使用 xtext 和 maven 解决构建问题

Question

我正在尝试使用 xtend-maven-plugin 和 xtext-maven-plugin 在我的 maven 构建中编译 xtext 和 xtend 文件。但是，在尝试运行构建时，Maven 在尝试解决依赖关系时似乎遇到了问题。我认为我已将错误范围缩小到依赖项

<dependency>
    <groupId>org.eclipse.xtext</groupId>
    <artifactId>org.eclipse.xtext</artifactId>
    <version>2.21.0</version>
</dependency>

当它试图解决一些传递依赖时，问题似乎出现了。堆栈跟踪是：

java.lang.NullPointerException
    at java.util.Hashtable$Entry.setValue(Hashtable.java:1286)
    at org.apache.maven.model.interpolation.StringVisitorModelInterpolator$ModelVisitor.visit(StringVisitorModelInterpolator.java:1429)
    at org.apache.maven.model.interpolation.StringVisitorModelInterpolator$ModelVisitor.visit(StringVisitorModelInterpolator.java:1027)
    at org.apache.maven.model.interpolation.StringVisitorModelInterpolator$ModelVisitor.visit(StringVisitorModelInterpolator.java:170)
    at org.apache.maven.model.interpolation.StringVisitorModelInterpolator.interpolateModel(StringVisitorModelInterpolator.java:107)
    at org.apache.maven.model.building.DefaultModelBuilder.interpolateModel(DefaultModelBuilder.java:789)
    at org.apache.maven.model.building.DefaultModelBuilder.build(DefaultModelBuilder.java:393)
    at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom(DefaultArtifactDescriptorReader.java:292)
    at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.readArtifactDescriptor(DefaultArtifactDescriptorReader.java:171)
    at org.eclipse.aether.internal.impl.collect.DefaultDependencyCollector.resolveCachedArtifactDescriptor(DefaultDependencyCollector.java:541)
    at org.eclipse.aether.internal.impl.collect.DefaultDependencyCollector.getArtifactDescriptorResult(DefaultDependencyCollector.java:524)
    at org.eclipse.aether.internal.impl.collect.DefaultDependencyCollector.processDependency(DefaultDependencyCollector.java:412)
    at org.eclipse.aether.internal.impl.collect.DefaultDependencyCollector.processDependency(DefaultDependencyCollector.java:365)
    at org.eclipse.aether.internal.impl.collect.DefaultDependencyCollector.process(DefaultDependencyCollector.java:352)
    at org.eclipse.aether.internal.impl.collect.DefaultDependencyCollector.doRecurse(DefaultDependencyCollector.java:509)
    at org.eclipse.aether.internal.impl.collect.DefaultDependencyCollector.processDependency(DefaultDependencyCollector.java:461)
    at org.eclipse.aether.internal.impl.collect.DefaultDependencyCollector.processDependency(DefaultDependencyCollector.java:365)
    at org.eclipse.aether.internal.impl.collect.DefaultDependencyCollector.process(DefaultDependencyCollector.java:352)
    at org.eclipse.aether.internal.impl.collect.DefaultDependencyCollector.collectDependencies(DefaultDependencyCollector.java:254)
    at org.eclipse.aether.internal.impl.DefaultRepositorySystem.collectDependencies(DefaultRepositorySystem.java:284)
    at org.apache.maven.plugin.internal.DefaultPluginDependenciesResolver.resolveInternal(DefaultPluginDependenciesResolver.java:205)
    at org.apache.maven.plugin.internal.DefaultPluginDependenciesResolver.resolve(DefaultPluginDependenciesResolver.java:152)
    at org.apache.maven.plugin.internal.DefaultMavenPluginManager.createPluginRealm(DefaultMavenPluginManager.java:404)
    at org.apache.maven.plugin.internal.DefaultMavenPluginManager.setupPluginRealm(DefaultMavenPluginManager.java:374)
    at org.apache.maven.plugin.DefaultBuildPluginManager.getPluginRealm(DefaultBuildPluginManager.java:234)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:105)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute(MavenCli.java:957)
    at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:289)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:193)
    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.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:347)

我尝试使用 mvnDebug 调试代码，但不幸的是 StringVisitorModelInterpolator 类不提供源代码。我可以看到一些变量：

我猜inter 变量正在被插值，结果不知何故为 null 并传递给 Entry 对象，然后引发异常。

不幸的是，我没有找到提供编译所需的类的不同依赖项。 我不确定，但这个问题可能与这个讨论有关：Link to maven Github pull request discussion

除了他们在 GitHub 上解决这个问题之外，还有其他方法可以解决这个问题吗？

提前致谢。

Answer 1

我碰巧在一个使用 xtend 和 xtext 的项目中工作。这是我对 xtend-maven 插件的配置：

            <plugin><!--xtend-maven-plugin-->
                <groupId>org.eclipse.xtend</groupId>
                <artifactId>xtend-maven-plugin</artifactId>
                <version>2.14.0</version>
                <configuration>
                    <encoding>${project.build.sourceEncoding}</encoding>
                    <maven.compiler.source>1.7</maven.compiler.source>
                    <jvmSettings>
                        <fork>true</fork>
                        <jvmArgs>
                            <jvmArg>-Xms100m</jvmArg>
                            <jvmArg>-Xmx500m</jvmArg>
                            <jvmArg>-XX:MaxPermSize=512m</jvmArg>
                        </jvmArgs>
                    </jvmSettings>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                        </goals>
                        <configuration>
                            <!-- need to prefix by basedir to generate to currently built module -->
                            <outputDirectory>${basedir}/xtend-gen</outputDirectory>
                        </configuration>
                    </execution>
                </executions>
                <dependencies>
                    <!-- these dependencies are contributed in Eclipse by the "Xtend Library" 
                        classpath container -->
                    <dependency>
                        <groupId>org.eclipse.xtend</groupId>
                        <artifactId>org.eclipse.xtend.lib</artifactId>
                        <version>2.14.0</version>
                        <type>pom</type>
                    </dependency>
                    <dependency>
                        <groupId>org.eclipse.platform</groupId>
                        <artifactId>org.eclipse.equinox.common</artifactId>
                        <version>3.10.0</version>
                    </dependency>
                    <dependency>
                        <groupId>org.eclipse.emf</groupId>
                        <artifactId>org.eclipse.emf.codegen</artifactId>
                        <version>2.11.0</version>
                    </dependency>
                </dependencies>
            </plugin>           

希望这会有所帮助。我没有为您配置 xtext-maven-plugin，我们使用 exec-maven-plugin 执行来运行 MWE 工作流来生成我们的 xtext 类。

由于您询问了类路径，我的 MWE 工作流程如下所示：

var rootPath = ".."
var fileExtensions = "ext"
var projectName = "myProject"
var runtimeProject = "../${projectName}"
var languageName = "mylanguage"
var grammarURI = "platform:/resource/myProject/src/myPackage/myGrammar.xtext"

Workflow {
    bean = StandaloneSetup {
        scanClassPath = true
        platformUri = "${runtimeProject}/.."
    }
    component = XtextGenerator {
        configuration = {
            project = StandardProjectConfig {
                baseName = projectName
                rootPath = rootPath
                runtimeTest = {
                    enabled = true
                }
                eclipsePlugin = {
                    enabled = true
                }
                eclipsePluginTest = {
                    enabled = true
                    name = "${projectName}.tests"
                }
                createEclipseMetaData = true
            }
            code = {
                encoding = "UTF-8"
                fileHeader = "/*\n * generated by Xtext \${version}\n */"
            }
        }

        language = XtextGeneratorLanguage {
            name = languageName
            grammarUri = grammarURI
            referencedResource = protoBufGenModelPath
            fileExtensions = fileExtensions
            fragment = grammarAccess.GrammarAccessFragment2 {}
            fragment = ecore.EMFGeneratorFragment2 {}
            fragment = resourceFactory.ResourceFactoryFragment2 {}
            fragment = parser.antlr.XtextAntlrGeneratorFragment2 {}

            // An adapter to old fragment since support for this is not present in the latest versions.
            fragment = org.eclipse.xtext.generator.adapter.FragmentAdapter {
                fragment = org.eclipse.xtext.generator.parser.antlr.XtextAntlrUiGeneratorFragment {}
            }
            fragment = exporting.QualifiedNamesFragment2 {}
            fragment = serializer.SerializerFragment2 {
                generateStub = false
            }
            // An adapter to old fragment since support for this is not present in the latest versions.
            fragment = org.eclipse.xtext.generator.adapter.FragmentAdapter {
                fragment = org.eclipse.xtext.generator.formatting.FormatterFragment {
                    generateStub = false
                }
            }
            fragment = ui.labeling.LabelProviderFragment2 {}
            fragment = ui.outline.OutlineTreeProviderFragment2 {}
            fragment = ui.outline.QuickOutlineFragment2 {}
            fragment = ui.quickfix.QuickfixProviderFragment2 {}
            fragment = ui.contentAssist.ContentAssistFragment2 {}
            fragment = ui.refactoring.RefactorElementNameFragment2 {}
            fragment = junit.JUnitFragment {}

        }
    }
}

然后我只需在 pom 中使用 exec-maven-plugin 调用它：

            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <version>1.6.0</version>
                <executions>
                    <execution>
                        <phase>generate-sources</phase>
                        <goals>
                            <goal>java</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <killAfter>-1</killAfter>
                    <cleanupDaemonThreads>false</cleanupDaemonThreads>
                    <includeProjectDependencies>true</includeProjectDependencies>
                    <includePluginDependencies>true</includePluginDependencies>
                    <mainClass>org.eclipse.emf.mwe2.launch.runtime.Mwe2Launcher</mainClass>
                    <arguments>
                        <argument>file://${project.basedir}/src/myPackage/myGrammar.mwe2</argument>
                        <argument>-p</argument>
                        <argument>runtimeProject=plugins/${project.artifactId}</argument>
                        <argument>rootPath=plugins</argument>
                    </arguments>
                    <includeProjectDependencies>true</includeProjectDependencies>
                </configuration>
                <dependencies>
                    <dependency>
                        <groupId>org.eclipse.emf</groupId>
                        <artifactId>org.eclipse.emf.mwe2.launch</artifactId>
                        <version>${mwe2-version}</version>
                    </dependency>
                    <dependency>
                        <groupId>org.eclipse.xtext</groupId>
                        <artifactId>org.eclipse.xtext.common.types</artifactId>
                        <version>${xtext-version}</version>
                    </dependency>
                    <dependency>
                        <groupId>org.eclipse.xtext</groupId>
                        <artifactId>org.eclipse.xtext.generator</artifactId>
                        <version>${xtext-version}</version>
                    </dependency>
                    <dependency>
                        <groupId>org.eclipse.xtext</groupId>
                        <artifactId>org.eclipse.xtext.xtext.generator</artifactId>
                        <version>${xtext-version}</version>
                    </dependency>
                    <dependency>
                        <groupId>org.eclipse.xtext</groupId>
                        <artifactId>org.eclipse.xtext.xbase</artifactId>
                        <version>${xtext-version}</version>
                    </dependency>
                    <dependency>
                        <groupId>org.xtext</groupId>
                        <artifactId>antlr-generator</artifactId>
                        <version>3.2.1</version>
                    </dependency>
                    <!-- avoid warning concerning too old asm library (https://github.com/xtext-dev/maven-xtext-example/issues/25) -->
                    <dependency>
                        <groupId>org.apache.maven.plugins</groupId>
                        <artifactId>maven-plugin-plugin</artifactId>
                        <version>3.2</version>
                        <exclusions>
                            <exclusion>
                                <groupId>asm</groupId>
                                <artifactId>asm</artifactId>
                            </exclusion>
                            <exclusion>
                                <groupId>asm</groupId>
                                <artifactId>asm-commons</artifactId>
                            </exclusion>
                            <exclusion>
                                <groupId>asm</groupId>
                                <artifactId>asm-tree</artifactId>
                            </exclusion>
                        </exclusions>
                    </dependency>
                </dependencies>
            </plugin>