Servlet [Jersey REST服务]的Servlet.service（）java.lang.NullPointerException

Question

谁能帮我解决这个问题。 这是我第一次创建Restful API。

web.xml中

 <display-name>1FxAll</display-name>
<servlet>
    <servlet-name>Jersey REST Service</servlet-name>
    <servlet-class>
  org.glassfish.jersey.servlet.ServletContainer
</servlet-class>
    <init-param>
      <param-name>jersey.config.server.provider.packages</param-name>
      <param-value>com.sample.blitz</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>Jersey REST Service</servlet-name>
    <url-pattern>/api/*</url-pattern>
  </servlet-mapping>

UserController.java

package com.sample.blitz;

@Path("/user")
public class UserController{
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String test(){
        return "user";
    }
}

完整的stacktrace错误。

SEVERE: Servlet.service() for servlet [Jersey REST Service] in context with path [/1FxAll] threw exception [java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at com.sample.blitz.UserController.test(UserController.java:28)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:151)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:171)
    at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:195)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:104)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:384)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:342)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:101)
    at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:271)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:297)
    at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:254)
    at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1030)
    at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:373)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:381)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:344)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:221)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

它总是说错误在UserController第28行，但是当我检查时没有第28行。

我正在使用Tomcat 7.0。 我也尝试切换到glassfish，但是遇到了同样的错误。

谢谢..

Answer 1

我将在这里发布我的答案。

我不确定glassfish 4.0和4.1有什么关系，但是在我将glassfish版本从4.0更改为4.1并从lib文件夹中删除jersey文件后，它似乎可以正常工作，但在tomcat中我仍然收到NullPointerException。 这仅适用于glassfish 4.1 。

Answer 2

从@Path("/user")删除/ ，使其成为@Path("user") 。 Bcoz，U已经给予类似的路径/api/*中<url-pattern>我认为这是双重的出现/

将您的UserController类更改为

package com.sample.blitz;

@Path("user")
public class UserController{
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String test(){
        return "user";
    }
}

Answer 3

您已为RESTFull添加以下依赖项

<dependency>
    <groupId>org.glassfish.jersey.ext</groupId>
    <artifactId>jersey-spring3</artifactId>
</dependency>

<dependency>
    <groupId>org.glassfish.jersey.ext</groupId>
    <artifactId>jersey-bean-validation</artifactId>
</dependency>

Answer 4

创建服务对象时，请使用新关键字实例化它。

Xservice x = new Xservice();