使用spring jdbc示例获取NullPointerException
java.lang.NullPointerException
at com.net.technicalkeeda.dao.PersonDaoImpl.findTotalCustomer(PersonDaoImpl.java:46)
当我从控制器调用findTotalCustomer方法时，这是我将jdbcTemplate设为NULL的方法。但是在服务器启动时，它会将值分配给datasource和jdbctemplate。那么请你帮我解释为什么有一个NULL值。
这是我的控制器类，我正在访问dao方法
public class HelloController implements Controller {
public ModelAndView handleRequest(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
ApplicationContext ctx = new FileSystemXmlApplicationContext("classpath*:/WEB-INF/springtutorial-servlet.xml");
if (ctx != null) {
personDao = (PersonDaoImpl)ctx.getBean("personDao");
}
personDao.findTotalCustomer();
return new ModelAndView("hello.jsp");
}
}
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName"><value>com.mysql.jdbc.Driver</value></property>
<property name="url"><value>jdbc:mysql://localhost:3306/technicalkeeda</value></property>
<property name="username"><value>root</value></property>
<property name="password"><value></value></property>
</bean>
<bean id="personDao" class="com.net.technicalkeeda.dao.PersonDaoImpl">
<property name="dataSource"><ref local="dataSource" /></property>
</bean>
package com.net.technicalkeeda.dao;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Collection;
import javax.sql.DataSource;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.RowMapper;
import com.net.technicalkeeda.bean.Person;
/**
* @author Yashwant Chavan
*
*/
public class PersonDaoImpl {
private DataSource dataSource;
private JdbcTemplate jdbcTemplate;
public void setDataSource(DataSource dataSource) {
this.dataSource = dataSource;
this.jdbcTemplate = new JdbcTemplate(dataSource);
System.out.println("Updated Datasouce---->" + dataSource);
System.out.println("Updated Jdbctemplate---->" + jdbcTemplate);
}
/* Display all persons */
public Collection<Person> findAll() {
System.out.println("Calling............." + this.jdbcTemplate);
return jdbcTemplate.query(
"select emp_name, emp_salary from trn_employee",
new PersonMapper());
}
public int findTotalCustomer(){
String sql = "SELECT COUNT(*) FROM trn_employee";
System.out.println("jdbcTemplate" + jdbcTemplate);
int total = jdbcTemplate.queryForInt(sql);
return total;
}
private static final class PersonMapper implements RowMapper {
public Object mapRow(ResultSet rs, int rowNum) throws SQLException {
Person person = new Person();
person.setFirstName(rs.getString("emp_name"));
return person;
}
}
}
控制台日志
17 Jul, 2012 8:08:52 PM org.apache.catalina.loader.WebappClassLoader validateJarFile
INFO: validateJarFile(C:\javaworkspace\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\SpringTutorial\WEB-INF\lib\j2ee.jar) - jar not loaded. See Servlet Spec 2.3, section 9.7.2. Offending class: javax/servlet/Servlet.class
17 Jul, 2012 8:08:52 PM org.apache.catalina.core.ApplicationContext log
INFO: Initializing Spring FrameworkServlet 'springtutorial'
17 Jul, 2012 8:08:52 PM org.springframework.web.servlet.FrameworkServlet initServletBean
INFO: FrameworkServlet 'springtutorial': initialization started
17 Jul, 2012 8:08:52 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.web.context.support.XmlWebApplicationContext@7ab2c6a6: display name [WebApplicationContext for namespace 'springtutorial-servlet']; startup date [Tue Jul 17 20:08:52 IST 2012]; root of context hierarchy
17 Jul, 2012 8:08:52 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from ServletContext resource [/WEB-INF/springtutorial-servlet.xml]
17 Jul, 2012 8:08:52 PM org.springframework.context.support.AbstractApplicationContext obtainFreshBeanFactory
INFO: Bean factory for application context [org.springframework.web.context.support.XmlWebApplicationContext@7ab2c6a6]: org.springframework.beans.factory.support.DefaultListableBeanFactory@2d8e8541
17 Jul, 2012 8:08:52 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@2d8e8541: defining beans [dataSource,personDao,helloController,loggerInterceptor,performanceInterceptor,urlMapping]; root of factory hierarchy
17 Jul, 2012 8:08:53 PM org.springframework.jdbc.datasource.DriverManagerDataSource setDriverClassName
INFO: Loaded JDBC driver: com.mysql.jdbc.Driver
**Updated Datasouce---->org.springframework.jdbc.datasource.DriverManagerDataSource@38827968
Updated Jdbctemplate---->org.springframework.jdbc.core.JdbcTemplate@7df0b7d3**
17 Jul, 2012 8:08:53 PM org.springframework.web.servlet.FrameworkServlet initServletBean
INFO: FrameworkServlet 'springtutorial': initialization completed in 453 ms
17 Jul, 2012 8:08:53 PM org.apache.coyote.http11.Http11BaseProtocol start
INFO: Starting Coyote HTTP/1.1 on http-8080
17 Jul, 2012 8:08:53 PM org.apache.jk.common.ChannelSocket init
INFO: JK: ajp13 listening on /0.0.0.0:8009
17 Jul, 2012 8:08:53 PM org.apache.jk.server.JkMain start
INFO: Jk running ID=0 time=0/0 config=null
17 Jul, 2012 8:08:53 PM org.apache.catalina.storeconfig.StoreLoader load
INFO: Find registry server-registry.xml at classpath resource
17 Jul, 2012 8:08:53 PM org.apache.catalina.startup.Catalina start
INFO: Server startup in 1749 ms
答案 0 :(得分：2)
我的猜测是Spring实例化它的bean并注入DataSource，但是不是从Spring bean工厂获取bean，而是自己实例化一个bean，因此使用另一个实例，而不是在Spring的控制下，因此没有初始化的数据源。
你永远不应该new SomeSpringBean()。所有bean引用都应该注入依赖项，或者应该通过向bean bean bean工厂获取它来获得。
因此，如果您的代码执行new PersonDaoImpl()，那么就会出现问题。
答案 1 :(得分：0)
我会冒险猜测并且说你没有正确地从你的上下文文件中获取你的bean。新的操作员和弹簧不好玩。我假设你知道如何从application-context.xml中取出豆子，但如果没有，我会把它留在这里。
//simple singleton
private static void initApplicationContext() {
if (_applicationContext == null)
_applicationContext = new ClassPathXmlApplicationContext("PersistenceHelper-context.xml");
}
//get bean
Datasource dataSource = (DataSource) _applicationContext.getBean("dataSource");