Question

I just moved my Spring application which is running fine on localhost to a shared web hosting server on mochahost, and I’m seeing the below exception (truncated) in the root cause:

root cause

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'adDaoImpl': Injection of autowired dependencies failed; nested exception is java.lang.NullPointerException
    org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:288)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1074)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
(truncated)

and below that:

root cause

    java.lang.NullPointerException
        com.adsense.connection.MySqlDBPooling.getConnection(MySqlDBPooling.java:28)
        com.adsense.dao.impl.AdDaoImpl.setDataSource(AdDaoImpl.java:21)
        sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        java.lang.reflect.Method.invoke(Method.java:597)
        org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:588)
(truncated)

AdDaoImpl.java

@Repository
public class AdDaoImpl implements AdDao{

    Connection conn;

    @Autowired
    public void setDataSource(){
        try{
            conn = (new MySqlDBPooling()).getConnection();
        }catch(SQLException e){
            e.printStackTrace();
        }
    }

    ...
    ...
}

MySqlDBPooling.java

package com.adsense.connection;

import java.sql.Connection;
import java.sql.SQLException;
import javax.naming.*;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.sql.DataSource;

public class MySqlDBPooling implements ServletContextListener{

    private static DataSource ds;

    public MySqlDBPooling(){
    }

    public void contextInitialized(ServletContextEvent sce){
        try{
            Context envCtx = (Context)(new InitialContext()).lookup("java:comp/env");
            ds = (DataSource)envCtx.lookup("jdbc/AdSenseDB");
            System.out.println((new StringBuilder("MySqlDBPooling is set to ")).append(ds.toString()).toString());
        }catch(NamingException e){
            e.printStackTrace();
        }
    }

    public Connection getConnection() throws SQLException{
        return ds.getConnection(); // getting NullPointerException here
    }

    public void contextDestroyed(ServletContextEvent servletcontextevent){
    }
}

Context.xml

<?xml version="1.0" encoding="UTF-8"?>
<Context antiResourceLocking="false" privileged="true" version="5.0">
    <Resource 
       name="jdbc/AdSenseDB"
       auth="Container"
       type="javax.sql.DataSource"
       removeAbandoned="true"
       removeAbandonedTimeout="30"
       maxActive="300"
       maxIdle="300"
       maxWait="1000"
       username="<username here>"
       password="<password here>"
       driverClassName="com.mysql.jdbc.Driver"
       url="jdbc:mysql://localhost:3306/adsense_adsense"/>
</Context>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>Adsense</display-name>
  <listener>
    <listener-class>com.adsense.connection.MySqlDBPooling</listener-class>
  </listener>
  <servlet>
    <servlet-name>spring</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>spring</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>*.css</url-pattern>
    <url-pattern>*.js</url-pattern>
    <url-pattern>*.jpg</url-pattern>
    <url-pattern>*.jpeg</url-pattern>
    <url-pattern>*.png</url-pattern>
    <url-pattern>*.gif</url-pattern>
    <url-pattern>*.ico</url-pattern>
  </servlet-mapping>
</web-app>

Some points:

1. I have placed my jars (including mysql-connector-java-5.1.10.jar) at /WEB-INF/lib. On localhost, the mysqlconnector is placed in tomcat libs. But since this is a shared server, i have no access to tomcat libs. WEB-INF/lib might be a wrong place for mysql connector.

2. WEB-INF/lib might be a wrong place for placing libs. In my other app (not related to this) running on Amazon web server, I have placed all libraries in tomcat libs folder.

3. In context.xml, i even changed url to jdbc:mysql://domain.com:3306/adsense_adsense i.e. replaced localhost to actual domain, but that didn’t help.

4. In MySqlDBPooling.java, if ds is null, why did it not throw NullPointerException earlier at

System.out.println((new StringBuilder(“MySqlDBPooling is set to
“)).append(ds.toString()).toString());

which is executed during server start (MySqlDBPooling class is added as a listener in web.xml)

Thanks for your attention.

James

EDIT:

It worked after I updated MySqlDBPooling.java as suggested (get datasource using Spring) by @JB Nizet to:

package com.adsense.connection;

import java.sql.Connection;
import java.sql.SQLException;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import org.springframework.jdbc.datasource.DriverManagerDataSource;

public class MySqlDBPooling implements ServletContextListener{

    private static DriverManagerDataSource ds;

    public MySqlDBPooling(){
    }

    public void contextInitialized(ServletContextEvent sce){
        try{
            ds = new DriverManagerDataSource();
            ds.setDriverClassName( "com.mysql.jdbc.Driver");
            ds.setUrl( "jdbc:mysql://localhost:3306/adsense_adsense");
            ds.setUsername( "USERNAME");
            ds.setPassword( "PASSWORD"); 
            System.out.println("Datasource is: "+ds.toString());
        }catch(Exception e){
            e.printStackTrace();
        }
    }

    public Connection getConnection() throws SQLException{
        return ds.getConnection();
    }

    public void contextDestroyed(ServletContextEvent servletcontextevent){
    }
}

Answer 1

If you declare a DataSource in the context.xml, Tomcat tries to instantiate it using its own classloader, and not the classloader of the webapp. So the driver jar in WEB-INF/lib is not in its classpath and the driver can’t be loaded.

The reason you don’t see an NPE sooner is that the JNDI lookup probably fails with a NamingException. You should see the stack trace of this exception in the log, at deployment time.

Since you’re using Spring, you could create the DataSource from Spring (using a stand-alone connection pool) instead of letting Tomcat create it. See http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/htmlsingle/spring-framework-reference.html#jdbc-datasource