压缩和解压缩java中的字符串数据

Question

我使用以下代码来压缩和解压缩字符串数据,但我面临的问题是,它很容易被压缩而没有错误,但解压缩方法会引发跟随错误.

线程"main"中的异常java.io.IOException:不是GZIP格式

public static void main(String[] args) throws Exception {
        String string = "I am what I am hhhhhhhhhhhhhhhhhhhhhhhhhhhhh"
                + "bjggujhhhhhhhhh"
                + "rggggggggggggggggggggggggg"
                + "esfffffffffffffffffffffffffffffff"
                + "esffffffffffffffffffffffffffffffff"
                + "esfekfgy enter code here`etd`enter code here wdd"
                + "heljwidgutwdbwdq8d"
                + "skdfgysrdsdnjsvfyekbdsgcu"
                +"jbujsbjvugsduddbdj";

       System.out.println("after compress:");
        String compressed = compress(string);
        System.out.println(compressed);
        System.out.println("after decompress:");
        String decomp = decompress(compressed);
        System.out.println(decomp);
    }


     public static String compress(String str) throws Exception {
        if (str == null || str.length() == 0) {
            return str;
        }
        System.out.println("String length : " + str.length());
        ByteArrayOutputStream obj=new ByteArrayOutputStream();
        GZIPOutputStream gzip = new GZIPOutputStream(obj);
        gzip.write(str.getBytes("UTF-8"));
        gzip.close();
        String outStr = obj.toString("UTF-8");
        System.out.println("Output String length : " + outStr.length());
        return outStr;
     }

      public static String decompress(String str) throws Exception {
        if (str == null || str.length() == 0) {
            return str;
        }
        System.out.println("Input String length : " + str.length());
        GZIPInputStream gis = new GZIPInputStream(new ByteArrayInputStream(str.getBytes("UTF-8")));
        BufferedReader bf = new BufferedReader(new InputStreamReader(gis, "UTF-8"));
        String outStr = "";
        String line;
        while ((line=bf.readLine())!=null) {
          outStr += line;
        }
        System.out.println("Output String lenght : " + outStr.length());
        return outStr;
     }

仍然无法弄清楚如何解决这个问题!

Answer 1

这是因为

String outStr = obj.toString("UTF-8");

发送byte[]您可以从中获得的,ByteArrayOutputStream并在您ByteArrayInputStream的构建中使用它GZIPInputStream.以下是您的代码中需要进行的更改.

byte[] compressed = compress(string); //In the main method

public static byte[] compress(String str) throws Exception {
    ...
    ...
    return obj.toByteArray();
}

public static String decompress(byte[] bytes) throws Exception {
    ...
    GZIPInputStream gis = new GZIPInputStream(new ByteArrayInputStream(bytes));
    ...
}

Answer 2

上述答案解决了我们的问题,但除此之外.如果我们试图解压缩未压缩的("不是zip格式")byte [].我们将获得"Not GZIP格式"异常消息.

为了解决这个问题,我们可以在我们的类中添加额外代

public static boolean isCompressed(final byte[] compressed) {
    return (compressed[0] == (byte) (GZIPInputStream.GZIP_MAGIC)) && (compressed[1] == (byte) (GZIPInputStream.GZIP_MAGIC >> 8));
}

我的压缩/解压缩完整压缩类看起来像:

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;

public class GZIPCompression {
  public static byte[] compress(final String str) throws IOException {
    if ((str == null) || (str.length() == 0)) {
      return null;
    }
    ByteArrayOutputStream obj = new ByteArrayOutputStream();
    GZIPOutputStream gzip = new GZIPOutputStream(obj);
    gzip.write(str.getBytes("UTF-8"));
    gzip.flush();
    gzip.close();
    return obj.toByteArray();
  }

  public static String decompress(final byte[] compressed) throws IOException {
    final StringBuilder outStr = new StringBuilder();
    if ((compressed == null) || (compressed.length == 0)) {
      return "";
    }
    if (isCompressed(compressed)) {
      final GZIPInputStream gis = new GZIPInputStream(new ByteArrayInputStream(compressed));
      final BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(gis, "UTF-8"));

      String line;
      while ((line = bufferedReader.readLine()) != null) {
        outStr.append(line);
      }
    } else {
      outStr.append(compressed);
    }
    return outStr.toString();
  }

  public static boolean isCompressed(final byte[] compressed) {
    return (compressed[0] == (byte) (GZIPInputStream.GZIP_MAGIC)) && (compressed[1] == (byte) (GZIPInputStream.GZIP_MAGIC >> 8));
  }
}

Answer 3

如果您需要通过网络传输压缩内容或将其存储为文本,则必须使用Base64编码器(例如apache commons编解码器Base64)将字节数组转换为Base64字符串,并将字符串解码回字节数组at远程客户端.在Use Zip Stream和Base64 Encoder中找到一个压缩大字符串数据的例子!

Answer 4

另一个正确压缩和解压的例子：

@Slf4j
public class GZIPCompression {
    public static byte[] compress(final String stringToCompress) {
        if (isNull(stringToCompress) || stringToCompress.length() == 0) {
            return null;
        }

        try (final ByteArrayOutputStream baos = new ByteArrayOutputStream();
            final GZIPOutputStream gzipOutput = new GZIPOutputStream(baos)) {
            gzipOutput.write(stringToCompress.getBytes(UTF_8));
            gzipOutput.finish();
            return baos.toByteArray();
        } catch (IOException e) {
            throw new UncheckedIOException("Error while compression!", e);
        }
    }

    public static String decompress(final byte[] compressed) {
        if (isNull(compressed) || compressed.length == 0) {
            return null;
        }

        try (final GZIPInputStream gzipInput = new GZIPInputStream(new ByteArrayInputStream(compressed));
             final StringWriter stringWriter = new StringWriter()) {
            IOUtils.copy(gzipInput, stringWriter, UTF_8);
            return stringWriter.toString();
        } catch (IOException e) {
            throw new UncheckedIOException("Error while decompression!", e);
        }
    }
}

Answer 5

问题是这一行:

    String outStr = obj.toString("UTF-8");

字节数组obj包含任意二进制数据.您无法"解码"任意二进制数据,就像它是UTF-8一样.如果你尝试,你将得到一个不能被"编码"回字节的字符串.或者至少,你得到的字节将与你开始的字节不同......只要它们不再是有效的GZIP流.

修复是按原样存储或传输字节数组的内容.不要尝试将其转换为String.它是二进制数据,而不是文本.

Answer 6

客户端发送一些需要压缩的消息，服务器（kafka）解压字符串meesage

下面是我的样本：

压缩：

   public static String compress(String str, String inEncoding) {
        if (str == null || str.length() == 0) {
            return str;
        }
        try {
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            GZIPOutputStream gzip = new GZIPOutputStream(out);
            gzip.write(str.getBytes(inEncoding));
            gzip.close();
            return URLEncoder.encode(out.toString("ISO-8859-1"), "UTF-8");
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

解压：

    public static String decompress(String str, String outEncoding) {
        if (str == null || str.length() == 0) {
            return str;
        }

        try {
            String decode = URLDecoder.decode(str, "UTF-8");

            ByteArrayOutputStream out = new ByteArrayOutputStream();
            ByteArrayInputStream in = new ByteArrayInputStream(decode.getBytes("ISO-8859-1"));
            GZIPInputStream gunzip = new GZIPInputStream(in);
            byte[] buffer = new byte[256];
            int n;
            while ((n = gunzip.read(buffer)) >= 0) {
                out.write(buffer, 0, n);
            }
            return out.toString(outEncoding);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }