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ProGuardCORE is a free library to read, analyze, modify, and write Java class files.
There is a newer version: 9.1.6
/*
 * ProGuardCORE -- library to process Java bytecode.
 *
 * Copyright (c) 2002-2020 Guardsquare NV
 *
 * 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 proguard.io;

import java.io.IOException;
import java.nio.charset.*;
import java.util.Enumeration;
import java.util.zip.*;

/**
 * This {@link DataEntryReader} lets a given {@link DataEntryReader} read all data entries of the
 * read archive data entries.
 *
 * @author Eric Lafortune
 */
public class JarReader implements DataEntryReader {
  private final boolean jmod;
  private final DataEntryReader dataEntryReader;

  /**
   * Creates a new JarReader.
   *
   * @param dataEntryReader the reader that can process the jar entries.
   */
  public JarReader(DataEntryReader dataEntryReader) {
    this(false, dataEntryReader);
  }

  /**
   * Creates a new JarReader that optionally reads jmod files.
   *
   * @param jmod specifies whether the input jar is actually a jmod file.
   * @param dataEntryReader the reader that can process the jar entries.
   */
  public JarReader(boolean jmod, DataEntryReader dataEntryReader) {
    this.jmod = jmod;
    this.dataEntryReader = dataEntryReader;
  }

  // Implementation for DataEntryReader.

  @Override
  public void read(DataEntry dataEntry) throws IOException {
    // Can we parse the jar entries more robustly from a file?
    if (dataEntry instanceof FileDataEntry) {
      // Read the data entry using its file.
      FileDataEntry fileDataEntry = (FileDataEntry) dataEntry;

      ZipFile zipFile = new ZipFile(fileDataEntry.getFile(), StandardCharsets.UTF_8);

      try {
        Enumeration entries = zipFile.entries();

        // Get all entries from the input jar.
        while (entries.hasMoreElements()) {
          ZipEntry zipEntry = (ZipEntry) entries.nextElement();

          // Delegate the actual reading to the data entry reader.
          dataEntryReader.read(new ZipFileDataEntry(dataEntry, zipEntry, zipFile));
        }
      } finally {
        zipFile.close();
      }
    } else {
      if (jmod) {
        // Eat the magic bytes
        dataEntry.getInputStream().read(new byte[4]);
      }

      // Read the data entry using its stream.
      ZipInputStream zipInputStream =
          new ZipInputStream(dataEntry.getInputStream(), StandardCharsets.UTF_8);

      try {
        // Get all entries from the input jar.
        while (true) {
          // Can we get another entry?
          ZipEntry zipEntry = zipInputStream.getNextEntry();
          if (zipEntry == null) {
            break;
          }

          // Delegate the actual reading to the data entry reader.
          dataEntryReader.read(new ZipDataEntry(dataEntry, zipEntry, zipInputStream));
        }
      } finally {
        dataEntry.closeInputStream();
      }
    }
  }
}