java - 尝试读取 WEB-INF 中的属性文件时 InputStream 为空

Question

每当我尝试读取位于“/WEB-INF”中的属性文件时，我的 InputStream 对象都会让控制台打印出 NullPointerException。但是当我执行 InputStream.toString() 时，它会打印出 java.io.FileInputStream@1933968 而不是实际的 null 值。

这是我返回的堆栈跟踪:

SEVERE: Servlet.service() for servlet [spring] in context with path [/translator] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
at com.webclaims.translator.TranslatorApi.readPropertiesFile(TranslatorApi.java:149)
at com.webclaims.translator.TranslatorApi.writePropertiesFile(TranslatorApi.java:128)
at com.webclaims.translator.controllers.TestController.editableWebpage(TestController.java:45)

/WEB-INF的布局；

WEB-INF-|
        |-jsp
        |-configDummy.properties
        |-spring-servlet.xml
        |-web.xml

我正在使用 Java 8 的 Tomcat v8 服务器上运行这个项目。

spring-servlet.xml;

<?xml version="1.0" encoding="UTF-8"?>  
<beans xmlns="http://www.springframework.org/schema/beans"    
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    
xmlns:p="http://www.springframework.org/schema/p"    
xmlns:mvc="http://www.springframework.org/schema/mvc"   
xmlns:context="http://www.springframework.org/schema/context"    
xsi:schemaLocation="http://www.springframework.org/schema/beans    
                    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd  
                    http://www.springframework.org/schema/mvc   
                    http://www.springframework.org/schema/mvc/spring-mvc-4.3.xsd
                    http://www.springframework.org/schema/context    
                    http://www.springframework.org/schema/context/spring-context-4.3.xsd">

<mvc:annotation-driven/> 
<context:component-scan base-package="com.webclaims.*" />
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix" value="/WEB-INF/jsp/"></property>
    <property name="suffix" value=".jsp"></property>
</bean>
<bean id="propertiesFile" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="properties" value="/WEB-INF/configDummy.properties"></property>
</bean>

网络.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1">
  <display-name>translator</display-name>

  <context-param>
    <param-name>contextConfigLocation</param-name> 
    <param-value>/WEB-INF/spring-servlet.xml</param-value> 
  </context-param>
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener> 
  <servlet>
    <servlet-name>spring</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>spring</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

TestController.java(包含异常入口点)

@Controller
@PropertySource("/WEB-INF/configDummy.properties")
public class TestController {

private static final Logger LOGGER = Logger.getLogger(TestController.class.getName());

private static final String PROPS_FILE = "/WEB-INF/configDummy.properties";

@RequestMapping(value = "/test")
public ModelAndView originalWebpage() {
    return new ModelAndView("testpage");
}

@CrossOrigin()
@RequestMapping(value = "/test", method = RequestMethod.POST, consumes = MediaType.APPLICATION_JSON_VALUE)
public @ResponseBody String editableWebpage(@RequestBody String data, HttpServletRequest request) {
    InputStream inputStream = request.getSession().getServletContext()
            .getResourceAsStream(PROPS_FILE);
    System.out.println(inputStream);

    JsonParser parser = new JsonParser(data);
    Elements elements = parser.jsonToElements();
    TranslatorApi t = new TranslatorApi();
    t.writePropertiesFile(elements, inputStream);
    return data;
}
}

TranslatorApi.java

@PropertySource("/WEB-INF/configDummy.properties")
public class TranslatorApi {

@Autowired
private Properties properties;

private static final Logger LOGGER = Logger.getLogger(TranslatorApi.class.getName());

public TranslatorApi() {}

public Properties getProperties() {
    return properties;
}

public void setProperties(Properties properties) {
    this.properties = properties;
}

public void writePropertiesFile(Elements elements, InputStream inputStream) {
    System.out.println("write opertion executed");
    System.out.println(elements);
    try {
        readPropertiesFile(inputStream);

        for(Element e : elements) {
            properties.setProperty(e.className(), e.text());
        }

        String path=Thread.currentThread().getContextClassLoader()
                .getResource("src/main/webapp/WEB-INF/props/configDummy.properties").toString();
        File file = new File(path);
        FileOutputStream fileOut = new FileOutputStream(file);
        properties.store(fileOut, "DUMMY");
        fileOut.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

private void readPropertiesFile(InputStream inputStream) throws IOException {
    try {
        properties.load(inputStream);
        inputStream.close();
    } catch(FileNotFoundException e) {
        LOGGER.log(Level.SEVERE, "FileNotFoundException has occured", e);
    } catch(IOException e) {
        LOGGER.log(Level.SEVERE, "IOException has occured", e);     
    } 
}

这里的大多数人建议我应该将属性文件放在类路径中。如果我有它，我将来可以写信给它吗？

Answer 1

对我而言，您的 NPE 与 TranslatorApi 中的字段 properties 是 null 这一事实更为相关，因为它没有被正确注入(inject)。

尝试使用 Environment 类作为下一个:

@Autowired
private Environment properties;

这是一个很好的例子 how to inject properties in your class .