问题
I am new to Spring. I am trying to develop REST API using Spring web MVC. I am trying to fetch some data using JdbcTemplate from my database (MySQL). But when i run the code in the server I am getting 500- Internal Server Error and the stack trace shows java.lang.NullPointerException. When i tried to debug the code i found out that jdbcTemplate variable has null value. I have tried every solution provided in web but still getting the same error.
Here is my applicationContext.xml file
<context:component-scan base-package="com.cinema.repository" />
<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
<property name="dataSource" ref="dataSource" />
</bean>
<bean id="userDao" class="com.cinema.repository.UserDaoImpl">
<property name="jdbcTemplate" ref="jdbcTemplate" />
</bean>
<bean id="dataSource"
class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<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>
<context:property-placeholder location="/WEB-INF/jdbc.properties" />
My UserDaoImpl.java looks is:
public class UserDaoImpl implements UserDao {
private JdbcTemplate jdbcTemplate;
public JdbcTemplate getJdbcTemplate() {
return jdbcTemplate;
}
@Autowired
public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
public User getUser(int userId) {
String sql ="SELECT * FROM user_tbl WHERE user_id = ?";
return this.jdbcTemplate.queryForObject(sql,new Object[]{new Integer(userId)}, new UserMapper() );
}
private static final class UserMapper implements RowMapper<User>{
public User mapRow(ResultSet rs, int rowCount) throws SQLException {
User u = new User();
u.setUserId(rs.getInt("user_id"));
u.setUserName(rs.getString("username"));
u.setPassword(rs.getString("password"));
u.setEmailId(rs.getString("email"));
u.setRole(rs.getString("role"));
return u;
}
}
}
And my controller class is UserController.java:
@RestController
@RequestMapping(value="/user")
public class UserController {
@RequestMapping(method = RequestMethod.GET, value="/{userId}", produces = {MediaType.APPLICATION_JSON_VALUE})
ResponseEntity<User> getUser(@PathVariable int userId){
UserDaoImpl user = new UserDaoImpl();
User u = new User();
u=user.getUser(userId);
return new ResponseEntity<User>(u, HttpStatus.OK);
}
}
and i am getting the following stack trace while running the application:
10-Feb-2016 02:50:28.165 SEVERE [tomcat-http--5] org.apache.catalina.core.StandardWrapperValve.invoke Servlet.service() for servlet [spring] in context with path [/booking] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
at com.cinema.repository.UserDaoImpl.getUser(UserDaoImpl.java:31)
at com.cinema.web.UserController.getUser(UserController.java:21)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:222)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:814)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:737)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:969)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:860)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:845)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:277)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Please tell me what i am doing wrong here. I have been stuck on this problem for a week now and still cannot make my code work. Thanks in advance.
回答1:
In your controller, you are creating a new UserDaoImpl :
@RequestMapping(method = RequestMethod.GET, value="/{userId}", produces = {MediaType.APPLICATION_JSON_VALUE})
ResponseEntity<User> getUser(@PathVariable int userId){
UserDaoImpl user = new UserDaoImpl(); // <-- HERE
User u = new User();
u=user.getUser(userId);
return new ResponseEntity<User>(u, HttpStatus.OK);
}
This UserDaoImpl is not managed by spring, and not configured/autowired. You should inject in your controller the instance of UserDao configured in the xml :
@Autowired
private UserDao userDao;
@RequestMapping(method = RequestMethod.GET, value="/{userId}", produces = {MediaType.APPLICATION_JSON_VALUE})
ResponseEntity<User> getUser(@PathVariable int userId){
User u = userDao.getUser(userId);
return new ResponseEntity<User>(u, HttpStatus.OK);
}
回答2:
Try these changes:
@Repository("userDao")
public class UserDaoImpl implements UserDao {
@Autowired
private JdbcTemplate jdbcTemplate;
// Rest of your stuff here.
}
来源：https://stackoverflow.com/questions/35302501/jdbctemplate-is-null-and-throws-null-pointer-exception