Java/hibernate : Decompressing a compressed result

Question

我正在尝试解压缩 MySQL 的 COMPRESS 函数返回的值:

SQLQuery query = session
            .createSQLQuery("SELECT ID, COMPRESS(TEXT_COL) AS TEXT_COL FROM TABLE WHERE ID IN (1,2,3,...);")
            .addScalar("ID", Hibernate.INTEGER)
            .addScalar("TEXT_COL", Hibernate.TEXT);
List<Object[]> list = query.list();
for (Object[] result : list) {
   String text = decompress(((String) result[1]).getBytes());
}

(...)
private String decompress(byte[] bs) {
    InputStream in = new InflaterInputStream(new ByteArrayInputStream(bs));
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    try {
        byte[] buffer = new byte[8192];
        int len;
        while((len = in.read(buffer))>0)
            baos.write(buffer, 0, len);
        return new String(baos.toByteArray(), "UTF-8");
    } catch (IOException e) {
        throw new AssertionError(e);
    }
}

我得到了 java.lang.AssertionError: java.util.zip.ZipException: incorrect header check

如何解压这样的mysql结果或者我的代码有什么问题？

提前致谢，迭戈。

编辑:感谢 Joni 的建议，我最终将代码更改为

SQLQuery query = session
            .createSQLQuery("SELECT ID, COMPRESS(TEXT_COL) AS TEXT_COL FROM TABLE WHERE ID IN (1,2,3,...);")
            .addScalar("ID", Hibernate.INTEGER)
            .addScalar("TEXT_COL", Hibernate.BINARY);
List<Object[]> list = query.list();
for (Object[] result : list) {
   String text = decompress(((byte[]) result[1]));
}

(...)
private String decompress(byte[] bs) {
    InputStream in = new InflaterInputStream(new ByteArrayInputStream(bs, 4, bs.length-4));
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    try {
        byte[] buffer = new byte[8192];
        int len;
        while((len = in.read(buffer))>0)
            baos.write(buffer, 0, len);
        return new String(baos.toByteArray(), "UTF-8");
    } catch (IOException e) {
        throw new AssertionError(e);
    }
}

Answer 1

您必须在流的开头跳过 4 个字节:

InputStream in = new InflaterInputStream(
                     new ByteArrayInputStream(bs, 4, bs.length-4));

这是因为 COMPRESS函数返回一个字符串，其中前四个字节给出压缩数据的长度，后面的字节是实际的压缩数据。

此外，您应该尝试找到一种直接以字节形式获取结果的方法。压缩后的结果是二进制数据，可能无法安全地转换为字符串。