在AWS SDK 2中使用假设角色需要进行以下步骤：

1. 创建STS客户端对象：

AwsCredentialsProvider credentialsProvider = StaticCredentialsProvider.create(AwsBasicCredentials.create(accessKeyId, secretAccessKey));
StsClient stsClient = StsClient.builder()
                        .region(Region.AWS_GLOBAL)
                        .credentialsProvider(credentialsProvider)
                        .build();

2. 创建AssumeRole请求对象：

AssumeRoleRequest assumeRoleRequest = AssumeRoleRequest.builder()
                        .roleArn(roleArn)
                        .roleSessionName(roleSessionName)
                        .build();

3. 发送AssumeRole请求并获取AssumeRole响应对象：

AssumeRoleResponse assumeRoleResponse = stsClient.assumeRole(assumeRoleRequest);
Credentials assumedRoleCredentials = assumeRoleResponse.credentials();

4. 使用获取到的AssumedRole凭证创建新的STS客户端对象：

AwsCredentialsProvider assumedRoleCredentialsProvider = StaticCredentialsProvider.create(AwsBasicCredentials.create(assumedRoleCredentials.accessKeyId(), assumedRoleCredentials.secretAccessKey(), assumedRoleCredentials.sessionToken()));
StsClient assumedRoleStsClient = StsClient.builder()
                        .region(Region.AWS_GLOBAL)
                        .credentialsProvider(assumedRoleCredentialsProvider)
                        .build();

5. 使用AssumedRole客户端对象执行需要使用假设角色的操作：

// 示例：列出S3存储桶的内容
ListBucketsResponse response = assumedRoleStsClient.listBuckets();
List buckets = response.buckets();
for (S3Bucket bucket : buckets) {
    System.out.println(bucket.name());
}

请注意，以上代码示例中的变量需要根据实际情况进行替换。