Issue checkstyle#20: Configuration Component

config/import-control.xml

@@ -9,6 +9,12 @@
     <allow pkg="com.github.checkstyle.regression.data"/>
     <allow pkg="org.immutables.value"/>
 
+    <subpackage name="configuration">
+        <allow pkg="javax.xml"/>
+        <allow pkg="org.w3c.dom"/>
+        <allow pkg="org.xml"/>
+    </subpackage>
+
     <subpackage name="data">
         <!-- it is only allowed until https://github.com/checkstyle/checkstyle/issues/3492 -->
         <allow pkg="org.immutables.gson"/>

pom.xml

@@ -285,6 +285,11 @@
                                         <branchRate>0</branchRate>
                                         <lineRate>0</lineRate>
                                     </regex>
+                                    <regex>
+                                        <pattern>com.github.checkstyle.regression.configuration.ConfigGenerator</pattern>
+                                        <branchRate>83</branchRate>
+                                        <lineRate>92</lineRate>
+                                    </regex>
                                     <regex>
                                         <pattern>com.github.checkstyle.regression.module.ModuleUtils</pattern>
                                         <branchRate>28</branchRate>

src/main/java/com/github/checkstyle/regression/configuration/ConfigGenerator.java

@@ -0,0 +1,200 @@
+////////////////////////////////////////////////////////////////////////////////
+// checkstyle: Checks Java source code for adherence to a set of rules.
+// Copyright (C) 2001-2017 the original author or authors.
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+////////////////////////////////////////////////////////////////////////////////
+
+package com.github.checkstyle.regression.configuration;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.StringWriter;
+import java.util.List;
+
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.parsers.ParserConfigurationException;
+import javax.xml.transform.OutputKeys;
+import javax.xml.transform.Transformer;
+import javax.xml.transform.TransformerConfigurationException;
+import javax.xml.transform.TransformerException;
+import javax.xml.transform.TransformerFactory;
+import javax.xml.transform.dom.DOMSource;
+import javax.xml.transform.stream.StreamResult;
+
+import org.w3c.dom.Document;
+import org.w3c.dom.Element;
+import org.w3c.dom.Node;
+import org.w3c.dom.NodeList;
+import org.xml.sax.SAXException;
+
+import com.github.checkstyle.regression.data.ModuleInfo;
+
+/**
+ * Generates the config XML and output it to a specific file.
+ * @author LuoLiangchen
+ */
+public final class ConfigGenerator {
+    /** The parent name "Checker". */
+    private static final String PARENT_CHECKER = "Checker";
+
+    /** The parent name "TreeWalker". */
+    private static final String PARENT_TREE_WALKER = "TreeWalker";
+
+    /** The name of a module element. */
+    private static final String ELEMENT_MODULE = "module";
+
+    /** The name of a property element. */
+    private static final String ELEMENT_PROPERTY = "property";
+
+    /** The attribute name "name". */
+    private static final String ATTR_NAME = "name";
+
+    /** The attribute name "value". */
+    private static final String ATTR_VALUE = "value";
+
+    /** The "doctype-public" value of the config. */
+    private static final String DOCTYPE_PUBLIC =
+            "-//Puppy Crawl//DTD Check Configuration 1.3//EN";
+
+    /** The "doctype-system" value of the config. */
+    private static final String DOCTYPE_SYSTEM =
+            "http://www.puppycrawl.com/dtds/configuration_1_3.dtd";
+
+    /** Prevents instantiation. */
+    private ConfigGenerator() {
+    }
+
+    /**
+     * Creates a new {@link Document} instance from the {@code BASE_CONFIG}.
+     * @return a new {@link Document} instance
+     */
+    private static Document createXmlDocument() {
+        final Document document;
+
+        try {
+            final File baseConfig = new File("src/main/resources/com/github/checkstyle/regression/"
+                    + "configuration/base_config.xml");
+            document = DocumentBuilderFactory.newInstance().newDocumentBuilder()
+                    .parse(baseConfig);
+        }
+        catch (ParserConfigurationException | SAXException | IOException ex) {
+            throw new IllegalStateException("cannot instantiate Document instance", ex);
+        }
+
+        return document;
+    }
+
+    /**
+     * Creates a new {@link Transformer} instance and do initialization.
+     * @return a new {@link Transformer} instance
+     */
+    private static Transformer createXmlTransformer() {
+        final Transformer transformer;
+
+        try {
+            transformer = TransformerFactory.newInstance().newTransformer();
+            transformer.setOutputProperty(OutputKeys.INDENT, "yes");
+            transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "2");
+            transformer.setOutputProperty(OutputKeys.DOCTYPE_PUBLIC, DOCTYPE_PUBLIC);
+            transformer.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, DOCTYPE_SYSTEM);
+        }
+        catch (TransformerConfigurationException ex) {
+            throw new IllegalStateException("cannot instantiate Transformer instance", ex);
+        }
+
+        return transformer;
+    }
+
+    /**
+     * Generates the plain text of the config XML from the given module infos.
+     * @param moduleInfos the given module infos
+     * @return the generated plain text of the config
+     * @throws TransformerException failure of transforming the XML document
+     */
+    public static String generateConfigText(List<ModuleInfo> moduleInfos)
+            throws TransformerException {
+        final Document document = createXmlDocument();
+
+        final Node checkerNode = getCheckerModuleNode(document);
+        final Node treeWalkerNode = getTreeWalkerModuleNode(document);
+        for (ModuleInfo moduleInfo : moduleInfos) {
+            final Node moduleNode = createModuleNode(document, moduleInfo);
+            final String parent = moduleInfo.moduleExtractInfo().parent();
+            if (PARENT_CHECKER.equals(parent)) {
+                checkerNode.appendChild(moduleNode);
+            }
+            else if (PARENT_TREE_WALKER.equals(parent)) {
+                treeWalkerNode.appendChild(moduleNode);
+            }
+        }
+
+        final Transformer transformer = createXmlTransformer();
+        final StringWriter writer = new StringWriter();
+        transformer.transform(new DOMSource(document), new StreamResult(writer));
+        return writer.getBuffer().toString().replaceAll("\r\n", "\n");
+    }
+
+    /**
+     * Creates a XML element node which represents the settings of a checkstyle module.
+     * The information to create the node is grabbed from the given module info.
+     * @param document   the XML document to create element
+     * @param moduleInfo the given module info
+     * @return a checkstyle module node
+     */
+    private static Node createModuleNode(Document document, ModuleInfo moduleInfo) {
+        final Element moduleNode = document.createElement(ELEMENT_MODULE);
+        moduleNode.setAttribute(ATTR_NAME, moduleInfo.name());
+
+        for (ModuleInfo.Property property : moduleInfo.properties()) {
+            final Element propertyNode = document.createElement(ELEMENT_PROPERTY);
+            propertyNode.setAttribute(ATTR_NAME, property.name());
+            propertyNode.setAttribute(ATTR_VALUE, property.value());
+            moduleNode.appendChild(propertyNode);
+        }
+        return moduleNode;
+    }
+
+    /**
+     * Gets the "TreeWalker" element node of the config document.
+     * @param document the XML document to search
+     * @return the "TreeWalker" element node
+     */
+    private static Node getTreeWalkerModuleNode(Document document) {
+        Node returnValue = null;
+        final NodeList nodeList = document.getDocumentElement()
+                .getElementsByTagName(ELEMENT_MODULE);
+
+        for (int i = 0; i < nodeList.getLength(); ++i) {
+            final Node node = nodeList.item(i);
+            final Node nameAttr = node.getAttributes().getNamedItem(ATTR_NAME);
+            if (PARENT_TREE_WALKER.equals(nameAttr.getNodeValue())) {
+                returnValue = node;
+                break;
+            }
+        }
+
+        return returnValue;
+    }
+
+    /**
+     * Gets the "Checker" element node of the config document.
+     * @param document the XML document to search
+     * @return the "Checker" element node
+     */
+    private static Node getCheckerModuleNode(Document document) {
+        return document.getDocumentElement();
+    }
+}

src/main/java/com/github/checkstyle/regression/configuration/package-info.java

@@ -0,0 +1,24 @@
+////////////////////////////////////////////////////////////////////////////////
+// checkstyle: Checks Java source code for adherence to a set of rules.
+// Copyright (C) 2001-2017 the original author or authors.
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Lesser General Public
+// License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public
+// License along with this library; if not, write to the Free Software
+// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Contains the config XML generation classes.
+ * @author LuoLiangchen
+ */
+package com.github.checkstyle.regression.configuration;

src/main/resources/com/github/checkstyle/regression/configuration/base_config.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<module name="Checker">
+  <property name="charset" value="UTF-8"/>
+  <!-- do not change severity to 'error', as that will hide errors caused by exceptions -->
+  <property name="severity" value="warning"/>
+  <!-- haltOnException is required for exception fixes and reporting of all exceptions -->
+  <property name="haltOnException" value="false"/>
+  <!-- BeforeExecutionFileFilters is required for sources of java9 -->
+  <module name="BeforeExecutionExclusionFileFilter">
+    <property name="fileNamePattern" value="module\-info\.java$"/>
+  </module>
+
+  <!-- Contents below are generated by regression-tool. -->
+  <module name="TreeWalker"/></module>