自己写一个
例如：
修改前：
<?xml version="1.0" encoding="UTF-8"?>
/p>

"-//Puppy Crawl//DTD Check Configuration 1.3//EN"
"http://www.puppycrawl.com/dtds/suppressions_1_0.dtd">

修改后：
文件：checkstyle-suppressions.xml
<?xml version="1.0" encoding="UTF-8"?>

增加文件：suppressions.dtd