This guide walks you through the process of accessing relational data with Spring.

What you’ll build

You’ll build an application using Spring’s JdbcTemplate to access data stored in a relational database.

What you’ll need

How to complete this guide

Like most Spring Getting Started guides, you can start from scratch and complete each step, or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.

To start from scratch, move on to Build with Gradle.

To skip the basics, do the following:

When you’re finished, you can check your results against the code in gs-relational-data-access/complete.

Build with Gradle

Build with Gradle

First you set up a basic build script. You can use any build system you like when building apps with Spring, but the code you need to work with Gradle and Maven is included here. If you’re not familiar with either, refer to Building Java Projects with Gradle or Building Java Projects with Maven.

Create the directory structure

In a project directory of your choosing, create the following subdirectory structure; for example, with mkdir -p src/main/java/hello on *nix systems:

└── src
    └── main
        └── java
            └── hello

Create a Gradle build file

Below is the initial Gradle build file.

build.gradle

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:2.1.4.RELEASE")
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'

bootJar {
    baseName = 'gs-relational-data-access'
    version =  '0.1.0'
}

repositories {
    mavenCentral()
}

sourceCompatibility = 1.8
targetCompatibility = 1.8

dependencies {
    compile("org.springframework.boot:spring-boot-starter")
    compile("org.springframework:spring-jdbc")
    compile("com.h2database:h2")
    testCompile("junit:junit")
}

The Spring Boot gradle plugin provides many convenient features:

  • It collects all the jars on the classpath and builds a single, runnable "über-jar", which makes it more convenient to execute and transport your service.

  • It searches for the public static void main() method to flag as a runnable class.

  • It provides a built-in dependency resolver that sets the version number to match Spring Boot dependencies. You can override any version you wish, but it will default to Boot’s chosen set of versions.

Build with Maven

Build with Maven

First you set up a basic build script. You can use any build system you like when building apps with Spring, but the code you need to work with Maven is included here. If you’re not familiar with Maven, refer to Building Java Projects with Maven.

Create the directory structure

In a project directory of your choosing, create the following subdirectory structure; for example, with mkdir -p src/main/java/hello on *nix systems:

└── src
    └── main
        └── java
            └── hello

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.springframework</groupId>
    <artifactId>gs-relational-data-access</artifactId>
    <version>0.1.0</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.4.RELEASE</version>
    </parent>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
        </dependency>
    </dependencies>


    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

The Spring Boot Maven plugin provides many convenient features:

  • It collects all the jars on the classpath and builds a single, runnable "über-jar", which makes it more convenient to execute and transport your service.

  • It searches for the public static void main() method to flag as a runnable class.

  • It provides a built-in dependency resolver that sets the version number to match Spring Boot dependencies. You can override any version you wish, but it will default to Boot’s chosen set of versions.

Build with your IDE

Build with your IDE

Create a Customer object

The simple data access logic you will work with below manages first and last names of customers. To represent this data at the application level, create a Customer class.

src/main/java/hello/Customer.java

package hello;

public class Customer {
    private long id;
    private String firstName, lastName;

    public Customer(long id, String firstName, String lastName) {
        this.id = id;
        this.firstName = firstName;
        this.lastName = lastName;
    }

    @Override
    public String toString() {
        return String.format(
                "Customer[id=%d, firstName='%s', lastName='%s']",
                id, firstName, lastName);
    }

    // getters & setters omitted for brevity
}

Store and retrieve data

Spring provides a template class called JdbcTemplate that makes it easy to work with SQL relational databases and JDBC. Most JDBC code is mired in resource acquisition, connection management, exception handling, and general error checking that is wholly unrelated to what the code is meant to achieve. The JdbcTemplate takes care of all of that for you. All you have to do is focus on the task at hand.

src/main/java/hello/Application.java

package hello;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.jdbc.core.JdbcTemplate;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

@SpringBootApplication
public class Application implements CommandLineRunner {

    private static final Logger log = LoggerFactory.getLogger(Application.class);

    public static void main(String args[]) {
        SpringApplication.run(Application.class, args);
    }

    @Autowired
    JdbcTemplate jdbcTemplate;

    @Override
    public void run(String... strings) throws Exception {

        log.info("Creating tables");

        jdbcTemplate.execute("DROP TABLE customers IF EXISTS");
        jdbcTemplate.execute("CREATE TABLE customers(" +
                "id SERIAL, first_name VARCHAR(255), last_name VARCHAR(255))");

        // Split up the array of whole names into an array of first/last names
        List<Object[]> splitUpNames = Arrays.asList("John Woo", "Jeff Dean", "Josh Bloch", "Josh Long").stream()
                .map(name -> name.split(" "))
                .collect(Collectors.toList());

        // Use a Java 8 stream to print out each tuple of the list
        splitUpNames.forEach(name -> log.info(String.format("Inserting customer record for %s %s", name[0], name[1])));

        // Uses JdbcTemplate's batchUpdate operation to bulk load data
        jdbcTemplate.batchUpdate("INSERT INTO customers(first_name, last_name) VALUES (?,?)", splitUpNames);

        log.info("Querying for customer records where first_name = 'Josh':");
        jdbcTemplate.query(
                "SELECT id, first_name, last_name FROM customers WHERE first_name = ?", new Object[] { "Josh" },
                (rs, rowNum) -> new Customer(rs.getLong("id"), rs.getString("first_name"), rs.getString("last_name"))
        ).forEach(customer -> log.info(customer.toString()));
    }
}

@SpringBootApplication is a convenience annotation that adds all of the following:

  • @Configuration tags the class as a source of bean definitions for the application context.

  • @EnableAutoConfiguration tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings.

  • @ComponentScan tells Spring to look for other components, configurations, and services in the the hello package. In this case, there aren’t any.

The main() method uses Spring Boot’s SpringApplication.run() method to launch an application. Did you notice that there wasn’t a single line of XML? No web.xml file either. This web application is 100% pure Java and you didn’t have to deal with configuring any plumbing or infrastructure.

Spring Boot supports H2, an in-memory relational database engine, and automatically creates a connection. Because we are using spring-jdbc, Spring Boot automatically creates a JdbcTemplate. The @Autowired JdbcTemplate field automatically loads it and makes it available.

This Application class implements Spring Boot’s CommandLineRunner, which means it will execute the run() method after the application context is loaded up.

First, you install some DDL using JdbcTemplate’s `execute method.

Second, you take a list of strings and using Java 8 streams, split them into firstname/lastname pairs in a Java array.

Then you install some records in your newly created table using JdbcTemplate’s `batchUpdate method. The first argument to the method call is the query string, the last argument (the array of Object s) holds the variables to be substituted into the query where the “?” characters are.

For single insert statements, JdbcTemplate’s `insert method is good. But for multiple inserts, it’s better to use batchUpdate.
Use ? for arguments to avoid SQL injection attacks by instructing JDBC to bind variables.

Finally you use the query method to search your table for records matching the criteria. You again use the “?” arguments to create parameters for the query, passing in the actual values when you make the call. The last argument is a Java 8 lambda used to convert each result row into a new Customer object.

Java 8 lambdas map nicely onto single method interfaces, like Spring’s RowMapper. If you are using Java 7 or earlier, you can easily plug in an anonymous interface implementation and have the same method body as the lambda expresion’s body contains, and it will work with no fuss from Spring.

Build an executable JAR

You can run the application from the command line with Gradle or Maven. Or you can build a single executable JAR file that contains all the necessary dependencies, classes, and resources, and run that. This makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.

If you are using Gradle, you can run the application using ./gradlew bootRun. Or you can build the JAR file using ./gradlew build. Then you can run the JAR file:

java -jar build/libs/gs-relational-data-access-0.1.0.jar

If you are using Maven, you can run the application using ./mvnw spring-boot:run. Or you can build the JAR file with ./mvnw clean package. Then you can run the JAR file:

java -jar target/gs-relational-data-access-0.1.0.jar
The procedure above will create a runnable JAR. You can also opt to build a classic WAR file instead.

You should see the following output:

2015-06-19 10:58:31.152  INFO 67731 --- [           main] hello.Application                        : Creating tables
2015-06-19 10:58:31.219  INFO 67731 --- [           main] hello.Application                        : Inserting customer record for John Woo
2015-06-19 10:58:31.220  INFO 67731 --- [           main] hello.Application                        : Inserting customer record for Jeff Dean
2015-06-19 10:58:31.220  INFO 67731 --- [           main] hello.Application                        : Inserting customer record for Josh Bloch
2015-06-19 10:58:31.220  INFO 67731 --- [           main] hello.Application                        : Inserting customer record for Josh Long
2015-06-19 10:58:31.230  INFO 67731 --- [           main] hello.Application                        : Querying for customer records where first_name = 'Josh':
2015-06-19 10:58:31.242  INFO 67731 --- [           main] hello.Application                        : Customer[id=3, firstName='Josh', lastName='Bloch']
2015-06-19 10:58:31.242  INFO 67731 --- [           main] hello.Application                        : Customer[id=4, firstName='Josh', lastName='Long']
2015-06-19 10:58:31.244  INFO 67731 --- [           main] hello.Application                        : Started Application in 1.693 seconds (JVM running for 2.054)

Summary

Congratulations! You’ve just used Spring to develop a simple JDBC client.

Spring Boot has many features for configuring and customizing the connection pool, for instance to connect to an external database instead of an in-memory one. Please refer to the User Guide for more detail.

See Also

The following guides may also be helpful:

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All guides are released with an ASLv2 license for the code, and an Attribution, NoDerivatives creative commons license for the writing.