src/com/facebook/buck/java/abi/StubJar.java

/*
 * Copyright 2014-present Facebook, 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.facebook.buck.java.abi;

import static org.objectweb.asm.ClassReader.SKIP_CODE;
import static org.objectweb.asm.ClassReader.SKIP_DEBUG;
import static org.objectweb.asm.ClassReader.SKIP_FRAMES;

import com.facebook.buck.io.ProjectFilesystem;
import com.google.common.base.Preconditions;
import com.google.common.collect.Sets;

import org.objectweb.asm.ClassReader;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.file.Path;
import java.util.SortedSet;
import java.util.jar.JarOutputStream;

public class StubJar {

  private final Path toMirror;
  private final SortedSet<ClassMirror> classes;

  public StubJar(Path toMirror) {
    this.toMirror = Preconditions.checkNotNull(toMirror);
    this.classes = Sets.newTreeSet();
  }

  public void writeTo(ProjectFilesystem filesystem, Path path) throws IOException {
    Preconditions.checkState(!filesystem.exists(path), "Output file already exists: %s)", path);

    if (path.getParent() != null && !filesystem.exists(path.getParent())) {
      filesystem.createParentDirs(path);
    }

    Walker walker = Walkers.getWalkerFor(toMirror);
    walker.walk(
        new FileAction() {
          @Override
          public void visit(Path relativizedPath, InputStream stream) throws IOException {
            String fileName = relativizedPath.toString();
            if (!fileName.endsWith(".class")) {
              return;
            }

            ClassReader classReader = new ClassReader(stream);
            ClassMirror visitor = new ClassMirror(fileName);
            classes.add(visitor);
            classReader.accept(visitor, SKIP_CODE | SKIP_DEBUG | SKIP_FRAMES);
          }
        });

    try (
        OutputStream fos = filesystem.newFileOutputStream(path);
        JarOutputStream jar = new JarOutputStream(fos)) {
      for (ClassMirror aClass : classes) {
        aClass.writeTo(jar);
      }
    }
  }
}