JPA EntityManager find() method

By
Rakesh
-

In this post, we will see JPA EntityManager find() method using Spring Boot.

The find() method used to retrieve an entity defined as below in the EntityManager interface.

T find(Class<T> entityClass, Object primaryKey) –  Returns entity for the given primary key.

It returns null if entity is not found in the database.

Note – The EntityManger interface is available in javax.persistence package. There are four overloaded versions of find() method which we will see at the end of the post.

Let’s see how to use EntityManager find() method.

First, we need to create a reference of the EntityManger.

@PersistenceContext
private EntityManager entityManger;

Using this we can call find() method.

package com.javatute.impl;

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

	@PersistenceContext
	private EntityManager entityManger;

	@Transactional
	public Student find(int id) {
		Student response = (Student) entityManger.find(Student.class, id);
		return response;
	}


}

 

Note – Implementation of EntityManger find() has been given in Hibernate’s SessionImpl.java as below.

@Override
public <T> T find(Class<T> entityClass, Object primaryKey) {
return find( entityClass, primaryKey, null, null );
}

 

Note – Just an additional note Crudrepository’s finById() method internally uses EntityManger find() method. See an example here.

Let’s see a complete example of JPA EntityManager find() method 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 – entitymanagerfind, ArtifactId – entitymanagerfind and name – entitymanagerfind) 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>entitymanagerfind</groupId>
	<artifactId>entitymanagerfind</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>entitymanagerfind</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.

Directory structure –

Spring Data JPA Is and Equals

 

Let’s see about JPA EntityManager find() method.

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 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.service.StudentService;

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

	@Autowired
	private StudentService studentService;

	@RequestMapping(value = "/save", method = RequestMethod.POST)
	@ResponseBody
	public Student saveStudent(@RequestBody Student student) {
		Student studentResponse = (Student) studentService.saveStudent(student);
		return studentResponse;
	}

	@RequestMapping(value = "/find/{id}", method = RequestMethod.GET)
	@ResponseBody
	public Student findByName(@PathVariable int id) {

		Student studentResponse = (Student) studentService.find(id);
		return studentResponse;
	}

}

 

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

StudentRepository.java – interface

package com.javatute.repository;

import java.io.Serializable;

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> {

}

StudentService.java – interface

package com.javatute.service;

import org.springframework.stereotype.Component;

import com.javatute.entity.Student;

@Component
public interface StudentService {
	public Student saveStudent(Student student);
	public Student find(int id);

}

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

StudentServiceImpl.java

package com.javatute.impl;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

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.StudentRepository;
import com.javatute.service.StudentService;

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

	@Autowired
	private StudentRepository studentRepository;

	@PersistenceContext
	private EntityManager entityManger;

	@Transactional
	public Student saveStudent(Student student) {
		Student response = (Student) studentRepository.save(student);
		return response;
	}

	@Transactional
	public Student find(int id) {
		Student response = (Student) entityManger.find(Student.class, id);
		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 save operation first using below REST API.

http://localhost:9091/student/save

    {
        "name": "john",
        "rollNumber": "120",
        "university":"rgtu"
    }

 

Response Data.

    {
        "id": 1,
        "name": "john",
        "rollNumber": "120",
        "university": "rgtu"
    }

 

http://localhost:9091/student/find/1

JPA EntityManager find() method

Query genrated for above operation using JPA Entitymanger find() method.

Hibernate:
select
student0_.id as id1_0_0_,
student0_.name as name2_0_0_,
student0_.roll_number as roll_number3_0_0_,
student0_.university as university4_0_0_
from
student student0_
where
student0_.id=?

There are four overloaded versions of find() method defined in the EntityManger interface.

T find(Class<T> entityClass, Object primaryKey) –  Returns entity for given primary key.
T find(Class<T> entityClass, Object primaryKey, LockModeType lockMode) – Returns entity for given primary key and lock type.
T find(Class<T> entityClass, Object primaryKey, LockModeType lockMode, Map<String,Object> properties) – Returns entity for given primary key, lock type and using the specified properties
T find(Class<T> entityClass, Object primaryKey, Map<String,Object> properties) – Returns entity for given primary key, lock type and using the specified properties.

 

That’s all about JPA EntityManager find() method using Spring Boot.

Spring Data JPA examples.

Other Spring Data JPA and Hibernate tutorials.

EntityManger docs.

Summary – We have seen about JPA EntityManager find() method. We also covered how to retreive a record from Database.

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