从Java代码执行Cypher查询时出现Null Exception错误。 （Neo4j的）

Question

I have been digging into Neo4j 2.0 GA release and learning to work with it in a sample Java application. I am using a standalone Neo4j db and connecting to it via the java rest bindings from the neo4j-rest-graphdb:2.0.0 dependency jar. Below in the code I am working with...

import org.apache.log4j.Logger;
import org.neo4j.cypher.javacompat.ExecutionEngine;
import org.neo4j.cypher.javacompat.ExecutionResult;
import org.neo4j.graphdb.GraphDatabaseService;
import org.neo4j.graphdb.Transaction;
import org.neo4j.rest.graphdb.RestGraphDatabase;

public class NeoService {

Logger log = Logger.getLogger(this.getClass());
GraphDatabaseService gd; 
ExecutionEngine engine;

public NeoService(){
    gd = new RestGraphDatabase("http://neo4jbox:7474/db/data/");
    engine = new ExecutionEngine(gd);
}


public String createPerson() {
    ExecutionResult result;

    try(Transaction tx = gd.beginTx()){
        log.info("Returned person: " + gd.getNodeById(177L).getProperty("username").toString());
        String query = "match (p:Person{username:'someusername'}) return p";
        result = engine.execute(query);
        tx.success();
        log.info(query);
        log.info(result.dumpToString());
        return result.dumpToString();
    }
}
}

Just to be sure my db was up and running, I added a line to query for a known existing node and I do get a result back. However, when I attempt to execute the query, I get the following error...

2014-01-15 09:51:20.477  INFO 18078 --- [nio-8080-exec-1] com.yookos.neostart.services.DbService   : Returned person: jomski2009
2014-01-15 09:51:20.752 ERROR 18078 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException: null
at org.neo4j.cypher.ExecutionEngine.prepare(ExecutionEngine.scala:75)
at org.neo4j.cypher.ExecutionEngine.profile(ExecutionEngine.scala:43)
at org.neo4j.cypher.ExecutionEngine.profile(ExecutionEngine.scala:51)
at org.neo4j.cypher.javacompat.ExecutionEngine.profile(ExecutionEngine.java:94)
at com.yookos.neostart.services.DbService.createPerson(DbService.java:35)
at com.yookos.neostart.controller.HomeController.createPerson(HomeController.java:25)
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.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:214)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:748)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:689)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:83)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:945)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:876)
at org.sprinork.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:931)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:822)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:807)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilter(WebRequestTraceFilter.java:114)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.boot.actuate.autoconfigure.EndpointWebMvcAutoConfiguration$1.doFilterInternal(EndpointWebMvcAutoConfiguration.java:126)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.springframework.boot.actuate.autoconfigure.MetricFilterAutoConfiguration$MetricsFilter.doFilter(MetricFilterAutoConfiguration.java:97)
at org.springframework.boot.actuate.autoconfigure.MetricFilterAutoConfiguration$MetricsFilter.doFilter(MetricFilterAutoConfiguration.java:82)
at org.apache.catalina.core.ApplicationFiln.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.valves.RemoteIpValve.invoke(RemoteIpValve.java:680)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1721)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1679)
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:744)

As you can see from the first line in the logs, the db does return the user I requested for. Is there anything I am missing out?

EDIT: I can successfully run these queries on the db from the browser console. I also did try this using an embedded database and it ran successfully from the code. Is there some db configuration on the standalone instance that may be causing this?

Thanks for your help.

Answer 1

You have to use new RestCypherQueryEngine(gd.getRestApi()) and

then use

QueryResult<Map<String, Object>> engine.query(String statement, Map<String, Object> params)

You can also use RestAPI directly:

QueryResult<Map<String, Object>> restApi.query(String statement, Map<String, Object> params, ResultConverter resultConverter);

NEVER DO, DOESN'T WORK:

gd = new RestGraphDatabase("http://neo4jbox:7474/db/data/");
engine = new ExecutionEngine(gd);