Camel简单表达式抛出NPE

Question

在Camel（JBoss Fuse，特别是Spring DSL）中，我试图用Camel简单表达式读取布尔值。

<simple resultType="java.lang.Boolean">${body} != null and ${body.fielda} != null and ${body.fielda.fieldb} != null and ${body.fielda.fieldb}</simple>

<simple resultType="java.lang.Boolean">${body?.fielda?.fieldb}</simple>

${body}是一个有效的非空POJO，'fielda'是另一个嵌套POJO，fieldb是一个布尔值。Fielda可以为空，但body不能为空。

当fielda为非null时，我能够读取值而不会出错。

从各种文档来源（Apache Camel Simple、JBoss Fuse）可以看出

？。

构造可以用作空安全字段读取。

当field da为null并且实际上我无法在这里提供null安全读取时，上述两个都抛出NPE。谢谢你的帮助。

堆栈如下所示：

 java.lang.NullPointerException
 at org.apache.camel.component.bean.ConstantBeanHolder.<init>(ConstantBeanHolder.java:43)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.language.bean.BeanExpression$OgnlInvokeProcessor.process(BeanExpression.java:264)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.language.bean.BeanExpression.evaluate(BeanExpression.java:114)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.language.bean.BeanExpression.evaluate(BeanExpression.java:132)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.model.language.ExpressionDefinition.evaluate(ExpressionDefinition.java:120)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.model.language.ExpressionDefinition.evaluate(ExpressionDefinition.java:112)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.builder.ExpressionBuilder$34.evaluate(ExpressionBuilder.java:843)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.support.ExpressionAdapter.evaluate(ExpressionAdapter.java:36)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.builder.BinaryPredicateSupport.matchesReturningFailureMessage(BinaryPredicateSupport.java:60)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.builder.BinaryPredicateSupport.matches(BinaryPredicateSupport.java:50)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.language.simple.ast.BinaryExpression$5.evaluate(BinaryExpression.java:227)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.util.ExpressionToPredicateAdapter.matches(ExpressionToPredicateAdapter.java:37)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.builder.SimpleBuilder.matches(SimpleBuilder.java:76)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.ChoiceProcessor.process(ChoiceProcessor.java:90)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.management.InstrumentationProcessor.process(InstrumentationProcessor.java:77)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.interceptor.TraceInterceptor.process(TraceInterceptor.java:163)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.RedeliveryErrorHandler.process(RedeliveryErrorHandler.java:448)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.CamelInternalProcessor.process(CamelInternalProcessor.java:191)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.Pipeline.process(Pipeline.java:118)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.Pipeline.process(Pipeline.java:80)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.CamelInternalProcessor.process(CamelInternalProcessor.java:191)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.component.direct.DirectProducer.process(DirectProducer.java:51)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.RoutingSlip$2.doInAsyncProducer(RoutingSlip.java:301)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.impl.ProducerCache.doInAsyncProducer(ProducerCache.java:304)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.RoutingSlip.processExchange(RoutingSlip.java:294)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.RoutingSlip.doRoutingSlip(RoutingSlip.java:215)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.RoutingSlip.process(RoutingSlip.java:146)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.management.InstrumentationProcessor.process(InstrumentationProcessor.java:77)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.interceptor.TraceInterceptor.process(TraceInterceptor.java:163)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.CamelInternalProcessor.process(CamelInternalProcessor.java:191)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.TryProcessor.process(TryProcessor.java:113)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.TryProcessor.process(TryProcessor.java:84)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.management.InstrumentationProcessor.process(InstrumentationProcessor.java:77)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.interceptor.TraceInterceptor.process(TraceInterceptor.java:163)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.CamelInternalProcessor.process(CamelInternalProcessor.java:191)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.Pipeline.process(Pipeline.java:118)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.Pipeline.process(Pipeline.java:80)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.processor.CamelInternalProcessor.process(CamelInternalProcessor.java:191)[111:org.apache.camel.camel-core:2.15.1.redhat-620133]
 at org.apache.camel.component.jetty.CamelContinuationServlet.service(CamelContinuationServlet.java:162)[133:org.apache.camel.camel-jetty-common:2.15.1.redhat-620133]
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:668)[66:org.apache.geronimo.specs.geronimo-servlet_3.0_spec:1.0.0]
 at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:684)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1496)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.servlets.MultiPartFilter.doFilter(MultiPartFilter.java:136)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.apache.camel.component.jetty.CamelFilterWrapper.doFilter(CamelFilterWrapper.java:43)[133:org.apache.camel.camel-jetty-common:2.15.1.redhat-620133]
 at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1467)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:501)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:429)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.server.Server.handle(Server.java:370)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:494)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:982)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:1043)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:865)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:240)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:696)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:53)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:608)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:543)[70:org.eclipse.jetty.aggregate.jetty-all-server:8.1.17.v20150415]
 at java.lang.Thread.run(Thread.java:745)[:1.8.0_66]

Answer 1

如果这些字段可用，可以对其使用getter方法：

${body.getFielda} != null and ${body.fetFielda.getFieldb} != null

Answer 2

这个您尝试使用的语法仅适用于Spring表达式语言（SPEL）。请在此处查看Camel文档：http://camel.apache.org/spel.html

下面是该页面中的一个示例：

<route>
  <from uri="direct:foo"/>
  <filter>
    <spel>#{request.headers['foo'] == 'bar'}</spel>
    <to uri="direct:bar"/>
  </filter>
</route>

Answer 3

       <setProperty propertyName="propName">
           <xpath resultType="java.lang.Boolean">//*[local-name()='NodeName'][text() = 'true']</xpath>
       </setProperty>

这绝对可靠，而且是以零安全的方式工作的。我非常失望，骆驼。