使用 Spring Boot JdbcTemplate 获取 java.lang.NullPointerException

Question

General Information: New to Spring Boot and wanted to test out my JDBC connections via unit tests. I made a simple class to connect to my database and a simple test class to follow up with the proper test case.

Problem: Continuously receiving a java.lang.NullPointerException when performing jdbcTemplate.getDataSource().getConnection(); I am having a hard time understanding why. I tried using different databases, and ensured that I could make a connection with the regular JDBC. I have referred to numerous other questions on Stack Overflow but I have still been stuck on this for the past two days without any progress. I even tried to use different types of DataSource libraries but all of them yield the same result.

Question: How do I solve this? If anyone can also explain why the issue is happening, and why do we need to use the Spring JDBC on an enterprise level, that would be great.

---

My code:

DatabaseTableService.java

import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import com.vertica.jdbc.DataSource;

@RestController
@RequestMapping("/databaseServices")
public class DatabaseTableService {

    private JdbcTemplate jdbcTemplate;
    private DataSource dataSource;


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


    @RequestMapping("/testConnection")
    @ResponseBody
    public boolean canConnectToDB() {
        boolean result;
        try {
            jdbcTemplate.getDataSource().getConnection();
            result = true;
        } catch (Exception e) {
            e.printStackTrace();
            result = false;
        }
        return result;
    }

}

---

beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       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.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

    <context:component-scan base-package="com.company.project"></context:component-scan>

    <mvc:annotation-driven/>

    <bean id="dataSource"
          class="com.vertica.jdbc.DataSource">
        <property name="URL" value="DBURLHERE"/>
        <property name="userID" value="USERIDHERE"/>
        <property name="password" value="PASSWORDHERE"/>
    </bean>






    <bean id="databaseTableService"
          class="com.company.project.services.DatabaseTableService">
        <property name="dataSource" ref="dataSource"></property>
    </bean>


    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix">
            <value>/WEB-INF/</value>
        </property>
        <property name="suffix">
            <value>.jsp</value>
        </property>
    </bean>

</beans>

---

DatabaseTableServiceTest.java

import org.junit.After;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.SpringApplicationConfiguration;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import org.springframework.test.context.web.WebAppConfiguration;
import org.springframework.test.web.servlet.MockMvc;
import org.springframework.test.web.servlet.setup.MockMvcBuilders;
import org.springframework.web.context.WebApplicationContext;

import com.vertica.jdbc.DataSource;


@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = ApplicationController.class)
@WebAppConfiguration
public class DatabaseTableServiceTest {

    @Autowired
    private WebApplicationContext webApplicationContext;

    private JdbcTemplate jdbcTemplate;
    private MockMvc mockMvc;
    DatabaseTableService databaseTableServiceObject;
    DataSource testDataSource = new DataSource();

    @Before
    public void setUp() throws Exception {
        mockMvc = MockMvcBuilders.webAppContextSetup(webApplicationContext)
                .build();

        databaseTableServiceObject = new DatabaseTableService();
    }




    @Test
    public void setDataSource() throws Exception {
        databaseTableServiceObject.setDataSource(testDataSource);
    }

    @Test
    public void validateCanConnectToDB() throws Exception {
        Assert.assertTrue(databaseTableServiceObject.canConnectToDB());
    }


    @After
    public void tearDown() throws Exception {
        mockMvc = null;
        databaseTableServiceObject = null;
        testDataSource = null;
    }

}

---

ApplicationController.java

import org.springframework.boot.*;
import org.springframework.boot.autoconfigure.*;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.stereotype.*;
import org.springframework.web.bind.annotation.*;


@SpringBootApplication
@ImportResource({"beans.xml"})
@ComponentScan(basePackages = "com.company.project")
public class ApplicationController {

    public static void main(String[] args) throws Exception {

        SpringApplication.run(ApplicationController.class, args);
    }
}

---

Folder Structure

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Spring Application Context Information

Answer 1

You are using Spring Boot and next try very hard not to. Remove your beans.xml and the @ImportResource from your ApplicationController (which isn't a controller but your actual application btw, as your service is your actual controller). Also assuming that your ApplicationController is in the same package you can remove the @ComponentScan as well.

Then in your application.properties add the following

spring.datasource.url=<your-url>
spring.datasource.username=<your-username>
spring.datasource.password=<your-password>
spring.datasource.type=com.vertica.jdbc.DataSource

spring.mvc.view.prefix=/WEB-INF/
spring.mvc.view.suffix=.jsp

Spring Boot will create a DataSource and a JdbcTemplate for you, so no need to create that yourself. Just @Autowire the JdbcTemplate in your class.

@RestController
@RequestMapping("/databaseServices")
public class DatabaseTableService {

    private final JdbcTemplate jdbcTemplate;

    @Autowired
    public DatabaseTableService(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate=jdbcTeplate;
    }

    @RequestMapping("/testConnection")
    @ResponseBody
    public boolean canConnectToDB() {
        boolean result;
        try {
            jdbcTemplate.getDataSource().getConnection();
            result = true;
        } catch (Exception e) {
            e.printStackTrace();
            result = false;
        }
        return result;
    }
}

Now your test, it is quite a mess. You are using Spring but are doing things yourself, so not sure what you are trying to achieve there.

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = ApplicationController.class)
@WebAppConfiguration
public class DatabaseTableServiceTest {

    @Autowired
    private WebApplicationContext webApplicationContext;

    private MockMvc mockMvc;
    private DatabaseTableService databaseTableServiceObject;

    @Before
    public void setUp() throws Exception {
        mockMvc = MockMvcBuilders.webAppContextSetup(webApplicationContext)
                .build();
    }

    @Test
    public void setDataSource() throws Exception {
        databaseTableServiceObject.setDataSource(testDataSource);
    }

    @Test
    public void validateCanConnectToDB() throws Exception {
        Assert.assertTrue(databaseTableServiceObject.canConnectToDB());
    }

}

You can just @Autowired the service which is now fully constructed.

Final thing is that your canConnectToDB method is flawed. You are obtaining a connection but are never returning/closing it. So after calling this method for a couple of times your application will stop work as the connection pool will be depleted or your database stops accepting connections.

In short work with the framework instead of against/around the framework. Read the documentation instead of trying to hack your way around it.