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，当尝试运行构建时，Maven在尝试解决依赖关系时似乎遇到了问题。我尝试将错误范围缩小为依赖项

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

当尝试解决某些传递依赖项时，似乎出现了问题。 stacktrace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)

我已经尝试使用mvnDebug调试代码，但是很不幸，StringVisitorModelInterpolator类不提供源代码。我可以看到一些变量：

我猜想是inter变量正在被插值，并且以某种方式变为null并传递给Entry对象，然后抛出该异常。

不幸的是，我没有找到提供我需要编译的类的其他依赖项。我不确定，但是此问题可能与以下讨论有关：Link to maven Github pull request discussion

除了在GitHub上解决此问题的方法，还有其他方法可以解决此问题吗？

提前感谢。

Answer 1

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

            <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的配置，我们使用exec-maven-plugin执行来运行MWE工作流程以生成我们的xtext类。