API Explorer 给出错误 - 无法检索状态为 500 的 API 配置

Question

我一直在使用 GAE 为我的 Android 应用程序构建一个后端，并且我正在使用 Endpoints API。到目前为止，我已经能够在开发服务器上成功部署后端。今天，出乎意料的是，我在部署后端时遇到了这个异常。我根本没有更改后端代码，而是专门在前端工作。以下是例外：

    "C:\Program Files\Java\jdk1.8.0_102\bin\java" -javaagent:C:\Users\Digvijay\.gradle\appengine-sdk\appengine-java-sdk-1.9.49\lib\agent\appengine-agent.jar -Xbootclasspath/p:C:\Users\Digvijay\.gradle\appengine-sdk\appengine-java-sdk-1.9.49\lib\override\appengine-dev-jdk-overrides.jar -Didea.launcher.port=7533 "-Didea.launcher.bin.path=C:\Program Files\Android\Android Studio\bin" -Dfile.encoding=windows-1252 -classpath "C:\Users\Digvijay\.gradle\appengine-sdk\appengine-java-sdk-1.9.49\lib\appengine-tools-api.jar;C:\Program Files\Android\Android Studio\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain com.google.appengine.tools.development.DevAppServerMain --address=localhost --port=8080 C:\Users\Digvijay\AndroidStudioProjects\LearnCity\backend\build\exploded-app
    Feb 09, 2017 9:51:16 PM java.util.prefs.WindowsPreferences <init>
    WARNING: Could not open/create prefs root node Software\JavaSoft\Prefs at root 0x80000002. Windows RegCreateKeyEx(...) returned error code 5.
    Feb 09, 2017 9:51:18 PM com.google.appengine.tools.development.SystemPropertiesManager setSystemProperties
    INFO: Overwriting system property key 'java.util.logging.config.file', value 'C:\Users\Digvijay\.gradle\appengine-sdk\appengine-java-sdk-1.9.49\config\sdk\logging.properties' with value 'WEB-INF/logging.properties' from 'C:\Users\Digvijay\AndroidStudioProjects\LearnCity\backend\build\exploded-app\WEB-INF\appengine-web.xml'
    Feb 09, 2017 9:51:18 PM com.google.apphosting.utils.jetty.JettyLogger info
    INFO: Logging to JettyLogger(null) via com.google.apphosting.utils.jetty.JettyLogger
    Feb 09, 2017 4:21:18 PM com.google.apphosting.utils.jetty.JettyLogger info
    INFO: jetty-6.1.x
    Feb 09, 2017 4:21:19 PM com.google.apphosting.utils.jetty.JettyLogger info
    INFO: Started SelectChannelConnector@localhost:8080
    Feb 09, 2017 4:21:19 PM com.google.appengine.tools.development.AbstractModule startup
    INFO: Module instance default is running at http://localhost:8080/
    Feb 09, 2017 4:21:19 PM com.google.appengine.tools.development.AbstractModule startup
    INFO: The admin console is running at http://localhost:8080/_ah/admin
    Feb 09, 2017 9:51:19 PM com.google.appengine.tools.development.DevAppServerImpl doStart
    INFO: Dev App Server is now running
    Feb 09, 2017 9:51:48 PM com.google.appengine.tools.development.LocalResourceFileServlet doGet
    WARNING: No file found for: /favicon.ico
    Feb 09, 2017 9:51:50 PM com.google.apphosting.utils.jetty.JettyLogger warn
    WARNING: Error for /_ah/spi/BackendService.getApiConfigs
    java.lang.StackOverflowError
        at java.lang.System.getProperty(System.java:714)
        at com.google.appengine.tools.development.agent.runtime.Runtime.checkRestricted(Runtime.java:62)
        at com.googlecode.objectify.impl.FieldProperty.<init>(FieldProperty.java:36)
        at com.googlecode.objectify.impl.translate.ClassPopulator.getDeclaredProperties(ClassPopulator.java:209)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:84)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEmbeddedClassTranslator(ClassTranslatorFactory.java:75)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:50)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEntityClassTranslator(ClassTranslatorFactory.java:66)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:49)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEmbeddedClassTranslator(ClassTranslatorFactory.java:75)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:50)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEntityClassTranslator(ClassTranslatorFactory.java:66)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:49)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEmbeddedClassTranslator(ClassTranslatorFactory.java:75)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:50)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at 
  com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEntityClassTranslator(ClassTranslatorFactory.java:66)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:49)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEmbeddedClassTranslator(ClassTranslatorFactory.java:75)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:50)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEntityClassTranslator(ClassTranslatorFactory.java:66)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:49)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEmbeddedClassTranslator(ClassTranslatorFactory.java:75)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:50)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEntityClassTranslator(ClassTranslatorFactory.java:66)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:49)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEmbeddedClassTranslator(ClassTranslatorFactory.java:75)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:50)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEntityClassTranslator(ClassTranslatorFactory.java:66)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:49)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEmbeddedClassTranslator(ClassTranslatorFactory.java:75)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:50)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEntityClassTranslator(ClassTranslatorFactory.java:66)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:49)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEmbeddedClassTranslator(ClassTranslatorFactory.java:75)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:50)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)
        at com.googlecode.objectify.impl.translate.Translators.get(Translators.java:117)
        at com.googlecode.objectify.impl.translate.CreateContext.getTranslator(CreateContext.java:27)
        at com.googlecode.objectify.impl.translate.ClassPopulator.<init>(ClassPopulator.java:88)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.createEntityClassTranslator(ClassTranslatorFactory.java:66)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:49)
        at com.googlecode.objectify.impl.translate.ClassTranslatorFactory.create(ClassTranslatorFactory.java:36)
        at com.googlecode.objectify.impl.translate.Translators.create(Translators.java:138)

    Feb 09, 2017 9:51:50 PM com.google.apphosting.utils.jetty.JettyLogger warn
    WARNING: /_ah/api/explorer: java.io.IOException: Failed to retrieve API configs with status: 500
    Feb 09, 2017 9:52:07 PM com.google.apphosting.utils.jetty.JettyLogger warn
    WARNING: /_ah/spi/BackendService.getApiConfigs
    java.lang.NullPointerException
        at com.google.api.server.spi.SystemServiceServlet.execute(SystemServiceServlet.java:100)
        at com.google.api.server.spi.SystemServiceServlet.doPost(SystemServiceServlet.java:71)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
        at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
        at com.googlecode.objectify.ObjectifyFilter.doFilter(ObjectifyFilter.java:48)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:128)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:63)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:48)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:122)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectRequest(DevAppServerModulesFilter.java:366)
        at com.google.appengine.tools.development.DevAppServerModulesFilter.doDirectModuleRequest(DevAppServerModulesFilter.java:349)
        at com.google.appengine.tools.development.DevAppServerModulesFilter.doFilter(DevAppServerModulesFilter.java:116)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
        at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
        at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
        at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
        at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
        at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:95)
        at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
        at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:508)
        at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
        at org.mortbay.jetty.Server.handle(Server.java:326)
        at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
        at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)
        at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
        at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
        at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
        at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
        at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

    Feb 09, 2017 9:52:07 PM com.google.apphosting.utils.jetty.JettyLogger warn
    WARNING: /_ah/api/discovery/v1/apis/myApi/v1/rest: java.io.IOException: Failed to retrieve API configs with status: 500

    Process finished with exit code -1

有人对上述问题有任何线索吗？

Answer 1

我在黑暗中拍摄了几个小时的答案后发布了答案。

第一条线索：异常跟踪显示 Objectify 反复调用，并且 @stickfigure 要求我发布我试图坚持的实体，他的猜测是正确的 - 问题在于实体。

我不知道这是有意的还是偶然的，但我现在要公开的是 Objectify 的一个警告。我正在使用 Objectify 5.1.14（目前最新），这可能也适用于旧版本。

显然 Objectify 不允许 2 个具有交叉引用的实体。例如，我有两个实体 Entity1 和 Entity2 如下：

@Entity
public class Entity1 {

    @Id
    private long id;
    private Entity2 entity2;
}

@Entity
public class Entity2 {

    @Id
    private long id;
    private Entity1 entity1;
}

如果您为它们生成端点（您自己或 GAE 插件），后端将编译得很好并且应该被部署。但是任何持久化或访问 API Explorer 的尝试都会导致上述异常。

解决方案：显而易见的解决方案是不使用交叉引用。还有另一种解决方案，但如果您不关心交叉引用不会保留在数据存储中 - 请使用 @Ignore Objectify 注释，如下所示：

@Entity
    public class Entity1 {

    @Id
    private long id;
    @Ignore
    private Entity2 entity2;
}

@Entity
public class Entity2 {

    @Id
    private long id;
    @Ignore
    private Entity1 entity1;
}

注意：任何一个实体只要有 1 个 @Ignore 就可以了。

您可以测试上述场景，并在交叉引用的情况下得到异常。

最后，我不确定，但根据搜索，问题似乎出在发现文档的生成中。