Question

我想在控制器中使用buisness层方法，并且我不断得到nullPointerException。嗯，我知道这是因为我无法实现一个商务对象suince我正在处理界面。那么如何通过商务界面从控制器调用商务方法呢？这是一个示例商务界面：

public interface ICompagnieBuisness {
public String depa="";
String depString(String dep);   }

这里是conroller，我想调用depString（String dep）方法返回一个String，我将把它放在视图中使用的消息中：

`package com.crun.controller;
@Controller
public class HelloWorld {
@Autowired
private static ICompagnieBuisness icb;
public void setIcb() {
    this.icb = icb;
    }
@RequestMapping("/welcome")
public ModelAndView helloWorld() {
    String dep=icb.depString(a);
    String message = "<br><div style='text-align:center;'>"
            + "<h3>***Hello World, Spring MVC Tutorial</h3>      </div><br><br>";
    return new ModelAndView("welcome", "message", message);
}
}`

这是商务舱：包com.crun.buisness;

import java.util.List;

import com.crunc.dao.ICompagnieDAO;

public class ICompagnieBuisnessImpl implements ICompagnieBuisness{
private static ICompagnieDAO dao;
public String depa;
public String depString(String dep) {
    dep="Message sent from buisness layer";
    return dep;
}
}

这是错误

GRAVE: Servlet.service() for servlet [crun] in context with path     [/CrunSpringMVCTutorial] threw exception [Request processing failed; nested     exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
at com.crun.controller.CrunHelloWorld.helloWorld(CrunHelloWorld.java:34)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at   org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandl    erMethod(HandlerMethodInvoker.java:175)
at     org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.in    vokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446)
at  org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.ha ndle(AnnotationMethodHandlerAdapter.java:434)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:957)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:620)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)

非常感谢！

Answer 1

为了将ICompagnieBuisness的实例注入控制器，请确保Spring知道接口的实现（它应该是一个Spring bean）。您可以使用@Component，@Repository或@Service对其进行注释，使其成为Spring bean。在您的情况下，使用@Service在上下文中更正确，因为它是业务层。此外，您无法将spring bean自动装配到静态字段，因此请在字段声明中删除static关键字。

从控制器

1 个答案: