Question

So, I have a simple REST web application and if my Controller calls the DAO directly, the JDBC calls work just fine, but if my controller calls another class that calls the DAO on my behalf, it fails with NullPointerException (NPE).

Here’s my Controller:

@Component
@Scope("request")
@Path("/emsrequest")
public class EMSRequest {

    // I'm using this for testing
    @GET
    @Path("/xml/{accountNumber}")
    @Produces({MediaType.TEXT_PLAIN})
    public String requestByAccountNumber_XML(
            @PathParam("accountNumber") String accountNumber) {

        ReqSubTest los = new ReqSubTest();

        return "account (LOS) number is : " + los.testSql(Integer.parseInt(accountNumber)) + "!";
    }
}

Here’s the intermediate (service) class:

package com.company.demo.mercury.processmanager.components;

import com.company.demo.pmrws.dao.EMSRequestDaoImpl;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class ReqSubTest {

    @Autowired
    EMSRequestDaoImpl dao = new EMSRequestDaoImpl();

    public int testSql(int quantity){
        return dao.getNextTableIds("sys_process_tbl", quantity);

    }
}

And here’s the DAO Implementation:

package com.company.demo.pmrws.dao;

import org.apache.log4j.Logger;
import org.springframework.jdbc.core.support.JdbcDaoSupport;

public class EMSRequestDaoImpl extends JdbcDaoSupport {

    private static final Logger logger = Logger.getLogger(EMSRequestDaoImpl.class);

    public int getNextTableIds(String tableName, int quantity) {

        if (logger.isDebugEnabled()) {
            logger.trace("Entering getNextTableIds");
        }

        if (getJdbcTemplate() == null) {
            System.out.println("UH OH!");
        }

        String selectSql = "select next_id "
                + "from sys_key_tbl "
                + "where table_name = ? ";
        String updateSql = "update sys_key_tbl "
                + "set next_id = ? "
                + "where table_name = ? and next_id = ? ";
        int lastId = -1;
        int updateCount = 0;
        while (updateCount == 0) {
            lastId = getJdbcTemplate().queryForInt(selectSql,
                    new Object[]{tableName});
            updateCount = getJdbcTemplate().update(updateSql,
                    new Object[]{lastId + quantity, tableName, lastId});
        }

        if (logger.isDebugEnabled()) {
            logger.trace("Leaving getNextTableIds");
        }
        return lastId + 1;
    }
}

The Application Context XML:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
   http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
   http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">
    <context:component-scan base-package="com.company.demo.pmrws"/>

    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
          destroy-method="close">
        <property name="driverClassName" value="com.sybase.jdbc3.jdbc.SybDataSource" />
        <property name="url"
                  value="jdbc:sybase:Tds:blah:10240/BLAH_DB1" />
        <property name="username" value="blah" />
        <property name="password" value="blah" />
    </bean>

    <bean id="dataSourceMain" class="org.apache.commons.dbcp.BasicDataSource"
          destroy-method="close">
        <property name="driverClassName" value="com.sybase.jdbc3.jdbc.SybDataSource" />
        <property name="url"
                  value="jdbc:sybase:Tds:blah:10240/BLAH_DB2" />
        <property name="username" value="blah" />
        <property name="password" value="blah" />
    </bean>
    </bean>

    <!--    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource" />
    </bean>-->

    <bean id="emsResponseDao" class="com.company.demo.pmrws.dao.EMSResponseDaoImpl">
        <property name="dataSource" ref="dataSource" />
    </bean>

    <bean id="emsStatusDao" class="com.company.demo.pmrws.dao.EMSStatusDaoImpl">
        <property name="dataSource" ref="dataSourceMain" />
    </bean>

<!--    <bean id="collateralSybaseEmsDao" class="com.company.demo.dao.CollateralSybaseEmsDaoImpl">
        <property name="dataSource" ref="dataSource" />
    </bean>

    <bean id="collateralSybaseDao" class="com.company.demo.dao.CollateralSybaseDaoImpl">
        <property name="dataSource" ref="dataSource" />
    </bean>-->

    <bean id="emsRequestDao" class="com.company.demo.pmrws.dao.EMSRequestDaoImpl">
        <property name="dataSource" ref="dataSource" />
    </bean>

    <context:component-scan base-package="com.company.demo.mercury.processmanager.components" />

</beans>

What am I missing? BTW, this is Spring 2.5.

Answer 1

It is because ReqSubTest los = new ReqSubTest(); create a new normal java Object instance but not a Spring Bean, therefore there get nothing injected into the los instance.

Three ways to fix it.

• instead of ReqSubTest los = new ReqSubTest(); inject los via Spring, but this requires that EMSRequest is a Spring bean too

Example:

@Component public class EMSRequest {

    @Autowire ReqSubTest los;

    public String requestByAccountNumber_XML(@PathParam("accountNumber") String accountNumber) {
        return "account (LOS) number is : " + los.testSql(Integer.parseInt(accountNumber)) + "!";
    } 
}

• instead of ReqSubTest los = new ReqSubTest(); use ReqSubTest los = springApplicationContext.getBean(ReqSubTest.class)
• If you use real AspectJ then you can add @Configurable and then Spring inject other beans even if an instance is created via new (Requires to be enabled via <context:spring-configured />) – You can add the annotation to EMSRequest and then use normal injection like suggeted in the first item, or add it to ReqSubTest