diff --git a/build.gradle b/build.gradle
index b0ba5b9..005f70f 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,12 +1,16 @@
 plugins {
     id 'java'
-    id 'org.springframework.boot' version '3.0.1'
+    id 'org.springframework.boot' version '3.2.5'
     id 'io.spring.dependency-management' version '1.1.0'
 }
 
 group = 'io.github.tttol'
 version = "1.1.6"
-sourceCompatibility = '17'
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_21
+    targetCompatibility = JavaVersion.VERSION_21
+}
 
 configurations {
     compileOnly {
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index 070cb70..17655d0 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-7.6-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.6-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
diff --git a/src/main/java/io/github/tttol/mrls/config/RestClientConfig.java b/src/main/java/io/github/tttol/mrls/config/RestClientConfig.java
new file mode 100644
index 0000000..8ce8ea2
--- /dev/null
+++ b/src/main/java/io/github/tttol/mrls/config/RestClientConfig.java
@@ -0,0 +1,43 @@
+package io.github.tttol.mrls.config;
+
+import io.micrometer.common.util.StringUtils;
+import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
+import org.apache.hc.client5.http.impl.classic.HttpClients;
+import org.apache.hc.core5.http.HttpHost;
+import org.apache.hc.core5.util.Timeout;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.http.client.ClientHttpRequestFactory;
+import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
+import org.springframework.http.client.SimpleClientHttpRequestFactory;
+import org.springframework.web.client.RestClient;
+
+import java.net.InetSocketAddress;
+import java.net.Proxy;
+
+@Configuration
+public class RestClientConfig {
+
+  @Value("${app.proxy.host}")
+  private String proxyHost;
+
+  @Value("${app.proxy.port}")
+  private int proxyPort;
+
+  @Bean
+  public RestClient restClient() {
+    if (StringUtils.isBlank(proxyHost)) {
+        return RestClient.create();
+    }
+
+    var httpClient = HttpClients.custom()
+            .setProxy(new HttpHost(proxyHost, proxyPort))
+            .build();
+    var httpComponentsClientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory(httpClient);
+
+    return RestClient.builder()
+            .requestFactory(httpComponentsClientHttpRequestFactory)
+            .build();
+  }
+}
diff --git a/src/main/java/io/github/tttol/mrls/external/GitLabApiExecutor.java b/src/main/java/io/github/tttol/mrls/external/GitLabApiExecutor.java
index ffd9e69..e997062 100644
--- a/src/main/java/io/github/tttol/mrls/external/GitLabApiExecutor.java
+++ b/src/main/java/io/github/tttol/mrls/external/GitLabApiExecutor.java
@@ -1,26 +1,27 @@
 package io.github.tttol.mrls.external;
 
-import io.github.tttol.mrls.dto.GitLabMergeRequestApiResponseDto;
-import io.github.tttol.mrls.exception.GitLabApiException;
 import java.net.URI;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Objects;
-import lombok.RequiredArgsConstructor;
-import lombok.extern.slf4j.Slf4j;
+
 import org.apache.commons.lang3.StringUtils;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.http.MediaType;
-import org.springframework.http.RequestEntity;
 import org.springframework.stereotype.Component;
-import org.springframework.web.client.RestTemplate;
+import org.springframework.web.client.RestClient;
+
+import io.github.tttol.mrls.dto.GitLabMergeRequestApiResponseDto;
+import io.github.tttol.mrls.exception.GitLabApiException;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
 
 @Component
 @RequiredArgsConstructor
 @Slf4j
 public class GitLabApiExecutor {
 
-  private final RestTemplate restTemplate;
+  private final RestClient restClient;
 
   @Value("${app.gitlab.api.endpoint}")
   private String endpoint;
@@ -28,21 +29,21 @@ public class GitLabApiExecutor {
   private String projectAccessToken;
 
   public List<GitLabMergeRequestApiResponseDto> getMergeRequests(String accessToken) {
-    // TODO 例外処理
     try {
-      var requestEntity = RequestEntity
-          .get(new URI(endpoint))
+      var token = StringUtils.isNotBlank(accessToken) ? accessToken : projectAccessToken;
+      var responseEntity = restClient.get()
+          .uri(new URI(endpoint))
           .accept(MediaType.APPLICATION_JSON)
-          .header("Authorization",
-              "Bearer %s".formatted(StringUtils.isNotBlank(accessToken) ?
-                  accessToken : projectAccessToken))
-          .build();
-      log.info("api url -> {}", requestEntity.getUrl());
-      var responseEntity = restTemplate.exchange(requestEntity,
-          GitLabMergeRequestApiResponseDto[].class);
-      log.debug("status code -> {}", responseEntity.getStatusCode());
-      var body = responseEntity.getBody();
-      return Objects.isNull(body) ? List.of() : Arrays.asList(body);
+          .header("Authorization", "Bearer %s".formatted(token))
+          .retrieve()
+          .toEntity(GitLabMergeRequestApiResponseDto[].class);
+      
+      if (responseEntity != null) {
+        log.info("status code -> {}", responseEntity.getStatusCode());
+        var body = responseEntity.getBody();
+        return Objects.isNull(body) ? List.of() : Arrays.asList(body);
+      }
+      return List.of();
     } catch (Exception e) {
       throw new GitLabApiException(e);
     }
diff --git a/src/main/resources/application-env.yml b/src/main/resources/application-env.yml
index 3344c18..661d3ca 100644
--- a/src/main/resources/application-env.yml
+++ b/src/main/resources/application-env.yml
@@ -1,4 +1,7 @@
 app:
+  proxy:
+    host:
+    port:
   gitlab:
     project:
       id:
diff --git a/src/main/resources/application.yml b/src/main/resources/application.yml
index c507b62..1584992 100644
--- a/src/main/resources/application.yml
+++ b/src/main/resources/application.yml
@@ -1,4 +1,9 @@
+server:
+  port: 8081
 app:
+  proxy:
+    host: ${PROXY_HOST}
+    port: ${PROXY_PORT}
   gitlab:
     host: ${GITLAB_HOST}
     project: