从 Java 代码执行 Cypher 查询时出现空异常错误。 (Neo4J)

Question

我一直在深入研究 Neo4j 2.0 GA 版本并学习在示例 Java 应用程序中使用它。我正在使用一个独立的 Neo4j 数据库，并通过 neo4j-rest-graphdb:2.0.0 依赖 jar 中的 java rest 绑定连接到它。在我正在使用的代码下面...

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();
    }
}
}

为了确保我的数据库已启动并运行，我添加了一行来查询已知的现有节点，我确实得到了结果。但是，当我尝试执行查询时，出现以下错误...

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)

从日志的第一行可以看出，数据库确实返回了我请求的用户。有什么我遗漏的吗？

编辑：我可以从浏览器控制台成功地在数据库上运行这些查询。我也使用嵌入式数据库进行了尝试，它从代码中成功运行。独立实例上是否有一些可能导致此问题的数据库配置？

感谢您的帮助。

Answer 1

你必须使用new RestCypherQueryEngine(gd.getRestApi())和

然后使用

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

你也可以直接使用RestAPI：

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

从不做，不工作：

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