public String installPendingTransactionFilter() {
    final String filterId = filterIdGenerator.nextId();
    filterRepository.save(new PendingTransactionFilter(filterId));
    return filterId;
  }
Installs a pending transaction filter

@return the transaction filter id
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/jsonrpc/internal/filter/FilterManager.java