java內置的解壓縮工具

時間  2020-12-29
標籤 java 服務器 code orm blog 資源 input 欄目 Java 简体版
原文   原文鏈接

簡介

java關於壓縮和解壓縮的核心類就是Defalter(壓縮)類和Inflater(解壓)類,操做GZip和Zip文件也是基於這兩個類。Tomcat對響應數據的壓縮就是基於GZip。java

使用Deflater和Inflater解壓縮

import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.InputStream;
import java.util.zip.Deflater;
import java.util.zip.Inflater;

public class Client {

  public static void main(String[] args) throws Exception {
    byte[] bytes = readFromFile("D:/testdeflate.txt");
    System.out.println("before compress: " + bytes.length);
    byte[] compressedBytes = compress(bytes);
    System.out.println("after compress: " + compressedBytes.length);
    byte[] decompressBytes = decompress(compressedBytes);
    System.out.println("after decompress: " + decompressBytes.length);
  }

  /**
   * 解壓數據
   *
   * @param bytes 源數據
   * @return 壓縮以後的數據
   */
  private static byte[] decompress(byte[] bytes) {
    Inflater inflater = new Inflater();
    //設置待解壓數據
    inflater.setInput(bytes);
    byte[] buf = new byte[1024];
    try (ByteArrayOutputStream output = new ByteArrayOutputStream()) {
      //是否已解壓完成
      while (!inflater.finished()) {
        //解壓
        int len = inflater.inflate(buf);
        output.write(buf, 0, len);
      }
      //關閉資源
      inflater.end();
      return output.toByteArray();
    } catch (Exception e) {
      e.printStackTrace();
    }
    return new byte[0];
  }

  /**
   * 壓縮數據
   *
   * @param bytes 源數據
   * @return 壓縮以後的數據
   */
  private static byte[] compress(byte[] bytes) {
    Deflater deflater = new Deflater();
    //設置待壓縮數據
    deflater.setInput(bytes);
    //表示壓縮以當前輸入內容結束，暫時不知道具體原理
    deflater.finish();
    byte[] buf = new byte[1024];
    try (ByteArrayOutputStream output = new ByteArrayOutputStream()) {
      //是否已壓縮完成
      while (!deflater.finished()) {
        //壓縮
        int len = deflater.deflate(buf);
        output.write(buf, 0, len);
      }
      //關閉資源
      deflater.end();
      return output.toByteArray();
    } catch (Exception e) {
      e.printStackTrace();
    }
    return new byte[0];
  }

  /**
   * 讀取文件內容
   *
   * @param filePath 文件路徑
   * @return 文件內容
   */
  private static byte[] readFromFile(String filePath) {
    int len = -1;
    byte[] buf = new byte[1024];
    try (InputStream input = new BufferedInputStream(new FileInputStream(filePath));
        ByteArrayOutputStream output = new ByteArrayOutputStream()) {
      while ((len = input.read(buf)) != -1) {
        output.write(buf, 0, len);
      }
      return output.toByteArray();
    } catch (Exception e) {
      e.printStackTrace();
    }
    return new byte[0];
  }
}

輸出結果爲服務器

before compress: 43435
after compress: 1168
after decompress: 43435

能夠看到數據從原來的43435字節壓縮到了1168字節。code

使用DeflaterOutputStream和InflaterOutputStream解壓縮

import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.DeflaterOutputStream;
import java.util.zip.InflaterInputStream;

public class Client {

  public static void main(String[] args) throws IOException {
    byte[] bytes = readFromFile("D:/testdeflate.txt");
    System.out.println("before compress: " + bytes.length);
    byte[] compressedBytes = readFromFileAndCompress("D:/testdeflate.txt");
    System.out.println("after compress: " + compressedBytes.length);
    byte[] decompressBytes = readAndDecompress(compressedBytes);
    System.out.println("after decompress: " + decompressBytes.length);
  }

  /**
   * 讀取文件內容並壓縮
   *
   * @param filePath 文件路徑
   * @return 文件內容
   */
  private static byte[] readFromFileAndCompress(String filePath) {
    int len = -1;
    byte[] buf = new byte[1024];
    try (InputStream input = new BufferedInputStream(new FileInputStream(filePath));
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        DeflaterOutputStream dos = new DeflaterOutputStream(output)) {
      //從輸入流讀取寫入到輸出流
      while ((len = input.read(buf)) != -1) {
        dos.write(buf, 0, len);
      }
      //必須
      dos.finish();
      return output.toByteArray();
    } catch (Exception e) {
      e.printStackTrace();
    }
    return new byte[0];
  }

  /**
   * 讀取文件內容
   *
   * @param filePath 文件路徑
   * @return 文件內容
   */
  private static byte[] readFromFile(String filePath) {
    int len = -1;
    byte[] buf = new byte[1024];
    try (InputStream input = new BufferedInputStream(new FileInputStream(filePath));
        ByteArrayOutputStream output = new ByteArrayOutputStream()) {
      while ((len = input.read(buf)) != -1) {
        output.write(buf, 0, len);
      }
      return output.toByteArray();
    } catch (Exception e) {
      e.printStackTrace();
    }
    return new byte[0];
  }

  /**
   * 讀取並解壓縮
   *
   * @param bytes 待解壓數據
   * @return 解壓以後的數據
   */
  private static byte[] readAndDecompress(byte[] bytes) {
    int len = -1;
    byte[] buf = new byte[1024];
    try (InputStream input = new InflaterInputStream(new ByteArrayInputStream(bytes));
        ByteArrayOutputStream output = new ByteArrayOutputStream()) {
      while ((len = input.read(buf)) != -1) {
        output.write(buf, 0, len);
      }
      return output.toByteArray();
    } catch (IOException e) {
      e.printStackTrace();
    }
    return new byte[0];
  }
}

輸出結果爲orm

before compress: 43435
after compress: 1168
after decompress: 43435

能夠看到和使用Deflater壓縮的效果是同樣的。DeflaterOutputStream寫入完成以後必須調用finish()方法。blog

/**
 * This class implements an output stream filter for compressing data in
 * the "deflate" compression format. It is also used as the basis for other
 * types of compression filters, such as GZIPOutputStream.
 *
 * @see         Deflater
 * @author      David Connelly
 * @since 1.1
 */
public
class DeflaterOutputStream extends FilterOutputStream {
    /**
     * 壓縮類
     */
    protected Deflater def;
    /**
     * 重寫了父類的write方法，先將數據壓縮再寫入
     */
    public void write(byte[] b, int off, int len) throws IOException {
        if (def.finished()) {
            throw new IOException("write beyond end of stream");
        }
        if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
            throw new IndexOutOfBoundsException();
        } else if (len == 0) {
            return;
        }
        if (!def.finished()) {
            def.setInput(b, off, len);
            while (!def.needsInput()) {
                deflate();
            }
        }
    }

   /**
     * 數據壓縮
     */
    protected void deflate() throws IOException {
        int len = def.deflate(buf, 0, buf.length);
        if (len > 0) {
            out.write(buf, 0, len);
        }
    }
}

能夠看到DeflaterOutputStream內部就是使用了Deflater來壓縮數據，InflaterInputStream也是相似。ip

使用GZipOutputStream和GZipInputStream解壓縮

import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;

public class Client {

  public static void main(String[] args) {
    byte[] bytes = readFromFile("D:/testdeflate.txt");
    System.out.println("before compress: " + bytes.length);
    byte[] compressedBytes = readFromFileAndCompress("D:/testdeflate.txt");
    System.out.println("after compress: " + compressedBytes.length);
    byte[] decompressBytes = readAndDecompress(compressedBytes);
    System.out.println("after decompress: " + decompressBytes.length);
  }

  /**
   * 讀取文件內容
   *
   * @param filePath 文件路徑
   * @return 文件內容
   */
  private static byte[] readFromFile(String filePath) {
    int len = -1;
    byte[] buf = new byte[1024];
    try (InputStream input = new BufferedInputStream(new FileInputStream(filePath));
        ByteArrayOutputStream output = new ByteArrayOutputStream()) {
      while ((len = input.read(buf)) != -1) {
        output.write(buf, 0, len);
      }
      return output.toByteArray();
    } catch (Exception e) {
      e.printStackTrace();
    }
    return new byte[0];
  }

  /**
   * 讀取文件內容並壓縮
   *
   * @param filePath 文件路徑
   * @return 文件內容
   */
  private static byte[] readFromFileAndCompress(String filePath) {
    int len = -1;
    byte[] buf = new byte[1024];
    try (InputStream input = new BufferedInputStream(new FileInputStream(filePath));
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        GZIPOutputStream dos = new GZIPOutputStream(output)) {
      while ((len = input.read(buf)) != -1) {
        dos.write(buf, 0, len);
      }
      //必須
      dos.finish();
      return output.toByteArray();
    } catch (Exception e) {
      e.printStackTrace();
    }
    return new byte[0];
  }

  /**
   * 讀取並解壓
   *
   * @param bytes 待解壓數據
   * @return 解壓以後的數據
   */
  private static byte[] readAndDecompress(byte[] bytes) {
    int len = -1;
    byte[] buf = new byte[1024];
    try (InputStream input = new GZIPInputStream(new ByteArrayInputStream(bytes));
        ByteArrayOutputStream output = new ByteArrayOutputStream()) {
      while ((len = input.read(buf)) != -1) {
        output.write(buf, 0, len);
      }
      return output.toByteArray();
    } catch (IOException e) {
      e.printStackTrace();
    }
    return new byte[0];
  }

}

輸出結果爲資源

before compress: 43435
after compress: 1180
after decompress: 43435

能夠看到使用GZip相比Deflater，壓縮以後的數據多了一些字節，這是由於GZipOutputStream就是DeflaterOutputStream的擴展類，在數據頭部加入了10個字節的header數據，尾部加入了8個字節的CRC32的檢驗數據。
input

能夠看到Tomcat服務器對響應數據的壓縮就使用到了GZipOutputStream。it

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