我一直在研究J2EE项目，我在其中使用连接池也是通过已部署在heroku上的数据库访问。我使用以下代码来设置Connection对象：
Context initContext=new InitialContext();
Context envContext=(Context)initContext.lookup("java:comp/env");
DataSource ds=(DataSource)envContext.lookup("jdbc/DB");
con=ds.getConnection();
我的META-INF文件夹中有一个context.xml文件，其中包含以下值：
<?xml version="1.0" encoding="UTF-8"?>
<Context>
<Resource
name="jdbc/DB"
auth="Container"
type="javax.sql.DataSource"
maxActive="100"
maxIdle="30"
maxWait="10000"
driverClassName="org.postgresql.Driver"
url="<connection_url>"
username="<user_name>"
password="<password>"/>
</Context>
数据库连接在我的本地tomcat v8服务器上工作得很好但是当我在heroku上部署了我的.war文件时，我的日志中出现了以下错误，我无法在我的网页中看到我的数据库数据。 / p>
javax.naming.NoInitialContextException: Need to specify class name in environment or system property, or as an applet parameter, or in an application resource file:
java.naming.factory.initial
at javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:662)
at javax.naming.InitialContext.getDefaultInitCtx(InitialContext.java:313)
at javax.naming.InitialContext.getURLOrDefaultInitCtx(InitialContext.java:350)
at javax.naming.InitialContext.lookup(InitialContext.java:417)
at com.controller.A.doPost(A.java:48)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
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.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$AbstractConnectionHandler.process(AbstractProtocol.java:668)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1521)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1478)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
java.lang.NullPointerException
at com.controller.A.doPost(A.java:81)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1521)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1478)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
我的A.java文件中标记的例外行是：
48:Context initContext=new InitialContext();
81:{ try
{ st.close();
con.close();
}
}