JPA EntityManager persist() method Example

By
Rakesh
-

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

The persist() method used to save an entity and defined in the EntityManager interface as below.

public void persist(Object entity); –  Used to save an entity.

Note – The EntityManger interface is available in javax.persistence package. The persist() method must be used to save only newly created entities. It throws EntityExistsException if the entity already exists in the database. In Spring Data JPA CrudRepository save() method internally uses EntityManager persist() method. See an example here.

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

First, we need to create a EntityManger reference.

@PersistenceContext
private EntityManager entityManger;

Using this we can call persist() method.

package com.javatute.impl;

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

import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

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

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

	@PersistenceContext
	private EntityManager entityManger;

	@Transactional
	public Student saveStudent(Student student) {
		entityManger.persist(student);
		return student;
	}

}

 

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

@Override
public void persist(Object object) throws HibernateException {
checkOpen();
firePersist( new PersistEvent( null, object, this ) );
}

Let’s see a complete example of JPA EntityManager persit() method 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 – entitymanager, ArtifactId – entitymanager and name – entitymanager) 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>entitymanager</groupId>
	<artifactId>entitymanager</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>entitymanager</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 directory structure of JPA EntityManager persist() method example as below.

Directory structure –

JPA EntityManager persist() Example

 

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;
	}

}

We have seen controller and serviceimpl, interface for JPA EntityManager persist() method Example.

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

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.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

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

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

	@PersistenceContext
	private EntityManager entityManger;

	@Transactional
	public Student saveStudent(Student student) {
		entityManger.persist(student);
		return student;
	}

	@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.

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"
    }

Below query get generated while saving student entity using persist() method.

Hibernate:
select
hibernate_sequence.nextval
from
dual

Hibernate:
insert
into
student
(name, roll_number, university, id)
values
(?, ?, ?, ?)

 

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

JPA EntityManager persist() 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=?

 

That’s all about JPA EntityManager persist() method example using Spring Boot and Oracle.

Spring Data JPA examples.

Other Spring Data JPA and Hibernate tutorials.

EntityManger docs.

Summary – We have seen about JPA EntityManager persist() method example. We also covered how to fetch an entity from the Database using find() method.

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