当我选择离开该字段时，我有一个带有用户名字段的表单我使用了 RESTFUL Web 服务调用控制器中的处理程序方法。该方法调用 DAO 类，如果用户名存在，则检查数据库。
这样可以正常工作，但是当表单发布到服务器时，我会调用我在调用处理器方法中调用的相同的函数，但是当它访问类时我得到 java.lang.NullPointerException 这会调用 DAO 对象。所以它第二次甚至都没有访问 DAO 对象。
我在调用所有类的调用中都有异常处理程序。关于为什么我会在第二次调用函数时得到 java.lang.NullPointerException 的任何想法。这与 Spring 实例化
这是第一次发生的事情使用Web服务调用方法（假设发生这种情况）：
13011 [http-8084-2] INFO com.crimetrack.jdbc.JdbcOfficersDAO - Inside jdbcOfficersDAO
13031 [http-8084-2] DEBUG org.springframework.jdbc.core.JdbcTemplate - Executing prepared SQL query
13034 [http-8084-2] DEBUG org.springframework.jdbc.core.JdbcTemplate - Executing prepared SQL statement [SELECT userName FROM crimetrack.tblofficers WHERE userName = ?]
13071 [http-8084-2] DEBUG org.springframework.jdbc.datasource.DataSourceUtils - Fetching JDBC Connection from DataSource
13496 [http-8084-2] DEBUG org.springframework.jdbc.core.StatementCreatorUtils - Setting SQL statement parameter value: column index 1, parameter value [adminz], value class [java.lang.String], SQL type unknown
13534 [http-8084-2] DEBUG org.springframework.jdbc.datasource.DataSourceUtils - Returning JDBC Connection to DataSource
13537 [http-8084-2] INFO com.crimetrack.jdbc.JdbcOfficersDAO - No username was found in exception
13537 [http-8084-2] INFO com.crimetrack.service.ValidateUserNameManager - UserName :adminz does NOT exist
第二次当表单为“发布”时，验证方法处理表单并调用Web服务调用的相同方法：
17199 [http-8084-2] INFO com.crimetrack.service.OfficerRegistrationValidation - UserName is not null so going to check if its valid for :adminz
17199 [http-8084-2] INFO com.crimetrack.service.OfficerRegistrationValidation - User Name in try.....catch block is adminz
17199 [http-8084-2] INFO com.crimetrack.service.ValidateUserNameManager - Inside Do UserNameExist about to validate with username : adminz
17199 [http-8084-2] INFO com.crimetrack.service.ValidateUserNameManager - UserName :adminz EXCEPTION OCCURED java.lang.NullPointerException
ValidateUserNameManager.java
public class ValidateUserNameManager implements ValidateUserNameIFace {
private OfficersDAO officerDao;
private final Logger logger = Logger.getLogger(getClass());
public boolean DoesUserNameExist(String userName) throws Exception {
logger.info("Inside Do UserNameExist about to validate with username : " + userName);
try{
if(officerDao.OfficerExist(userName) == true){
logger.info("UserName :" + userName + " does exist");
return true;
}else{
logger.info("UserName :" + userName + " does NOT exist");
return false;
}
}catch(Exception e){
logger.info("UserName :" + userName + " EXCEPTION OCCURED " + e.toString());
return false;
}
}
/**
* @return the officerDao
*/
public OfficersDAO getOfficerDao() {
return officerDao;
}
/**
* @param officerdao the officerDao to set
*/
public void setOfficerDao(OfficersDAO officerDao) {
this.officerDao = officerDao;
}
}
JdbcOfficersDAO.java
public boolean OfficerExist(String userName){
String dbUserName;
try{
logger.info("Inside jdbcOfficersDAO");
String sql = "SELECT userName FROM crimetrack.tblofficers WHERE userName = ?";
try{
dbUserName = (String)getJdbcTemplate().queryForObject(sql, new Object[]{userName},String.class);
logger.info("Just Returned from database");
}catch(Exception e){
logger.info("No username was found in exception");
return false;
}
if(dbUserName == null){
logger.info("Database did not find any matching records");
}
logger.info("after JdbcTemplate");
if (dbUserName.equals(userName)) {
logger.info("User Name Exists");
return true;
}else{
logger.info("User Name Does NOT Exists");
return false;
}
}catch(Exception e){
logger.info("Exception Message in JdbcOfficersDAO is "+e.getMessage());
return false;
}
}
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("UserName is not null so going to check if its valid for :" + userName);
try {
logger.info("User Name in try.....catch block is " + userName);
if (validateUserNameManager.DoesUserNameExist(userName)== true){
errors.rejectValue("userName", "userName.exist");
}
} catch (Exception e) {
logger.info("Error Occured When validating UserName");
errors.rejectValue("userName", "userName.error");
}
}
if(officer.getPassword()== null){
errors.rejectValue("password", "password.required");
}
if(officer.getPassword2()== null){
errors.rejectValue("password2", "password2.required");
}
if(officer.getfName() == null){
errors.rejectValue("fName","fName.required");
}
if(officer.getlName() == null){
errors.rejectValue("lName", "lName.required");
}
if (officer.getoName() == null){
errors.rejectValue("oName", "oName.required");
}
if (officer.getEmailAdd() == null){
errors.rejectValue("emailAdd", "emailAdd.required");
}
if (officer.getDob() == null){
errors.rejectValue("dob", "dob.required");
}
if (officer.getGenderId().equals("A")){
errors.rejectValue("genderId","genderId.required");
}
if(officer.getDivisionNo() == 1){
errors.rejectValue("divisionNo", "divisionNo.required");
}
if(officer.getPositionId() == 1){
errors.rejectValue("positionId", "positionId.required");
}
if (officer.getStartDate() == null){
errors.rejectValue("startDate","startDate.required");
}
if(officer.getEndDate() == null){
errors.rejectValue("endDate","endDate.required");
}
logger.info("The Gender ID is " + officer.getGenderId().toString());
if(officer.getPhoneNo() == null){
errors.rejectValue("phoneNo", "phoneNo.required");
}
}
/**
* @return the validateUserNameManager
*/
public ValidateUserNameManager getValidateUserNameManager() {
return validateUserNameManager;
}
/**
* @param validateUserNameManager the validateUserNameManager to set
*/
public void setValidateUserNameManager(
ValidateUserNameManager validateUserNameManager) {
this.validateUserNameManager = validateUserNameManager;
}
}
使用Logger.Error更新错误日志（“消息”，e）：
39024 [http-8084-2] INFO com.crimetrack.service.OfficerRegistrationValidation - UserName is not null so going to check if its valid for :adminz
39025 [http-8084-2] INFO com.crimetrack.service.OfficerRegistrationValidation - User Name in try.....catch block is adminz
39025 [http-8084-2] ERROR com.crimetrack.service.OfficerRegistrationValidation - Message
java.lang.NullPointerException
at com.crimetrack.service.OfficerRegistrationValidation.validate(OfficerRegistrationValidation.java:47)
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)
39025 [http-8084-2] INFO com.crimetrack.service.OfficerRegistrationValidation - Error Occured When validating UserName
更新
的applicationContext.xml
<beans>
<!-- __________________________________________________________________________________________________ -->
<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>
<!-- __________________________________________________________________________________________________ -->
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
<property name="driverClassName" value="${jdbc.driverClassName}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</bean>
<!-- __________________________________________________________________________________________________ -->
<bean id="propertyConfigurer"
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="locations">
<list>
<value>classpath:jdbc.properties</value>
</list>
</property>
</bean>
<!-- __________________________________________________________________________________________________ -->
<bean id="transactionManager"
class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="dataSource"/>
</bean>
</beans>
servlet.xml中
<beans>
<!-- __________________________________________________________________________________________________ -->
<bean name="/hello.htm" class="com.crimetrack.web.CountryListController">
<property name="countryManager" ref="countryManager"/>
</bean>
<bean name="/login.htm" class="com.crimetrack.web.AuthenticationController">
<property name="authenticationManager" ref="authenticationManager"/>
</bean>
<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>
<!-- __________________________________________________________________________________________________ -->
<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="viewClass" value="org.springframework.web.servlet.view.JstlView"></property>
<property name="prefix" value="/WEB-INF/jsp/"></property>
<property name="suffix" value=".jsp"></property>
</bean>
</beans>
答案 0 :(得分：1)
我认为您忘记在ValidateUserNameManager.java中自动装配officerDao字段
尝试添加@Autowire：
@Autowire
private OfficersDAO officerDao;
<强>更新
更新堆栈跟踪后，我认为它是OfficerRegistrationValidation.java中未自动装配的validateUserNameManager字段。但是，这取决于第47行在OfficerRegistrationValidation.java中的含义
答案 1 :(得分：0)
在每次调用时都会实例化OfficerRegistrationValidation类，如果这个类应该应用Factory bean来处理调用：
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");
}
}
在控制器中进行调用，如：`BeanFactory.getOfficerRegistrationValidation（）。validate（....）