我正在尝试DSS数字签名库5.12.1（https://ec.europa.eu/digital-building-blocks/sites/display/DIGITAL/Digital+Signature+Service+-++DSS）使用类TLValidationJob在本地存储欧盟信任的X509证书。运行onlineRefresh方法时，我遇到了意外异常“java.lang.NullPointerException：The onlineLoader must be defined！”
我已经正确运行了TLValidationJob.setOnlineDataLoader，并在运行了onlineRefresh方法后不久。它应该将源/证书信息放在我的缓存中，但onlineRefresh引发了异常“Unable to retrieve the content for url 'https：//ec.europa.eu/tools/lotl/eu-lotl.xml'”，原因：“java.lang.NullPointerException：The onlineLoader must be defined！"，怎么回事？这是我的准系统代码（有些是分开的）：

private static File tlCacheDirectory() {
    return new File("./myLOTLcache");
}
public static DSSFileLoader onlineLoader() {
    FileCacheDataLoader onlineFileLoader = new FileCacheDataLoader();
    onlineFileLoader.setCacheExpirationTime(-1); // negative value means cache never expires
    onlineFileLoader.setFileCacheDirectory(tlCacheDirectory());
    return onlineFileLoader;
}
public static CacheCleaner cacheCleaner() {
    CacheCleaner cacheCleaner = new CacheCleaner();
    cacheCleaner.setCleanMemory(true); // free the space in memory
    cacheCleaner.setCleanFileSystem(true); // and the filesystem
    cacheCleaner.setDSSFileLoader(onlineLoader());
    return cacheCleaner;
}
public static LOTLSource europeanLOTLSource() {
    LOTLSource lotlSource = new LOTLSource();
    lotlSource.setUrl("https://ec.europa.eu/tools/lotl/eu-lotl.xml");
    // I know what "pivot" is here, but "pivot support"?
    lotlSource.setPivotSupport(true);
    lotlSource.setLotlPredicate(TLPredicateFactory.createEULOTLPredicate());
    lotlSource.setTlPredicate(TLPredicateFactory.createEUTLPredicate());
    return lotlSource;
}
public static void main(String[] args) {
    TrustedListsCertificateSource myTLcertSource = new TrustedListsCertificateSource();
    TLValidationJob tlValidationJob = new TLValidationJob();
    LOTLSource mylotl = europeanLOTLSource();
    tlValidationJob.setListOfTrustedListSources(mylotl);
    // set the TrustedListsCertificateSource to be filled with the job results,
    // i.e. the list[s] should go into myTLcertSource
    tlValidationJob.setTrustedListCertificateSource(myTLcertSource);
    tlValidationJob.setOnlineDataLoader(onlineLoader());
    tlValidationJob.onlineRefresh();
}

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