Question

我正在实现一个读取.properties文件的Properties bean。这个类被注入到控制器中，因此它们可以获得属性。

@Service
public class PropertiesUtils {

    @Autowired
    private ServletContext context;

    private Properties properties;

    public PropertiesUtils() {
        this.properties = new Properties();
        try {
            **this.properties.load(new FileInputStream(this.context.getRealPath("/WEB-INF/context.properties")));**
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

   ...
}

但是，当我启动应用程序时，Apache会抛出异常：

java.lang.NullPointerException
    at com.destrozatumente.utils.PropertiesUtils.<init>(PropertiesUtils.java:29)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:126)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:74)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:958)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:911)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:485)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:293)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:290)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:192)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:848)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:790)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:707)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:480)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:84)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:285)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1074)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:293)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:290)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:192)
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1075)
    at org.springframework.web.servlet.handler.AbstractUrlHandlerMapping.registerHandler(AbstractUrlHandlerMapping.java:383)
    at org.springframework.web.servlet.handler.AbstractUrlHandlerMapping.registerHandler(AbstractUrlHandlerMapping.java:362)
    at org.springframework.web.servlet.handler.AbstractDetectingUrlHandlerMapping.detectHandlers(AbstractDetectingUrlHandlerMapping.java:82)
    at org.springframework.web.servlet.handler.AbstractDetectingUrlHandlerMapping.initApplicationContext(AbstractDetectingUrlHandlerMapping.java:58)
    at org.springframework.context.support.ApplicationObjectSupport.initApplicationContext(ApplicationObjectSupport.java:119)
    at org.springframework.web.context.support.WebApplicationObjectSupport.initApplicationContext(WebApplicationObjectSupport.java:72)
    at org.springframework.context.support.ApplicationObjectSupport.setApplicationContext(ApplicationObjectSupport.java:73)
    at org.springframework.context.support.ApplicationContextAwareProcessor.invokeAwareInterfaces(ApplicationContextAwareProcessor.java:109)
    at org.springframework.context.support.ApplicationContextAwareProcessor.postProcessBeforeInitialization(ApplicationContextAwareProcessor.java:88)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:394)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1413)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:519)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:293)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:290)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:192)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:585)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:895)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:425)
    at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:467)
    at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:483)
    at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:358)
    at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:325)
    at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:127)
    at javax.servlet.GenericServlet.init(GenericServlet.java:160)
    at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1228)
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1147)
    at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1043)
    at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4957)
    at org.apache.catalina.core.StandardContext$3.call(StandardContext.java:5284)
    at org.apache.catalina.core.StandardContext$3.call(StandardContext.java:5279)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
    at java.util.concurrent.FutureTask.run(FutureTask.java:166)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)

为什么找不到ServletContext.getRealPath（）?,解决方案？

Answer 1

可能会抛出NullPointerException，因为您在构造函数中引用了this.context。必须在任何@Autowired之前调用构造函数 - 可以设置属性（因为它们是对象的成员，因此需要首先构造对象），因此context - 属性在构造函数中为null 。也许试试这个：

@Service
public class PropertiesUtils {

    private ServletContext context;

    private Properties properties;

    @Autowired 
    public PropertiesUtils(ServletContext context) {
        this.context = context;
        this.properties = new Properties();
        try {
            **this.properties.load(new FileInputStream(this.context.getRealPath("/WEB-INF/context.properties")));**
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

   ...
}

在@Service中@Autowired ServletContext

1 个答案: