com.google.enterprise.connector.db.diffing.DBSnapshot.java Source code

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Here is the source code for com.google.enterprise.connector.db.diffing.DBSnapshot.java

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// Copyright 2011 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.enterprise.connector.db.diffing;

import com.google.enterprise.connector.db.DBException;
import com.google.enterprise.connector.db.DocIdUtil;
import com.google.enterprise.connector.db.ValueOrdering;
import com.google.enterprise.connector.spi.RepositoryException;
import com.google.enterprise.connector.spi.SpiConstants;
import com.google.enterprise.connector.util.diffing.DocumentHandle;
import com.google.enterprise.connector.util.diffing.DocumentSnapshot;

import org.json.JSONException;
import org.json.JSONObject;

import java.util.Date;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Represents both flavors of snapshot, from a snapshot file and from
 * a {@code SnapshotRepository}.
 */
public class DBSnapshot implements DocumentSnapshot, Comparable<DocumentSnapshot> {

    private static final Logger LOG = Logger.getLogger(DBSnapshot.class.getName());

    /** An optional document holder, may be null. */
    private final DocumentBuilder.DocumentHolder docHolder;
    private final String documentId;
    private final String jsonString;
    private final ValueOrdering valueOrdering;

    /** Constructs a snapshot from a {@code DBSnapshotRepository}. */
    public DBSnapshot(ValueOrdering valueOrdering, String documentId, String jsonString,
            DocumentBuilder.DocumentHolder docHolder) {
        this.valueOrdering = valueOrdering;
        this.docHolder = docHolder;
        this.documentId = documentId;
        this.jsonString = jsonString;
    }

    /** Reconstructs a snapshot from a snapshot file. */
    public DBSnapshot(ValueOrdering valueOrdering, String jsonString) {
        this.valueOrdering = valueOrdering;
        this.docHolder = null;
        try {
            JSONObject jo = new JSONObject(jsonString);
            this.documentId = jo.getString(SpiConstants.PROPNAME_DOCID);
        } catch (JSONException e) {
            LOG.log(Level.SEVERE, "Invalid serialized snapshot: " + jsonString, e);
            throw new IllegalArgumentException("Invalid serialized snapshot: " + jsonString, e);
        }
        this.jsonString = jsonString;
    }

    @Override
    public String getDocumentId() {
        return documentId;
    }

    /**
     * Compares this {@link DBSnapshot} to the referenced document on the GSA
     * to detect inserted or deleted records.  If, by returning 0, this snapshot
     * represents the same record as the supplied paramenter, then a subsequent
     * call to {@link #getUpdate(DocumentSnapshot)} may be made to determine
     * whether the record changed.
     *
     * @return a negative integer, zero, or a positive integer as this snapshot
     *         is less than, equal to, or greater than the specified snapshot.
     * @throws NullPointerException if the specified snapshot is null.
     */
    @Override
    public int compareTo(DocumentSnapshot onGsa) throws ClassCastException {
        return DocIdUtil.compare(valueOrdering, documentId, onGsa.getDocumentId());
    }

    /**
     * Returns a {@link DocumentHandle} for updating the referenced document on
     * the GSA or null if the document on the GSA does not need updating.
     */
    @Override
    public DocumentHandle getUpdate(DocumentSnapshot onGsa) throws RepositoryException {
        if (docHolder == null) {
            throw new UnsupportedOperationException("getUpdate called on deserialized snapshot.");
        }

        // The diffing framework sends in a null to indicate that it has not seen
        // this snapshot before. So we return the corresponding handle.
        if (onGsa == null) {
            return getDocumentHandle();
        }

        // If the parameter is non-null, then it should be an DBSnapshot
        // (it was created via a DBSnapshotFactory).
        if (!(onGsa instanceof DBSnapshot)) {
            throw new IllegalArgumentException("Illegal parameter passed to getUpdate. "
                    + "The parameter passed is not an instance of DBSnapshot.");
        }

        // We just assume that if the serialized form is the same, then nothing
        // has changed.
        if (jsonString.equals(onGsa.toString())) {
            // null return tells the diffing framework to do nothing
            return null;
        }

        // Something has changed, so return the corresponding handle
        // and set the changed flag of the document.
        LOG.info("Change for Document with Id " + getDocumentId() + " at time " + new Date());
        return getDocumentHandle();
    }

    private DocumentHandle getDocumentHandle() {
        try {
            return docHolder.getDocumentHandle();
        } catch (DBException e) {
            // If we can't get the document handle, return null to indicate no
            // change. The most likely source of errors is the XSLT transform.
            // See the similar log message in RepositoryHandler.getDocList.
            LOG.log(Level.WARNING, "Cannot convert database record to snapshot " + "for record " + getDocumentId(),
                    e);
            return null;
        }
    }

    @Override
    public String toString() {
        LOG.log(Level.FINEST, "Serializing document snapshot for {0}", documentId);
        return jsonString;
    }
}