[MTOOLCHAINS-49] Automatic discovery of JDK toolchains

pom.xml

@@ -90,6 +90,28 @@ under the License.
       <artifactId>maven-plugin-annotations</artifactId>
       <scope>provided</scope>
     </dependency>
+    <dependency>
+      <groupId>org.codehaus.plexus</groupId>
+      <artifactId>plexus-utils</artifactId>
+      <version>4.0.0</version>
+    </dependency>
+    <dependency>
+      <groupId>org.codehaus.plexus</groupId>
+      <artifactId>plexus-xml</artifactId>
+      <version>3.0.0</version>
+    </dependency>
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-api</artifactId>
+      <version>1.7.36</version>
+    </dependency>
+
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <version>5.10.2</version>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
   <build>
@@ -114,5 +136,11 @@ under the License.
         </plugin>
       </plugins>
     </pluginManagement>
+    <plugins>
+      <plugin>
+        <groupId>org.eclipse.sisu</groupId>
+        <artifactId>sisu-maven-plugin</artifactId>
+      </plugin>
+    </plugins>
   </build>
 </project>

src/main/java/org/apache/maven/plugins/toolchain/jdk/DisplayDiscoveredJdkToolchainsMojo.java

@@ -0,0 +1,75 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+package org.apache.maven.plugins.toolchain.jdk;
+
+import javax.inject.Inject;
+
+import java.util.List;
+
+import org.apache.maven.plugin.AbstractMojo;
+import org.apache.maven.plugins.annotations.Mojo;
+import org.apache.maven.plugins.annotations.Parameter;
+import org.apache.maven.toolchain.model.PersistedToolchains;
+import org.apache.maven.toolchain.model.ToolchainModel;
+import org.codehaus.plexus.util.xml.Xpp3Dom;
+
+import static java.util.Comparator.comparing;
+import static org.apache.maven.plugins.toolchain.jdk.ToolchainDiscoverer.SORTED_PROVIDES;
+
+/**
+ * Discover the JDK toolchains and print them to the console.
+ */
+@Mojo(name = "display-discovered-jdk-toolchains", requiresProject = false)
+public class DisplayDiscoveredJdkToolchainsMojo extends AbstractMojo {
+
+    /**
+     * Comparator used to sort JDK toolchains for selection.
+     * This property is a comma separated list of values which may contains:
+     * <ul>
+     * <li>{@code lts}: prefer JDK with LTS version</li>
+     * <li>{@code current}: prefer the current JDK</li>
+     * <li>{@code env}: prefer JDKs defined using {@code JAVA\{xx\}_HOME} environment variables</li>
+     * <li>{@code version}: prefer JDK with higher versions</li>
+     * <li>{@code vendor}: order JDK by vendor name (usually as a last comparator to ensure a stable order)</li>
+     * </ul>
+     */
+    @Parameter(property = "toolchain.jdk.comparator", defaultValue = "lts,current,env,version,vendor")
+    String comparator;
+
+    /**
+     * Toolchain discoverer
+     */
+    @Inject
+    ToolchainDiscoverer discoverer;
+
+    @Override
+    public void execute() {
+        PersistedToolchains toolchains = discoverer.discoverToolchains(comparator);
+        List<ToolchainModel> models = toolchains.getToolchains();
+        getLog().info("Discovered " + models.size() + " JDK toolchains:");
+        for (ToolchainModel model : models) {
+            getLog().info("  - "
+                    + ((Xpp3Dom) model.getConfiguration()).getChild("jdkHome").getValue());
+            getLog().info("    provides:");
+            model.getProvides().entrySet().stream()
+                    .sorted(comparing(e -> SORTED_PROVIDES.indexOf(e.getKey().toString())))
+                    .forEach(e -> getLog().info("      " + e.getKey() + ": " + e.getValue()));
+        }
+    }
+}

src/main/java/org/apache/maven/plugins/toolchain/jdk/GenerateJdkToolchainsXmlMojo.java

@@ -0,0 +1,75 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+package org.apache.maven.plugins.toolchain.jdk;
+
+import javax.inject.Inject;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.io.Writer;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import org.apache.maven.plugin.AbstractMojo;
+import org.apache.maven.plugin.MojoFailureException;
+import org.apache.maven.plugins.annotations.Mojo;
+import org.apache.maven.plugins.annotations.Parameter;
+import org.apache.maven.toolchain.model.PersistedToolchains;
+import org.apache.maven.toolchain.model.io.xpp3.MavenToolchainsXpp3Writer;
+
+/**
+ * Run the JDK toolchain discovery mechanism and generates a toolchains XML.
+ */
+@Mojo(name = "generate-jdk-toolchains-xml", requiresProject = false)
+public class GenerateJdkToolchainsXmlMojo extends AbstractMojo {
+
+    /**
+     * The path and name pf the toolchain XML file that will be generated.
+     * If not provided, the XML will be written to the standard output.
+     */
+    @Parameter(property = "toolchain.file")
+    String file;
+
+    /**
+     * Toolchain discoverer
+     */
+    @Inject
+    ToolchainDiscoverer discoverer;
+
+    @Override
+    public void execute() throws MojoFailureException {
+        try {
+            PersistedToolchains toolchains = discoverer.discoverToolchains();
+            if (file != null) {
+                Path file = Paths.get(this.file).toAbsolutePath();
+                Files.createDirectories(file.getParent());
+                try (Writer writer = Files.newBufferedWriter(file)) {
+                    new MavenToolchainsXpp3Writer().write(writer, toolchains);
+                }
+            } else {
+                StringWriter writer = new StringWriter();
+                new MavenToolchainsXpp3Writer().write(writer, toolchains);
+                System.out.println(writer);
+            }
+        } catch (IOException e) {
+            throw new MojoFailureException("Unable to generate toolchains.xml", e);
+        }
+    }
+}