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This post demonstrates how to use Spring’s RestTemplate to consume RESTful web services in Java. The codes used are used in a SOA or Microservices context but the key code snippet is about RestTemplate.

3 Maven Projects

There are 3 Maven projects used for this post:

common-dto-api
- This contains all Data Transfer Objects (DTOs) used, in this case, to exchange data between a config server and a client service.
com-turreta-soademo-configserver
- This represents the config server.
- For this demo, it is configured to run on port 8080.
com-turreta-soademo-clientservice
- This represents the client service that consumes (RESTful) services available on the config server
- For this demo, it is configured to run on port 8081.
- It has a single @RestController which you can test if the two applications work nicely with each other. See Demo Test section below.

Remote Service to Test RestTemplate

Our config server provides a RESTful web service for our client to consume using RestTemplate.

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package com.turreta.soademo.configserver;

import com.turreta.soademo.common.dto.AppConfigDTO;
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.RestController;

import javax.annotation.PostConstruct;
import java.util.ArrayList;
import java.util.List;

@RestController
public class ConfigController {

    private List<AppConfigDTO> predefinedConfigList = new ArrayList<>();

    @PostConstruct
    public void postContruct() {

        AppConfigDTO dto1 = new AppConfigDTO();
        dto1.setApplicationName("app-1");
        dto1.setVersion("1.2.3");
        dto1.setIsEnabled(false);

        AppConfigDTO dto2 = new AppConfigDTO();
        dto2.setApplicationName("app-2");
        dto2.setVersion("1.2.3");
        dto2.setIsEnabled(true);


        predefinedConfigList.add(dto1);
        predefinedConfigList.add(dto2);
    }

    @RequestMapping(value = "/get-config-by-name", method = RequestMethod.POST)
    public AppConfigDTO findConfig(@RequestBody AppConfigDTO findDTO) {

        AppConfigDTO rtnDto = null;

        for(AppConfigDTO d: this.predefinedConfigList) {
            if(d.getApplicationName().equals(findDTO.getApplicationName())) {
                rtnDto = d;
                break;
            }
        }

        return rtnDto;
    }
}

package com.turreta.soademo.configserver;

import com.turreta.soademo.common.dto.AppConfigDTO;

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.RestController;

import javax.annotation.PostConstruct;

import java.util.ArrayList;

import java.util.List;

@RestController

public class ConfigController {

private List<AppConfigDTO> predefinedConfigList = new ArrayList<>();

@PostConstruct

public void postContruct() {

AppConfigDTO dto1 = new AppConfigDTO();

dto1.setApplicationName("app-1");

dto1.setVersion("1.2.3");

dto1.setIsEnabled(false);

AppConfigDTO dto2 = new AppConfigDTO();

dto2.setApplicationName("app-2");

dto2.setVersion("1.2.3");

dto2.setIsEnabled(true);

predefinedConfigList.add(dto1);

predefinedConfigList.add(dto2);

}

@RequestMapping(value = "/get-config-by-name", method = RequestMethod.POST)

public AppConfigDTO findConfig(@RequestBody AppConfigDTO findDTO) {

AppConfigDTO rtnDto = null;

for(AppConfigDTO d: this.predefinedConfigList) {

if(d.getApplicationName().equals(findDTO.getApplicationName())) {

rtnDto = d;

break;

}

return rtnDto;

}

Our Client Service

Our client service has one @RestController. The important lines are lines 24-27 which enable us to perform HTTP POST using RestTemplate.

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package com.turreta.soademo.clientservice;

import com.turreta.soademo.common.dto.AppConfigDTO;
import org.springframework.http.HttpEntity;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

@RestController
public class ClientController {
    @RequestMapping("/get-config-from-config-server/{app-name}")
    public AppConfigDTO getRemoteConfig(@PathVariable("app-name") String appName) {

        RestTemplate restTemplate = new RestTemplate();

        AppConfigDTO dto = new AppConfigDTO();
        dto.setApplicationName(appName);
        HttpEntity<AppConfigDTO> request = new HttpEntity<>(dto);

        String fooResourceUrl
                = "http://localhost:8080/get-config-by-name";
        ResponseEntity<AppConfigDTO> response
                = restTemplate.postForEntity(fooResourceUrl,request, AppConfigDTO.class);

        return response.getBody();
    }
}

package com.turreta.soademo.clientservice;

import com.turreta.soademo.common.dto.AppConfigDTO;

import org.springframework.http.HttpEntity;

import org.springframework.http.ResponseEntity;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;

import org.springframework.web.client.RestTemplate;

@RestController

public class ClientController {

@RequestMapping("/get-config-from-config-server/{app-name}")

public AppConfigDTO getRemoteConfig(@PathVariable("app-name") String appName) {

RestTemplate restTemplate = new RestTemplate();

AppConfigDTO dto = new AppConfigDTO();

dto.setApplicationName(appName);

HttpEntity<AppConfigDTO> request = new HttpEntity<>(dto);

String fooResourceUrl

= "http://localhost:8080/get-config-by-name";

ResponseEntity<AppConfigDTO> response

= restTemplate.postForEntity(fooResourceUrl,request, AppConfigDTO.class);

return response.getBody();

}

HTTP GET, PUT, and DELETE

This post demonstrates the use of HTTP POST using RestTemplate.Here are code snippets when using the other 3 important HTTP methods.

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HTTP GET

AppConfig config = restTemplate.getForObject(fooResourceUrl + "/1", AppConfig.class);

1	AppConfig config = restTemplate.getForObject(fooResourceUrl + "/1", AppConfig.class);

HTTP PUT

restTemplate.put(fooResourceUrl,request, AppConfigDTO.class);

1	restTemplate.put(fooResourceUrl,request, AppConfigDTO.class);

HTTP DELETE

restTemplate.delete(entityUrl);

1	restTemplate.delete(entityUrl);

Demo Test

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Download the Codes

The codes are available on GitHub.com and are 3 Maven projects in a single repository. You may need to build them individually first starting with the DTO project. Please see Build/Install Maven Projects in Separate Directors in Travis CI via GitHub