public long createSession(ApplicationId applicationId, TimeoutBudget timeoutBudget, InputStream in,
                              String contentType, DeployLogger logger) {
        File tempDir = uncheck(() -> Files.createTempDirectory("deploy")).toFile();
        long sessionId;
        try {
            sessionId = createSession(applicationId, timeoutBudget, decompressApplication(in, contentType, tempDir), logger);
        } finally {
            cleanupTempDirectory(tempDir, logger);
        }
        return sessionId;
    }
Gets the active Session for the given application id.

@return the active session, or null if there is no active session for the given application id.
configserver/src/main/java/com/yahoo/vespa/config/server/ApplicationRepository.java