Ebooks

Spring Boot Querydsl

last modified July 16, 2023

Spring Boot Querydsl tutorial shows how to use Querydsl to create database queries in a Spring Boot application.

Querydsl

Querydsl is a framework that enables the construction of statically typed SQL-like queries through its fluent API. Spring Data modules offer integration with Querydsl through QuerydslPredicateExecutor.

Spring Querydsl example

The following application creates queries with Querydsl using an entity manager and a repository.

pom.xml
src
├───main
│ ├───java
│ │ └───com
│ │ └───zetcode
│ │ │ Application.java
│ │ │ MyRunner.java
│ │ ├───model
│ │ │ City.java
│ │ └───repository
│ │ CityRepository.java
│ └───resources
│ application.properties
│ data-h2.sql
│ schema-h2.sql
└───test
 └───java

This is the project structure.

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
 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <groupId>com.zetcode</groupId>
 <artifactId>springbootquerydsl</artifactId>
 <version>1.0-SNAPSHOT</version>
 <packaging>jar</packaging>
 <properties>
 <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 <maven.compiler.source>17</maven.compiler.source>
 <maven.compiler.target>17</maven.compiler.target>
 </properties>
 <parent>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-parent</artifactId>
 <version>2.6.7</version>
 </parent>
 <dependencies>
 <dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-data-jpa</artifactId>
 </dependency>
 <dependency>
 <groupId>com.h2database</groupId>
 <artifactId>h2</artifactId>
 <scope>runtime</scope>
 </dependency>
 <dependency>
 <groupId>com.querydsl</groupId>
 <artifactId>querydsl-apt</artifactId>
 <version>4.2.1</version>
 <scope>provided</scope>
 </dependency>
 <dependency>
 <groupId>com.querydsl</groupId>
 <artifactId>querydsl-jpa</artifactId>
 <version>4.2.1</version>
 </dependency>
 </dependencies>
 <build>
 <plugins>
 <plugin>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-maven-plugin</artifactId>
 <version>2.6.7</version>
 </plugin>
 <!--Plugin for query-dsl-->
 <plugin>
 <groupId>com.mysema.maven</groupId>
 <artifactId>apt-maven-plugin</artifactId>
 <version>1.1.3</version>
 <executions>
 <execution>
 <phase>generate-sources</phase>
 <goals>
 <goal>process</goal>
 </goals>
 <configuration>
 <outputDirectory>target/generated-sources/java</outputDirectory>
 <processor>com.querydsl.apt.jpa.JPAAnnotationProcessor</processor>
 </configuration>
 </execution>
 </executions>
 </plugin>
 </plugins>
 </build>
</project>

The Maven POM file contains dependencies for Spring Data JPA, H2 database, and Querydsl. JPAAnnotationProcessor finds domain types annotated with Entity and generates query types for them.

Annotation processing is a tool build in javac for scanning and processing annotations at compile time.

resources/application.properties

spring.main.banner-mode=off
spring.datasource.platform=h2
spring.jpa.hibernate.ddl-auto=none
logging.pattern.console=%d{dd-MM-yyyy HH:mm:ss} %magenta([%thread]) %highlight(%-5level) %logger.%M - %msg%n

The application.properties is the main Spring Boot configuration file. With the spring.main.banner-mode property we turn off the Spring banner. The spring.datasource.platform sets the vendor name of the database. It is used in the initialization scripts. Finally, the spring.jpa.hibernate.ddl-auto disables the automatic creation of schemas from entities. The logging.pattern.console defines the log pattern for the console.

resources/schema-h2.sql

CREATE TABLE cities(id INT PRIMARY KEY AUTO_INCREMENT,
 name VARCHAR(255), population INT);

When the application is started, the schema-h2.sql script is executed. It creates a new database table.

resources/data-h2.sql

INSERT INTO cities(name, population) VALUES('Bratislava', 432000);
INSERT INTO cities(name, population) VALUES('Budapest', 1759000);
INSERT INTO cities(name, population) VALUES('Prague', 1280000);
INSERT INTO cities(name, population) VALUES('Warsaw', 1748000);
INSERT INTO cities(name, population) VALUES('Los Angeles', 3971000);
INSERT INTO cities(name, population) VALUES('New York', 8550000);
INSERT INTO cities(name, population) VALUES('Edinburgh', 464000);
INSERT INTO cities(name, population) VALUES('Suzhou', 4327066);
INSERT INTO cities(name, population) VALUES('Zhengzhou', 4122087);
INSERT INTO cities(name, population) VALUES('Berlin', 3671000);
INSERT INTO cities(name, population) VALUES('Brest', 139163);
INSERT INTO cities(name, population) VALUES('Bucharest', 1836000);

Later, the data-h2.sql file is executed. It fills the table with data.

com/zetcode/model/City.java

package com.zetcode.model;
import java.util.Objects;
import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;
import jakarta.persistence.Table;
@Entity
@Table(name = "cities")
public class City {
 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)
 private Long id;
 private String name;
 private int population;
 public City() {
 }
 public City(String name, int population) {
 this.name = name;
 this.population = population;
 }
 public Long getId() {
 return id;
 }
 public void setId(Long id) {
 this.id = id;
 }
 public String getName() {
 return name;
 }
 public void setName(String name) {
 this.name = name;
 }
 public int getPopulation() {
 return population;
 }
 public void setPopulation(int population) {
 this.population = population;
 }
 @Override
 public int hashCode() {
 int hash = 7;
 hash = 79 * hash + Objects.hashCode(this.id);
 hash = 79 * hash + Objects.hashCode(this.name);
 hash = 79 * hash + this.population;
 return hash;
 }
 @Override
 public boolean equals(Object obj) {
 if (this == obj) {
 return true;
 }
 if (obj == null) {
 return false;
 }
 if (getClass() != obj.getClass()) {
 return false;
 }
 final City other = (City) obj;
 if (this.population != other.population) {
 return false;
 }
 if (!Objects.equals(this.name, other.name)) {
 return false;
 }
 return Objects.equals(this.id, other.id);
 }
 @Override
 public String toString() {
 var builder = new StringBuilder();
 builder.append("City{id=").append(id).append(", name=")
 .append(name).append(", population=")
 .append(population).append("}");
 return builder.toString();
 }
}

This is the City entity.

com/zetcode/repository/CityRepository.java

package com.zetcode.repository;
import com.zetcode.model.City;
import org.springframework.data.querydsl.QuerydslPredicateExecutor;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;
@Repository
public interface CityRepository extends CrudRepository<City, Long>,
 QuerydslPredicateExecutor<City> {
}

To enable Querydsl in our repository, we extend from QuerydslPredicateExecutor.

com/zetcode/MyRunner.java

package com.zetcode;
import com.querydsl.core.types.OrderSpecifier;
import com.querydsl.core.types.dsl.BooleanExpression;
import com.querydsl.jpa.impl.JPAQuery;
import com.zetcode.model.QCity;
import com.zetcode.repository.CityRepository;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;
import jakarta.persistence.EntityManager;
import jakarta.persistence.PersistenceContext;
@Component
@SuppressWarnings({ "rawtypes", "unchecked" })
public class MyRunner implements CommandLineRunner {
 private static final Logger logger = LoggerFactory.getLogger(MyRunner.class);
 @PersistenceContext
 private EntityManager entityManager;
 @Autowired
 private CityRepository cityRepository;
 @Override
 public void run(String... args) throws Exception {
 var qCity = QCity.city;
 var query = new JPAQuery(entityManager);
 query.from(qCity).where(qCity.name.eq("Bratislava")).distinct();
 var c1 = query.fetch();
 logger.info("{}", c1);
 var query2 = new JPAQuery(entityManager);
 query2.from(qCity).where(qCity.name.endsWith("est").and(qCity.population.lt(1800000)));
 var cities = query2.fetch();
 logger.info("{}", cities);
 BooleanExpression booleanExpression = qCity.population.goe(2_000_000);
 OrderSpecifier<String> orderSpecifier = qCity.name.asc();
 var cities2 = cityRepository.findAll(booleanExpression, orderSpecifier);
 logger.info("{}", cities2);
 }
}

We use EntityManager and CityRepository to create Querydsl queries.

var qCity = QCity.city;

Querydsl creates a QCity type.

var query = new JPAQuery(entityManager);

In the first two queries, we use entity manager.

query.from(qCity).where(qCity.name.eq("Bratislava")).distinct();
var c1 = query.fetch();
logger.info("{}", c1);

Using the Querydsl's fluent API, we fetch a distinct city object.

var query2 = new JPAQuery(entityManager);
query2.from(qCity).where(qCity.name.endsWith("est").and(qCity.population.lt(1800000)));
var cities = query2.fetch();
logger.info("{}", cities);

A more complex query fetches multiple cities.

BooleanExpression booleanExpression = qCity.population.goe(2_000_000);
OrderSpecifier<String> orderSpecifier = qCity.name.asc();
var cities2 = cityRepository.findAll(booleanExpression, orderSpecifier);
logger.info("{}", cities2);

In the third query, we utilize the repository.

Note: In Java enterprise applications it is a good practice to define a service layer that works with repositories. For simplicity reasons, we skip the service layer.

com/zetcode/Application.java

package com.zetcode;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class Application {
 public static void main(String[] args) {
 SpringApplication.run(Application.class, args);
 }
}

The Application sets up the Spring Boot application. The @SpringBootApplication enables auto-configuration and component scanning.

$ mvn spring-boot:run
...
04-06-2019 13:22:13 [main] INFO com.zetcode.MyRunner.run - [City{id=1, name=Bratislava, population=432000}]
04-06-2019 13:22:13 [main] INFO com.zetcode.MyRunner.run - [City{id=2, name=Budapest, population=1759000}, 
City{id=11, name=Brest, population=139163}]
04-06-2019 13:22:13 [main] INFO com.zetcode.MyRunner.run - [City{id=10, name=Berlin, population=3671000}, 
City{id=5, name=Los Angeles, population=3971000}, City{id=6, name=New York, population=8550000}, 
City{id=8, name=Suzhou, population=4327066}, City{id=9, name=Zhengzhou, population=4122087}]
...

We run the application.

In this article we have showed how to use Querydsl to generate queries in a Spring Boot application.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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