Java 拆分为字符串数组时出现空指针异常

所以我试图从一个文件读取器中填充两个数组。我认为这需要嵌套循环。我想我走对了方向，但从昨天起我就有点困了。此程序的目的是通过jsp启动程序，并动态读取值。任何帮助都将不胜感激。我想我走对了方向，但我似乎无法独自完成。fxRates.csv的第一行应填充到currencyCodes数组中，其余行应填充到二维数组fxExchangeRates中。我得到的代码没有任何错误，但现在我得到的是当我尝试运行程序时：

以下是错误日志：

 Info:   visiting unvisited references
Info:   visiting unvisited references
Info:   visiting unvisited references
Warning:   Ignore WEB-INF/sun-web.xml in archive /G:/School/Java II/Labs/MidtermAD/build/web/, as WLS counterpart runtime xml WEB-INF/glassfish-web.xml is present in the same archive.
Info:   Loading application [MidtermAD] at [/MidtermAD]
Info:   MidtermAD was successfully deployed in 464 milliseconds.
Warning:   StandardWrapperValve[jsp]: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
    at java.lang.String.split(String.java:2337)
    at java.lang.String.split(String.java:2422)
    at data.FxDataModel.<init>(FxDataModel.java:38)
    at org.apache.jsp.fxCalc_jsp.jspInit(fxCalc_jsp.java:45)
    at org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:92)
    at org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:210)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:473)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:377)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:415)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:282)
    at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
    at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:201)
    at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:175)
    at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
    at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:284)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:201)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:133)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:112)
    at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
    at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:561)
    at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:565)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:545)
    at java.lang.Thread.run(Thread.java:745)

fxRates.csv文件还包含以下代码：

CAD,EUR,GBP,USD
1.0,0.624514066,0.588714763,0.810307
1.601244959,1.0,0.942676548,1.2975
1.698615463,1.060809248,1.0,1.3764
1.234100162,0.772200772,.726532984,1.0

在FxDataModel.Java类中 您将属性引用声明为

private properties fxProps

但您没有为对象指定属性。默认情况下，它被分配了
null
，在您调用的
fxProps.getProperty（FX\u RATES\u FILE\u DLMTR\u KEY）的空值上。因此，JVM在运行时抛出NullPointerException

解决方案：

private Properties fxProps = new Properties();
fxProps .setProperty(FX_RATES_FILE_DLMTR_KEY,"fx.rates.file.dlmtr");
private String delimiter = fxProps.getProperty( FX_RATES_FILE_DLMTR_KEY );

太多的代码。仅提供相关内容。可以谢谢我删除了一些内容并缩小了问题的范围。您从未使用任何值填充
fxProps
属性。TL；博士可能重复的话题：你应该让你的。。。了解情况。检查FxDataModel.Java的更新。我按照你的建议做了，但仍然得到一个NullPointerException。它总是指向第38行，也就是我使用分隔符拆分文件的第一行时。这里是您的示例：String delimiter=fxProps.getProperty（FX_RATES_FILE_DLMTR_KEY）；//返回null fxCurrences=reader.nextLine（）.split（分隔符）；所以，这个拆分（null）方法抛出NullPointerException。但分隔符怎么可能是null呢。我将其设置为String delimiter=fxProps.getProperty（FX\u RATES\u FILE\u DLMTR\u KEY）；就像你告诉我的那样，我发起了fxProps。是否还有其他原因导致该值为null？是的，您提供的分隔符值为null。（fxProps.getProperty（FX\u RATES\u FILE\u DLMTR\u KEY）返回null）这就是它引发异常的原因。我该如何修复它？为什么（fxProps.getProperty（FX\u RATES\u FILE\u DLMTR\u KEY）没有从文件返回值？它甚至定义为：公共静态最终字符串FX\u RATES\u FILE\u DLMTR\u KEY=“FX.RATES.FILE.DLMTR”；这就是为什么我如此困惑。
    <%@include file="fxInit.jsp"%>
<%      
        Properties fxProps = fxDataModel.getFxProps();
        String srcAmtName = fxProps.getProperty(FxDataModel.SRC_AMT_KEY );
        String dstAmtName = fxProps.getProperty(FxDataModel.DST_AMT_KEY );
        String srcCucyName = fxProps.getProperty(FxDataModel.SRC_CUCY_KEY );
        String dstCucyName = fxProps.getProperty(FxDataModel.DST_CUCY_KEY );
        String Curr1 = request.getParameter(srcAmtName);
        String Curr2 = request.getParameter(dstAmtName);
        String formInput;
        String formOutput;

        String[] currencies = fxDataModel.getFxCurrencies();


        try {

          formInput = request.getParameter(srcAmtName);
          Double formDouble = Double.parseDouble(formInput);
          Double Conversion = fxDataModel.getFxRate(Curr1,Curr2)*formDouble;
          formOutput = String.valueOf(Conversion);

         } catch (NumberFormatException ex) {
             Curr1= Curr2 = currencies[0];
             formInput = ("");
             formOutput = ("");   
         } catch (NullPointerException npe){

            Curr1= Curr2 = currencies[0];
            formInput = ("");
            formOutput = ("");

        }

%>

<html>
    <head>
        <title>F/X Calculator</title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
    </head>

    <style>

        h1{
            color: white;
            font-family: verdana;
            font-size: 200%;
            font-style: italic;
            text-align: center;
        }
        hr{
            color:white;

        }

        select{
            margin-top: 30px;
            margin-right:10px;
        }
        input{

            margin-top: 30px;
            margin-right:10px;
        }
    </style>


    <body bgcolor = "blue">

        <h1>
            Money Banks F/X Calculator<br>
        </h1>
        <hr>
        <div align="center">
        <form name ="fxCalc" action="fxCalc.jsp" method="POST">


        <select name="<%=srcCucyName%>">
            <% for (String currency : currencies) { %>
              <option value="<%=currency%>" <%=currency.equals(Curr1)?"selected":""%>><%=currency%></option>
            <%}%>
        </select>


            <input name="<%=srcAmtName%>" type="text" value = <%=formInput%> >

        <select name="<%=dstCucyName%>">
            <% for (String currency : currencies) { %>
              <option value="<%=currency%>" <%=currency.equals(Curr2)?"selected":""%>><%=currency%></option>
            <%}%>
        </select>


            <input name="<%=dstAmtName%>" type="text" disabled="disabled" value = <%=formOutput%>>

            <br>


            <input name="submitbutton" type="submit" value="Convert" name="Convert"/>
            <input name="resetbutton" type="reset" value="Reset"/>  




       <form/> 
       <div/>
    </body>
</html>

dst.amt=dstAmt
dst.cucy=dstCucy
fx.rates.file.dlmtr=,
fx.rates.file.name=/WEB-INF/fxRates.csv
src.amt=srcAmt
src.cucy=srcCucy

CAD,EUR,GBP,USD
1.0,0.624514066,0.588714763,0.810307
1.601244959,1.0,0.942676548,1.2975
1.698615463,1.060809248,1.0,1.3764
1.234100162,0.772200772,.726532984,1.0

private Properties fxProps = new Properties();
fxProps .setProperty(FX_RATES_FILE_DLMTR_KEY,"fx.rates.file.dlmtr");
private String delimiter = fxProps.getProperty( FX_RATES_FILE_DLMTR_KEY );