java.lang.NullPointerException Spring Mvc

Question

我得到一个 java.lang.NullPointerException:

我为 validateUserNameManager 设置了 getter 和 setter。我正在使用基于 xml 的配置，而不是使用@Autowire。很明显，当处理到达 validateUserNameManager 时，它会得到 NP 异常我不确定我的配置和接线是否准确。

if (validateUserNameManager.DoesUserNameExist(officer.getUserName()) == true){

                    errors.rejectValue("userName", "userName.exist");
                }

OfficerRegistrationValidation.java

public class OfficerRegistrationValidation implements Validator{

    private final Logger logger = Logger.getLogger(getClass());


    private ValidateUserNameManager validateUserNameManager;


    public boolean supports(Class<?> clazz) {

        return Officers.class.equals(clazz);
    }


    public void validate(Object target, Errors errors) {

        Officers officer = (Officers) target;

        if (officer.getUserName() == null){

            errors.rejectValue("userName", "userName.required");

        }else{

            String userName = officer.getUserName();                    

            logger.info("OfficerRegistrationValidation - UserName is not null so going to check if its valid for :" + userName);

            try {

                logger.info("OfficerRegistrationValidation - Just before try.....catch block...userName is :" + userName);  

                logger.info("OfficerRegistrationValidation - about to evaluate if (validateUserNameManager.DoesUserNameExist(officer.getUserName()) == true)" );


                if (validateUserNameManager.DoesUserNameExist(officer.getUserName()) == true){

                    errors.rejectValue("userName", "userName.exist");
                }
            } catch (Exception e) {

                logger.info("OfficerRegistrationValidation - Error Occured When validating UserName");
                logger.error("Message", e);
                errors.rejectValue("userName", "userName.error");
            }

        }

/**
     * @return the validateUserNameManager
     */
    public ValidateUserNameManager getValidateUserNameManager() {
        logger.info("Getting - ValidateUserNameManager");
        return validateUserNameManager;
    }


    /**
     * @param validateUserNameManager the validateUserNameManager to set
     */
    public void setValidateUserNameManager(
            ValidateUserNameManager validateUserNameManager) {

        logger.info("Setting - ValidateUserNameManager");
        this.validateUserNameManager = validateUserNameManager;
    }       

}

ApplicationContext.xml

<bean id="officerRegistrationValidation" class="com.crimetrack.service.OfficerRegistrationValidation">

        <property name="validateUserNameManager" ref="validateUserNameManager"/>
</bean>

<bean id="validateUserNameManager" class="com.crimetrack.service.ValidateUserNameManager">
        <property name="officerDao" ref="officerDao"/>
</bean>


<bean id="officerDao" class="com.crimetrack.jdbc.JdbcOfficersDAO" >
        <property name="dataSource" ref="dataSource" />
</bean>

Servlet.xml

   <bean name="/officer_registration.htm" class="com.crimetrack.web.OfficerRegistrationController">
        <property name="divisionManager" ref="divisionManager" />
        <property name="positionManager" ref="positionManager" />
        <property name="genderManager" ref="genderManager"/>  
    </bean>

<!-- __________________________________________________________________________________________________ -->    

    <bean name="/validateUserName.htm" class="com.crimetrack.web.OfficerRegistrationController">

        <property name="validateUserNameManager" ref="validateUserNameManager"/>    

    </bean>    


<!-- __________________________________________________________________________________________________ -->    

堆栈跟踪:

47840 [http-8084-1] DEBUG org.springframework.beans.TypeConverterDelegate  - Converting String to [class java.lang.String] using property editor [org.springframework.beans.propertyeditors.StringTrimmerEditor@7079b2]
47840 [http-8084-1] INFO  com.crimetrack.service.OfficerRegistrationValidation  - OfficerRegistrationValidation - UserName is not null so going to check if its valid for :adminzz
47840 [http-8084-1] INFO  com.crimetrack.service.OfficerRegistrationValidation  - OfficerRegistrationValidation - Just before try.....catch block...userName is :adminzz
47840 [http-8084-1] INFO  com.crimetrack.service.OfficerRegistrationValidation  - OfficerRegistrationValidation - about to evaluate if (validateUserNameManager.DoesUserNameExist(officer.getUserName()) == true)
47840 [http-8084-1] INFO  com.crimetrack.service.OfficerRegistrationValidation  - OfficerRegistrationValidation - Error Occured When validating UserName
47840 [http-8084-1] ERROR com.crimetrack.service.OfficerRegistrationValidation  - Message
java.lang.NullPointerException
    at com.crimetrack.service.OfficerRegistrationValidation.validate(OfficerRegistrationValidation.java:51)
    at org.springframework.validation.DataBinder.validate(DataBinder.java:725)
    at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.doBind(HandlerMethodInvoker.java:815)
    at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveHandlerArguments(HandlerMethodInvoker.java:367)
    at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:171)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:436)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:424)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:789)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Unknown Source)

Answer 1

问题是您通过新调用实例化了 OfficerRegistrationValidaton。这意味着 Spring 不会知道有关该对象的任何信息，因此不会将任何内容连接到它。

您需要通过 Spring 机制加载对象，通过 @Autowire/@Inject，或通过创建 BeanFactory，如下所示:

public final class BeanFactory() {

    private static ClassPathXmlApplicationContext context;

    private static ClassPathXmlApplicationContext getContext() {
        if (context== null) {
            context = new ClassPathXmlApplicationContext("applicationContext.xml");
        }
        return context;
    }

    public static OfficerRegistrationValidation getOfficerRegistrationValidation() {
        return (OfficerRegistrationValidation) getContext().getBean("officerRegistrationValidation");
    }
}

然后，在你的 Controller 中:

    BeanFactory.getOfficerRegistrationValidation().validate(....)

注意:新建 ClassPathXmlApplicationContext 时要小心，如果操作不当可能会导致内存泄漏。创建一个将新建它一次的静态工厂，并在任何后续调用中返回相同的实例。