[maven-plugin] Generate hash from actual resolved spec rather than inputSpec file (#18849)

* Ensure temp directories are deleted after test execution

* Implement test that external $ref changes are reflected in checksum

* Generate hash checksum from actual resolved spec instead of inputSpec file

Otherwise regeneration will not happen when skipIfSpecIsUnchanged is enabled,
although formally the spec content has changed.

Fixes #4512 and #16489

* Use try-with-resources to ensure stream is closed properly on exit

* Fix deprecation warning on SimpleLocalRepositoryManagerFactory no-arg constructor

* Apply minor code cleanup

- use fluent setters where possible
- remove undocumented @throws from JavaDoc
- use List.of() instead of Arrays.asList() for single-element-collection
  (more memory efficient)
- fix some grammar issues in comments and JavaDoc

* Use non-blocking java.nio API for file existence checks

modules/openapi-generator-maven-plugin/src/main/java/org/openapitools/codegen/plugin/CodeGenMojo.java

@@ -17,40 +17,14 @@
 
 package org.openapitools.codegen.plugin;
 
-import static org.apache.commons.lang3.StringUtils.isNotEmpty;
+import com.google.common.hash.Hashing;
-import static org.openapitools.codegen.config.CodegenConfiguratorUtils.*;
+import com.google.common.io.Files;
-
+import io.swagger.parser.OpenAPIParser;
 import io.swagger.v3.core.util.Json;
 import io.swagger.v3.core.util.Yaml;
 import io.swagger.v3.parser.OpenAPIResolver;
 import io.swagger.v3.parser.OpenAPIV3Parser;
-import io.swagger.v3.parser.core.models.AuthorizationValue;
-import java.io.File;
-import java.io.FileOutputStream;
-import java.io.IOException;
-import java.net.MalformedURLException;
-import java.net.URI;
-import java.net.URISyntaxException;
-import java.net.URL;
-import java.net.URLClassLoader;
-import java.net.URLConnection;
-import java.nio.channels.Channels;
-import java.nio.channels.FileChannel;
-import java.nio.channels.ReadableByteChannel;
-import java.nio.charset.StandardCharsets;
-import java.nio.file.Path;
-import java.text.MessageFormat;
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Locale;
-import java.util.Map;
-import java.util.Set;
-
-import com.google.common.io.ByteSource;
-import com.google.common.io.CharSource;
 import io.swagger.v3.parser.core.models.ParseOptions;
-import io.swagger.v3.parser.util.ClasspathHelper;
 import lombok.Setter;
 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.FilenameUtils;
@@ -59,30 +33,28 @@ import org.apache.maven.artifact.Artifact;
 import org.apache.maven.plugin.AbstractMojo;
 import org.apache.maven.plugin.MojoExecution;
 import org.apache.maven.plugin.MojoExecutionException;
-import org.apache.maven.plugins.annotations.Component;
+import org.apache.maven.plugins.annotations.*;
-import org.apache.maven.plugins.annotations.LifecyclePhase;
-import org.apache.maven.plugins.annotations.Mojo;
-import org.apache.maven.plugins.annotations.Parameter;
-import org.apache.maven.plugins.annotations.ResolutionScope;
 import org.apache.maven.project.MavenProject;
-
 import org.apache.maven.project.MavenProjectHelper;
-import org.openapitools.codegen.CliOption;
+import org.openapitools.codegen.*;
-import org.openapitools.codegen.ClientOptInput;
-import org.openapitools.codegen.CodegenConfig;
-import org.openapitools.codegen.CodegenConstants;
-import org.openapitools.codegen.DefaultGenerator;
-import org.openapitools.codegen.auth.AuthParser;
 import org.openapitools.codegen.config.CodegenConfigurator;
 import org.openapitools.codegen.config.GlobalSettings;
 import org.openapitools.codegen.config.MergedSpecBuilder;
-import org.sonatype.plexus.build.incremental.BuildContext;
-import org.sonatype.plexus.build.incremental.DefaultBuildContext;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import org.sonatype.plexus.build.incremental.BuildContext;
+import org.sonatype.plexus.build.incremental.DefaultBuildContext;
 
-import com.google.common.hash.Hashing;
+import java.io.File;
-import com.google.common.io.Files;
+import java.io.IOException;
+import java.net.*;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Path;
+import java.text.MessageFormat;
+import java.util.*;
+
+import static org.apache.commons.lang3.StringUtils.isNotEmpty;
+import static org.openapitools.codegen.config.CodegenConfiguratorUtils.*;
 
 /**
  * Goal which generates client/server code from a OpenAPI json/yaml definition.
@@ -609,19 +581,11 @@ public class CodeGenMojo extends AbstractMojo {
             }
 
             if (Boolean.TRUE.equals(skipIfSpecIsUnchanged)) {
-                File storedInputSpecHashFile = getHashFile(inputSpecFile);
+                final File storedInputSpecHashFile = getHashFile(inputSpecFile);
                 if (storedInputSpecHashFile.exists()) {
-                    String inputSpecHash = null;
-                    try {
-                        inputSpecHash = calculateInputSpecHash(inputSpecFile);
-                    } catch (IOException ex) {
-                        ex.printStackTrace();
-                    }
-                    @SuppressWarnings("UnstableApiUsage")
                     String storedInputSpecHash = Files.asCharSource(storedInputSpecHashFile, StandardCharsets.UTF_8).read();
-                    if (storedInputSpecHash.equals(inputSpecHash)) {
+                    if (storedInputSpecHash.equals(calculateInputSpecHash(inputSpec))) {
-                        getLog().info(
+                        getLog().info("Code generation is skipped because input was unchanged");
-                                "Code generation is skipped because input was unchanged");
                         return;
                     }
                 }
@@ -1010,8 +974,6 @@ public class CodeGenMojo extends AbstractMojo {
 
             // Store a checksum of the input spec
             File storedInputSpecHashFile = getHashFile(inputSpecFile);
-            String inputSpecHash = calculateInputSpecHash(inputSpecFile);
-
             if (storedInputSpecHashFile.getParent() != null && !new File(storedInputSpecHashFile.getParent()).exists()) {
                 File parent = new File(storedInputSpecHashFile.getParent());
                 if (!parent.mkdirs()) {
@@ -1019,8 +981,8 @@ public class CodeGenMojo extends AbstractMojo {
                                                " to store the checksum of the input spec.");
                 }
             }
-            Files.asCharSink(storedInputSpecHashFile, StandardCharsets.UTF_8).write(inputSpecHash);
 
+            Files.asCharSink(storedInputSpecHashFile, StandardCharsets.UTF_8).write(calculateInputSpecHash(inputSpec));
         } catch (Exception e) {
             // Maven logs exceptions thrown by plugins only if invoked with -e
             // I find it annoying to jump through hoops to get basic diagnostic information,
@@ -1035,45 +997,21 @@ public class CodeGenMojo extends AbstractMojo {
     }
 
     /**
-     * Calculate openapi specification file hash. If specification is hosted on remote resource it is downloaded first
+     * Calculate an SHA256 hash for the openapi specification. 
+     * If the specification is hosted on a remote resource it is downloaded first.
      *
-     * @param inputSpecFile - Openapi specification input file to calculate its hash.
+     * @param inputSpec - Openapi specification input file. Can denote a URL or file path.
-     *                        Does not take into account if input spec is hosted on remote resource
+     * @return openapi specification hash
-     * @return openapi specification file hash
-     * @throws IOException
      */
-    private String calculateInputSpecHash(File inputSpecFile) throws IOException {
+    private String calculateInputSpecHash(String inputSpec) {
-
+        final ParseOptions parseOptions = new ParseOptions();
-        URL inputSpecRemoteUrl = inputSpecRemoteUrl();
+        parseOptions.setResolve(true);
-
+        
-        File inputSpecTempFile = inputSpecFile;
+        final URL remoteUrl = inputSpecRemoteUrl();
-
+        return Hashing.sha256().hashBytes(
-        if (inputSpecRemoteUrl != null) {
+            new OpenAPIParser().readLocation(remoteUrl == null ? inputSpec : remoteUrl.toString(), null, parseOptions)
-            inputSpecTempFile = java.nio.file.Files.createTempFile("openapi-spec", ".tmp").toFile();
+                .getOpenAPI().toString().getBytes(StandardCharsets.UTF_8)
-
+        ).toString();
-            URLConnection conn = inputSpecRemoteUrl.openConnection();
-            if (isNotEmpty(auth)) {
-                List<AuthorizationValue> authList = AuthParser.parse(auth);
-                for (AuthorizationValue a : authList) {
-                    conn.setRequestProperty(a.getKeyName(), a.getValue());
-                }
-            }
-            try (ReadableByteChannel readableByteChannel = Channels.newChannel(conn.getInputStream())) {
-                FileChannel fileChannel;
-                try (FileOutputStream fileOutputStream = new FileOutputStream(inputSpecTempFile)) {
-                    fileChannel = fileOutputStream.getChannel();
-                    fileChannel.transferFrom(readableByteChannel, 0, Long.MAX_VALUE);
-                }
-            }
-        }
-
-        ByteSource inputSpecByteSource =
-                inputSpecTempFile.exists()
-                        ? Files.asByteSource(inputSpecTempFile)
-                        : CharSource.wrap(ClasspathHelper.loadFileFromClasspath(inputSpecTempFile.toString().replaceAll("\\\\","/")))
-                        .asByteSource(StandardCharsets.UTF_8);
-
-        return inputSpecByteSource.hash(Hashing.sha256()).toString();
     }
 
     /**

modules/openapi-generator-maven-plugin/src/test/java/org/openapitools/codegen/plugin/CodeGenMojoTest.java

@@ -16,17 +16,6 @@
 
 package org.openapitools.codegen.plugin;
 
-import static org.junit.jupiter.api.Assertions.assertThrows;
-
-import java.io.File;
-import java.nio.file.Files;
-import java.nio.file.Path;
-import java.util.Arrays;
-import java.util.Comparator;
-import java.util.List;
-import java.util.Map;
-import java.util.stream.Collectors;
-
 import org.apache.commons.io.FileUtils;
 import org.apache.maven.artifact.Artifact;
 import org.apache.maven.execution.DefaultMavenExecutionRequest;
@@ -39,9 +28,24 @@ import org.apache.maven.project.ProjectBuilder;
 import org.apache.maven.project.ProjectBuildingRequest;
 import org.apache.maven.repository.internal.MavenRepositorySystemUtils;
 import org.eclipse.aether.DefaultRepositorySystemSession;
+import org.eclipse.aether.internal.impl.DefaultLocalPathComposer;
 import org.eclipse.aether.internal.impl.SimpleLocalRepositoryManagerFactory;
 import org.eclipse.aether.repository.LocalRepository;
 
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
 public class CodeGenMojoTest extends BaseTestCase {
     @Override
     protected void setUp() throws Exception {
@@ -62,8 +66,7 @@ public class CodeGenMojoTest extends BaseTestCase {
 
     @SuppressWarnings("unchecked")
     private void testCommonConfiguration(String profile) throws Exception {
-        File folder = Files.createTempDirectory("test").toFile();
+        CodeGenMojo mojo = loadMojo(newTempFolder(), "src/test/resources/default", profile);
-        CodeGenMojo mojo = loadMojo(folder, "src/test/resources/default", profile);
         mojo.execute();
         assertEquals("java", getVariableValueFromObject(mojo, "generatorName"));
         assertEquals("jersey2", getVariableValueFromObject(mojo, "library"));
@@ -79,43 +82,42 @@ public class CodeGenMojoTest extends BaseTestCase {
 
     public void testHashGenerationFileContainsExecutionId() throws Exception {
         // GIVEN
-        Path folder = Files.createTempDirectory("test");
+        final Path tempDir = newTempFolder();
-        CodeGenMojo mojo = loadMojo(folder.toFile(), "src/test/resources/default", "file", "executionId");
+        CodeGenMojo mojo = loadMojo(tempDir, "src/test/resources/default", "file", "executionId");
 
         // WHEN
         mojo.execute();
 
         // THEN
-        Path hashFolder = folder.resolve("target/generated-sources/common-maven/remote-openapi/.openapi-generator");
+        assertTrue(Files.exists(tempDir.resolve(
-        assertTrue(hashFolder.resolve("petstore.yaml-executionId.sha256").toFile().exists());
+            "target/generated-sources/common-maven/remote-openapi/.openapi-generator/petstore.yaml-executionId.sha256"
+        )));
     }
 
     /**
-     * For a Pom file which refers to a input file which will be on the classpath, as opposed to a file path,
+     * For a Pom file which refers to an input file which will be on the classpath, as opposed to a file path,
      * test that the spec is not regenerated when the hash has not changed. 
-     * 
-     * @throws Exception
      */
     public void testSkipRegenerationForClasspathSpecFileNoChange() throws Exception {
-
         //GIVEN
-        /* Setup the mojo */
+        /* Set up the mojo */
-        final Path folder = Files.createTempDirectory("test-classpath");
+        final Path tempDir = newTempFolder();
-        final CodeGenMojo mojo = loadMojo(folder.toFile(), "src/test/resources/classpath", null, "executionId");
+        final CodeGenMojo mojo = loadMojo(tempDir, "src/test/resources/classpath", null, "executionId");
 
         /* Perform an initial generation */
         mojo.execute();
 
         /* Check the hash file was created */
-        final Path hashFolder = folder.resolve("target/generated-sources/common-maven/remote-openapi/.openapi-generator");
+        final Path generatedDir = tempDir.resolve("target/generated-sources/common-maven/remote-openapi");
-        assertTrue(hashFolder.resolve("petstore-on-classpath.yaml-executionId.sha256").toFile().exists());
+        assertTrue(Files.exists(
+            generatedDir.resolve(".openapi-generator/petstore-on-classpath.yaml-executionId.sha256")
+        ));
 
         /* Remove the generated source */
-        Files.walk(folder.resolve("target/generated-sources/common-maven/remote-openapi/src"))
+        try (Stream<Path> files = Files.walk(generatedDir.resolve("src"))) {
-            .sorted(Comparator.reverseOrder())
+            //noinspection ResultOfMethodCallIgnored
-            .map(Path::toFile)
+            files.sorted(Comparator.reverseOrder()).map(Path::toFile).forEach(File::delete);
-            .forEach(File::delete);
+        }
-
 
         // WHEN
         /* Execute the mojo again */
@@ -123,41 +125,37 @@ public class CodeGenMojoTest extends BaseTestCase {
 
         // THEN
         /* Verify that the source directory has not been repopulated. If it has then we generated code again */
-        assertFalse("src directory should not have been regenerated", 
+        assertFalse("src directory should not have been regenerated", Files.exists(generatedDir.resolve("src")));
-            folder.resolve("target/generated-sources/common-maven/remote-openapi/src").toFile().exists());
-
     }
 
     /**
-     * For a Pom file which refers to a input file which will be on the classpath, as opposed to a file path,
+     * For a Pom file which refers to an input file which will be on the classpath, as opposed to a file path,
      * test that the generated source is regenerated when the hash has changed. 
-     * 
-     * @throws Exception
      */
     public void testSkipRegenerationForClasspathSpecFileWithChange() throws Exception {
-
         //GIVEN
-        /* Setup the mojo */
+        /* Set up the mojo */
-        final Path folder = Files.createTempDirectory("test-classpath");
+        final Path tempDir = newTempFolder();
-        final CodeGenMojo mojo = loadMojo(folder.toFile(), "src/test/resources/classpath", null, "executionId");
+        final CodeGenMojo mojo = loadMojo(tempDir, "src/test/resources/classpath", null, "executionId");
 
         /* Perform an initial generation */
         mojo.execute();
 
         /* Check the hash file was created, proving a generation occurred */
-        final Path hashFolder = folder.resolve("target/generated-sources/common-maven/remote-openapi/.openapi-generator");
+        final Path generatedDir = tempDir.resolve("target/generated-sources/common-maven/remote-openapi");
-        assertTrue(hashFolder.resolve("petstore-on-classpath.yaml-executionId.sha256").toFile().exists());
+        assertTrue(Files.exists(generatedDir.resolve(".openapi-generator/petstore-on-classpath.yaml-executionId.sha256")));
 
         /* Update the hash contents to be a different value, simulating a spec change */
         Files.write(
-            hashFolder.resolve("petstore-on-classpath.yaml-executionId.sha256"), 
+            generatedDir.resolve(".openapi-generator/petstore-on-classpath.yaml-executionId.sha256"),
-            Arrays.asList("bd1bf4a953c858f9d47b67ed6029daacf1707e5cbd3d2e4b01383ba30363366f"));
+            List.of("bd1bf4a953c858f9d47b67ed6029daacf1707e5cbd3d2e4b01383ba30363366f")
+        );
 
         /* Remove the generated source */
-        Files.walk(folder.resolve("target/generated-sources/common-maven/remote-openapi/src"))
+        try(Stream<Path> files = Files.walk(generatedDir.resolve("src"))) {
-            .sorted(Comparator.reverseOrder())
+            //noinspection ResultOfMethodCallIgnored
-            .map(Path::toFile)
+            files.sorted(Comparator.reverseOrder()).map(Path::toFile).forEach(File::delete);
-            .forEach(File::delete);
+        }
 
 
         // WHEN
@@ -165,29 +163,27 @@ public class CodeGenMojoTest extends BaseTestCase {
         mojo.execute();
 
         // THEN
-        /* Verify that the source directory has not been repopulated. If it has then we generated code again */
+        /* Verify that the source directory has been repopulated. */
-        assertTrue("src directory should have been regenerated", 
+        assertTrue("src directory should have been regenerated", Files.exists(generatedDir.resolve("src")));
-            folder.resolve("target/generated-sources/common-maven/remote-openapi/src").toFile().exists());
-
     }
 
     public void testCollapsedSpecProduced() throws Exception {
         // GIVEN
-        Path folder = Files.createTempDirectory("test");
+        final Path tempDir = newTempFolder();
-        CodeGenMojo mojo = loadMojo(folder.toFile(), "src/test/resources/default", "file", "executionId");
+        CodeGenMojo mojo = loadMojo(tempDir, "src/test/resources/default", "file", "executionId");
 
         // WHEN
         mojo.execute();
 
         // THEN
-        File collapseSpecFile = folder.resolve("target/generated-sources/common-maven/remote-openapi/petstore-full-spec.yaml").toFile();
+        assertTrue(Files.exists(
-        assertTrue(collapseSpecFile.exists());
+            tempDir.resolve("target/generated-sources/common-maven/remote-openapi/petstore-full-spec.yaml")
+        ));
     }
 
     public void testCollapsedSpecAddedToArtifacts() throws Exception {
         // GIVEN
-        Path folder = Files.createTempDirectory("test");
+        CodeGenMojo mojo = loadMojo(newTempFolder(), "src/test/resources/default", "file", "executionId");
-        CodeGenMojo mojo = loadMojo(folder.toFile(), "src/test/resources/default", "file", "executionId");
 
         // WHEN
         mojo.execute();
@@ -201,8 +197,7 @@ public class CodeGenMojoTest extends BaseTestCase {
 
     public void testAnyInputSpecMustBeProvided() throws Exception {
         // GIVEN
-        Path folder = Files.createTempDirectory("test");
+        CodeGenMojo mojo = loadMojo(newTempFolder(), "src/test/resources/default", "file", "executionId");
-        CodeGenMojo mojo = loadMojo(folder.toFile(), "src/test/resources/default", "file", "executionId");
         mojo.inputSpec = null;
         mojo.inputSpecRootDirectory = null;
 
@@ -215,8 +210,8 @@ public class CodeGenMojoTest extends BaseTestCase {
 
     public void testInputSpecRootDirectoryDoesNotRequireInputSpec() throws Exception {
         // GIVEN
-        Path folder = Files.createTempDirectory("test");
+        final Path tempDir = newTempFolder();
-        CodeGenMojo mojo = loadMojo(folder.toFile(), "src/test/resources/default", "file", "executionId");
+        CodeGenMojo mojo = loadMojo(tempDir, "src/test/resources/default", "file", "executionId");
         mojo.inputSpec = null;
         mojo.inputSpecRootDirectory = "src/test/resources/default";
 
@@ -225,17 +220,43 @@ public class CodeGenMojoTest extends BaseTestCase {
 
         // THEN
         /* Check the hash file was created */
-        final Path hashFolder = folder.resolve("target/generated-sources/common-maven/remote-openapi/.openapi-generator");
+        final Path hashFolder = tempDir.resolve("target/generated-sources/common-maven/remote-openapi/.openapi-generator");
-        assertTrue(hashFolder.resolve("_merged_spec.yaml-executionId.sha256").toFile().exists());
+        assertTrue(Files.exists(hashFolder.resolve("_merged_spec.yaml-executionId.sha256")));
     }
 
-    protected CodeGenMojo loadMojo(File temporaryFolder, String projectRoot, String profile) throws Exception {
+    /**
+     * Regression test for <a href="https://github.com/OpenAPITools/openapi-generator/issues/16489">#16489</a>
+     */
+    public void test_skipIfSpecIsUnchanged_recognizesUpdatesInExternalReferencedFile() throws Exception {
+
+        //GIVEN
+        final Path tempDir = newTempFolder();
+        final Path generatedDir = tempDir.resolve("target/generated-sources/issue-16489");
+        final Path hashFile = generatedDir.resolve(".openapi-generator/petstore.yaml-default.sha256");
+        final CodeGenMojo mojo = loadMojo(tempDir, "src/test/resources/issue-16489", null);
+        mojo.execute(); // Perform an initial generation 
+        var currentHash = Files.readString(hashFile);   // read hash
+        FileUtils.deleteDirectory(generatedDir.resolve("src").toFile());    // Remove the generated source
+        Files.writeString(  // change schema definition in external file
+            tempDir.resolve("schemas/Pet.yaml"),"\n  wrapped: true", StandardOpenOption.APPEND
+        );
+
+        // WHEN
+        mojo.execute(); // Execute the mojo again
+
+        // THEN
+        assertNotEquals(
+            Files.readString(hashFile), currentHash, "Checksum should not be the same after external file change"
+        );         
+        assertTrue("Src directory should have been regenerated", Files.exists(generatedDir.resolve("src")));
+    }
+
+    protected CodeGenMojo loadMojo(Path temporaryFolder, String projectRoot, String profile) throws Exception {
         return loadMojo(temporaryFolder, projectRoot, profile, "default");
     }
 
-    protected CodeGenMojo loadMojo(File temporaryFolder, String projectRoot, String profile, String executionId) throws Exception {
+    protected CodeGenMojo loadMojo(Path temporaryFolder, String projectRoot, String profile, String executionId) throws Exception {
-        File file = new File(projectRoot);
+        FileUtils.copyDirectory(new File(projectRoot), temporaryFolder.toFile());
-        FileUtils.copyDirectory(file, temporaryFolder);
         MavenProject project = readMavenProject(temporaryFolder, profile);
         MavenSession session = newMavenSession(project);
         MojoExecution execution = newMojoExecution("generate");
@@ -249,22 +270,29 @@ public class CodeGenMojoTest extends BaseTestCase {
         return executionWithId;
     }
 
-    protected MavenProject readMavenProject(File basedir, String profile)
+    protected MavenProject readMavenProject(Path basedir, String profile) throws Exception {
-            throws Exception {
+        LocalRepository localRepo = new LocalRepository(basedir.resolve("local-repo").toFile());
-        File pom = new File(basedir, "pom.xml");
-        LocalRepository localRepo = new LocalRepository(new File(basedir, "local-repo"));
         DefaultRepositorySystemSession session = MavenRepositorySystemUtils.newSession();
-        session.setLocalRepositoryManager(new SimpleLocalRepositoryManagerFactory().newInstance(session, localRepo));
+        session.setLocalRepositoryManager(
-        MavenExecutionRequest request = new DefaultMavenExecutionRequest();
+            new SimpleLocalRepositoryManagerFactory(new DefaultLocalPathComposer()).newInstance(session, localRepo)
-        request.setBaseDirectory(basedir);
+        );
+        MavenExecutionRequest request = new DefaultMavenExecutionRequest().setBaseDirectory(basedir.toFile());
         if (profile != null) {
             request.addActiveProfile(profile);
         }
-        ProjectBuildingRequest configuration = request.getProjectBuildingRequest();
+        ProjectBuildingRequest configuration = request.getProjectBuildingRequest()
-        configuration.setRepositorySession(session);
+            .setRepositorySession(session)
-        configuration.setResolveDependencies(true);
+            .setResolveDependencies(true);
-        MavenProject project = lookup(ProjectBuilder.class).build(pom, configuration).getProject();
+        MavenProject project = lookup(ProjectBuilder.class)
+            .build(basedir.resolve("pom.xml").toFile(), configuration)
+            .getProject();
         assertNotNull(project);
         return project;
     }
+
+    static private Path newTempFolder() throws IOException {
+        final Path tempDir = Files.createTempDirectory("test");
+        tempDir.toFile().deleteOnExit();
+        return tempDir;
+    }
 }

modules/openapi-generator-maven-plugin/src/test/resources/issue-16489/petstore.yaml

@@ -0,0 +1,105 @@
+openapi: 3.0.0
+servers:
+  - url: 'http://petstore.swagger.io/v2'
+info:
+  description: Sample file with just two endpoints and one schema (defined in an external file $ref) 
+  version: 1.0.0
+  title: OpenAPI Petstore
+paths:
+  /pet:
+    post:
+      tags:
+        - pet
+      summary: Add a new pet to the store
+      description: ''
+      operationId: addPet
+      responses:
+        '200':
+          description: successful operation
+          content:
+            application/xml:
+              schema:
+                $ref: '#/components/schemas/Pet'
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Pet'
+        '405':
+          description: Invalid input
+      security:
+        - petstore_auth:
+            - 'write:pets'
+            - 'read:pets'
+      requestBody:
+        $ref: '#/components/requestBodies/Pet'
+  '/pet/{petId}':
+    get:
+      tags:
+        - pet
+      summary: Find pet by ID
+      description: Returns a single pet
+      operationId: getPetById
+      parameters:
+        - name: petId
+          in: path
+          description: ID of pet to return
+          required: true
+          schema:
+            type: integer
+            format: int64
+      responses:
+        '200':
+          description: successful operation
+          content:
+            application/xml:
+              schema:
+                $ref: '#/components/schemas/Pet'
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Pet'
+        '400':
+          description: Invalid ID supplied
+        '404':
+          description: Pet not found
+      security:
+        - api_key: []
+    delete:
+      tags:
+        - pet
+      summary: Deletes a pet
+      description: ''
+      operationId: deletePet
+      parameters:
+        - name: api_key
+          in: header
+          required: false
+          schema:
+            type: string
+        - name: petId
+          in: path
+          description: Pet id to delete
+          required: true
+          schema:
+            type: integer
+            format: int64
+      responses:
+        '400':
+          description: Invalid pet value
+      security:
+        - petstore_auth:
+            - 'write:pets'
+            - 'read:pets'
+components:
+  requestBodies:
+    Pet:
+      content:
+        application/json:
+          schema:
+            $ref: 'schemas/Pet.yaml'
+        application/xml:
+          schema:
+            $ref: 'schemas/Pet.yaml'
+      description: Pet object that needs to be added to the store
+      required: true
+  schemas:
+    Pet:
+      $ref: 'schemas/Pet.yaml'

modules/openapi-generator-maven-plugin/src/test/resources/issue-16489/pom.xml

@@ -0,0 +1,61 @@
+<!--
+  ~ Copyright 2020 OpenAPI-Generator Contributors (https://openapi-generator.tech)
+  ~
+  ~ 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>
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>common.maven</groupId>
+    <artifactId>issue-16489</artifactId>
+    <packaging>jar</packaging>
+    <version>1.0.0-SNAPSHOT</version>
+    <name>OpenAPI Generator Configuration Test</name>
+    <url>https://openapi-generator.tech/</url>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.openapitools</groupId>
+                <artifactId>openapi-generator-maven-plugin</artifactId>
+                <version>7.6.0</version>
+                <configuration>
+                    <generatorName>java</generatorName>
+                    
+                    <skipIfSpecIsUnchanged>true</skipIfSpecIsUnchanged>
+                    
+                    <library>native</library>
+                    <output>${basedir}/target/generated-sources/issue-16489</output>
+                    <additionalProperties>hideGenerationTimestamp=true</additionalProperties>
+                    <inputSpec>${basedir}/petstore.yaml</inputSpec>
+                    <generateModelTests>false</generateModelTests>
+                    <generateModelDocumentation>false</generateModelDocumentation>
+                    <generateApiTests>false</generateApiTests>
+                    <generateApis>false</generateApis>
+                    <generateSupportingFiles>false</generateSupportingFiles>
+                    <configOptions>
+                        <interfaceOnly>true</interfaceOnly>
+                    </configOptions>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>generate</id>
+                        <phase>generate-sources</phase>
+                        <goals>
+                            <goal>generate</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+</project>

modules/openapi-generator-maven-plugin/src/test/resources/issue-16489/schemas/Pet.yaml

@@ -0,0 +1,29 @@
+title: a Pet
+description: A pet for sale in the pet store
+type: object
+required:
+  - name
+  - photoUrls
+properties:
+  id:
+    type: integer
+    format: int64
+  name:
+    type: string
+    example: doggie
+  photoUrls:
+    type: array
+    xml:
+      name: photoUrl
+      wrapped: true
+    items:
+      type: string
+  status:
+    type: string
+    description: pet status in the store
+    enum:
+      - available
+      - pending
+      - sold
+xml:
+  name: Pet