Servlet.service() for servlet [dispatcher] in context with path [/***] threw exception

Question

I am getting below error while creating spring maven rest webservice. When trying to call DAO class with bean name defined in application_config.xml, getting NullPointerException

SEVERE: Servlet.service() for servlet [dispatcher] in context with path [/riceAppService] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at com.ganeshTrading.riceAppService.controller.UserController.getAllUsers(UserController.java:46)
    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:221)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
    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:141)
    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:528)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1099)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:670)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1520)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1476)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)

Here, is my code

UserController.java

    @RestController
public class UserController {

    private JdbcUserDAO jdbcUserDAO;


    public JdbcUserDAO getJdbcUserDAO() {
        return jdbcUserDAO;
    }

    public void setJdbcUserDAO(JdbcUserDAO jdbcUserDAO) {
        this.jdbcUserDAO = jdbcUserDAO;
    }

    @RequestMapping("/")
    @ResponseBody
    public String welcome() {
        return "Welcome to RestTemplate Example.";
    }

    @RequestMapping(value="/users", method=RequestMethod.GET, produces=MediaType.APPLICATION_JSON_VALUE)
    @ResponseBody   
    public List<User> getAllUsers() {
        System.out.println("jdbcUserDAO"+jdbcUserDAO);
        List<User> userList = jdbcUserDAO.getAllUsers();
        System.out.println(userList);
        return userList;
    }

}

UserDAO.java

public interface UserDAO {

    public List<User> getAllUsers();
}

JdbcUserDAO.java

public class JdbcUserDAO implements UserDAO {

    DataSource dataSource;


    public void setDataSource(DataSource dataSource) {
        this.dataSource = dataSource;
    }


    @Override
    public List<User> getAllUsers() {
        String sql = "select * from customer";
        JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
        System.out.println("getJdbcTemplate() "+jdbcTemplate);
        List<User> userList = jdbcTemplate.query(sql, new UserMapper());
        return userList;
    }

}

servlet-context.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" 
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xsi:schemaLocation=" http://www.springframework.org/schema/beans  
 http://www.springframework.org/schema/beans/spring-beans-4.3.xsd 
 http://www.springframework.org/schema/context 
 http://www.springframework.org/schema/context/spring-context-4.3.xsd
 http://www.springframework.org/schema/mvc 
 http://www.springframework.org/schema/mvc/spring-mvc-4.3.xsd">



<context:annotation-config />
<mvc:annotation-driven />

<import resource="classpath:application_config.xml" /> 
<context:component-scan base-package="com.ganeshTrading.riceAppService" />

</beans>

application_config.xml

    <?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd">


    <bean id="jdbcUserDAO" class="com.ganeshTrading.riceAppService.dao.impl.JdbcUserDAO">
        <property name="dataSource" ref="dataSource" />
    </bean>

   <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="com.mysql.jdbc.Driver"></property>
    <property name="url" value="jdbc:mysql://localhost:3306/ganeshricetrading"></property>
    <property name="username" value="root"></property>
    <property name="password" value="sql"></property>
   </bean>    

</beans>

web.xml

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns:xsi="w3.org/2001/XMLSchema-instance" xmlns="xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="xmlns.jcp.org/xml/ns/javaee xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
      <display-name>Archetype Created Web Application</display-name>
  <servlet>
    <servlet-name>appServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/servlet-context.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>appServlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

ApplicationConfiguration.java

@ComponentScan(basePackages = {"com.ganeshTrading.riceAppService"})
@Configuration
@EnableWebMvc
public class ApplicationConfiguration {

}

Please advise what is wrong in my code. Thanks in advance.

Answer 1

Although you have defined the jdbcUserDAO bean, you have not wired it into the UserController class. This causes a NullPointerException because the jdbcUserDAO field is null, which results in the exception when jdbcUserDAO.getAllUsers() is called. To solve this, annotate the jdbcUserDAO setter in the UserController with @Autowired, as in:

@RestController
public class UserController {

    private JdbcUserDAO jdbcUserDAO;

    public JdbcUserDAO getJdbcUserDAO() {
        return jdbcUserDAO;
    }

    @Autowired
    public void setJdbcUserDAO(JdbcUserDAO jdbcUserDAO) {
        this.jdbcUserDAO = jdbcUserDAO;
    }

    @RequestMapping("/")
    @ResponseBody
    public String welcome() {
        return "Welcome to RestTemplate Example.";
    }

    @RequestMapping(value="/users", method=RequestMethod.GET, produces=MediaType.APPLICATION_JSON_VALUE)
    @ResponseBody   
    public List<User> getAllUsers() {
        System.out.println("jdbcUserDAO"+jdbcUserDAO);
        List<User> userList = jdbcUserDAO.getAllUsers();
        System.out.println(userList);
        return userList;
    }

}

The @Autowired annotation tells Spring that a bean that matches the interface of the parameter for the setter (in this case, JdbcUserDAO) should be injected into the setter, which results in the jdbcUserDAO field being set to your JdbcUserDAO bean defined in application_config.xml.

You could also simplify your UserController and annotate the field (removing the getter and setter):

@RestController
public class UserController {

    @Autowired
    private JdbcUserDAO jdbcUserDAO;

    @RequestMapping("/")
    @ResponseBody
    public String welcome() {
        return "Welcome to RestTemplate Example.";
    }

    @RequestMapping(value="/users", method=RequestMethod.GET, produces=MediaType.APPLICATION_JSON_VALUE)
    @ResponseBody   
    public List<User> getAllUsers() {
        System.out.println("jdbcUserDAO"+jdbcUserDAO);
        List<User> userList = jdbcUserDAO.getAllUsers();
        System.out.println(userList);
        return userList;
    }

}

For more information, see Guide to Spring @Autowired.

---

It also looks like your application_config.xml is not being included in Spring's application context. To include this XML file, change your ApplicationConfiguration class to resemble the following:

@ComponentScan(basePackages = {"com.ganeshTrading.riceAppService"})
@Configuration
@EnableWebMvc
@ImportResource("classpath:/path/to/application_config.xml")
public class ApplicationConfiguration {

}

Note that classpath:/path/to/application_config.xml is an example and the actual location of your application_config.xml file should be used instead.