java - 注释处理期间的 GWT RfValidator NPE

Question

使用aspectjweaver 1.11版本和高于1.8.5版本的aspectjrt会导致在使用Java 8构建GWT 1.8.2应用程序期间出现多个NPE:

[INFO] --- aspectj-maven-plugin:1.11:compile (compile) @ myproject ---
...
[ERROR] java.lang.NullPointerException
    at org.aspectj.org.eclipse.jdt.internal.compiler.lookup.FieldBinding.sourceField(FieldBinding.java:437)
    at org.aspectj.org.eclipse.jdt.internal.compiler.apt.model.TypeElementImpl$SourceLocationComparator.determineSourceStart(TypeElementImpl.java:110)
    at org.aspectj.org.eclipse.jdt.internal.compiler.apt.model.TypeElementImpl$SourceLocationComparator.getSourceStart(TypeElementImpl.java:74)
    at org.aspectj.org.eclipse.jdt.internal.compiler.apt.model.TypeElementImpl$SourceLocationComparator.compare(TypeElementImpl.java:67)
    at org.aspectj.org.eclipse.jdt.internal.compiler.apt.model.TypeElementImpl$SourceLocationComparator.compare(TypeElementImpl.java:1)
    at java.util.TimSort.countRunAndMakeAscending(TimSort.java:360)
    at java.util.TimSort.sort(TimSort.java:234)
    at java.util.Arrays.sort(Arrays.java:1512)
    at java.util.ArrayList.sort(ArrayList.java:1462)
    at java.util.Collections.sort(Collections.java:175)
    at org.aspectj.org.eclipse.jdt.internal.compiler.apt.model.TypeElementImpl.getEnclosedElements(TypeElementImpl.java:168)
    at com.google.web.bindery.requestfactory.apt.DomainChecker.isDefaultInstantiable(DomainChecker.java:407)
    at com.google.web.bindery.requestfactory.apt.DomainChecker.visitType(DomainChecker.java:253)
    at com.google.web.bindery.requestfactory.apt.DomainChecker.visitType(DomainChecker.java:44)
    at org.aspectj.org.eclipse.jdt.internal.compiler.apt.model.TypeElementImpl.accept(TypeElementImpl.java:139)
    at javax.lang.model.util.ElementScanner6.scan(ElementScanner6.java:146)
    at com.google.web.bindery.requestfactory.apt.ScannerBase.scan(ScannerBase.java:76)
    at com.google.web.bindery.requestfactory.apt.State.executeJobs(State.java:248)
    at com.google.web.bindery.requestfactory.apt.RfValidator.process(RfValidator.java:86)
    at org.aspectj.org.eclipse.jdt.internal.compiler.apt.dispatch.RoundDispatcher.handleProcessor(RoundDispatcher.java:142)
    at org.aspectj.org.eclipse.jdt.internal.compiler.apt.dispatch.RoundDispatcher.round(RoundDispatcher.java:124)
    at org.aspectj.org.eclipse.jdt.internal.compiler.apt.dispatch.BaseAnnotationProcessorManager.processAnnotations(BaseAnnotationProcessorManager.java:171)
    at org.aspectj.org.eclipse.jdt.internal.compiler.Compiler.processAnnotations(Compiler.java:956)
    at org.aspectj.org.eclipse.jdt.internal.compiler.Compiler.compile(Compiler.java:451)
    at org.aspectj.org.eclipse.jdt.internal.compiler.Compiler.compile(Compiler.java:427)
    at org.aspectj.ajdt.internal.core.builder.AjBuildManager.performCompilation(AjBuildManager.java:1107)
    at org.aspectj.ajdt.internal.core.builder.AjBuildManager.performBuild(AjBuildManager.java:276)
    at org.aspectj.ajdt.internal.core.builder.AjBuildManager.batchBuild(AjBuildManager.java:189)
    at org.aspectj.ajdt.ajc.AjdtCommand.doCommand(AjdtCommand.java:114)
    at org.aspectj.ajdt.ajc.AjdtCommand.runCommand(AjdtCommand.java:60)
    at org.aspectj.tools.ajc.Main.run(Main.java:371)
    at org.aspectj.tools.ajc.Main.runMain(Main.java:248)
    at org.codehaus.mojo.aspectj.AbstractAjcCompiler.execute(AbstractAjcCompiler.java:544)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:137)
    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:956)
    at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:288)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:192)
    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)

这种情况发生在所有 @ProxyFor 类中，这些类是项目外部类的代理(通过 Maven 依赖项解决)。

@ProxyFor(value = ClassOfOtherProject.class)
public interface ClassOfOtherProjectProxy extends EntityProxy { // <- NPE happens in this Line!

    ...

}

摘自 pom.xml:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.8.1</version>
    <configuration>
        <source>1.8</source>
        <target>1.8</target>
        <useIncrementalCompilation>false</useIncrementalCompilation>
        <encoding>UTF-8</encoding>
        <annotationProcessors>
            <annotationProcessor>com.google.web.bindery.requestfactory.apt.RfValidator</annotationProcessor>
        </annotationProcessors>
    </configuration>
    <dependencies>
        <dependency>
            <groupId>com.google.web.bindery</groupId>
            <artifactId>requestfactory-apt</artifactId>
            <version>2.8.2</version>
        </dependency>
    </dependencies>
</plugin>

仅在aspectjrt 1.8.4(或更低版本)下才能正常运行。我应该怎么办？从 Java 7 迁移到 8 以及 GWT 1.7.x 迁移到 1.8.2 后，这些错误仍然存​​在。如何更新aspectjrt而不获取这些NPE？

Answer 1

这并不是 GWT 编译失败，而只是在将 java 源代码编译为字节码的过程中失败。 GWT 的 RequestFactory 使用注释处理器来验证每个代理是否正确匹配它们在服务器上映射到的实体/值/服务类型，并且此版本的aspectjrt和jdt似乎无法正确查找成员ClassOfOtherProject 的内容，以便可以对其进行过滤以查找构造函数。从您的堆栈跟踪中，com/google/web/bindery/requestfactory/apt/DomainChecker.java:407:

List<ExecutableElement> constructors = ElementFilter.constructorsIn(x.getEnclosedElements());

这是在注释处理器中执行操作的一种非常标准的方法 - 如果调用 TypeElement.getEnclosureElements() 因该注释处理器的 NPE 失败，我也会担心此构建中的其他错误。任何注释处理器都很有可能发生这种情况，与 GWT 无关。