与Google App Engine一起使用JAX-RS Web服务时，FilteringJacksonJaxbJsonProvider上的NullPointerException

问题描述 投票：0回答：1

我有一个使用JAX-RS Web服务的Maven Google App Engine Java项目。当项目部署在Google Cloud Platform上时，有时访问/api/sites时会收到500服务器错误响应。

    org.eclipse.jetty.servlet.ServletHandler doHandle:  (ServletHandler.java:624)
javax.servlet.ServletException: java.lang.NullPointerException
    at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:432)
    at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:370)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:389)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:342)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:229)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:848)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1772)
    at com.googlecode.objectify.ObjectifyFilter.doFilter(ObjectifyFilter.java:48)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759)
    at ro.h23.pricechecker.productgaewebserver.filters.URLFilter.doFilter(URLFilter.java:64)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759)
    at com.googlecode.objectify.ObjectifyFilter.doFilter(ObjectifyFilter.java:48)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759)
    at com.google.apphosting.utils.servlet.JdbcMySqlConnectionCleanupFilter.doFilter(JdbcMySqlConnectionCleanupFilter.java:60)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1759)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:582)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:524)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:226)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:134)
    at com.google.apphosting.runtime.jetty9.ParseBlobUploadHandler.handle(ParseBlobUploadHandler.java:120)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1182)
    at com.google.apphosting.runtime.jetty9.AppEngineWebAppContext.doHandle(AppEngineWebAppContext.java:171)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:512)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1112)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
    at com.google.apphosting.runtime.jetty9.AppVersionHandlerMap.handle(AppVersionHandlerMap.java:297)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:134)
    at org.eclipse.jetty.server.Server.handle(Server.java:534)
    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:320)
    at com.google.apphosting.runtime.jetty9.RpcConnection.handle(RpcConnection.java:202)
    at com.google.apphosting.runtime.jetty9.RpcConnector.serviceRequest(RpcConnector.java:81)
    at com.google.apphosting.runtime.jetty9.JettyServletEngineAdapter.serviceRequest(JettyServletEngineAdapter.java:123)
    at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.dispatchServletRequest(JavaRuntime.java:693)
    at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.dispatchRequest(JavaRuntime.java:655)
    at com.google.apphosting.runtime.JavaRuntime$RequestRunnable.run(JavaRuntime.java:625)
    at com.google.apphosting.runtime.JavaRuntime$NullSandboxRequestRunnable.run(JavaRuntime.java:819)
    at com.google.apphosting.runtime.ThreadGroupPool$PoolEntry.run(ThreadGroupPool.java:274)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
    at org.glassfish.jersey.jackson.internal.FilteringJacksonJaxbJsonProvider.writeTo(FilteringJacksonJaxbJsonProvider.java:130)
    at org.glassfish.jersey.message.internal.WriterInterceptorExecutor$TerminalWriterInterceptor.invokeWriteTo(WriterInterceptorExecutor.java:266)
    at org.glassfish.jersey.message.internal.WriterInterceptorExecutor$TerminalWriterInterceptor.aroundWriteTo(WriterInterceptorExecutor.java:251)
    at org.glassfish.jersey.message.internal.WriterInterceptorExecutor.proceed(WriterInterceptorExecutor.java:163)
    at org.glassfish.jersey.server.internal.JsonWithPaddingInterceptor.aroundWriteTo(JsonWithPaddingInterceptor.java:109)
    at org.glassfish.jersey.message.internal.WriterInterceptorExecutor.proceed(WriterInterceptorExecutor.java:163)
    at org.glassfish.jersey.server.internal.MappableExceptionWrapperInterceptor.aroundWriteTo(MappableExceptionWrapperInterceptor.java:85)
    at org.glassfish.jersey.message.internal.WriterInterceptorExecutor.proceed(WriterInterceptorExecutor.java:163)
    at org.glassfish.jersey.message.internal.MessageBodyFactory.writeTo(MessageBodyFactory.java:1135)
    at org.glassfish.jersey.server.ServerRuntime$Responder.writeResponse(ServerRuntime.java:662)
    at org.glassfish.jersey.server.ServerRuntime$Responder.processResponse(ServerRuntime.java:395)
    at org.glassfish.jersey.server.ServerRuntime$Responder.process(ServerRuntime.java:385)
    at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:280)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:272)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:268)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:316)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:298)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:268)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:289)
    at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:256)
    at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:703)
    at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:416)
    ... 40 more

Jersey Web服务的代码是：

@GET
@Produces({MediaType.APPLICATION_JSON})
public List<Site> getSites() {
    //List<Site> siteList = DatastoreDBManager.getInstance().getSites();
    List<Site> siteList = ofy().load().type(Site.class).list();
    //return Response.status(Status.OK).entity(new GenericEntity<List<Site>>(siteList){}).build(); 
    return siteList;
}

Maven pom：

<dependency>
        <groupId>com.google.appengine</groupId>
        <artifactId>appengine-api-1.0-sdk</artifactId>
        <version>1.9.64</version>
</dependency>
....
<dependency>
    <groupId>org.glassfish.jersey.core</groupId>
    <artifactId>jersey-client</artifactId>
    <version>2.26</version>
</dependency>
<dependency>
    <groupId>org.glassfish.jersey.core</groupId>
    <artifactId>jersey-server</artifactId>
    <version>2.26</version>
</dependency>
<dependency>
    <groupId>org.glassfish.jersey.containers</groupId>
    <artifactId>jersey-container-servlet-core</artifactId>
    <version>2.26</version>
</dependency>
<dependency>
    <groupId>org.glassfish.jersey.containers</groupId>
    <artifactId>jersey-container-servlet</artifactId>
    <version>2.26</version>
</dependency>
<dependency>
    <groupId>org.glassfish.jersey.inject</groupId>
    <artifactId>jersey-hk2</artifactId>
    <version>2.26</version>
</dependency>
<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-json-jackson</artifactId>
    <version>2.26</version>
</dependency>

据我所知，由于NullPointerException，唯一可能的解释是该提供程序未注入到FilteringJacksonJaxbJsonProvider类中。为什么？我缺少依赖吗？为什么这种情况仅在某些时候发生？

我已经尝试使用以下依赖项并获得类似结果：

<dependency>
    <groupId>com.fasterxml.jackson.jaxrs</groupId>
    <artifactId>jackson-jaxrs-json-provider</artifactId>
    <version>2.9.4</version>
</dependency>

奇怪的是，有时当我部署应用程序时，它不起作用，有时却可以。一段时间后，它不再起作用，再过一段时间后，它将再次起作用。 Google Cloud Platform动态管理应用程序实例的数量。似乎对于某些实例，我得到了500个HTTP响应代码。

Site类只有四个字符串属性。我知道我可以用return new Gson().toJson(siteList);替换Web服务，但是我真的想使用内置的转换功能。

有什么想法吗？

java json google-app-engine jax-rs
1个回答
0
投票

我遇到了完全相同的问题，经过大量调试，我发现问题出在我使用的CORSFilter上。

import java.io.IOException;

import javax.ws.rs.container.ContainerRequestContext;
import javax.ws.rs.container.ContainerResponseContext;
import javax.ws.rs.container.ContainerResponseFilter;
import javax.ws.rs.ext.Provider;

@Provider
public class CORSFilter implements ContainerResponseFilter {

    @Override
    public void filter(ContainerRequestContext requestContext, ContainerResponseContext responseContext)
            throws IOException {

        responseContext.getHeaders().add("Access-Control-Allow-Origin", "*");
        responseContext.getHeaders().add("Access-Control-Allow-Headers", "Content-Type");
        responseContext.getHeaders().add("Access-Control-Allow-Methods", "DELETE");

    }

}

删除该过滤器可以解决此问题。希望对您有所帮助。

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