java.lang.NullPointerException：加载属性文件时，inStream 参数为 null

Question

I have created a ZK web application project in Eclipse , and deployed the same in Apache Tomcat 9.0.37 . 我有一个要读取的属性文件（ aws.properties ） - 它位于WEB-INF正下方。

我在加载属性文件时遇到困难 - 获取NullpointeException

Eclipse ZK项目

项目结构：

我尝试了以下所有 3 种方法，它们java.lang.NullPointerException: inStream parameter is null PROPERTIES.load(inputStream);

代码：

private static final String PROPERTIES_FILE = "aws.properties";
private static final Properties PROPERTIES = new Properties();
...
...
...

// APPROACH 1.
InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream(PROPERTIES_FILE);

// APPROACH 2.
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
InputStream inputStream = classLoader.getResourceAsStream(PROPERTIES_FILE);

// APPROACH 3.
ClassLoader classLoader = getClass().getClassLoader();
InputStream inputStream = classLoader.getResourceAsStream(PROPERTIES_FILE);
        
PROPERTIES.load(inputStream);

堆栈跟踪：

java.lang.NullPointerException: inStream parameter is null
    at java.base/java.util.Objects.requireNonNull(Objects.java:246)
    at java.base/java.util.Properties.load(Properties.java:404)
    at in.net.cadentic.core.database.AmazonDynamoDBClientHandler.createNewClient(AmazonDynamoDBClientHandler.java:75)
    at in.net.cadentic.core.dao.UsermasterDao.findBypassword(UsermasterDao.java:27)
    at in.net.cadentic.composers.LoginComposer.onClick$loginButton(LoginComposer.java:71)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at org.zkoss.zk.ui.event.GenericEventListener.onEvent(GenericEventListener.java:80)
    at org.zkoss.zk.ui.AbstractComponent.onEvent(AbstractComponent.java:3184)
    at org.zkoss.zk.ui.AbstractComponent.service(AbstractComponent.java:3154)
    at org.zkoss.zk.ui.AbstractComponent.service(AbstractComponent.java:3096)
    at org.zkoss.zk.ui.impl.EventProcessor.process(EventProcessor.java:138)
    at org.zkoss.zk.ui.event.Events.sendEvent(Events.java:353)
    at org.zkoss.zk.ui.event.Events.sendEvent(Events.java:377)
    at org.zkoss.zk.ui.AbstractComponent$ForwardListener.onEvent(AbstractComponent.java:3629)
    at org.zkoss.zk.ui.AbstractComponent.onEvent(AbstractComponent.java:3184)
    at org.zkoss.zk.ui.AbstractComponent.service(AbstractComponent.java:3154)
    at org.zkoss.zk.ui.AbstractComponent.service(AbstractComponent.java:3096)
    at org.zkoss.zk.ui.impl.EventProcessor.process(EventProcessor.java:138)
    at org.zkoss.zk.ui.impl.UiEngineImpl.processEvent(UiEngineImpl.java:1851)
    at org.zkoss.zk.ui.impl.UiEngineImpl.process(UiEngineImpl.java:1623)
    at org.zkoss.zk.ui.impl.UiEngineImpl.execUpdate(UiEngineImpl.java:1326)
    at org.zkoss.zk.au.http.DHtmlUpdateServlet.process(DHtmlUpdateServlet.java:611)
    at org.zkoss.zk.au.http.DHtmlUpdateServlet.doGet(DHtmlUpdateServlet.java:487)
    at org.zkoss.zk.au.http.DHtmlUpdateServlet.doPost(DHtmlUpdateServlet.java:495)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:652)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.base/java.lang.Thread.run(Thread.java:834)

问题：

这里做错了什么？

Answer 1

您的属性文件属于 WEB-INF/classes。 class 加载程序不会在 WEB-INF 中查找单个文件，因为 servlet 规范说它不应该在那里查找单个文件。

Answer 2

除了VGR 的响应之外，还可以直接从 WEB-INF 文件夹中读取.properties文件。 它可以从ServletContext object 中读取，而不是通过类加载器从类路径加载它。

假设您可以访问 ServletContext object。 下面的示例展示了如何通过WebApps.getCurrent()实例获取 ServletContext。

// using ZK specific WebApps util
ServletContext servletContext = WebApps.getCurrent().getServletContext();
// Servlet API
InputStream inputStream = servletContext.getResourceAsStream("/WEB-INF/aws.properties");
Properties myProps = new Properties();
myProps.load(inputStream);

一个快捷方式是直接调用WebApps.getCurrent().getResourceAsStream("/WEB-INF/aws.properties") 。

我仍然希望将配置文件保留在类路径中，而不是使 Dao 类依赖于 ServletContext 的存在。 但是，您的代码示例并未具体说明您的配置在哪一层被读取。