docker-docs/content/guides/testcontainers-java-service-configuration/exec-in-container.md

title, linkTitle, description, weight

title	linkTitle	description	weight
Execute commands inside containers	Execute commands	Run commands inside running containers to initialize services for testing.	20

Some Docker containers provide CLI tools for performing actions. You can use container.execInContainer(String...) to run any available command inside a running container.

Example: Create an S3 bucket in LocalStack

The LocalStack module emulates AWS services. To test S3 file uploads, create a bucket before running tests:

package com.testcontainers.demo;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.testcontainers.containers.localstack.LocalStackContainer.Service.S3;

import java.io.IOException;
import java.net.URI;
import java.util.List;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;
import org.testcontainers.containers.localstack.LocalStackContainer;
import org.testcontainers.junit.jupiter.Container;
import org.testcontainers.junit.jupiter.Testcontainers;
import org.testcontainers.utility.DockerImageName;
import software.amazon.awssdk.auth.credentials.AwsBasicCredentials;
import software.amazon.awssdk.auth.credentials.StaticCredentialsProvider;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.Bucket;

@Testcontainers
class LocalStackTest {

  static final String bucketName = "mybucket";

  @Container
  static LocalStackContainer localStack = new LocalStackContainer(
    DockerImageName.parse("localstack/localstack:3.4.0")
  );

  @BeforeAll
  static void beforeAll() throws IOException, InterruptedException {
    localStack.execInContainer("awslocal", "s3", "mb", "s3://" + bucketName);

    org.testcontainers.containers.Container.ExecResult execResult =
      localStack.execInContainer("awslocal", "s3", "ls");
    String stdout = execResult.getStdout();
    int exitCode = execResult.getExitCode();
    assertTrue(stdout.contains(bucketName));
    assertEquals(0, exitCode);
  }

  @Test
  void shouldListBuckets() {
    URI s3Endpoint = localStack.getEndpointOverride(S3);
    StaticCredentialsProvider credentialsProvider =
      StaticCredentialsProvider.create(
        AwsBasicCredentials.create(
          localStack.getAccessKey(),
          localStack.getSecretKey()
        )
      );
    S3Client s3 = S3Client
      .builder()
      .endpointOverride(s3Endpoint)
      .credentialsProvider(credentialsProvider)
      .region(Region.of(localStack.getRegion()))
      .build();

    List<String> s3Buckets = s3
      .listBuckets()
      .buckets()
      .stream()
      .map(Bucket::name)
      .toList();

    assertTrue(s3Buckets.contains(bucketName));
  }
}

The execInContainer("awslocal", "s3", "mb", "s3://mybucket") call runs the awslocal CLI tool (provided by the LocalStack image) to create an S3 bucket.

You can capture the output and exit code from any command:

Container.ExecResult execResult =
    localStack.execInContainer("awslocal", "s3", "ls");
String stdout = execResult.getStdout();
int exitCode = execResult.getExitCode();

Note

The withCopyFileToContainer() and execInContainer() methods are inherited from GenericContainer, so they're available for all Testcontainers modules.

Summary

• Use withCopyFileToContainer() to place initialization files inside containers before they start.
• Use execInContainer() to run commands inside running containers for setup tasks like creating buckets, topics, or queues.

Further reading

• Getting started with Testcontainers for Java
• Testcontainers Postgres module
• Testcontainers LocalStack module