如何在Spring中通过ApplicationContext即时直接使用bean

时间：2018-12-28 11:28:29

标签： java spring applicationcontext spring-bean



我正在尝试在Spring中使用UserService访问ApplicationContext类。
这是我的控制器课 

package com.dilini.controller;

import com.dilini.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class HelloController {

    @Autowired
    private ApplicationContext applicationContext;
    UserService userService = (UserService) applicationContext.getBean(UserService.class);

    @RequestMapping("hi")
    @ResponseBody
    public String hi() {
        return "User count is " + userService.findNumberOfUsers();
    }

}

这是我的服务班

package com.dilini.service;

import org.springframework.stereotype.Service;

@Service
public interface UserService {

    public int findNumberOfUsers();
}

这是我的服务实现类。

package com.dilini.service.impl;

import com.dilini.service.UserService;
import org.springframework.stereotype.Service;


@Service("UserService")
public class UserServiceImpl implements UserService {

    @Override
    public int findNumberOfUsers() {
        return 50;
    }
}

运行应用程序时，我得到一个Null point exception。

Exception

javax.servlet.ServletException: Servlet.init() for servlet [dispatcher] threw exception
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Thread.java:745)



Root Cause

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'helloController' defined in file [C:\Users\dilin\Documents\NetBeansProjects\mvcquick\target\mvcquick-1.0-SNAPSHOT\WEB-INF\classes\com\dilini\controller\HelloController.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.dilini.controller.HelloController]: Constructor threw exception; nested exception is java.lang.NullPointerException
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1101)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1046)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:504)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
    org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
    org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
    org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:663)
    org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:535)
    org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:489)
    org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
    javax.servlet.GenericServlet.init(GenericServlet.java:158)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Thread.java:745)

Root Cause

org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.dilini.controller.HelloController]: Constructor threw exception; nested exception is java.lang.NullPointerException
    org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:163)
    org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1094)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1046)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:504)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
    org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
    org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
    org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:663)
    org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:535)
    org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:489)
    org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
    javax.servlet.GenericServlet.init(GenericServlet.java:158)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Thread.java:745)

Root Cause

java.lang.NullPointerException
    com.dilini.controller.HelloController.<init>(HelloController.java:25)
    sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    java.lang.reflect.Constructor.newInstance(Constructor.java:422)
    org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:147)
    org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:89)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1094)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1046)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:504)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
    org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
    org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
    org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
    org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
    org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
    org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:663)
    org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:535)
    org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:489)
    org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
    javax.servlet.GenericServlet.init(GenericServlet.java:158)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Thread.java:745)

您能告诉我为什么会这样吗？
我没有正确使用注释。请帮我。
谢谢。

修改
我在Spring CookBook教程中关注。我直接在Bean内使用Autowired访问了UserService。 

@Autowired
UserService userService;

@RequestMapping("hi")
@ResponseBody
public String hi() {
return "nb of users: " + userService.findNumberOfUsers();
}

现在我正在尝试这种ApplicationContext方法。

2 个答案:

答案 0 :(得分：3)

您应该通过让Spring在类中注入bean来做到这一点。例如，使用@Autowired 

@Autowired
UserService userService;

然后，userService变量将正确引用您的UserService bean。

编辑： 如果要专门从applicationContext获取Bean，则必须将此代码UserService userService = (UserService) applicationContext.getBean(UserService.class);放入hi（）方法中，以确保Spring在调用它之前已创建并注入了所有必需的依赖项。

答案 1 :(得分：1)

尝试将UserService userService = (UserService) applicationContext.getBean(UserService.class);代码移至hi()方法中，例如：

 @RequestMapping("hi")
    @ResponseBody
    public String hi() {
        return "User count is " + (UserService) applicationContext.getBean(UserService.class).findNumberOfUsers();
    }

如果要在单例bean中注入原型bean，这将很有用

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