hollow/src/main/java/com/netflix/hollow/core/util/StateEngineRoundTripper.java
public static void roundTripSnapshot(HollowWriteStateEngine writeEngine, HollowReadStateEngine readEngine, HollowFilterConfig filter) throws IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        HollowBlobWriter writer = new HollowBlobWriter(writeEngine);
        writer.writeSnapshot(baos);
        writeEngine.prepareForNextCycle();


        HollowBlobReader reader = new HollowBlobReader(readEngine);
        InputStream is = new ByteArrayInputStream(baos.toByteArray());
        if(filter == null)
            reader.readSnapshot(is);
        else
            reader.readSnapshot(is, filter);
    }
public static void roundTripSnapshot(HollowWriteStateEngine writeEngine, HollowReadStateEngine readEngine, HollowFilterConfig filter) throws IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        HollowBlobWriter writer = new HollowBlobWriter(writeEngine);
        writer.writeSnapshot(baos);
        writeEngine.prepareForNextCycle();


        HollowBlobReader reader = new HollowBlobReader(readEngine);
        InputStream is = new ByteArrayInputStream(baos.toByteArray());
        if(filter == null)
            reader.readSnapshot(is);
        else
            reader.readSnapshot(is, filter);
    }
Populate the provided {@link HollowReadStateEngine} with the dataset currently in the provided {@link HollowWriteStateEngine}.
<p>
Apply the provided {@link HollowFilterConfig}.

@param writeEngine the write state engine
@param readEngine the read state engine
@param filter the filter configuration
@throws IOException if the round trip from write to read state failed