Tomcat 8上Eclipse项目的WebServlet中的java.lang.NullPointerException

当我在Tomcat服务器上运行应用程序时，出现了这个错误。欢迎文件index.html是一个空主体的html文件，当我启动应用程序显示任何内容时会完全打开，当访问servlet方向时会出现问题，无论您做什么，总会发生NullPointerException

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    id="WebApp_ID" version="2.5">
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
    </welcome-file-list>
    <servlet>
        <description></description>
        <display-name>ListaCorreosServlet</display-name>
        <servlet-name>ListaCorreosServlet</servlet-name>
        <servlet-class>comunicacion.ListaCorreosServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ListaCorreosServlet</servlet-name>
        <url-pattern>/ListaCorreosServlet</url-pattern>
    </servlet-mapping>
</web-app>

控制台输出

nov 14, 2015 5:22:21 PM org.apache.catalina.core.StandardWrapperValve invoke
GRAVE: Servlet.service() for servlet ListaCorreosServlet throws exception
java.lang.NullPointerException
    at comunicacion.ListaCorreosServlet.doPost(ListaCorreosServlet.java:32)
    at comunicacion.ListaCorreosServlet.doGet(ListaCorreosServlet.java:23)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:217)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

---

我不知道我是做错了什么，还是又一个Eclipse bug。

感谢大家。我不知道到底是哪里出了问题，但是用Eclipse向导创建servlet（它实际上生成完全相同的代码）非常有效；这意味着，Eclipse列表中还有一个bug

---

顺便说一句，我以前尝试过清理和重建应用程序至少十几次，包括应用程序和服务器，但仍然出现相同的错误；就是这样，我想这将是Eclipse的一个错误。

您没有运行您认为正在运行的代码。清理、重建、重新部署、重新启动等等@electron：对不起，你的猜测是胡说八道。这根本不能解释堆栈轨迹。试试这个解决方案吧，我认为它是相同的@electron一个空的如何抛出NPE？？？@Abdelhak：对不起，你的猜测也是胡说八道。它根本无法解释堆栈跟踪。

nov 14, 2015 5:22:21 PM org.apache.catalina.core.StandardWrapperValve invoke
GRAVE: Servlet.service() for servlet ListaCorreosServlet throws exception
java.lang.NullPointerException
    at comunicacion.ListaCorreosServlet.doPost(ListaCorreosServlet.java:32)
    at comunicacion.ListaCorreosServlet.doGet(ListaCorreosServlet.java:23)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:217)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1500)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1456)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)