JPA EntityManager remove() example Using Spring Boot

In this post, we will see JPA EntityManager remove() example using Spring Boot and Oracle.

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

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

Note – The EntityManger interface is available in javax.persistence package. The remove() method throws IllegalArgumentException if the instance is not an entity or is a detached entity. In Spring Data JPA CrudRepository delete() method internally uses EntityManager remove() method. See an example here.

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

First, we need to create an EntityManger reference.


@PersistenceContext
private EntityManager entityManger;

Using this we can call persist() method.

package com.netsurfingzone.impl;

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

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

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

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

	@PersistenceContext
	private EntityManager entityManger;

	@Transactional
	public Student deleteStudent(Student student) {
		if (entityManger.contains(student)) {
			entityManger.remove(student);
		} else {
			entityManger.remove(entityManger.merge(student));
		}

		return student;
	}

}

 

Did you notice in above code snippet we are checking entityManger.contains(student)? If the entityManger doesn’t contain the entity we want to delete then first we need to call merge() method then only we should call remove() method otherwise we will get java.lang.IllegalArgumentException: Removing a detached instance.

 

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

public void remove(Object entity) {
    delete( entity );
}

Let’s see JPA EntityManager remove() 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 remove() example as below.

Directory structure –

JPA EntityManager remove() example Using Spring Boot

 

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

Student.java

package com.netsurfingzone.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.netsurfingzone.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.netsurfingzone.entity.Student;
import com.netsurfingzone.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 = "/delete", method = RequestMethod.POST)
	@ResponseBody
	public Student deleteStudent(@RequestBody Student student) {
		Student studentResponse = (Student) studentService.deleteStudent(student);
		return studentResponse;
	}

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

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

}

We have seen controller and serviceimpl, interface for JPA EntityManager remove() example.


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

StudentService.java – interface

package com.netsurfingzone.service;

import org.springframework.stereotype.Component;

import com.netsurfingzone.entity.Student;

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

	public Student deleteStudent(Student student);

	public Student getStudent(int id);

}

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

StudentServiceImpl.java

package com.netsurfingzone.impl;

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

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

import com.netsurfingzone.entity.Student;
import com.netsurfingzone.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 deleteStudent(Student student) {
		entityManger.detach(student);
		return student;
	}

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

}

SpringMain.java


package com.netsurfingzone.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.netsurfingzone.entity")
public class SpringMain {
	public static void main(String[] args) {

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

}

Note – See more details about @ComponentScan here.

Configuration file for JPA EntityManager remove() example.

JpaConfig.java

package com.netsurfingzone.config;

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

@Configuration
@EnableJpaRepositories(basePackages = "com.netsurfingzone.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"
    }

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
(?, ?, ?, ?)

 

DELETE – http://localhost:9091/student/delete

JPA EntityManager remove() example

 

delete
from
student
where
id=?

 

 

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

If you try to fetch student using id 1, will not get any record.

 

That’s all about JPA EntityManager remove() 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 remove() example.