FileSnap.java

找到100個snapshot文件，按zxid降序排序
遍歷找到的snapshot文件，從zxid最大的開始
將快照文件反序列化化
校驗快照完整性，通過提取內(nèi)容的checksum與文件中的val字段比較
如果有一個文件是完整的，則退出循環(huán)。

 public long deserialize(DataTree dt, Map<Long, Integer> sessions) throws IOException {
        // we run through 100 snapshots (not all of them)
        // if we cannot get it running within 100 snapshots
        // we should  give up
        List<File> snapList = findNValidSnapshots(100);
        if (snapList.size() == 0) {
            return -1L;
        }
        File snap = null;
        long snapZxid = -1;
        boolean foundValid = false;
        for (int i = 0, snapListSize = snapList.size(); i < snapListSize; i++) {
            snap = snapList.get(i);
            LOG.info("Reading snapshot {}", snap);
            snapZxid = Util.getZxidFromName(snap.getName(), SNAPSHOT_FILE_PREFIX);
            try (CheckedInputStream snapIS = SnapStream.getInputStream(snap)) {
                InputArchive ia = BinaryInputArchive.getArchive(snapIS);
                deserialize(dt, sessions, ia);
                SnapStream.checkSealIntegrity(snapIS, ia);

                // Digest feature was added after the CRC to make it backward
                // compatible, the older code can still read snapshots which
                // includes digest.
                //
                // To check the intact, after adding digest we added another
                // CRC check.
                if (dt.deserializeZxidDigest(ia, snapZxid)) {
                    SnapStream.checkSealIntegrity(snapIS, ia);
                }

                foundValid = true;
                break;
            } catch (IOException e) {
                LOG.warn("problem reading snap file {}", snap, e);
            }
        }
        if (!foundValid) {
            throw new IOException("Not able to find valid snapshots in " + snapDir);
        }
        dt.lastProcessedZxid = snapZxid;
        lastSnapshotInfo = new SnapshotInfo(dt.lastProcessedZxid, snap.lastModified() / 1000);

        // compare the digest if this is not a fuzzy snapshot, we want to compare
        // and find inconsistent asap.
        if (dt.getDigestFromLoadedSnapshot() != null) {
            dt.compareSnapshotDigests(dt.lastProcessedZxid);
        }
        return dt.lastProcessedZxid;
    }