Spring Boot – @LoadBalanced Annotation with Example

The @LoadBalanced annotation creates an instance of created RestTemplate load-balanced. There is no code you need to write to make the RestTemplate load-balance HTTP request it sends to an internal microservice. The RestTemplate bean will be intercepted and auto-configured by Spring Cloud. In brief, we need to use the @LoadBalanced Annotation in our configuration class while creating the Bean of RestTemplate. Below is the sample code for the same.

@Configuration
public class SampleConfig {
    @LoadBalanced
    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

Let’s see the whole implementation by developing 2 Microservices and 1 Service Discovery.

Developing Service Discovery

Please refer to this article and develop a service discovery: Java Spring Boot Microservices – Developing Service Discovery.

Developing address-service Step by Step

Step 1: Create a New Spring Boot Project in Spring Initializr

To create a new Spring Boot project, please refer to How to Create a Spring Boot Project in Spring Initializr and Run it in IntelliJ IDEA. For this project choose the following things

• Project: Maven
• Language: Java
• Packaging: Jar
• Java: 17

 Please choose the following dependencies while creating the project.

• Spring Boot DevTools
• Spring Data JPA
• MySQL Driver
• Spring Web
• Eureka Discovery Client

Generate the project and run it in IntelliJ IDEA by referring to the above article.

Note: We have used the MySQL database in this project.

Step 2: Create Schema in MySQL Workbench and Put Some Sample Data

Go to your MySQL Workbench and create a schema named gfgmicroservicesdemo and inside that create a table called address and put some sample data as shown in the below image. 

Address Table:

Here we have created 4 columns and put some sample data.

1. id
2. city
3. state
4. employee_id

Note: In the Address table, employee_id is a foreign key so create it accordingly. We are going to perform a SQL join operation in our native SQL query. So create tables carefully.

Before moving to IntelliJ IDEA let’s have a look at the complete project structure for our Microservices.

Step 3: Make Changes in Your application.properties File

Now make the following changes in your application.properties file.

spring.datasource.url=jdbc:mysql://localhost:3306/gfgmicroservicesdemospring.datasource.username=put your username herespring.datasource.password=put your password herespring.application.name=address-serviceserver.port=8081server.servlet.context-path=/address-serviceeureka.instance.metadata-map.configPath=/address-service

Step 4: Create Your Entity/Model Class

Go to the src > main > java > entity and create a class Address and put the below code. This is our model class.

Java

package com.gfg.addressapp.entity;

import jakarta.persistence.*;

@Entity
@Table(name = "address")
public class Address {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

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

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

    public int getId() {
        return id;
    }

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

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }
}

Step 5: Create Your Repository Interface

Go to the src > main > java > repository and create an interface AddressRepo and put the below code. This is our repository where we write code for all the database-related stuff.

Java

package com.gfg.addressapp.repository;

import com.gfg.addressapp.entity.Address;
import java.util.Optional;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;

@Repository
public interface AddressRepo extends JpaRepository<Address, Integer> {

    @Query(
        nativeQuery = true,
        value
        = "SELECT ea.id, ea.city, ea.state FROM gfgmicroservicesdemo.address ea join gfgmicroservicesdemo.employee e on e.id = ea.employee_id where ea.employee_id=:employeeId")
       Optional<Address> findAddressByEmployeeId(@Param("employeeId") int employeeId);
}

Note: Please refer to this article to know more about JpaRepository.

Step 6: Create an AddressResponse Class

Go to the src > main > java > response and create a class AddressResponse and put the below code.

Java

package com.gfg.addressapp.response;

public class AddressResponse {

    private int id;
    private String city;
    private String state;

    public int getId() {
        return id;
    }

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

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }
}

Step 7: Create Your Service Class

Go to the src > main > java > service and create a class AddressService and put the below code. This is our service class where we write our business logic.

Java

package com.gfg.addressapp.service;

import com.gfg.addressapp.entity.Address;
import com.gfg.addressapp.repository.AddressRepo;
import com.gfg.addressapp.response.AddressResponse;
import org.modelmapper.ModelMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.Optional;

@Service
public class AddressService {

    @Autowired
    private AddressRepo addressRepo;

    @Autowired
    private ModelMapper mapper;

    public AddressResponse findAddressByEmployeeId(int employeeId) {
        Optional<Address> addressByEmployeeId = addressRepo.findAddressByEmployeeId(employeeId);
        AddressResponse addressResponse = mapper.map(addressByEmployeeId, AddressResponse.class);
        return addressResponse;
    }

}

Step 8: Create an Address Controller

Go to the src > main > java > controller and create a class AddressController and put the below code. Here we are going to create an endpoint “/address/{employeeId}” to find the address using employee_id. Thats why we have created a foreign key in the Address table and we have performed the SQL join operation in the native query to get our desired result.

Java

package com.gfg.addressapp.controller;

import com.gfg.addressapp.response.AddressResponse;
import com.gfg.addressapp.service.AddressService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class AddressController {

    @Autowired
    private AddressService addressService;

    @GetMapping("/address/{employeeId}")
    public ResponseEntity<AddressResponse> getAddressByEmployeeId(@PathVariable("employeeId") int employeeId) {
        AddressResponse addressResponse = addressService.findAddressByEmployeeId(employeeId);
        return ResponseEntity.status(HttpStatus.OK).body(addressResponse);
    }

}

Step 9: Create a Configuration Class

Go to the src > main > java > configuration and create a class AddressConfig and put the below code.

Java

package com.gfg.addressapp.configuration;

import com.gfg.addressapp.service.AddressService;
import org.modelmapper.ModelMapper;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AddressConfig {

    @Bean
    public ModelMapper modelMapperBean() {
        return new ModelMapper();
    }

}

Note: You may refer to these two articles

• Spring @Configuration Annotation with Example
• Spring @Bean Annotation with Example

Before running the Microservice below is the complete pom.xml file. Please cross-verify if you have missed some dependencies

XML

<?xml version="1.0" encoding="UTF-8"?>
<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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.0.2</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.gfg.addressapp</groupId>
    <artifactId>address-service</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>address-service</name>
    <description>Address Service</description>
    <properties>
        <java.version>17</java.version>
        <spring-cloud.version>2022.0.2</spring-cloud.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.modelmapper</groupId>
            <artifactId>modelmapper</artifactId>
            <version>3.1.1</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

    </dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

    <repositories>
        <repository>
            <id>netflix-candidates</id>
            <name>Netflix Candidates</name>
            <url>https://artifactory-oss.prod.netflix.net/artifactory/maven-oss-candidates</url>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories>

</project>

Developing Employee-Service Step by Step

Step 1: Create a New Spring Boot Project in Spring Initializr

To create a new Spring Boot project, please refer to How to Create a Spring Boot Project in Spring Initializr and Run it in IntelliJ IDEA. For this project choose the following things

• Project: Maven
• Language: Java
• Packaging: Jar
• Java: 17

 Please choose the following dependencies while creating the project.

• Spring Boot DevTools
• Spring Data JPA
• MySQL Driver
• Spring Web
• Eureka Discovery Client

Generate the project and run it in IntelliJ IDEA by referring to the above article.

Note: We have used the MySQL database in this project.

Step 2: Create Schema in MySQL Workbench and Put Some Sample Data

Go to your MySQL Workbench and create a schema named gfgmicroservicesdemo and inside that create a table called employee and put some sample data as shown in the below image. Here we have created 4 columns and put some sample data.

1. id
2. name
3. email
4. age

Now we are going to fetch Employee Data from Employee Table in our Spring Boot project. To do it refer to the following steps. Before moving to IntelliJ IDEA let’s have a look at the complete project structure for our Microservices.

Step 3: Make Changes in Your application.properties File

Now make the following changes in your application.properties file.

spring.datasource.url=jdbc:mysql://localhost:3306/gfgmicroservicesdemospring.datasource.username=put your username herespring.datasource.password=put your password herespring.application.name=employee-serviceserver.port=8080# Set Your Context Path Hereserver.servlet.context-path=/employee-service

You may also refer to the below image

Step 4: Create Your Entity/Model Class

Go to the src > main > java > entity and create a class Employee and put the below code. This is our model class.

Java

package com.gfg.employeaap.entity;

import jakarta.persistence.*;

@Entity
@Table(name = "employee")
public class Employee {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private int id;

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

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

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

    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 getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }
}

Step 5: Create Your Repository Interface

Go to the src > main > java > repository and create an interface EmployeeRepo and put the below code. This is our repository where we write code for all the database-related stuff.

Java

package com.gfg.employeaap.repository;

import com.gfg.employeaap.entity.Employee;
import org.springframework.data.jpa.repository.JpaRepository;

@Repository
public interface EmployeeRepo extends JpaRepository<Employee, Integer> {

}

Note: Please refer to this article to know more about JpaRepository.

Step 6: Create an EmployeeResponse Class

Go to the src > main > java > response and create a class EmployeeResponse and put the below code.

Java

package com.gfg.employeaap.response;

public class EmployeeResponse {

    private int id;
    private String name;
    private String email;
    private String age;

    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 getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }
}

Step 7: Create Your Service Class

Go to the src > main > java > service and create a class EmployeeService and put the below code. This is our service class where we write our business logic.

Java

package com.gfg.employeaap.service;

import com.gfg.employeaap.entity.Employee;
import com.gfg.employeaap.repository.EmployeeRepo;
import com.gfg.employeaap.response.AddressResponse;
import com.gfg.employeaap.response.EmployeeResponse;
import org.modelmapper.ModelMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.loadbalancer.LoadBalancerClient;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

import java.util.Optional;

@Service
public class EmployeeService {

    @Autowired
    private EmployeeRepo employeeRepo;

    @Autowired
    private ModelMapper mapper;

    @Autowired
    private RestTemplate restTemplate;

    @Autowired
    private LoadBalancerClient loadBalancerClient;

    public EmployeeResponse getEmployeeById(int id) {

        Optional<Employee> employee = employeeRepo.findById(id);
        EmployeeResponse employeeResponse = mapper.map(employee, EmployeeResponse.class);

        AddressResponse addressResponse = restTemplate.getForObject("http://ADDRESS-SERVICE/address-service/address/{id}", AddressResponse.class, id);

        employeeResponse.setAddressResponse(addressResponse);
        return employeeResponse;
    }

}

Step 8: Create an Employee Controller

Go to the src > main > java > controller and create a class EmployeeController and put the below code. Here we are going to create an endpoint “/employees/{id}” to find an employee using id.

Java

package com.gfg.employeaap.controller;

import com.gfg.employeaap.response.EmployeeResponse;
import com.gfg.employeaap.service.EmployeeService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class EmployeeController {

    @Autowired
    private EmployeeService employeeService;

    @GetMapping("/employees/{id}")
    private ResponseEntity<EmployeeResponse> getEmployeeDetails(@PathVariable("id") int id) {
        EmployeeResponse employee = employeeService.getEmployeeById(id);
        return ResponseEntity.status(HttpStatus.OK).body(employee);
    }

}

Step 9: Create a Configuration Class

Go to the src > main > java > configuration and create a class EmployeeConfig and put the below code.

Java

package com.gfg.employeaap.configuration;

import com.gfg.employeaap.service.EmployeeService;
import org.modelmapper.ModelMapper;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class EmployeeConfig {

    @Bean
    public ModelMapper modelMapperBean() {
        return new ModelMapper();
    }

      @LoadBalanced
     @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }

}

Note: You may refer to these two articles

• Spring @Configuration Annotation with Example
• Spring @Bean Annotation with Example

Before running the Microservice below is the complete pom.xml file. Please cross-verify if you have missed some dependencies

XML

<?xml version="1.0" encoding="UTF-8"?>
<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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.0.2</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.gfg.employeaap</groupId>
    <artifactId>employee-service</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>employee-service</name>
    <description>Employee Service</description>
    <properties>
        <java.version>17</java.version>
        <spring-cloud.version>2022.0.2</spring-cloud.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.modelmapper</groupId>
            <artifactId>modelmapper</artifactId>
            <version>3.1.1</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        <dependency>
            <groupId>io.projectreactor</groupId>
            <artifactId>reactor-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

    </dependencies>


    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

    <repositories>
        <repository>
            <id>netflix-candidates</id>
            <name>Netflix Candidates</name>
            <url>https://artifactory-oss.prod.netflix.net/artifactory/maven-oss-candidates</url>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories>

</project>

Run Your Services

Now run your both Address and Employee Microservices along with your Discovery Service. If everything goes well then you may see the following screen in your Eureka dashboard. Please refer to the below image.

Test Your Endpoint in Postman

Now open Postman and hit the following URL

GET: http://localhost:8080/employee-service/employees/2

And you can see the following response

{    "id": 2,    "name": "Asish",    "email": "asis@gmail",    "age": "30",    "addressResponse": {        "id": 1,        "city": "BLS",        "state": "Odisha"    }}

Please refer to the below image.