Spring Data JPA Projection Example

By
Rakesh
-

In this tutorial, we will see Spring Data JPA Projection Example using Spring Boot and oracle. We will see how to implement Projection using Spring Data JPA.

Consider we have an entity called Student.java as below.

package com.javatute.entity;

@Entity
public class Student {

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private int id;

	@Column(name = "name")
	private String name;

	@Column(name = "roll_number")
	private String rollNumber;

	@Column(name = "university")
	String university;
	

}

 

and we have some record in the database as below.

Spring Data JPA Projection Example

We want to fetch any single column. For example, we want all student name as below.

 

Spring Data JPA Projection Example

 

Let’s see how to define Projection for the above requirement.

Define Interface with some method.

package com.javatute.repository;

public interface StudentName {
	String getName();
}

 

Define Repository as below.

@Repository
public interface StudentRepository extends JpaRepository<Student, Serializable> {
	
	
	List<StudentName> findAllBy();

}

 

Generated query.

Hibernate:
select
student0_.name as col_0_0_
from
student student0_

Running below example we should able to fetch name column details as below.

Spring Data JPA Projection Example

Spring Data JPA Projection Example using  Spring Boot and Oracle.

Open eclipse and create maven project, Don’t forget to check ‘Create a simple project (skip)’ click on next.  Fill all details(GroupId – springdataprojection, ArtifactId – springdataprojection and name – springdataprojection) and click on finish. Keep packaging as the jar.

Modify pom.xml

<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>springdataprojection</groupId>
	<artifactId>springdataprojection</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>springdataprojection</name>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.0.2.RELEASE</version>
	</parent>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>

		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-data-jpa</artifactId>
		</dependency>

		<dependency>
			<groupId>com.oracle</groupId>
			<artifactId>ojdbc6</artifactId>
			<version>11.2.0.3</version>
		</dependency>

	</dependencies>
	<build>
		<finalName>${project.artifactId}</finalName>
		<plugins>

			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.1</version>
				<configuration>
					<fork>true</fork>
					<executable>C:\Program Files\Java\jdk1.8.0_131\bin\javac.exe</executable>
				</configuration>
			</plugin>


		</plugins>
	</build>
</project>

Note – In pom.xml we have defined javac.exe path in configuration tag. You need to change accordingly i.e where you have installed JDK.

If you see any error for oracle dependency then follow these steps.

 

Let’s see the entity for Spring Data JPA Projection Example using Spring Boot.

Student.java

package com.javatute.entity;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Student {

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private int id;

	@Column(name = "name")
	private String name;

	@Column(name = "roll_number")
	private String rollNumber;

	@Column(name = "university")
	String university;

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getRollNumber() {
		return rollNumber;
	}

	public void setRollNumber(String rollNumber) {
		this.rollNumber = rollNumber;
	}

	public String getUniversity() {
		return university;
	}

	public void setUniversity(String university) {
		this.university = university;
	}

}

StudentController.java

package com.javatute.controller;

import java.util.ArrayList;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;

import com.javatute.entity.Student;
import com.javatute.repository.StudentName;
import com.javatute.service.StudentService;

@RestController
@RequestMapping(value = "/student")
public class StudentController {

	@Autowired
	private StudentService studentService;

	@RequestMapping(value = "/saveall", method = RequestMethod.POST)
	@ResponseBody
	public List<Student> saveAllStudents(@RequestBody List<Student> studentList) {
		List<Student> studentResponse = (List<Student>) studentService.saveAllStudent(studentList);
		return studentResponse;
	}

	@RequestMapping(value = "/findallname", method = RequestMethod.GET)
	@ResponseBody
	public List<String> findAllBy() {

		List<StudentName> studentResponse = (List<StudentName>) studentService.findAllBy();
		List<String> nameList = new ArrayList<String>();
		for(StudentName studentName : studentResponse) {
			nameList.add(studentName.getName());
		}
		return nameList;
	}

}

 

Note – See more details about @Controller and RestController here.

StudentRepository.java – interface

package com.javatute.repository;

import java.io.Serializable;
import java.util.List;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import com.javatute.entity.Student;

@Repository
public interface StudentRepository extends JpaRepository<Student, Serializable> {
	
	
	List<StudentName> findAllBy();

}

Define Interface StudentName with method getName..

package com.javatute.repository;

public interface StudentName {
	String getName();
}

 

StudentService.java – interface

package com.javatute.service;

import java.util.List;

import org.springframework.stereotype.Component;

import com.javatute.entity.Student;
import com.javatute.repository.StudentName;

@Component
public interface StudentService {
	public List<Student> saveAllStudent(List<Student> studentList);

	List<StudentName> findAllBy();

}

Note – See here more about @Component, @Controller, @Service and @Repository annotations here.

StudentServiceImpl.java

package com.javatute.impl;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import com.javatute.entity.Student;
import com.javatute.repository.StudentName;
import com.javatute.repository.StudentRepository;
import com.javatute.service.StudentService;

@Service("studentServiceImpl")
public class StudentServiceImpl implements StudentService {

	@Autowired
	private StudentRepository studentRepository;

	@Transactional
	public List<Student> saveAllStudent(List<Student> studentList) {
		List<Student> response = (List<Student>) studentRepository.saveAll(studentList);
		return response;
	}

	@Transactional
	public List<StudentName> findAllBy() {
		List<StudentName> response = (List<StudentName>) studentRepository.findAllBy();
		return response;
	}
}

SpringMain.java

package com.javatute.main;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.domain.EntityScan;
import org.springframework.context.annotation.ComponentScan;

@SpringBootApplication
@ComponentScan(basePackages = "com.*")
@EntityScan("com.javatute.entity")
public class SpringMain {
	public static void main(String[] args) {

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

}

Note – See more details about @ComponentScan here.

JpaConfig.java

package com.javatute.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;

@Configuration
@EnableJpaRepositories(basePackages = "com.javatute.repository")
public class JpaConfig {

}

Note – See more details about @Configuration annotations here.

application.properties

# Connection url for the database
spring.datasource.url=jdbc:oracle:thin:@localhost:1521:XE
spring.datasource.username=SYSTEM
spring.datasource.password=oracle2
spring.datasource.driver-class-name=oracle.jdbc.driver.OracleDriver
# Show or not log for each sql query
spring.jpa.show-sql = true
spring.jpa.properties.hibernate.format_sql=true 
 
spring.jpa.hibernate.ddl-auto =create
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.Oracle10gDialect
 
server.port = 9091

#show sql values
logging.level.org.hibernate.type.descriptor.sql=trace

#hibernate.show_sql = true
#spring.jpa.hibernate.logging.level.sql =FINE
#show sql statement
#logging.level.org.hibernate.SQL=debug

Let’s run the SpringMain class(run as java application).

Perform saveall operation first using below REST API.

http://localhost:9091/student/saveall

[
    {
        "name": "john",
        "rollNumber": "120",
        "university":"rgtu"
    },
    {
        "name": "mark",
        "rollNumber": "121",
        "university":"rgtu"
    },
    {
        "name": "aric",
        "rollNumber": "123",
        "university":"rgtu"
    },
    {
        "name": "hira",
        "rollNumber": "124",
        "university":"rgtu"
    }
]

Let’s see response data for Spring Data JPA Projection Example.

Response Data.

[
    {
        "id": 1,
        "name": "john",
        "rollNumber": "120",
        "university": "rgtu"
    },
    {
        "id": 2,
        "name": "mark",
        "rollNumber": "121",
        "university": "rgtu"
    },
    {
        "id": 3,
        "name": "aric",
        "rollNumber": "123",
        "university": "rgtu"
    },
    {
        "id": 4,
        "name": "hira",
        "rollNumber": "124",
        "university": "rgtu"
    }
]

 

http://localhost:9091/student/findallname

Spring Data JPA Projection Example

That’s all about Spring Data JPA Projection Example Using Spring Boot and oracle.

 

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