com.google.gerrit.server.edit.tree.TreeCreator.java Source code

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Here is the source code for com.google.gerrit.server.edit.tree.TreeCreator.java

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// Copyright (C) 2017 The Android Open Source Project
//
// 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.gerrit.server.edit.tree;

import static com.google.common.base.Preconditions.checkNotNull;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.eclipse.jgit.dircache.DirCache;
import org.eclipse.jgit.dircache.DirCacheBuilder;
import org.eclipse.jgit.dircache.DirCacheEditor;
import org.eclipse.jgit.dircache.DirCacheEntry;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.ObjectInserter;
import org.eclipse.jgit.lib.ObjectReader;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;

/**
 * A creator for a new Git tree. To create the new tree, the tree of another commit is taken as a
 * basis and modified.
 */
public class TreeCreator {

    private final RevCommit baseCommit;
    private final List<TreeModification> treeModifications = new ArrayList<>();

    public TreeCreator(RevCommit baseCommit) {
        this.baseCommit = checkNotNull(baseCommit, "baseCommit is required");
    }

    /**
     * Apply modifications to the tree which is taken as a basis. If this method is called multiple
     * times, the modifications are applied subsequently in exactly the order they were provided.
     *
     * @param treeModifications modifications which should be applied to the base tree
     */
    public void addTreeModifications(List<TreeModification> treeModifications) {
        checkNotNull(treeModifications, "treeModifications must not be null");
        this.treeModifications.addAll(treeModifications);
    }

    /**
     * Creates the new tree. When this method is called, the specified base tree is read from the
     * repository, the specified modifications are applied, and the resulting tree is written to the
     * object store of the repository.
     *
     * @param repository the affected Git repository
     * @return the {@code ObjectId} of the created tree
     * @throws IOException if problems arise when accessing the repository
     */
    public ObjectId createNewTreeAndGetId(Repository repository) throws IOException {
        DirCache newTree = createNewTree(repository);
        return writeAndGetId(repository, newTree);
    }

    private DirCache createNewTree(Repository repository) throws IOException {
        DirCache newTree = readBaseTree(repository);
        List<DirCacheEditor.PathEdit> pathEdits = getPathEdits(repository);
        applyPathEdits(newTree, pathEdits);
        return newTree;
    }

    private DirCache readBaseTree(Repository repository) throws IOException {
        try (ObjectReader objectReader = repository.newObjectReader()) {
            DirCache dirCache = DirCache.newInCore();
            DirCacheBuilder dirCacheBuilder = dirCache.builder();
            dirCacheBuilder.addTree(new byte[0], DirCacheEntry.STAGE_0, objectReader, baseCommit.getTree());
            dirCacheBuilder.finish();
            return dirCache;
        }
    }

    private List<DirCacheEditor.PathEdit> getPathEdits(Repository repository) throws IOException {
        List<DirCacheEditor.PathEdit> pathEdits = new ArrayList<>();
        for (TreeModification treeModification : treeModifications) {
            pathEdits.addAll(treeModification.getPathEdits(repository, baseCommit));
        }
        return pathEdits;
    }

    private static void applyPathEdits(DirCache tree, List<DirCacheEditor.PathEdit> pathEdits) {
        DirCacheEditor dirCacheEditor = tree.editor();
        pathEdits.forEach(dirCacheEditor::add);
        dirCacheEditor.finish();
    }

    private static ObjectId writeAndGetId(Repository repository, DirCache tree) throws IOException {
        try (ObjectInserter objectInserter = repository.newObjectInserter()) {
            ObjectId treeId = tree.writeTree(objectInserter);
            objectInserter.flush();
            return treeId;
        }
    }
}