public
List<Employee> findTop3ByOrderByIdAsc();
Get top 3
records order by id in ascending order.
public
List<Employee> findTop3ByOrderByIdDesc();
Get top 3
records order by id in descending order.
public List<Employee>
findTop3ByOrderByFirstNameAscIdDesc();
Get top 3
records order by firstName in ascending order and id in descending order.
Follow
below step-by-step procedure to build complete working application.
Step 1:
Create new maven
project ‘get-top-n-records’.
Step 2:
Update pom.xml with
maven dependencies.
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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.sample.app</groupId>
<artifactId>get-top-n-records</artifactId>
<version>1</version>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.6.RELEASE</version>
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
</dependency>
</dependencies>
</project>
Step 3:
Create
application.properties file under src/main/resources folder.
application.properties
logging.level.root=WARN
logging.level.org.hibernate=ERROR
## H2 specific properties
spring.h2.console.enabled=true
spring.h2.console.path=/h2
spring.datasource.url=jdbc:h2:file:~/db/myOrg.db;DB_CLOSE_ON_EXIT=FALSE;DB_CLOSE_DELAY=-1;
spring.datasource.username=krishna
spring.datasource.password=password123
spring.datasource.driverClassName=org.h2.Driver
## JPA specific properties
# Creates the schema, destroying previous data.
spring.jpa.hibernate.ddl-auto=create
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.jpa.show-sql=false
spring.jpa.properties.hibernate.format_sql=false
## Database connection pooling properties
# Number of ms to wait before throwing an exception if no connection is available.
spring.datasource.max-wait=10000
# Maximum number of active connections that can be allocated from this pool at the same time.
spring.datasource.tomcat.max-active=10
spring.datasource.tomcat.max-idle=5
spring.datasource.tomcat.min-idle=3
Step 4:
Define Employee
entity.
Employee.java
package com.sample.app.entity;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name = "my_employee")
public class Employee {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;
@Column(name = "first_name")
private String firstName;
@Column(name = "last_name")
private String lastName;
@Column(name = "age")
private int age;
@Column(name = "salary")
private double salary;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public static EmployeeBuilder builder() {
return new EmployeeBuilder();
}
public static class EmployeeBuilder {
private Employee emp;
public EmployeeBuilder() {
emp = new Employee();
}
public EmployeeBuilder firstName(String firstName) {
emp.setFirstName(firstName);
return this;
}
public EmployeeBuilder lastName(String lastName) {
emp.setLastName(lastName);
return this;
}
public EmployeeBuilder age(int age) {
emp.setAge(age);
return this;
}
public EmployeeBuilder salary(double salary) {
emp.setSalary(salary);
return this;
}
public Employee build() {
return emp;
}
}
@Override
public String toString() {
StringBuilder builder = new StringBuilder();
builder.append("Employee [id=").append(id).append(", firstName=").append(firstName).append(", lastName=")
.append(lastName).append(", age=").append(age).append(", salary=").append(salary).append("]");
return builder.toString();
}
}
Step 5:
Define
EmployeeRepository interface.
EmployeeRepository.java
package com.sample.app.repository;
import java.util.List;
import org.springframework.data.jpa.repository.JpaRepository;
import com.sample.app.entity.Employee;
public interface EmployeeRepository extends JpaRepository<Employee, Integer>{
public List<Employee> findTop3ByOrderByIdAsc();
public List<Employee> findTop3ByOrderByIdDesc();
public List<Employee> findTop3ByOrderByFirstNameAscIdDesc();
}
Step 6:
Define main
application class.
App.java
package com.sample.app;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;
import com.sample.app.entity.Employee;
import com.sample.app.repository.EmployeeRepository;
@SpringBootApplication
public class App {
public static void main(String args[]) {
SpringApplication.run(App.class, args);
}
public void printEmployees(Iterable<Employee> emps, String msg) {
System.out.println(msg);
for (Employee emp : emps) {
System.out.println(emp);
}
System.out.println();
}
@Bean
public CommandLineRunner demo(EmployeeRepository employeeRepository) {
return (args) -> {
Employee emp1 = Employee.builder().firstName("Ram").lastName("Gurram").age(32).salary(100000.23).build();
Employee emp2 = Employee.builder().firstName("Ram").lastName("Chelli").age(43).salary(60000).build();
Employee emp3 = Employee.builder().firstName("Gopi").lastName("Battu").age(45).salary(1000000).build();
Employee emp4 = Employee.builder().firstName("Ram").lastName("Srikanth").age(39).salary(60000).build();
Employee emp5 = Employee.builder().firstName("Surendra").lastName("Sami").age(32).salary(100000.23).build();
employeeRepository.save(emp1);
employeeRepository.save(emp2);
employeeRepository.save(emp3);
employeeRepository.save(emp4);
employeeRepository.save(emp5);
Iterable<Employee> emps = employeeRepository.findTop3ByOrderByIdAsc();
printEmployees(emps, "Top 3 records order by id in ascending order.");
emps = employeeRepository.findTop3ByOrderByIdDesc();
printEmployees(emps, "Top 3 records order by id in descending order");
emps = employeeRepository.findTop3ByOrderByFirstNameAscIdDesc();
printEmployees(emps, "Top 3 records order by firstName in ascending order and id in descending order");
};
}
}
Total
project structure looks like below.
Run
App.java, you will see below messages in console.
Top 3 records order by id in ascending order.
Employee [id=1, firstName=Ram, lastName=Gurram, age=32, salary=100000.23]
Employee [id=2, firstName=Ram, lastName=Chelli, age=43, salary=60000.0]
Employee [id=3, firstName=Gopi, lastName=Battu, age=45, salary=1000000.0]
Top 3 records order by id in descending order
Employee [id=5, firstName=Surendra, lastName=Sami, age=32, salary=100000.23]
Employee [id=4, firstName=Ram, lastName=Srikanth, age=39, salary=60000.0]
Employee [id=3, firstName=Gopi, lastName=Battu, age=45, salary=1000000.0]
Top 3 records order by firstName in ascending order and id in descending order
Employee [id=3, firstName=Gopi, lastName=Battu, age=45, salary=1000000.0]
Employee [id=4, firstName=Ram, lastName=Srikanth, age=39, salary=60000.0]
Employee [id=2, firstName=Ram, lastName=Chelli, age=43, salary=60000.0]
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